Feigin and Cherry’s Textbook of Pediatric Infectious Diseases [8 ed.] 9780323376921

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Feigin and Cherry’s

Textbook of

Pediatric Infectious Diseases

Feigin and Cherry’s

Textbook of

Pediatric Infectious Diseases EIGHTH EDITION

JAMES D. CHERRY, MD, MSc

Distinguished Research Professor of Pediatrics David Geffen School of Medicine at UCLA; Attending Physician Pediatric Infectious Diseases Mattel Children’s Hospital UCLA Los Angeles, California

GAIL J. HARRISON, MD

Professor Department of Pediatrics Section of Infectious Diseases Baylor College of Medicine; Attending Physician Infectious Diseases Service Texas Children’s Hospital Houston, Texas

SHELDON L. KAPLAN, MD

Professor and Executive Vice-Chair Head, Section of Infectious Diseases Department of Pediatrics Baylor College of Medicine; Chief, Infectious Disease Service Head, Department of Pediatric Medicine Texas Children’s Hospital Houston, Texas

WILLIAM J. STEINBACH, MD

Professor of Pediatrics Professor in Molecular Genetics and Microbiology Chief, Pediatric Infectious Diseases Director, Duke Pediatric Immunocompromised Host Program Director, International Pediatric Fungal Network Duke University School of Medicine Durham, North Carolina

PETER J. HOTEZ, MD, PhD

Dean, National School of Tropical Medicine Professor, Pediatrics and Molecular & Virology and Microbiology Head, Section of Pediatric Tropical Medicine Baylor College of Medicine; Endowed Chair of Tropical Pediatrics Center for Vaccine Development Texas Children’s Hospital; Professor, Department of Biology Baylor University Waco, Texas; Baker Institute Fellow in Disease and Poverty Rice University Houston, Texas; Co-Editor-in-Chief, PLoS Neglected Tropical Diseases

1600 John F. Kennedy Blvd. Ste 1800 Philadelphia, PA 19103-2899

FEIGIN AND CHERRY’S TEXTBOOK OF PEDIATRIC INFECTIOUS DISEASES, EIGHTH EDITION

ISBN: 978-0-323-37692-1

Copyright © 2019 by Elsevier, Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein).

Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. With respect to any drug or pharmaceutical products identified, readers are advised to check the most current information provided (i) on procedures featured or (ii) by the manufacturer of each product to be administered, to verify the recommended dose or formula, the method and duration of administration, and contraindications. It is the responsibility of practitioners, relying on their own experience and knowledge of their patients, to make diagnoses, to determine dosages and the best treatment for each individual patient, and to take all appropriate safety precautions. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Previous editions copyrighted © 2014, 2009, 2004, 1998, 1992, 1987, 1981 by Saunders, an imprint of Elsevier, Inc. Chapters 189 and 232 are in the public domain. Hookworm and tick images courtesy of Anna Grove Photography. Staphylococcus aureus image from CDC Public Health Image Library (provided by Frank DeLeo, National Institute of Allergy and Infectious Diseases). Mosquito scanning electron micrograph from DCD Public Health Imaging Library (provided by Dr. Paul Howell, CDC). ISBN: 978-0-323-37692-1

Senior Acquisitions Editor: Kate Dimock Senior Content Development Specialist: Jennifer Shreiner Publishing Services Manager: Patricia Tannian Senior Project Manager: Carrie Stetz Design Direction: Maggie Reid

Printed in China Last digit is the print number: 9 8 7 6 5 4 3 2 1

To my wife, Jeanne M. Cherry, who passed away on June 2, 2017 To my children, James Cherry, Jeffrey Cherry and Kass Hogan, Susan Cherry, and Kenneth and Jennifer Cherry To my grandchildren, Ferguson, Dennis, and Siena Rose Cherry James Cherry

To my husband, Neil Harrison To my children and sons-in-law, Emily Wolfe and Josh Wolfe, Kelly Green and Daniel Green, Matthew Demmler, Amy Demmler, Anna Rose Demmler, and Haley Harrison To my grandchildren, Jensen Wolfe and William Green To my brother, Loddie Naymola Gail Harrison

To my wife, Marsha Kaplan To my children, Lauren Kaplan, Mindy Kaplan Langland, and son-in-law Lance Langland To my grandchildren, Reece and Macy Langland Sheldon Kaplan

To my wife, Sandy Steinbach To my children, Amelia Steinbach, Aidan Steinbach, and Conner Franzen To my parents, Charles and Kathy Steinbach William Steinbach

To my wife, Ann Hotez To my children, Matthew, Emily, Rachel, and Daniel Hotez To my mother, Jean Hotez, and mother-in-law, Marcia Frifield To the memories of my father, Ed Hotez, and father-in-law, Don Frifield Peter Hotez

Ralph D. Feigin, MD

April 3, 1938–August 14, 2008

This eighth edition of the Textbook of Pediatric Infectious Diseases is dedicated to Ralph D. Feigin. As everyone in pediatrics and, in particular, pediatric infectious diseases, knows, Ralph was an extraordinary individual, and his untimely death in 2008 leaves a void that will never be filled. Ralph Feigin was born in New York City on April 3, 1938. He graduated from Columbia College in New York City in 1958 and received his M.D. from Boston University School of Medicine in 1962. He married Judith S. Zobel, a childhood friend, in 1960 while in medical school. Ralph completed his first two years of pediatric residency at Boston City Hospital and his third year at the Massachusetts General Hospital. He then fulfilled his military service requirement at the United States Army Research Institute of Infectious Diseases, Ft. Detrick, Frederick, Maryland. While at the United States Army Research Institute, he participated in significant studies relating to circadian periodicity and susceptibility to infections, as well as other studies that resulted in eight publications for which he was the first author. After completing his service commitment, he was Chief Resident at Massachusetts General Hospital during the 1967-68 academic year. Ralph was recruited to Washington University in St. Louis by Phil Dodge in 1968, and soon thereafter he and one of us (JDC), who was then at St. Louis University, got together and forged an academic and personal friendship that continued until the time of his death. Over 40 years ago, Ralph and Jim recognized the need for a comprehensive book on pediatric infectious diseases, but because of their busy schedules the plan was put on hold, and in 1973 Jim moved to California. In 1976, the pediatric research meetings were held in St. Louis, and at this time Jim and Ralph met with W. B. Saunders representatives, and the book was conceived. The first edition of the textbook was published 5 years later in the fall of 1981. In comparison with this 8th edition, it was a modest effort, with 44 chapters and 124 contributors.

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At Washington University and St. Louis Children’s Hospital, Ralph developed one of the finest infectious diseases divisions in the country. His “Feigin Rounds” were an unparalleled learning experience and were legendary among medical students and residents. In 1977, Ralph moved to Houston, Texas, to accept the challenge of being the Chair of Pediatrics for Baylor College of Medicine and the Physician-in-Chief at Texas Children’s Hospital. During the ensuing 30 years, the Department grew from 43 faculty members to almost 500. One of us (SLK) came under Ralph’s spell in St. Louis and moved to Houston with him. Another one of us (GJH), an intern in Houston in 1977, was waiting for Dr. Feigin when he arrived. In Houston, Ralph served as the Chair of Pediatrics for Baylor College of Medicine and the Physician-in-Chief at Texas Children’s Hospital for 31 years. For 7 years of his tenure, he also served as President and CEO of Baylor College of Medicine. In addition to his commitments in Houston, Ralph served in leadership roles on more than 100 local, regional, and national committees and professional societies. His efforts in persuading government officials of all ranks helped children in Texas, the United States, and in all parts of the world. Many consider him to have been the foremost pediatrician in the world. Not only was Dr. Feigin a powerhouse of energy, speed, and unsurpassed accomplishments, but he also was a gentleman, full of compassion, warmth, and kindness, and a man who kept people and patients first in his heart and mind. He was a loving husband to his wife, Judy, and a proud father to his three children, Susan, Debra, and Michael; doting grandfather to his six grandchildren, Rebecca, Matthew, Sarah, Rachel, Jacob, and Eli; and a mentor to so many in the field of pediatrics and pediatric infectious diseases. Ralph Feigin is missed by everyone who knew him, particularly by Judy Feigin and the family as well as by the present editors of this eighth edition of Feigin and Cherry.

James D. Cherry, MD, MSc Distinguished Research Professor of Pediatrics David Geffen School of Medicine at UCLA; Attending Physician Pediatric Infectious Diseases Mattel Children’s Hospital UCLA Los Angeles, California

Gail J. Harrison, MD Professor Department of Pediatrics Section of Infectious Diseases Baylor College of Medicine; Attending Physician Infectious Diseases Service Texas Children’s Hospital Houston, Texas

Sheldon L. Kaplan, MD Professor and Executive Vice-Chair Head, Section of Infectious Diseases Department of Pediatrics Baylor College of Medicine; Chief, Infectious Disease Service Head, Department of Pediatric Medicine Texas Children’s Hospital Houston, Texas

William J. Steinbach, MD Professor of Pediatrics Professor in Molecular Genetics and Microbiology Chief, Pediatric Infectious Diseases Director, Duke Pediatric Immunocompromised Host Program Director, International Pediatric Fungal Network Duke University School of Medicine Durham, North Carolina

Peter J. Hotez, MD, PhD Dean, National School of Tropical Medicine Professor, Pediatrics and Molecular & Virology and Microbiology Head, Section of Pediatric Tropical Medicine Baylor College of Medicine; Endowed Chair of Tropical Pediatrics Center for Vaccine Development Texas Children’s Hospital; Professor, Department of Biology Baylor University Waco, Texas; Baker Institute Fellow in Disease and Poverty Rice University Houston, Texas; Co-Editor-in-Chief, PLoS Neglected Tropical Diseases

Contributors

John Aaskov, BSc, PhD, FRCPath World Health Organization Collaborating Centre for Arbovirus Reference and Research Institute of Health and Biomedical Innovation Queensland University of Technology Brisbane, QLD, Australia Kristina Adachi, MD, MA Clinical Instructor Department of Pediatrics Division of Infectious Diseases David Geffen School of Medicine at UCLA Los Angeles, California Christoph Aebi, MD Professor of Pediatrics and Infectious Diseases Chairman, Department of Pediatrics University of Bern Bern, Switzerland Kenneth A. Alexander, MD, PhD Chief Division of Allergy, Immunology, Rheumatology, and Infectious Diseases Nemours Children’s Hospital; Professor of Pediatrics University of Central Florida College of Medicine Orlando, Florida Ghada N. Al-Rawahi, MD, DTM&H (London), D(ABMM), FRCPC Medical Microbiologist Children’s and Women’s Health Centre of British Columbia; Medical Lead, Infection Prevention & Control BC Cancer Agency; Clinical Associate Professor University of British Columbia Vancouver, BC, Canada Duha Al-Zubeidi, MD Children’s Mercy Hospital Kansas City, Missouri Seher Anjum, MD Professor, Division of Infectious Disease Department of Internal Medicine University of Texas Medical Branch Galveston, Texas Monica I. Ardura, DO, MSCS Associate Professor Department of Pediatrics Ohio State University; Medical Director, Host Defense Program Department of Pediatrics, Infectious Diseases, and Immunology Nationwide Children’s Hospital Columbus, Ohio Stephen S. Arnon, MD, MPH Founder and Chief Infant Botulism Treatment and Prevention Program California Department of Public Health Richmond, California viii

Amy Arrington, MD, PhD Section Chief, Global Biologic Preparedness Department of Pediatrics Baylor College of Medicine and Texas Children’s Hospital; Assistant Professor Department of Pediatric Critical Care Medicine Baylor College of Medicine Houston, Texas Ann M. Arvin, MD Lucile Salter Packard Professor of Pediatrics Professor of Microbiology and Immunology Stanford University School of Medicine Stanford, California Robert L. Atmar, MD Professor Department of Medicine Baylor College of Medicine Houston, Texas Amira Baker, MD Fellow, Pediatric Infectious Diseases Mattel Children’s Hospital University of California–Los Angeles Los Angeles, California Carol J. Baker, MD Professor Departments of Pediatrics and Molecular Virology & Microbiology Baylor College of Medicine Houston, Texas Robert S. Baltimore, MD Professor Departments of Pediatrics and Epidemiology Yale University School of Medicine; Associate Director of Infection Control Yale-New Haven Hospital New Haven, Connecticut Stephen J. Barenkamp, MD Professor of Pediatrics and Molecular Microbiology Department of Pediatrics St. Louis University School of Medicine; Director Division of Pediatric Infectious Diseases Cardinal Glennon Children’s Medical Center St. Louis, Missouri Elizabeth D. Barnett, MD Attending Physician Boston Medical Center Boston, Massachusetts Theresa Barton, MD Associate Professor Department of Pediatrics Baylor College of Medicine Houston, Texas

Contributors Gil Benard, MD, PhD Medical Researcher Departamento Dermatologia Faculdade de Medicina; Laboratorio de Micologia Medica Instituto de Medicina Tropical Universidade de São Paulo São Paolo, Brazil Jeffrey M. Bender, MD Assistant Professor Department of Pediatrics Division of Pediatric Infectious Diseases Children’s Hospital Los Angeles; Assistant Professor of Pediatrics and Pediatric Infectious Diseases University of Southern California Los Angeles, California Gregory J. Berry, PhD, D(ABMM) Assistant Medical Director Division of Infectious Disease Diagnostics Northwell Health Laboratories; Assistant Professor of Pathology and Laboratory Medicine Hofstra Northwell School of Medicine Lake Success, New York Amit Bhatt, MD Assistant Professor Department of Ophthalmology Baylor College of Medicine; Pediatric Ophthalmology Subsection Texas Children’s Hospital Houston, Texas Charles D. Bluestone, MD Distinguished Professor Emeritus of Otolaryngology University of Pittsburgh School of Medicine Pittsburgh, Pennsylvania Jeffrey L. Blumer, PhD, MD Professor and Chairman Department of Pediatrics The University of Toledo Toledo, Ohio Claire Bocchini, MD, MS Texas Children’s Hospital Houston, Texas Kenneth M. Boyer, MD Professor and Woman’s Board Chair Department of Pediatrics Rush Medical College of Rush University; Clinical Associate Department of Pediatrics University of Chicago Chicago, Illinois John S. Bradley, MD Professor and Chief Division of Infectious Diseases Department of Pediatrics University of California–San Diego School of Medicine San Diego, California Patricia Brasil, MD, PhD Clinical Researcher Instituto Nacional de Infectologia Fundação Oswaldo Cruz Rio de Janeiro, Brazil

William J. Britt, MD Charles A. Alford Professor of Pediatric Infectious Diseases Department of Pediatrics University of Alabama Birmingham, Alabama David E. Bronstein, MD, MS Department of Pediatrics Southern California Permanente Medical Group Palmdale, California David A. Bruckner, ScD Professor Emeritus Department of Pathology & Laboratory Medicine David Geffen School of Medicine at UCLA Los Angeles, California Kristina A. Bryant, MD Professor of Pediatric Diseases Department of Pediatrics University of Louisville Louisville, Kentucky Steven C. Buckingham, MD, MA† Associate Professor Department of Pediatrics University of Tennessee Health Science Center Memphis, Tennessee Carrie L. Byington, MD Vice Chancellor, Health Services Senior Vice President, Health Sciences Center Jean and Thomas McMullin Professor and Dean College of Medicine Texas A&M University and System Bryan, Texas Miguel M. Cabada, MD, MSc Assistant Professor Department of Internal Medicine Division of Infectious Diseases University of Texas Medical Branch Galveston, Texas Adriana Cadilla, MD Physician Department of Pediatric Infectious Disease Nemours Children’s Hospital Orlando, Florida Judith R. Campbell, MD Professor Department of Pediatrics Section of Infectious Diseases Baylor College of Medicine; Attending Physician Infectious Disease Service Texas Children’s Hospital Houston, Texas Justin E. Caron, MD Pathology Resident Department of Pathology University of Utah School of Medicine Salt Lake City, Utah

†

Deceased.

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Contributors

Maria Carrillo-Marquez, MD Assistant Professor Department of Pediatrics University of Tennessee Health Science Center Memphis, Tennessee

Tempe K. Chen, MD Assistant Clinical Professor Department of Pediatrics University of California Irvine School of Medicine Irvine, California

Janet R. Casey, MD Director of Research Legacy Pediatrics; Clinical Associate Professor of Pediatrics Department of Pediatrics University of Rochester Rochester, New York

James D. Cherry, MD, MSc Distinguished Research Professor of Pediatrics David Geffen School of Medicine at UCLA; Attending Physician Pediatric Infectious Diseases Mattel Children’s Hospital UCLA Los Angeles, California

Luis A. Castagnini, MD, MPH Assistant Professor Department of Pediatrics Baylor College of Medicine/Children’s Hospital of San Antonio San Antonio, Texas

Javier Chinen, MD, PhD Associate Professor Pediatrics, Allergy, and Immunology Baylor College of Medicine and Texas Children’s Hospital Houston, Texas

Mariam R. Chacko, MBBS Professor Department of Pediatrics Section of Adolescent Medicine and Sports Medicine Baylor College of Medicine and Texas Children’s Hospital; Medical Director, Adolescent Medicine Baylor Teen Health Clinics Houston, Texas

Natascha Ching, MD Assistant Clinical Professor Department of Pediatrics John A. Burns School of Medicine at the University of Hawaii; Physician Department of Pediatric Infectious Diseases Kapiolani Medical Center for Women and Children Kapiolani Medical Specialists Honolulu, Hawaii

Lakshmi Chandramohan, PhD, D(ABMM) Senior Scientist Biopharma Division NeoGenomics Laboratories Houston, Texas Louisa E. Chapman, MD, MSPH† Medical Epidemiologist Centers for Disease Control and Prevention Atlanta, Georgia Remi N. Charrel, MD, PhD UMR "Emergence des Pathologies Virales" Aix Marseille Université; Fondation IHU Mediterranée Infection APHM Public Hospitals of Marseille Marseille, France Elsa Chea-Woo, MD Professor Department of Pediatrics Universidad Peruana Cayetano Heredia Lima, Peru Ira M. Cheifetz, MD, FCCM, FAARC Chief Medical Officer Children’s Services Duke Children’s Hospital; Associate Chief Medical Officer Duke University Hospital; Division Chief, Pediatric Critical Care Medicine Professor, Departments of Pediatrics and Anesthesiology Duke University Medical Center Durham, North Carolina †

Deceased.

Ivan K. Chinn, MD Assistant Professor Department of Pediatrics Baylor College of Medicine and Texas Children’s Hospital Houston, Texas John C. Christenson, MD Professor of Clinical Pediatrics Ryan White Center for Pediatric Infectious Disease and Global Health Indiana University School of Medicine Indianapolis, Indiana Susan E. Coffin, MD, MPH Professor of Pediatrics Associate Chief Division of Infectious Diseases UPENN School of Medicine; Associate Hospital Epidemiologist Children’s Hospital of Philadelphia Philadelphia, Pennsylvania Armando G. Correa, MD Assistant Professor Department of Pediatrics Baylor College of Medicine; Attending Physician Texas Children’s Hospital Houston, Texas Elaine G. Cox, MD Professor of Clinical Pediatrics Ryan White Center for Pediatric Infectious Disease and Global Health Indiana University School of Medicine Indianapolis, Indiana

Contributors Jonathan D. Crews, MD, MS Assistant Professor Department of Pediatrics Baylor College of Medicine; Attending Physician Pediatric Infectious Diseases Children’s Hospital of San Antonio San Antonio, Texas Andrea T. Cruz, MD, MPH Assistant Professor Department of Pediatrics Baylor College of Medicine Houston, Texas Zev Davidovics, MD Department of Pediatric Gastroenterology, Digestive Diseases, Hepatology, and Nutrition Connecticut Children’s Medical Center Hartford, Connecticut; Assistant Professor of Pediatrics University of Connecticut School of Medicine Farmington, Connecticut Walter N. Dehority, MD, MSc Associate Professor Department of Pediatrics University of New Mexico Health Sciences Center Albuquerque, New Mexico Xavier de Lamballerie, MD Professor Emergence des Pathologies Virales Aix-Marseille Université; IRD French Institute of Research for Development EHESP French School of Public Health Laboratory of Virology IHU Mediterranée Infection APHM Public Hospitals of Marseille Marseille, France Penelope H. Dennehy, MD Director Division of Pediatric Infectious Diseases Hasbro Children’s Hospital; Professor and Vice Chair for Academic Affairs Department of Pediatrics Alpert Medical School of Brown University Providence, Rhode Island Minh L. Doan, MD, COL, MC, USA Chief, Division of Pediatric Pulmonology Brooke Army Medical Center San Antonio, Texas Simon R. Dobson, MD, FRCPC Medical Director, Infection Prevention and Control Antimicrobial Stewardship Consultant Sidra Medical and Research Center Qatar Foundation Doha, Qatar Jan E. Drutz, MD Professor Department of Pediatrics Baylor College of Medicine and Texas Children’s Hospital Houston, Texas

Kara A. Dubray, MD Clinical Instructor Pediatric Infectious Disease Lucile Packard Children’s Hospital Palo Alto, California Andrea Duppenthaler, MD Pediatric Infectious Diseases Children’s University Hospital Bern, Switzerland Christopher C. Dvorak, MD Professor & Chief Department of Pediatric Allergy, Immunology, & Bone Marrow Transplant University of California–San Francisco Benioff Children’s Hospital San Francisco, California Paul H. Edelstein, MD Professor Emeritus of Pathology and Laboratory Medicine University of Pennsylvania Perelman School of Medicine Philadelphia, Pennsylvania Kathryn M. Edwards, MD Sarah H. Sell and Cornelius Vanderbilt Chair in Pediatrics Department of Pediatrics Vanderbilt University School of Medicine Nashville, Tennessee Morven S. Edwards, MD Professor of Pediatrics Baylor College of Medicine; Attending Physician Pediatric Infectious Diseases Section Texas Children’s Hospital Houston, Texas Samer S. El-Kamary, MBChB, MS, MPH Associate Professor Department of Epidemiology and Public Health University of Maryland School of Medicine; Associate Professor Department of Pediatrics University of Maryland School of Medicine Baltimore, Maryland Janet A. Englund, MD Professor Department of Pediatrics University of Washington/Seattle Children’s Hospital Seattle, Washington Jessica Ericson, MD, MPH Assistant Professor Department of Pediatrics Division of Pediatric Infectious Diseases Pennsylvania State University College of Medicine Hershey, Pennsylvania Leland L. Fan, MD Professor Emeritus Department of Pediatrics University of Colorado School of Medicine Aurora, Colorado

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Contributors

Myke Federman, MD Associate Professor of Pediatrics Division of Pediatric Critical Care University of California–Los Angeles Los Angeles, California Pedro Fernando da C. Vasconcelos, MD, PhD Chief, Department of Arbovirology and Hemorrhagic Fevers Coordinator, National Reference Laboratory of Arboviruses Director, National Institute of Science and Technology for Viral Hemorrhagic Fevers Director, PAHO-WHO CC for Research and Diagnostic Reference on Arbovirus Instituto Evandro Chagas SVS/Ministry of Health Ananindeua, Brazil

Claudia Raja Gabaglia, MD, PhD Assistant Professor Biomedical Research Institute of Southern California Oceanside, California Lynne S. Garcia, MS, CLS, BLM, FAAM Director LSG & Associates Santa Monica, California Gregory M. Gauthier, MD, MS Associate Professor Department of Medicine University of Wisconsin Madison, Wisconsin

Philip R. Fischer, MD Professor of Pediatrics Mayo Clinic Rochester, Minnesota

Anne A. Gershon, MD Professor Department of Pediatrics Columbia University College of Physicians and Surgeons New York, New York

Brian T. Fisher, DO, MPH, MSCE Assistant Professor of Pediatrics and Epidemiology Perelman School of Medicine at the University of Pennsylvania; Division of Infectious Diseases Children’s Hospital of Philadelphia Philadelphia, Pennsylvania

Francis Gigliotti, MD Professor and Chief of Infectious Diseases Department of Pediatrics Associate Chair for Academic Affairs University of Rochester School of Medicine and Dentistry Rochester, New York

Randall G. Fisher, MD Professor Department of Pediatrics Eastern Virginia Medical School; Medical Director Division of Pediatric Infectious Diseases Children’s Hospital of The King’s Daughters Norfolk, Virginia

Mark A. Gilger, MD Pediatrician-in-Chief Children’s Hospital of San Antonio; Professor and Vice Chair Department of Pediatrics Baylor College of Medicine Houston, Texas

Douglas S. Fishman, MD Director of Gastrointestinal Endoscopy and Pancreaticobiliary Program Texas Children’s Hospital; Associate Professor of Pediatrics Baylor College of Medicine Houston, Texas Anthony R. Flores, MD, MPH, PhD Assistant Professor Department of Pediatrics Section of Infectious Diseases Texas Children’s Hospital Baylor College of Medicine Houston, Texas Catherine Foster, MD Clinical Postdoctoral Fellow Pediatrics, Section of Infectious Diseases Baylor College of Medicine Houston, Texas Ellen M. Friedman, MD Professor Department of Otolaryngology Texas Children’s Hospital; Director Center for Professionalism in Medicine Baylor College of Medicine Houston, Texas

Susan L. Gillespie, MD, PhD Associate Professor Department of Pediatrics Baylor College of Medicine Houston, Texas Carol A. Glaser, DVM, MPVM, MD Pediatric Infectious Diseases Permanente Medical Group Oakland Medical Center Oakland, California David L. Goldman, MD Associate Professor Department of Pediatrics Children’s Hospital at Montefiore/Albert Einstein College of Medicine New York, New York Jennifer L. Goldman, MD Department of Pediatrics Children’s Mercy Hospitals and Clinics Kansas City, Missouri Nira A. Goldstein, MD, MPH Professor and Attending Physician Department of Otolaryngology State University of New York Downstate Medical Center New York, New York

Contributors Blanca E. Gonzalez, MD Assistant Professor of Pediatrics Cleveland Clinic Lerner College of Medicine of Case Western Reserve University Center for Pediatric Infectious Diseases Cleveland Clinic Children’s Cleveland, Ohio Michael D. Green, MD, MPH Professor Department of Pediatrics, Surgery, & Clinical and Translational Research University of Pittsburgh School of Medicine Division of Pediatric Infectious Diseases Children’s Hospital of Pittsburgh of UPMC Pittsburgh, Pennsylvania Andreas Groll, MD Professor Department of Pediatric Hematology/Oncology University Children’s Hospital Muenster, Germany Charles Grose, MD Professor Department of Pediatrics Director of Infectious Diseases Children’s Hospital University of Iowa Iowa City, Iowa Duane J. Gubler, ScD, FAAAS, FIDSA, FASTMH Emeritus Professor Programme in Emerging Infectious Diseases Duke-NUS Medical School Singapore; Chair, Global Dengue and Aedes Transmitted Diseases Consortium International Vaccine Institute Seoul, Korea Javier Nieto Guevara, MD, MPH Infectious Diseases Specialist Panama City, Panama Caroline B. Hall, MD† Formerly Professor Department of Pediatrics and Medicine University of Rochester School of Medicine and Dentistry Rochester, New York Roy A. Hall, BSc(Hons), PhD Professor School of Chemistry and Molecular Biosciences University of Queensland St Lucia, QLD, Australia Scott B. Halstead, MD Adjunct Professor Preventive Medicine and Biostatistics Uniformed Services University of the Health Sciences Bethesda, Maryland Shinjiro Hamano, MD, PhD Professor Department of Parasitology Institute of Tropical Medicine Nagasaki University Nagasaki, Japan †

Deceased.

Margaret R. Hammerschlag, MD Professor of Pediatrics and Medicine SUNY Downstate Medical Center New York, New York Nicole L. Hannemann, MD Chief Resident and Clinical Instructor Department of Pediatrics Baylor College of Medicine and Texas Children’s Hospital Houston, Texas I. Celine Hanson, MD Professor Department of Pediatrics Baylor College of Medicine Houston, Texas Nada Harik, MD Associate Professor Department of Pediatrics Division of Pediatric Infectious Diseases George Washington University School of Medicine and Health Sciences Children’s National Medical Center Washington, DC Kathleen H. Harriman, PhD, MPH, RN Chief Vaccine Preventable Diseases Epidemiology Section Immunization Branch California Department of Public Health Richmond, California Gail J. Harrison, MD Professor Department of Pediatrics Section of Infectious Diseases Baylor College of Medicine; Attending Physician Infectious Diseases Service Texas Children’s Hospital Houston, Texas C. Mary Healy, MB BCh, BAO, MD Associate Professor Department of Pediatrics Division of Infectious Diseases Baylor College of Medicine and Texas Children’s Hospital Houston, Texas Ulrich Heininger, MD Chair, Pediatric Infectious Diseases University of Basel Children’s Hospital; Member, Medical Faculty University of Basel Basel, Switzerland Maria Hemming-Harlo, MD, PhD Medical Researcher Vaccine Research Center University of Tampere Tampere, Finland Sheryl L. Henderson, MD, PhD Assistant Professor Department of Pediatrics University of Wisconsin School of Medicine and Public Health American Family Children’s Hospital Madison, Wisconsin

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Contributors

Gloria P. Heresi, MD Professor Department of Pediatrics University of Texas Medical School at Houston Houston, Texas Peter W. Hiatt, MD Associate Professor of Pediatrics Section Head, Pediatric Pulmonology Baylor College of Medicine; Chief, Pulmonary Medicine Texas Children’s Hospital Houston, Texas Harry R. Hill, MD Professor Departments of Pediatrics, Pathology, and Internal Medicine University of Utah Salt Lake City, Utah David C. Hilmers, MD, EE, MPH Professor Departments of Internal Medicine and Pediatrics Baylor Global Initiatives Baylor Center for Space Medicine Baylor College of Medicine Houston, Texas Jill A. Hoffman, MD Associate Professor Department of Pediatrics Keck School of Medicine University of Southern California; Attending Physician Division of Infectious Diseases Children’s Hospital Los Angeles Los Angeles, California Peter J. Hotez, MD, PhD Dean, National School of Tropical Medicine Professor, Pediatrics and Molecular & Virology and Microbiology Head, Section of Pediatric Tropical Medicine Baylor College of Medicine; Endowed Chair of Tropical Pediatrics Center for Vaccine Development Texas Children’s Hospital; Professor, Department of Biology Baylor University Waco, Texas; Baker Institute Fellow in Disease and Poverty Rice University Houston, Texas; Co-Editor-in-Chief, PLoS Neglected Tropical Diseases Leigh M. Howard, MD, MPH Assistant Professor Department of Pediatric Infectious Diseases Vanderbilt University Medical Center Nashville, Tennessee Kristina G. Hulten, PhD Assistant Professor Department of Pediatrics Baylor College of Medicine Houston, Texas

Romney M. Humphries, PhD Chief Scientific Officer Accelerate Diagnostics Tucson, Arizona David A. Hunstad, MD Associate Professor Departments of Pediatrics and Molecular Microbiology Washington University School of Medicine St. Louis, Missouri W. Garrett Hunt, MD, MPH, DTM&H, FAAP Associate Professor Department of Pediatrics Section of Infectious Diseases Nationwide Children’s Hospital/Ohio State University Columbus, Ohio W. Charles Huskins, MD, MSc Professor of Pediatrics Mayo Clinic School of Medicine; Chair, Division of Pediatric Infectious Diseases Mayo Clinic; Vice Chair of Quality and Health Care Epidemiologist Mayo Clinic Children’s Center Rochester, Minnesota David Y. Hyun, MD Senior Officer Antibiotic Resistance Project Pew Charitable Trusts Philadelphia, Pennsylvania Mary Anne Jackson, MD Director, Infectious Diseases Children’s Mercy Kansas City Professor of Pediatrics UMKC School of Medicine Kansas City, Missouri Michael R. Jacobs, MB BCh, PhD Professor of Pathology and Medicine Department of Pathology Case Western Reserve University; Director of Clinical Microbiology Department of Pathology University Hospitals Cleveland Medical Center Cleveland, Ohio Richard F. Jacobs, MD, FAAP Robert H. Fiser Jr, MD, Endowed Chair in Pediatrics Pediatrician-in-Chief Department of Pediatrics Arkansas Children’s Hospital; Chairman and Professor Department of Pediatrics University of Arkansas for Medical Sciences Little Rock, Arkansas Ravi Jhaveri, MD Associate Professor Department of Pediatrics University of North Carolina at Chapel Hill School of Medicine Chapel Hill, North Carolina Audrey R. Odom John, MD, PhD Associate Professor Departments of Pediatrics and Molecular Microbiology Washington University School of Medicine Saint Louis, Missouri

Contributors Samantha H. Johnston, MD, MPH Associate Physician Pediatric Infectious Diseases UCSF Benioff Children’s Hospital Oakland Oakland, California Meena R. Julapalli, MD Assistant Professor Department of Dermatology University of Colorado Denver, Colorado Sheldon L. Kaplan, MD Professor and Executive Vice-Chair Head, Section of Infectious Diseases Department of Pediatrics Baylor College of Medicine; Chief, Infectious Disease Service Head, Department of Pediatric Medicine Texas Children’s Hospital Houston, Texas Gregory L. Kearns, PharmD, PhD President Arkansas Children’s Research Institute Senior Vice President and Chief Research Officer Arkansas Children’s; Ross and Mary Whipple Family Distinguished Research Scientist Professor of Pediatrics University of Arkansas for Medical Sciences Little Rock, Arkansas

Martin B. Kleiman, MD Ryan White Professor Emeritus of Pediatrics Ryan White Center for Pediatric Infectious Disease and Global Health Indiana University School of Medicine Indianapolis, Indiana Bruce S. Klein, MD Gerard B. Odell and Shirley S. Matchette Professor of Pediatrics Professor of Internal Medicine and Medical Microbiology and Immunology University of Wisconsin–Madison Madison, Wisconsin Stephan A. Kohlhoff, MD Associate Professor Departments of Pediatrics and Medicine State University of New York Downstate Medical Center New York, New York Tobias R. Kollmann, MD, PhD Professor of Pediatrics Interim Head, Division of Infectious Diseases University of British Columbia Vancouver, BC, Canada Poonum S. Korpe, MD Assistant Scientist Department of Epidemiology Johns Hopkins Bloomberg School of Public Health Baltimore, Maryland

Jessica M. Khouri, MD Senior Medical Officer Infant Botulism Treatment and Prevention Program California Department of Public Health Richmond, California

Margaret Kosek, MD Assistant Professor Department of International Health Johns Hopkins University Bloomberg School of Public Health Baltimore, Maryland

Kwang Sik Kim, MD Professor and Director Department of Pediatric Infectious Diseases Johns Hopkins University School of Medicine; Professor Department of Molecular Microbiology and Immunology Johns Hopkins University Bloomberg School of Public Health Baltimore, Maryland

Michael P. Koster, MD Division of Pediatric Hospital Medicine Hasbro Children’s Hospital; Associate Professor, Clinical Educator Department of Pediatrics Alpert Medical School of Brown University Providence, Rhode Island

Yae-Jean Kim, MD, PhD Associate Professor Department of Pediatrics Samsung Medical Center Sungkyungkwan University School of Medicine Seoul, Korea Katherine Y. King, MD, PhD Assistant Professor Department of Pediatric Infectious Diseases Baylor College of Medicine Houston, Texas Louis V. Kirchhoff, MD, MPH Professor Department of Internal Medicine (Infectious Diseases), Psychiatry, and Epidemiology Carver College of Medicine and College of Public Health University of Iowa Iowa City, Iowa

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Peter J. Krause, MD Senior Research Scientist Yale School of Public Health Yale School of Medicine New Haven, Connecticut Leonard R. Krilov, MD Chairman, Department of Pediatrics Chief, Pediatric Infectious Disease Children’s Medical Center NYU Winthrop Hospital Mineola, New York; Professor of Pediatrics State University of New York Stony Brook School of Medicine Stony Brook, New York Paul Krogstad, MD Professor Departments of Pediatrics and Molecular and Medical Pharmacology David Geffen School of Medicine at UCLA Los Angeles, California

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Contributors

Damian J. Krysan, MD, PHD Associate Professor Departments of Pediatrics and Microbiology/Immunology University of Rochester School of Medicine and Dentistry Rochester, New York Edward Kuan, MD, MBA Resident Physician Department of Head and Neck Surgery David Geffen School of Medicine at UCLA Los Angeles, California Thomas Kuhls, MD Department of Pediatrics Norman Pediatric Associates Norman, Oklahoma Sarah M. Labuda, MD, MPH Pediatric Infectious Diseases Fellow Tulane School of Medicine New Orleans, Louisiana Paul M. Lantos, MD Assistant Professor Division of Pediatric Infectious Diseases Division of General Internal Medicine Duke University School of Medicine Duke Global Health Institute Durham, North Carolina Timothy R. La Pine, MD Professor Department of Pediatrics and Pathology University of Utah; Director of Neonatology St. Mark’s Hospital Salt Lake City, Utah Suvi Heinimäki, PhD Project Researcher Vaccine Research Center University of Tampere Tampere, Finland Jerome M. Larkin, MD Division of Infectious Diseases Rhode Island Hospital Associate Professor, Clinical Educator Department of Medicine Alpert Medical School of Brown University Providence, Rhode Island Matthew B. Laurens, MD, MPH Associate Professor Institute for Global Health University of Maryland School of Medicine Baltimore, Maryland Charles T. Leach, MD Professor and Chief of Infectious Diseases Department of Pediatrics Baylor College of Medicine/Children’s Hospital of San Antonio San Antonio, Texas Amy Leber, PhD Director, Clinical Microbiology and Immunoserology Department of Pathology and Laboratory Medicine Nationwide Children’s Hospital Columbus, Ohio

Robert J. Leggiadro, MD Adjunct Professor Departments of Biology and Geography and the Environment Villanova University Villanova, Pennsylvania; Adjunct Clinical Professor Department of Pediatrics Donald and Barbara Zucker School of Medicine at Hofstra/ Northwell Hempstead, New York; Adjunct Attending Physician General Pediatrics Cohen Children’s Medical Center New Hyde Park, New York Deborah Lehman, MD Professor Department of Pediatrics David Geffen School of Medicine at UCLA Los Angeles, California Diana R. Lennon, MB CHB, FRACP Professor of Population Health, Child, and Youth Department of Pediatrics University of Auckland; Pediatrician in Infectious Diseases Department of Pediatrics Starship and KidzFirst Children’s Hospital Auckland, New Zealand Daniel H. Leung, MD Associate Professor of Pediatrics Division of Gastroenterology, Hepatology, and Nutrition Baylor College of Medicine; Director of Clinical Research Medical Director, Viral Hepatitis Program Texas Children’s Hospital Houston, Texas Moise L. Levy, MD Chief, Pediatric/Adolescent Dermatology Dell Children’s Medical Center; Professor of Pediatrics and Medicine (Dermatology) Dell Medical School University of Texas Austin, Texas; Clinical Professor of Dermatology and Pediatrics Baylor College of Medicine Houston, Texas W. Matthew Linam, MD, MS Medical Director of Infection Prevention and Hospital Epidemiology Associate Professor, Department of Pediatrics Division of Pediatric Infectious Diseases Arkansas Children’s Hospital University of Arkansas for Medical Sciences Little Rock, Arkansas Latania K. Logan, MD Chief, Pediatric Infectious Diseases Department of Pediatrics Rush University Medical Center Associate Professor Rush Medical College Chicago, Illinois

Contributors Timothy E. Lotze, MD Associate Professor of Pediatrics and Neurology Division of Child Neurology Baylor College of Medicine and Texas Children’s Hospital Houston, Texas Yalda C. Lucero, MD, PhD Pediatric Gastroenterologist Assistant Professor Microbiology and Mycology Program Institute of Biomedical Sciences Faculty of Medicine University of Chile and Northern Campus Department of Pediatrics Santiago, Chile Debra J. Lugo, MD Fellow, Pediatric Infectious Diseases Mattel Children’s Hospital University of California–Los Angeles Los Angeles, California Berkley Luk, BSc PhD Candidate Program in Integrative Molecular and Biomedical Sciences Baylor College of Medicine; Department of Pathology Texas Children’s Hospital Houston, Texas Susan A. Maloney, MD, MHSc Global Tuberculosis Coordinator Division of Global Migration and Quarantine National Center for Infectious Diseases Centers for Disease Control and Prevention Atlanta, Georgia Michelle C. Mann, MD Assistant Professor Department of Pediatrics Baylor College of Medicine Houston, Texas Lucila Marquez, MD, MPH Assistant Professor of Pediatrics, Section of Infectious Diseases Associate Medical Director, Infection Control and Prevention Baylor College of Medicine and Texas Children’s Hospital Houston, Texas Kimberly C. Martin, DO, MPH Assistant Professor of Pediatrics Division of Pediatric Infectious Diseases University of Oklahoma School of Community Medicine Tulsa, Oklahoma Laurene Mascola, MD, MPH, FAAP Epidemiology Consultant Acute Communicable Disease Program Los Angeles County Department of Public Health Los Angeles, California Edward O. Mason Jr, PhD Professor Department of Pediatrics Baylor College of Medicine Houston, Texas

Aldo Maspons, MD CEO/Cofounder VeMiDoc, LLC; Maspons Pediatric Gastro Pediatric Gastroenterology El Paso, Texas Marc A. Mazade, MD Consultant Pediatric Infectious Disease Cook Children’s Medical Center Fort Worth, Texas Holly E. McBride, MPH, MHS, PA-C Physician Assistant Internal Medicine University of Colorado Health Loveland, Colorado Jonathan A. McCullers, MD Chair Department of Pediatrics University of Tennessee Health Science Center Memphis, Tennessee Kenneth McIntosh, MD Professor Department of Pediatrics Harvard Medical School; Senior Physician Department of Medicine Children’s Hospital Boston, Massachusetts James E. McJunkin, MD Professor of Pediatrics Department of Pediatrics West Virginia University Health Sciences Center Charleston, West Virginia Kelly T. McKee Jr, MD, MPH Vice President Department of Public Health and Government Services QuintilesIMS Durham, North Carolina Ross McKinney Jr, MD Professor Emeritus Department of Pediatrics Duke University School of Medicine Durham, North Carolina; Chief Scientific Officer Association of American Medical Colleges Washington, DC J. Chase McNeil, MD Assistant Professor Department of Pediatrics Section of Infectious Diseases Baylor College of Medicine Houston, Texas Rojelio Mejia, MD Assistant Professor of Infectious Diseases and Pediatrics National School of Tropical Medicine Baylor College of Medicine Houston, Texas

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Contributors

Asuncion Mejias, MD, PhD Associate Professor of Pediatrics Ohio State University College of Medicine Department of Pediatrics Division of Infectious Diseases Nationwide Children’s Hospital Columbus, Ohio Maria José Soares Mendes Giannini, PhD Full Professor Department of Clinical Analysis Laboratory of Clinical Mycology São Paulo State University-UNESP Araraquara, São Paulo, Brazil Marian G. Michaels, MD, MPH Professor Department of Pediatrics and Surgery University of Pittsburgh School of Medicine Division of Pediatric Infectious Diseases Children’s Hospital of Pittsburgh of UPMC Pittsburgh, Pennsylvania Ian C. Michelow, MD, DTM&H Division of Pediatric Infectious Diseases Hasbro Children’s Hospital Associate Professor Department of Pediatrics Alpert Medical School of Brown University Providence, Rhode Island Marjorie J. Miller, DrPH Senior Specialist, Virology Department of Pathology and Laboratory Medicine UCLA Medical Center Los Angeles, California James N. Mills, PhD Adjunct Faculty Population Biology, Ecology, and Evolution Group Emory University Atlanta, Georgia Leena B. Mithal, MD, MSCI Attending Physician Department of Pediatric Infectious Diseases Ann & Robert H. Lurie Children’s Hospital of Chicago; Instructor, Department of Pediatrics Northwestern University Feinberg School of Medicine Chicago, Illinois Kathryn S. Moffett, MD Professor of Pediatrics Section Chief, Infectious Diseases Department of Pediatrics West Virginia University Morgantown, West Virginia Martin Montes, MD Assistant Professor Instituto de Medicina Tropica “Alexander von Humboldt” Universidad Peruana Cayetano Heridia Lima, Peru; Assistant Professor Department of Medicine Division of Infectious Diseases University of Texas Medical Branch Galveston, Texas

Martha Muller, MD Associate Professor Department of Pediatrics University of New Mexico Albuquerque, New Mexico Randy George Mungwira, MBBS, MPH Blantyre Malaria Project Blantyre, Malawi James R. Murphy, PhD Professor Department of Pediatrics University of Texas Houston, Texas Santhosh M. Nadipuram, MD Postdoctoral Fellow Department of Microbiology, Immunology, & Molecular Genetics University of California–Los Angeles Los Angeles, California James P. Nataro, MD, PhD, MBA Benjamin Armistead Shepherd Professor and Chair Department of Pediatrics University of Virginia School of Medicine; Physician-in-Chief University of Virginia Children’s Hospital Charlottesville, Virginia Heather Needham, MD, MPH Assistant Professor of Pediatrics Section of Adolescent Medicine & Sports Medicine Baylor College of Medicine and Texas Children’s Hospital Houston, Texas Karin Nielsen-Saines, MD, MPH Professor of Clinical Pediatrics Division of Pediatric Infectious Diseases David Geffen School of Medicine at UCLA; Director, Center for Brazilian Studies Los Angeles, California Delma J. Nieves, MD Assistant Clinical Professor Department of Pediatric Infectious Diseases University of California–Irvine School of Medicine Children’s Hospital of Orange County Orange, California Richard Oberhelman, MD Professor and Chair Global Community Health & Behavioral Sciences Tulane School of Public Health and Tropical Medicine; Professor of Pediatrics Tulane School of Medicine New Orleans, Louisiana

Contributors Theresa J. Ochoa, MD Associate Professor Department of Pediatrics Instituto de Medicina Tropical "Alexander von Humboldt" Universidad Peruana Cayetano Heredia Lima, Peru; Associate Professor Division of Epidemiology, Human Genetics, and Environmental Sciences Center for Infectious Diseases School of Public Health University of Texas Health Science Center at Houston Houston, Texas Rosemary M. Olivero, MD Clinical Associate Professor of Pediatrics and Human Development Michigan State College of Human Medicine; Attending Physician Section of Pediatric Infectious Diseases Helen DeVos Children’s Hospital Grand Rapids, Michigan Miguel O’Ryan, MD Professor, Pediatric Infectious Disease Millennium Institute of Immunology and Immunotherapy Faculty of Medicine Microbiology and Mycology Program Institute of Biomedical Sciences University of Chile Santiago, Chile Gary D. Overturf, MD Professor Emeritus Departments of Pediatrics and Pathology University of New Mexico School of Medicine; Medical Director, Infectious Diseases TriCore Reference Laboratories Albuquerque, New Mexico Debra L. Palazzi, MD, MEd Associate Professor of Pediatrics Section of Infectious Diseases Baylor College of Medicine; Chief, Infectious Diseases Clinic Texas Children’s Hospital Houston, Texas Pia S. Pannaraj, MD, MPH Associate Professor Pediatrics and Molecular Microbiology and Immunology University of Southern California/Children’s Hospital Los Angeles Los Angeles, California Janak A. Patel, MD Professor and Division Director Department of Pediatrics Division of Pediatric Infectious Disease and Immunology University of Texas Medical Branch Galveston, Texas Mary E. Paul, MD Associate Professor Department of Pediatrics Baylor College of Medicine Chief, Retrovirology and Global Health Texas Children’s Hospital Houston, Texas

Stephen I. Pelton, MD Professor of Pediatrics and Epidemiology Department of Pediatrics Boston University Schools of Medicine and Public Health; Chief, Section of Pediatric Infectious Diseases Department of Pediatrics Boston Medical Center Boston, Massachusetts Morgan A. Pence, PhD, D(ABMM) Clinical Microbiologist Department of Laboratory and Pathology Cook Children’s Medical Center Fort Worth, Texas John R. Perfect, MD James B. Duke Professor of Medicine Duke University Medical Center Durham, North Carolina C.J. Peters, MD Department of Microbiology and Immunology University of Texas Medical Branch Galveston, Texas William A. Petri Jr, MD, PhD Chief Division of Infectious Disease and International Health University of Virginia Health System; Wade Hampton Frost Professor of Epidemiology University of Virginia Charlottesville, Virginia Yen H. Pham, MD Assistant Professor Department of Pediatric Gastroenterology, Hepatology, and Nutrition Baylor College of Medicine and Texas Children’s Hospital Houston, Texas Francisco P. Pinheiro, MD Department of Arbovirus Instituto Evandro Chagas FNS Ministry of Health Belem, Brazil Benjamin A. Pinsky, MD, PhD Associate Professor Departments of Pathology and Medicine (Infectious Diseases) Stanford University School of Medicine; Medical Director Clinical Virology Laboratory Stanford Health Care and Stanford Children’s Health Stanford, California Alice Pong, MD Department of Pediatric Infectious Diseases University of California–San Diego; Department of Pediatric Infectious Diseases Rady Children’s Hospital San Diego San Diego, California Eric A. Porsch, PhD Department of Pediatrics Children’s Hospital of Philadelphia Philadelphia, Pennsylvania

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Contributors

Joan S. Purcell, MD Adolescent Medicine and Pediatrics STEP Pediatrics Woodlands, Texas Natalie M. Quanquin, MD, PhD Research Fellow Department of Microbiology, Immunology, and Molecular Genetics University of California–Los Angeles Los Angeles, California Kevin K. Quinn, MD Physician Department of Pediatric Infectious Diseases Southern California Permanente Medical Group Fontana, California Susan M. Abdel-Rahman, PharmD Chief, Section of Therapeutic Innovation Clinical Pharmacology, Medical Toxicology & Therapeutic Innovation Children’s Mercy–Kansas City; Professor of Pediatrics University of Missouri–Kansas City School of Medicine Kansas City, Missouri Octavio Ramilo, MD Henry G. Cramblett Chair in Medicine Professor of Pediatrics Ohio State University College of Medicine Department of Pediatrics Chief, Division of Infectious Diseases Nationwide Children’s Hospital Columbus, Ohio Ramya Ramraj, MD, MBBS Affiliate Assistant Professor Oregon Health and Sciences University; Attending Pediatrician and Pediatric Gastroenterologist Doernbecher Children’s Hospital and Kaiser NW Permanente Portland, Oregon Paula A. Revell, PhD Assistant Professor Departments of Pathology and Immunology and Pediatrics Baylor College of Medicine; Director of Microbiology and Virology Texas Children’s Hospital Houston, Texas Anne W. Rimoin, PhD, MPH Associate Professor Department of Epidemiology UCLA Fielding School of Public Health Los Angeles, California José R. Romero, MD Horace C. Cabe Professor of Infectious Diseases Department of Pediatrics University of Arkansas for Medical Sciences; Director, Pediatric Infectious Diseases Section Department of Pediatrics Arkansas Children’s Hospital; Director, Clinical Trials Research Arkansas Children’s Hospital Research Institute Little Rock, Arkansas

Lawrence Ross, MD, DTM&H Professor Emeritus Division of Pediatric Infectious Diseases Children’s Hospital of Los Angeles Keck School of Medicine at the University of Southern California Los Angeles, California Anne H. Rowley, MD Professor Department of Pediatrics and Microbiology/Immunology Northwestern University Feinberg School of Medicine Attending Physician, Division of Infectious Diseases Department of Pediatrics Ann & Robert H. Lurie Children’s Hospital of Chicago Chicago, Illinois Charles E. Rupprecht, VMD, MS, PhD Chief Executive Officer LYSSA, LLC Atlanta, Georgia Xavier Saez-Llorens, MD Professor of Pediatrics Head of Infectious Diseases Hospital del Niño “Dr. José Renán Esquivel” Distinguished Investigator, SNI, Senacyt Panama City, Panama Julia Shaklee Sammons, MD, MSCE Assistant Professor of Clinical Pediatrics Division of Infectious Diseases Perelman School of Medicine at the University of Pennsylvania; Medical Director and Hospital Epidemiologist Infection Prevention and Control Children’s Hospital of Philadelphia Philadelphia, Pennsylvania Pablo Sánchez, MD Prinicipal Investigator Center for Perinatal Research Fellow, Infectious Diseases Fellow, Neonatology Nationwide Children’s Hospital Columbus, Ohio Linette Sande, MD Assistant Professor of Pediatrics Department of Pediatric Infectious Diseases Loma Linda University; Attending Physician Department of Pediatric Infectious Diseases Loma Linda University Children’s Hospital Loma Linda, California Javier Santisteban-Ponce, MD Attending Physician Pediatric Infectious Disease Unit Department of Pediatrics Hospital Nacional Edgardo Rebagliati Martins-EsSalud; Lima, Peru Laura A. Sass, MD Assistant Professor Department of Pediatrics Eastern Virginia Medical School; Attending Physician Department of Pediatric Infectious Diseases Medical Director, Infection Prevention and Control, Antiobiotic Stewardship Children’s Hospital of The King’s Daughters Norfolk, Virginia

Contributors Stephen J. Scholand, MD Associate Professor Department of Medicine Frank Netter School of Medicine Quinnipiac University North Haven, Connecticut Danica J. Schulte, MD Assistant Professor in Residence Department of Pediatrics University of California–Los Angeles; Assistant Professor Departments of Pediatrics, Pediatric Infectious Diseases, Immunology and Allergy Cedars-Sinai Medical Center Los Angeles, California Jennifer E. Schuster, MD, MSCI Assistant Professor Department of Pediatrics Children’s Mercy Kansas City Kansas City, Missouri Gordon E. Schutze, MD, FAAP Professor of Pediatrics Executive Vice Chairman Martin I. Lorin, MD, Endowed Chair in Medical Education Department of Pediatrics Baylor College of Medicine; Vice President, International Programs Baylor International Pediatric AIDS Initiative at Texas Children’s Hospital Houston, Texas Patrick C. Seed, MD, PhD Assistant Professor Department of Pediatrics/Pediatric Infectious Diseases Duke University School of Medicine; Assistant Professor Department of Molecular Genetics and Microbiology Duke University School of Medicine Durham, North Carolina Jose A. Serpa, MD, MS Associate Professor Department of Medicine Baylor College of Medicine Houston, Texas Samir S. Shah, MD, MSCE Professor Department of Pediatrics University of Cincinnati College of Medicine; Director, Division of Hospital Medicine Attending Physician Divisions of Infectious Diseases and Hospital Medicine James M. Ewell Endowed Chair Cincinnati Children’s Hospital Medical Center Cincinnati, Ohio Eugene D. Shapiro, MD Professor Departments of Pediatrics, Epidemiology of Microbial Diseases, and Investigative Medicine Yale University New Haven, Connecticut

Nina L. Shapiro, MD Professor, Department of Head and Neck Surgery Director, Division of Pediatric Otolaryngology David Geffen School of Medicine at UCLA Los Angeles, California William T. Shearer, MD, PhD Professor of Pediatrics and Pathology and Immunology Distinguished Service Professor Baylor College of Medicine; Allergy and Immunology Service Texas Children’s Hospital Houston, Texas Robyn Shimizu-Cohen, CLS(ASCP) Specialist Department of Pathology and Laboratory Medicine University of California–Los Angeles Los Angeles, California Stanford T. Shulman, MD Chief Emeritus, Division of Infectious Diseases Ann & Robert H. Lurie Children’s Hospital of Chicago Virginia H. Rogers Professor of Pediatric Infectious Diseases Northwestern University Feinberg School of Medicine Chicago, Illinois Kareem W. Shehab, MD Assistant Professor Department of Pediatrics Section of Infectious Disease University of Arizona Tucson, Arizona Ziad M. Shehab, MD Professor of Pediatrics and Pathology University of Arizona Tucson, Arizona Constantine Simos, DMD Attending Surgeon Oral and Maxillofacial Surgery Robert Wood Johnson University Hospital Saint Peter’s University Hospital New Brunswick, New Jersey; Assistant Clinical Professor Oral and Maxillofacial Surgery Columbia University College of Dental Medicine New York, New York Michael A. Smit, MD, MSPH Division of Pediatric Infectious Diseases Hasbro Children’s Hospital Assistant Professor Department of Pediatrics Alpert Medical School of Brown University Providence, Rhode Island P. Brian Smith, MD, MPH, MHS Professor of Pediatrics Duke University Medical Center Duke Clinical Research Institute Durham, North Carolina Priya R. Soni, MD Fellow, Pediatric Infectious Disease Mattel Children’s Hospital University of California–Los Angeles Los Angeles, California

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Contributors

Sunil K. Sood, MBBS, DCH, MD Professor Departments of Pediatrics and Family Medicine Hofstra Northwell School of Medicine Hempstead, New York; Chair of Pediatrics Southside Hospital, Northwell Health Bay Shore, New York; Attending Physician Pediatric Infectious Diseases Cohen Children’s Medical Center New Hyde Park, New York Mary Allen Staat, MD, MPH Professor Department of Pediatrics University of Cincinnati College of Medicine; Director International Adoption Center Cincinnati Children’s Hospital Medical Center Cincinnati, Ohio Damien Stark, MSc, PhD, FASM, FACTM Associate, Department of Medical and Molecular Biosciences University of Technology Sydney Broadway, NSW, Australia; Senior Hospital Scientist Department of Microbiology St. Vincent’s Hospital Darlinghurst, NSW, Australia Jeffrey R. Starke, MD Professor Department of Pediatrics Baylor College of Medicine Houston, Texas Victoria A. Statler, MD, MSc Assistant Professor Department of Pediatric Infectious Diseases University of Louisville Louisville, Kentucky Barbara W. Stechenberg, MD Pediatric Infectious Diseases Specialist Department of Pediatrics Baystate Children’s Hospital Springfield, Massachusetts; Professor Emerita of Pediatrics Department of Pediatrics Tufts University School of Medicine Boston, Massachusetts William J. Steinbach, MD Professor of Pediatrics Professor in Molecular Genetics and Microbiology Chief, Pediatric Infectious Diseases Director, Duke Pediatric Immunocompromised Host Program Director, International Pediatric Fungal Network Duke University School of Medicine Durham, North Carolina Joseph W. St. Geme III, MD Professor of Pediatrics and Microbiology Chair, Department of Pediatrics Perelman School of Medicine at the University of Pennsylvania; Chair, Department of Pediatrics Physician-in-Chief Children’s Hospital of Philadelphia Philadelphia, Pennsylvania

Jeffrey Suen, MD Private Practice Bakersfield, California Lillian Sung, MD, PhD Professor Division of Haematology/Oncology Hospital for Sick Children Toronto, ON, Canada Douglas S. Swanson, MD Associate Professor of Pediatrics Department of Pediatric Infectious Diseases Children’s Mercy Kansas City; Associate Professor of Pediatrics University of Missouri–Kansas City Kansas City, Missouri Tina Q. Tan, MD Professor Department of Pediatrics Feinberg School of Medicine Northwestern University; Infectious Diseases Attending Physician Department of Pediatrics Ann & Robert H. Lurie Children’s Hospital Chicago, Illinois Ruston S. Taylor, PharmD Department of Pharmacy Legacy Community Health Houston, Texas Michael A. Tolle, MD, MPH Assistant Professor Department of Pediatrics Retrovirology and Global Health Section International Pediatrics AIDS Initiative (BIPAI) Baylor College of Medicine Children’s Foundation Texas Children’s Hospital Houston, Texas; Tanzania Buganda Medical Centre Mwanza, Tanzania Philip Toltzis, MD Professor Department of Pediatrics Rainbow Babies and Children’s Hospital Cleveland, Ohio Stuart R. Tomko, MD Division of Child Neurology Texas Children’s Hospital Houston, Texas Michael F. Tosi, MD Professor of Pediatrics Division of Pediatric Infectious Diseases Mount Sinai School of Medicine New York, New York Leidy J. Tovar Padua, MD Fellow Division of Pediatric Infectious Diseases Mattel Children’s Hospital of UCLA Los Angeles, California

Contributors Amelia P.A. Travassos da Rosa, BSc Research Associate Center for Tropical Diseases Department of Pathology University of Texas Medical Branch Galveston, Texas Theodore F. Tsai, MD, MPH Senior Vice President, Scientific Affairs Novartis Vaccines Cambridge, Massachusetts Andrew M. Vahabzadeh-Hagh, MD Resident Department of Head and Neck Surgery David Geffen School of Medicine at UCLA Los Angeles, California Jorge J. Velarde, MD, PhD Instructor Division of Infectious Diseases Boston Children’s Hospital Boston, Massachusetts Jesus G. Vallejo, MD Associate Professor Department of Pediatric Infectious Diseases Baylor College of Medicine Houston, Texas John A. Vanchiere, MD, PhD Professor and Chief Section of Pediatric Infectious Diseases Louisiana State University Health Sciences Center Shreveport, Louisiana Robert S. Venick, MD Associate Professor Departments of Pediatrics and Surgery David Geffin School of Medicine at UCLA Los Angeles, California Sanjay Verma, MBBS, MD Additional Professor of Pediatrics Advanced Pediatrics Centre Postgraduate Institute of Medical Education and Research Chandigarh, India James Versalovic, MD, PhD Pathologist-in-Chief Department of Pathology Texas Children’s Hospital; Milton J. Finegold Professor Department of Pathology and Immunology Baylor College of Medicine Houston, Texas Timo Vesikari, MD, PhD Director Vaccine Research Center University of Tampere Tampere, Finland Ellen R. Wald, MD Chair, Department of Pediatrics University of Wisconsin School of Medicine & Public Health; Pediatrician-in-Chief American Family Children’s Hospital Madison, Wisconsin

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Thomas J. Walsh, MD Director, Transplantation-Oncology Infectious Diseases Program Weill Cornell Medical Center of Cornell University New York, New York Mark A. Ward, MD Associate Professor Department of Pediatrics Baylor College of Medicine Houston, Texas Rachel L. Wattier, MD, MHS Assistant Clinical Professor Department of Pediatrics University of California–San Francisco San Francisco, California Sing Sing Way, MD, PhD Professor of Pediatrics Pauline and Lawson Reed Chair Division of Infectious Diseases Cincinnati Children’s Hospital University of Cincinnati College of Medicine Cincinnati, Ohio Jill Weatherhead, MD Assistant Professor of Infectious Diseases and Pediatrics National School of Tropical Medicine Baylor College of Medicine Houston, Texas Michelle Weinberg, MD, MPH Medical Epidemiologist Immigrant, Refugee, and Migrant Health Branch Division of Global Migration and Quarantine Centers for Disease Control and Prevention Atlanta, Georgia Nicholas Weinberg, MD Assistant Professor Department of Emergency Medicine Geisel School of Medicine Dartmouth-Hitchcock Medical Center Hanover, New Hampshire Melanie Wellington, MD, PhD Associate Professor Department of Pediatrics University of Rochester Medical Center Rochester, New York Robert C. Welliver Sr, MD Professor of Pediatrics Division of Pediatric Infectious Diseases University of Oklahoma Health Sciences Center Oklahoma City, Oklahoma; Emeritus Professor of Pediatrics Division of Pediatric Infectious Diseases SUNY at Buffalo and Children’s Hospital Buffalo, New York J. Gary Wheeler, MD, MPS Professor of Pediatrics Division of Infectious Diseases University of Arkansas for Medical Sciences Little Rock, Arkansas

xxiv

Contributors

A. Clinton White Jr, MD Professor, Division of Infectious Disease Department of Internal Medicine University of Texas Medical Branch Galveston, Texas

Terry W. Wright, PhD Associate Professor Department of Pediatrics University of Rochester Medical Center Rochester, New York

Suzanne Whitworth, MD Medical Director Department of Pediatric Infectious Diseases Cook Children’s Healthcare System Fort Worth, Texas

Nave Yeganeh, MD, MPH Assistant Professor Department of Pediatrics Division of Pediatric Infectious Diseases David Geffen School of Medicine at UCLA Los Angeles, California

Bernhard L. Wiedermann, MD, MA Professor Department of Pediatrics George Washington University School of Medicine and Health Sciences; Attending Physician Division of Infectious Diseases Children’s National Health System Washington, DC John V. Williams, MD Professor and Chief Pediatric Infectious Diseases Henry L. Hillman Chair in Pediatric Immunology Children’s Hospital of Pittsburgh of UPMC Pittsburgh, Pennsylvania Natalie M. Williams-Bouyer, PhD, D(ABMM) Associate Professor, Department of Pathology Associate Director, Division of Clinical Microbiology University of Texas Medical Branch; Clinical Consultant, Clinical Laboratory Services Shriners Hospitals for Children Galveston, Texas Charles R. Woods Jr, MD, MS Professor and Vice Chair for Faculty Development Department of Pediatrics University of Louisville School of Medicine Louisville, Kentucky

Edward J. Young, MD Professor of Medicine Baylor College of Medicine Houston, Texas Ramia Zakhour, MD Clinical Instructor Department of Pediatrics and Adolescent Medicine Division of Pediatric Infectious Diseases American University of Beirut Beirut, Lebanon Theoklis Zaoutis, MD, MSCE Professor of Pediatrics and Epidemiology Perelman School of Medicine at the University of Pennsylvania; Associate Chief Division of Infectious Diseases Children’s Hospital of Philadelphia Philadelphia, Pennsylvania

Preface

Morbidity and mortality rates related to infectious diseases decreased dramatically during the first half of the 20th century in the developed world because of major improvements in public health (e.g., clean water, adequate sanitation, and vector control) and personal health. Further major reductions occurred in the second half of that century following the introduction of antimicrobial therapy, as well as active and passive immunization efforts. Despite these advances, infectious diseases in the developed world remain the leading cause of morbidity in infants and children in the 21st century. Children in the United States continue to experience three to nine respiratory infections and one to three gastrointestinal illnesses annually, requiring visits to physicians that outnumber the visits made for the purpose of well-child care. Infectious diseases are also the most common cause of school absenteeism. Children in low and middle income countries also experience high rates of respiratory and gastrointestinal infections, which are often more severe and more frequent than those in children in the developed world. In addition, in the developing world there are great morbidity and mortality due to parasitic and vector-borne diseases. Also of importance are “spillover” infectious diseases such as Ebola, which because of increased urbanization resulted in an extensive epidemic in three African countries in 2014–15. In addition, mosquito-borne diseases such as Zika and Chikungunya have increased in prevalence in the Americas. In more recent years, the emergence of resistance to multiple antibiotics by a large number of bacterial microorganisms (e.g., communityassociated methicillin-resistant Staphylococcus aureus) has contributed to this infection-related morbidity and mortality, as have new infectious agents (e.g., SARS and MERS coronaviruses) and changes in the clinical manifestations and severity of established infectious agents (e.g., enterovirus 71, swine influenza). The first edition of Textbook of Pediatric Infectious Diseases was written because Drs. Feigin and Cherry and many of their colleagues were concerned that no single reference text existed that comprehensively covered infectious diseases in children and adolescents. With each subsequent edition, including this one, the goal has been to provide comprehensive coverage of all subjects pertinent to the study of infectious diseases in children. Any attempt to summarize our present understanding of infectious diseases for serious students of the subject is a formidable task. In many areas, new information continues to accrue so rapidly that material becomes dated before it can appear in a text of this magnitude. Nevertheless, in this edition the editors and their author colleagues have endeavored to provide the most comprehensive and up-to-date discussion of pediatric infectious diseases ever compiled. This new edition is available online as well as in print. Purchasers can access the online version by registering their personal identification number (PIN) (found on the inside front cover of the book) at expertconsult.inkling.com. Online access includes not only fully searchable text, photos, illustrations, and tables, but also references linked to PubMed. To provide a text as comprehensive and authoritative as possible, we, the editors, have enlisted contributions from a large number of individuals whose collective expertise is responsible for whatever success we may have had in meeting our objective. We offer our most profound appreciation to the 307 fellow contributors from nearly 100 universities or institutions in 18 countries for their professional expertise and devoted scholarship. Their cooperation and willingness to work with us leave us deeply in their debt. Of note is the fact that 10 authors (Carol Baker, Ken Boyer, Jim Cherry, Morven Edwards, Chuck Grose, Scott Halstead, Maggie Hammerschlag, Shelly Kaplan, Ed Mason, and Barbara Stechenberg) have contributed to all eight editions of Textbook of Pediatric Infectious Diseases. Once again, infectious diseases are discussed according to organ systems that may be affected, as well as individually by microorganisms. In all sections in which diseases related to specific agents are discussed,

emphasis has been placed, to the greatest extent possible, on the specificity of clinical manifestations that may be related to the organism causing the disease. Detailed information regarding the best means to establish a diagnosis and explicit recommendations for therapy are provided. In the present era of instant information, we have noted that historical perspectives relating to disease categories, as well as specific agents, are ignored. Because history is an important teacher, we have retained relevant historical details in this eighth edition. Throughout the 37 years and eight-edition history of the Textbook of Pediatric Infectious Diseases, a number of classic chapters exist (e.g., measles, rubella, enteroviruses, and mycoplasma infections). The data in these chapters are unavailable in any other single-source publication. The entire text of this eighth edition has been revised extensively. The seventh edition contained almost 4000 pages even though we included only new references in the print edition, which is close to the maximum that can be included in a two-volume book. Therefore, with this eighth edition, we were faced with a major dilemma: specifically, how to include new important material that had become available since the seventh edition but not to substantially increase the size of the book. We approached this dilemma in two ways. One problem in previous editions was redundancy, which we have addressed by combining information in some previous separate chapters into more concise single presentations and by shortening some chapters. The second way, which we introduced in the last edition, is to print only new references. The electronic version of the text contains all references. This edition continues the format that was initiated in the fourth edition, in that infections with specific microorganisms have been organized to provide appropriate emphasis on the common features that may relate specific microorganisms to one another. Thus, all grampositive coccal organisms are presented sequentially and are followed by gram-negative cocci, gram-positive bacilli, enterobacteria, gramnegative coccobacilli, Treponemataceae, anaerobic bacteria, and so forth. In addition, special sections of the text have been devoted to discussions of each of the following: molecular determinants of microbial pathogenesis; immunologic and phagocytic responses to infection; metabolic response of the host to infections; interaction of infection and nutrition; pathogenesis and treatment of fever; the human microbiome; epidemiology and biostatistics of infectious diseases; infections of the compromised host; Kawasaki disease; chronic fatigue syndrome; international travel issues for children; infectious disease problems of international adoptees and refugees; nosocomial infections; prevention and control of infections in hospitalized children; pharmacology and pharmacokinetics of antibacterial, antiviral, antifungal, and antiparasitic agents; immunomodulating agents; active and passive immunizing agents; public health considerations; infections in day care environments; and use of the bacteriology, mycology, parasitology, virology, and serology laboratories. The section on infections in the compromised host has again been expanded. This expansion has been necessitated by the large number of children, particularly transplant recipients, who have many infectious disease problems and constitute a large part of the consulting practice of many pediatric infectious disease physicians. With some sadness, we have retained a section on bioterrorism, which is necessitated by the current state of world affairs. The section on immunomodulating agents and their potential use in the treatment of infectious diseases has been expanded because information on this subject has become more extensive since the publication of the last edition. We have also expanded the section on Ebola virus and included a new chapter on Zika virus. This project could not have been brought to fruition without the help and assistance of many people whose names do not appear in the text. No words are sufficient to adequately convey our gratitude appropriately; we hope that they know they have our heartfelt thanks. xxv

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We would like to single out certain individuals for specific mention. First and foremost, we convey our appreciation to Laura Wennstrom Sheehan for the many hours she devoted to this edition. In her spare time between her position as Manager of Research Administration for the UCLA Department of Family Medicine and raising her young daughter, she coordinated the overall process of moving the book forward. She tended to numerous details relating to copyediting, transcribing, references, timing, and communication between the editors and Elsevier. Her expertise in EndNote was invaluable to the authors, editors, and publishing team for the organization of countless references throughout this edition. We are extremely grateful to have her as a part of our team. We would also like to acknowledge the hard work of Jordan Mann who assisted Laura throughout this process. The following students at UCLA played a key role in processing chapters and in particular helping with references: Lauren M. Nguyen, David Dang, and Jewel Powe. We would also like to thank Nathaniel Wilder Wolf at Baylor who coordinated all the parasite chapters. Of course this eighth edition of Textbook of Pediatric Infectious Diseases would not have been possible without Elsevier. We have been particularly

fortunate to have been able to work with Kate Dimock, Executive Content Strategist, Clinical Solutions at Elsevier throughout the whole process relating to this eighth edition. In addition, the initial planning contribution by Lauren Elise Boyle, Content Development Specialist, was invaluable. This was followed-up by the day-to-day contributions of Margaret Nelson, also a Content Development Specialist at Elsevier. Margaret kept everyone on track in meeting deadlines. Finally, we thank the Baylor College of Medicine and Texas Children’s Hospital in Houston, Texas, the David Geffen School of Medicine at UCLA and the Mattel Children’s Hospital UCLA in Los Angeles, California, and Duke University School of Medicine in Durham, North Carolina for providing an environment that is supportive of intellectual pursuits. James D. Cherry, MD Gail J. Harrison, MD Sheldon L. Kaplan, MD William J. Steinbach, MD Peter J. Hotez, MD

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Molecular Determinants of Microbial Pathogenesis David A. Hunstad • Ravi Jhaveri • Audrey R. Odom John • Joseph W. St. Geme III

Despite the availability of a wide variety of antimicrobial agents and expansion of vaccination programs, infectious diseases remain a leading cause of childhood morbidity and mortality worldwide. A number of factors contribute to the increasing importance of infectious agents: rates of antimicrobial resistance continue to rise, global travel has become routine, and the number of individuals with altered immunity has increased. Furthermore, in recent years, microorganisms have been implicated in diseases previously considered noninfectious, and a variety of new, emerging, and reemerging pathogens have been recognized. Pathogens are defined as microorganisms that are capable of causing disease. However, not all pathogens are equal with respect to their pathogenic potential (i.e., their virulence). Many pathogens are, in fact, commensal organisms that live in harmony with their host under most conditions, causing disease only when normal immune mechanisms are disrupted or absent. Other pathogens produce disease even in the setting of intact host defenses and almost always cause symptoms. For a given microbe, pathogenic potential is often determined by the genomic content and regulation of virulence-associated genes. Some bacterial species are capable of natural transformation and readily acquire fragments of DNA from other organisms, thus expanding or altering their genetic composition, occasionally with consequences related to virulence or antimicrobial resistance. A number of microorganisms carry virulence-associated genes on mobile genetic elements, including plasmids, transposons, and bacteriophages. These elements may equip the organism with genetic information that facilitates rapid adaptation to an unfavorable or changing environment. Comparison of genomes from pathogenic and nonpathogenic bacteria within a single genus or species has led to the identification of pathogenicity islands, which are large blocks of chromosomal DNA that are present in pathogens and absent from related nonpathogens. These blocks are flanked by insertion sequences or repeat elements and differ in nucleotide composition relative to the surrounding genome, suggesting acquisition by horizontal exchange. Pathogenicity islands in bacteria encode a variety of virulence factors, including protein secretion systems, secreted effector molecules, adhesins, and regulatory proteins. In an analogous way, some viral pathogens such as influenza virus are capable of exchanging nucleic acid segments with other viruses, leading to changes in pathogenicity, host tropism, and transmissibility. To be successful, a pathogen must enter the host, occupy an appropriate niche, and then multiply. Sometimes the pathogen will induce damage to the host and then spread to other tissues, either near the initial site of infection or more distant. Often the pathogen will stop short of causing death to the host, maintaining latent infection or producing symptoms such as cough or diarrhea that facilitate spread to another host. This chapter addresses several key steps in the pathogenic process, each illustrated with examples of pathogens and paradigms of relevance to infectious diseases in children.

COLONIZATION Most bacterial infections begin with microbial colonization of a host surface, typically the skin, the respiratory tract, the gastrointestinal tract, or the genitourinary tract. Although colonization is not sufficient for an organism to produce disease, it is a necessary prerequisite. The process of bacterial colonization requires specialized microbial factors, called adhesins, that promote adherence to host structures and enable these organisms to overcome local mechanical defenses such as mucociliary function, peristalsis, and urinary flow. The cognate receptors for these 2

interactions are generally either carbohydrate or protein structures, in some cases expressed on host cells and in other instances present in mucosal secretions or in submucosal tissue.

Pilus Adhesins Perhaps most common among bacterial adhesins are hairlike fibers called pili (also called fimbriae). Pili are heteropolymeric protein structures comprised largely of a major subunit usually ranging in size from 15 to 25 kDa. Because of their size and morphology, most pili can be visualized by negative-staining transmission electron microscopy. The prototype example among adhesive pili is the P (or Pap) pilus, which is expressed by uropathogenic Escherichia coli (UPEC) and has been strongly associated with pyelonephritis. P pili recognize globoseries glycolipids, which are host molecules that are characterized by a core structure consisting of Gal-α1,4-Gal. The globoseries glycolipids are especially abundant in renal epithelium,25 thus accounting for the predilection of P-piliated E. coli to adhere to kidney tissue and cause pyelonephritis. Type 1 pili are analogous fibers expressed by UPEC and bind mannosylated uroplakin proteins in the mammalian bladder to initiate cystitis.153 As shown in Fig. 1.1, P pili are composite structures and consist of two subassemblies, including a thick rod that emanates from the bacterial surface and a thin tip fibrillum that extends distally.173,270 The pilus rod is a right-handed helical cylinder and is composed of repeating PapA subunits, whereas the tip fibrillum has an open helical configuration and contains mostly repeating PapE subunits. The two subassemblies are joined to each other by the PapK adaptor protein. PapG contains the adhesive moiety and is located at the distal end of the tip fibrillum, joined to PapE by the PapF adaptor.150 P pili are assembled through a canonical process termed the chaperoneusher pathway that involves a periplasmic chaperone (PapD) and an outer membrane usher (PapC) (see Fig. 1.1).65,174 Subunit proteins (e.g., PapA) are translated in the bacterial cytoplasm, enter the periplasm through the inner membrane Sec machinery, and are stabilized by interaction with the chaperone, which ferries them to the usher. Extrusion of the nascent fiber is controlled by a “plug” domain in the usher pore; because the periplasm is devoid of adenosine triphosphate (ATP), the assembly process is energetically driven by the entropically favorable final conformation of the incorporated subunits.189,259 More than 30 different bacterial adhesive structures are assembled via this chaperoneusher pathway, with distinct PapD-like chaperones and PapC-like ushers. The PapD-like chaperones can be divided into two distinct subfamilies based on conserved structural differences that occur near the subunit binding site.138 One subfamily is involved in the assembly of rod-like pili similar to P pili, whereas the second subfamily participates in the biogenesis of more atypical filamentous structures, such as Caf1 of Yersinia pestis (the plague bacterium), which forms an amorphous “mat” on the bacterial surface. Thus the nature of the chaperone is directly correlated with the architecture of the adhesive appendage that it helps to assemble.285 Type 4 pili represent a second class of pili and are distinguished by a methylated first amino acid (usually phenylalanine); a short, positively charged leader sequence; a conserved hydrophobic Nterminal domain; and a tendency to form bundle-like structures. Type 4 pili have been identified in a number of gram-negative bacterial pathogens, including Neisseria gonorrhoeae, N. meningitidis, enteropathogenic E. coli (EPEC), Vibrio cholerae, Pseudomonas aeruginosa, Kingella kingae, Eikenella corrodens, Haemophilus influenzae, and Moraxella species.32,99,193,208,250,256,272,296,323 Although the mechanism of

CHAPTER 1  Molecular Determinants of Microbial Pathogenesis

3

G Tip fibrillum G

E. coli P Pilus

F E

Outer membrane C

D F D A

G D

Pilus rod

E

C

D K

G D

D E D K

C

D A D

D

DSBA Periplasm

D A Y Y E E G G

D

Cytoplasmic membrane pap Gene cluster I

B

A

Tip fibrillum components H

C

Regulation

Rod terminator Major Outer pilus subunit membrane usher

D Periplasmic chaperone

J

K

E

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Adaptor/ Adaptor/ initiator initiator Major tip Gal(1-4) galcomponent binding adhesin

FIG. 1.1  Biogenesis and structure of Escherichia coli P pili. The pap gene cluster and the function of each of the gene products are indicated in the lower portion of the figure. Nascent pilin subunits are complexed with the PapD chaperone and added to the base of the developing pilus via the PapC usher. The mature pilus rod is composed of repeating units of PapA; the tip fibrillum contains the adhesin PapG. The ultrastructure of the pilus is shown in the electron micrograph at the left side of the figure. (Courtesy S.J. Hultgren and F.J. Sauer.)

assembly of type 4 pili is still being elucidated, existing data suggest that the process is complex. For example, between 20 and 40 gene products are required for the assembly of P. aeruginosa type 4 pili, and at least 15 plasmid-encoded proteins are involved in the biogenesis of EPEC type 4 pili.127,294 Based on studies of P. aeruginosa, EPEC, Neisseria, and V. cholerae, the presence of an inner membrane prepilin peptidase appears to be a general prerequisite for type 4 pilus biogenesis.161,176,226 Type 4 pili are often glycosylated, with carbohydrate decoration affecting function in at least some cases and perhaps serving to obscure antigenic epitopes.33,190,278,319 However, despite marked differences in the assembly pathways for type 4 pili and P pili, shared structural themes exist. For example, gonococcal type 4 pili are composed predominantly of PilE structural subunits polymerized into a helical rod.235 A minor phasevariable adhesive protein called PilC is displayed at the tip of gonococcal pili and is essential for pilus-mediated binding to epithelial cells.154,267 These observations suggest that N. gonorrhoeae pili may be composite structures with a tip-associated adhesin, analogous to P pili and other pili assembled by the chaperone-usher pathway. Although adhesive pili are more prevalent in gram-negative bacteria, they are also found in some gram-positive species. One example is Streptococcus parasanguinis, an oral pathogen and a member of the S. sanguinis family. This organism binds to calcium phosphate (the primary mineral component of tooth enamel) and also to other oral bacteria, epithelial cells, platelets, and fibronectin. Several adhesins mediate these binding functions, including pili referred to as long fimbriae. Based on studies of S. parasanguinis strain FW213, long fimbriae are fashioned

primarily from Fap1, a 200-kDa protein that includes an unusually long (50 amino acids) signal sequence and a cell-wall sorting signal typical of other gram-positive bacterial surface proteins.338,339 Specific glycosylation of Fap1 appears critical to the adhesive function of this fimbrial protein.27,293,337 Interestingly, similar to gram-negative bacterial pili, long fimbriae appear to have a composite structure with a pilus tip. The tip contains an additional adhesin called FimA, which in purified form is capable of blocking bacterial adherence to saliva-coated hydroxyapatite.81,231 In work by Burnette-Curley and coworkers, disruption of the fimA gene resulted in a 7- to 20-fold reduction in the incidence of endocarditis after intravenous inoculation of rats.29 Other gram-positive organisms capable of expressing pili include Streptococcus pneumoniae (a common cause of respiratory tract and invasive disease),11,216 Streptococcus agalactiae (group B streptococcus; a common cause of neonatal pneumonia, sepsis, and meningitis),73,264 and Enterococcus faecalis (a cause of endocarditis and urinary tract infections).215,277

Nonpilus Adhesins Beyond pili, a variety of nonpilus adhesins exist. In most cases, nonpilus adhesins are surface-expressed monomeric or oligomeric proteins, although isolated examples of carbohydrate- and lipid-containing adhesive structures have been identified. In general, these molecules are more difficult to visualize by electron microscopy, reflecting their smaller size. Similar to pili, for the most part nonpilus adhesins can be classified according to their mechanism of secretion and presentation on the bacterial surface.

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PART I  Host-Parasite Relationships and the Pathogenesis of Infectious Diseases

Among the best-characterized bacterial nonpilus adhesins is filamentous hemagglutinin (FHA), a surface protein expressed by Bordetella pertussis and other Bordetella species. The export of FHA to the surface of the organism occurs via the so-called two-partner secretion (TPS) pathway, a conserved strategy in which a secreted protein (TpsA) interacts with a cognate outer membrane transporter (TpsB).128 In B. pertussis, the TpsA-type protein FHA is transported by a TpsB-type outer membrane protein called FhaC, which has β-barrel pore-forming properties and facilitates translocation of FHA across the outer membrane.333 Homologous TpsB proteins in other species export the hemolysins of Serratia marcescens, Proteus mirabilis, and Haemophilus ducreyi; the H. influenzae heme:hemopexin binding protein (HxuA); and the H. influenzae HMW1 and HMW2 adhesins, among others.9,46,234,249,287,316 The crystal structure of FhaC reveals a 16-stranded β-barrel that is occluded by an N-terminal α-helix and an extracellular loop and a periplasmic module composed of two polypeptide-transportassociated (POTRA) domains. Functional studies have demonstrated that the N terminus of FHA interacts with the FhaC POTRA 1 domain, illuminating what appears to be a general feature of interactions between TpsA and TpsB proteins.39,104 Examination of purified FHA by transmission electron microscopy and circular dichroism spectroscopy showed that the FHA molecule is 50 nm in length and adopts the shape of a horseshoe nail. It has a globular head, a 37-nm-long shaft that averages 4 nm in width but tapers slightly from the head end, and a small flexible tail (Fig. 1.2).157,188 In the crystal structure of the N terminus of FHA (the so-called TPS domain that interacts with FhaC), a series of 19-residue repeat motifs form a β-helix that is central to the overall structure of full-length FHA.40 Consistent with its large size, FHA contains at least five separate binding domains, four of which have been localized. The region involved

N

Sulfated saccharide binding domain

B0

R1

B1

RGD site Carbohydrate recognition domain

R2

B2 C FIG. 1.2  Ribbon representation model structure of filamentous hemagglutinin from Bordetella pertussis. There are five regions that are assigned β-helical coils, designated B0, R1, B1, R2, and B2. The N terminus of the protein is designated with “N,” and the C terminus of the protein is designated with “C.” The locations of the sulfated saccharide binding domain, the carbohydrate recognition domain, and the RGD tripeptide are noted. (From Kajava AV, Cheng N, Cleaver R, et al. Beta-helix model for the filamentous haemagglutinin adhesin of Bordetella pertussis and related bacterial secretory proteins. Mol Microbiol. 2001;42:279–92.)

in adherence to sulfated saccharides has been mapped to the N terminus of the FHA molecule.206 Sulfated saccharides such as heparin and heparan sulfate are a major component of mucus and extracellular matrix in the respiratory tract and are also found on the surface of epithelial cells.195,342 The region that recognizes lactosylceramides and promotes adherence to ciliated respiratory epithelial cells and macrophages has been localized to amino acids 1141 to 1279 (the carbohydrate recognition domain).251 An arginine-glycine-aspartic acid (RGD) tripeptide is located at amino acids 1097 to 1099 and interacts with leukocyte response integrin (LRI), a leukocyte integrin that stimulates upregulation of complement receptor type 3 (CR3).146 The C terminus of mature FHA has been demonstrated to interact with epithelial cells and macrophage-like cells and appears to modulate the immune response to Bordetella infection.155 Finally, FHA recognizes CR3 (CD11b/CD18), allowing organisms to be ingested by macrophages without stimulating an oxidative burst.258,336 The location of the CR3-binding domain is currently unknown. A growing number of nonpilus adhesins belong to the so-called autotransporter family. These proteins are synthesized as precursor proteins with three functional domains, including an N-terminal canonical signal sequence, an internal passenger domain, and a C-terminal outer membrane domain. The signal sequence directs the protein to the Sec machinery and is cleaved after it facilitates transport of the polypeptide from the cytoplasm to the periplasm. The C-terminal domain inserts into the outer membrane and forms a β-barrel with a central hydrophilic channel. Ultimately, the passenger domain is presented on the surface of the organism and influences interaction with host molecules.120 Recent studies have established that autotransporter proteins can be separated into two distinct groups, designated conventional autotransporters and trimeric autotransporters (Fig. 1.3).52 In conventional autotransporters, the C-terminal outer membrane domain contains roughly 300 amino acids and is a monomeric β-barrel with a single N-terminal α-helix spanning the pore (Fig. 1.4A).232,299 In trimeric autotransporters, the C-terminal outer membrane domain contains approximately 70 amino acids and forms heat- and detergent-resistant trimers in the outer membrane. Each trimer forms a β-barrel with four strands from each of the three subunits and with three N-terminal α-helices spanning the pore (Fig. 1.4B).204 One example of a conventional autotransporter adhesin is the H. influenzae Hap protein, which was discovered based on its ability to promote adherence and low-level invasion in assays with cultured human epithelial cells.286 Hap also promotes bacterial binding to extracellular matrix proteins and bacterial microcolony formation.83,121 Examination of chimeric proteins and studies with purified protein have demonstrated that the adhesive activity responsible for Hap-mediated adherence, invasion, binding to extracellular matrix proteins, and microcolony formation localizes to the passenger domain, referred to as HapS.83,121 More detailed characterization of HapS has established that the region responsible for interaction with host epithelial cells and microcolony formation resides in the C-terminal 311 amino acids and may have utility as a vaccine antigen.57,82,183 This region folds into a triangular prism-like structure that can mediate Hap-Hap dimerization and higher degrees of multimerization, thus facilitating interbacterial interaction and microcolony formation.202 A prototype member of the trimeric autotransporter subfamily is the H. influenzae Hia adhesin. This protein is expressed in a subset of nontypable H. influenzae strains and contains two homologous high-affinity trimeric binding domains, creating the potential for stable multivalent interaction with respiratory epithelial cells.175,203,343 Another group of nonpilus adhesins is typified by intimin, a protein expressed by enteropathogenic E. coli (EPEC), enterohemorrhagic E. coli (EHEC), and the murine pathogen Citrobacter rodentium. Intimin contains a flexible N terminus, a central β-barrel domain that integrates into the outer membrane, and a C-terminal binding domain that interacts with the translocated intimin receptor (Tir).311 Tir is an interesting example of a pathogen-derived receptor that is inserted into target host cells. After initial cell attachment mediated by type 4 pili, EPEC employs a type III secretion system (discussed in detail later in this chapter) to inject Tir into the host cell cytoplasm,164,335 from where it is then inserted into the host cell membrane.254 The subsequent interaction between

CHAPTER 1  Molecular Determinants of Microbial Pathogenesis

5

OM

IM

C′

N′

N′

Conventional autotransporters

C′ Trimeric autotransporters

FIG. 1.3  Autotransporter protein secretion pathway. Conventional autotransporter secretion is shown on the left, and trimeric autotransporter secretion is shown on the right. Autotransporter proteins are synthesized as preproteins with three functional domains, including an N-terminal signal sequence (shown in green), an internal passenger domain (shown in red), and a C-terminal outer membrane β-barrel domain (shown in blue). IM indicates inner membrane, and OM indicates outer membrane. Protein secretion begins with export of the protein from the cytoplasm via the inner membrane Sec machinery (Sec). Most conventional autotransporters are cleaved on the bacterial surface. (From Cotter SE, Surana NK, St Geme JW III. Trimeric autotransporters: a distinct subfamily of autotransporter proteins. Trends Microbiol. 2005;13:199–205.) N N

N

N

C

A

C

B

C C

FIG. 1.4  Crystal structures of the C-terminal outer membrane β-barrel of autotransporter proteins. (A) Crystal structure of NalP, a conventional autotransporter; β strands are shown in shades of blue, and the α-helix that crosses the channel is shown in red. (B) Crystal structure of Hia, a trimeric autotransporter; individual subunits are shown in red, green, and yellow. (A, From Surana NK, Cotter SE, Yeo HJ, et al. Structural determinants of Haemophilus influenzae adherence to host epithelium: variations on type V secretion. In: Waksman G, Caparon MG, Hultgren SJ, editors. Structural Basis of Bacterial Pathogenesis. Washington, DC: American Society for Microbiology; 2005:129–148. B, From Meng G, Surana NK, St Geme JW III, et al. Structure of the outer membrane translocator domain of the Haemophilus influenzae Hia trimeric autotransporter. EMBO J. 2006;25:2297–304.)

intimin (on the bacterial surface) and Tir (now present on the host cell surface) triggers receptor clustering, dramatic rearrangement of the actin cytoskeleton, and formation of a distinctive pedestal referred to as an attaching and effacing (A/E) lesion (Fig. 1.5).164,263 The bacterial genes essential for formation of A/E lesions reside within a 35-kb region of the EPEC chromosome called the locus of enterocyte effacement (LEE), an example of a pathogenicity island.70,196 This locus is highly conserved in content and organization across all A/E pathogens and contains the genes encoding intimin, Tir, and the requisite type III secretion system. The interactions of Tir and other type III secreted effectors with host proteins influencing actin polymerization are beginning to be understood.265,344 Tir contains domains analogous to host immunoreceptor tyrosine-based inhibition motifs (ITIM) important for regulation of eukaryotic signaling. On this basis, Tir recruits certain host proteins to regulate actin dynamics and inhibit proinflammatory signaling pathways.61,266,280,328 Given its central role in EHEC/EPEC pathogenesis and its immunogenicity, intimin is also being examined as a target for the development of antivirulence therapeutics or vaccines in A/E diseases. In recent years, investigators have identified a large family of nonpilus adhesins involved in adherence to host extracellular matrix proteins including fibronectin, laminin, vitronectin, collagen, fibrinogen, and a variety of proteoglycans. These adhesins have been classified as microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) and are especially prevalent among gram-positive bacteria.238 In gram-positive organisms these proteins are covalently anchored to the cell wall peptidoglycan and have a characteristic primary amino acid sequence. In particular, the C terminus contains a segment rich in proline and glycine residues, an LPXTG motif (involved in sorting and covalently anchoring the protein to the cell wall), a hydrophobic membrane-spanning domain, and a short positively charged segment that resides in the cytoplasm and serves as a cell wall retention signal. Adhesive functions are typically located near the N terminus.85 Staphylococcus aureus is a common gram-positive pathogen in children and is capable of producing a variety of MSCRAMMs, including collagen-binding protein (CNA), fibronectin-binding proteins A and B, and clumping factors A and B. Recent work indicates that although

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PART I  Host-Parasite Relationships and the Pathogenesis of Infectious Diseases

FIG. 1.5  Enteropathogenic E. coli are perched on pedestals in the attaching and effacing lesion. (Courtesy B.B. Finlay; from Rosenshine I, Ruschkowski S, Stein M, et al. A pathogenic bacterium triggers epithelial signals to form a functional bacterial receptor that mediates actin pseudopod formation. EMBO J. 1996;15:2613–24.)

these proteins mediate typical binding interactions with host proteins, they are not monospecific, and a given MSCRAMM may bind multiple host connective tissue components or multiple motifs within a single host fiber type.284 In addition, many are capable of provoking platelet activation. S. aureus strains recovered from patients with septic arthritis commonly express CNA, which mediates binding to cartilage in vitro and appears to play a key role in the pathogenesis of septic arthritis in experimental mice.237,239,300 Fibronectin-binding protein A (FnBPA) shares homology with S. pyogenes protein F and mediates binding to fibronectin and the γ chain of fibrinogen, as well as to elastin and tropoelastin.162,262,322 Accordingly, this protein is important in S. aureus endocarditis247 and in infections of implanted biomaterials, which become coated with fibrinogen and fibrin soon after implantation. Clumping factor (ClfA) was named based on the observation that it mediates bacterial clumping in the presence of soluble fibrinogen.197 Similar to FnBPA, ClfA mediates binding to fibrinogen-coated surfaces in vitro and probably contributes to infections of artificial surfaces.

Other Mechanisms of Adherence Candida albicans is a common inhabitant of mucosal surfaces and an important cause of systemic disease, especially in patients with compromised immunity. Candida blastospores are capable of efficient adhesion to epithelial cells, leading to budding and division. In addition, germ tube formation occurs, facilitating penetration through the epithelial barrier and then dissemination to distant sites.135 In recent years, several candidate C. albicans adhesins have been identified.10,134,180,346 Of particular interest is a protein called INT1, which shares functional homology with the vertebrate integrin family. Integrins are normally expressed by cells of the human immune system (neutrophils, monocytes, macrophages) and mediate cellular binding and shape-changing functions. Each integrin is a heterodimer of an α chain and a β chain. There are a number of distinct α and β chains, and each combination displays a unique binding specificity. INT1 is an α integrin–like protein that recognizes the RGD sequence of the C3 fragment iC3b on epithelial cells. In in vitro assays, short peptides encompassing the RGD sequence are capable of inhibiting C. albicans adherence by 50%, confirming that INT1 plays a significant role as an adhesin and suggesting that other adhesins also exist.135 Beyond promoting adherence to epithelium, INT1 disguises organisms as leukocytes, allowing evasion of phagocytosis. Of note, introduction of INT1 into Saccharomyces cerevisiae confers a

capacity for adherence and also results in germ tube formation, indicating a role for this protein in morphogenesis.95,94 The adhesive properties of C. albicans are closely tied to its morphologic state. For example, adherence to buccal epithelial cells is greater by organisms bearing germ tubes than by yeast forms.169 With this information in mind, Staab and coworkers searched a germ tube cDNA library and identified a putative adhesin called hyphal wall protein 1 (Hwp1) encoded by the hwp1 gene. Examination of the predicted amino acid sequence of Hwp1 revealed similarity to proteins that are substrates for mammalian transglutaminase enzymes.290 These enzymes form a cornified envelope on squamous epithelial cells (including buccal epithelial cells) by cross-linking relevant substrates.302 Interestingly, the interactions of germ tubes with buccal epithelial cells resist stresses (e.g., heating or treatment with sodium dodecylsulfate) capable of dissociating most typical microbe-host adhesive pairs, and elimination of expression of Hwp1 results in a marked reduction in adhesion to buccal epithelial cells.23,289 Thus Hwp1 represents a unique adhesive strategy, employing host transglutaminase enzymes to cross-link Hwp1 (via a glycosylphosphatidylinositol remnant anchor) directly to surface proteins on buccal epithelial cells.288 More recently, Hwp1 has been shown to be important for Candida biofilm formation,77,220 indicating that a similar mechanism may also support interactions between candidal cells.

TISSUE TROPISM Most microorganisms demonstrate restriction in the range of hosts, tissues, and cell types that they colonize. This restriction is referred to as tropism and generally reflects the specificity of the interaction between a given microbial adhesin and its cognate receptor. Accordingly, tropism is determined by the distribution of the relevant host receptor. P pili of uropathogenic E. coli serve as the platform for presentation of one of three different PapG variants, referred to as class I, class II, and class III PapG. All three variants recognize globoseries glycolipids, but each binds with a distinct specificity to the globoseries glycolipid isotypes. For example, class I PapG preferentially recognizes globotriosylceramide (GbO3, Gal-α1,4-Gal-β1,3-Glc-ceramide), class II PapG preferentially recognizes globoside (GbO4, GalNAc-β1,3-Gal-α1,4-Galβ1,3-Glc-ceramide), and class III PapG preferentially interacts with Forssman antigen (GbO5, GalNAc-α1,3-GalNAc-β1,3-Gal-α1,4-Galβ1,3-Glc-ceramide).297 Globoside is the dominant globoseries glycolipid expressed in human kidney, and most human isolates of E. coli associated with pyelonephritis express class II PapG. In contrast, Forssman antigen is the most abundant globoseries glycolipid in dog kidney, and more than 50% of canine urinary isolates of E. coli express class III PapG.341 E. coli–expressing P pili with class II PapG are not found as a cause of urinary tract infection in dogs. Thus the specificity of the PapG variant at the tip of the P pilus influences host range, favoring infection of either human or dog. The crystal structure of class II PapG bound to Gal-α1,4-Gal was solved by Dodson and coworkers, uncovering the structural basis of PapG binding specificity.66 Of particular interest, the PapG receptor binding site is located on the side of the molecule and must be oriented with its N- to C-terminal axis parallel to the host cell membrane to allow docking to the receptor. This orientation may be facilitated by the flexibility inherent in the tip fibrillum. The PapG binding site consists of two regions. The first forms a β-barrel, and the second is composed of a central antiparallel β-sheet that is flanked on one side by two 2-stranded β-sheets and on the other side by an α-helix. When class II PapG interacts with GbO4, the arginine residue at position 170 in PapG makes contact with the GbO4 side chain. Interestingly, in class I PapG, a histidine residue occupies position 170, interfering with potential contact with the GbO4 side chain. Similarly, class II PapG and class III PapG differ in amino acids required for interaction with the GbO5 side chain.66 Group A streptococcus (S. pyogenes) is a common cause of infections of skin and soft tissue, including impetigo, cellulitis, and necrotizing fasciitis. Adherence to host cells by S. pyogenes is influenced by nonpilus adhesins called M protein and protein F. M protein forms a fiber and consists of a C-terminal region that anchors the protein in the cell wall,

CHAPTER 1  Molecular Determinants of Microbial Pathogenesis a coiled-coil rod region extending approximately 50 nm from the cell wall, and a short nonhelical domain extending more distally.84 Protein F is a 120-kDa protein that is notable for a tandem repeat element consisting of up to six repeats of 32 to 44 amino acids adjacent to the C terminus.112,233 M protein promotes adherence to human keratinocytes via interaction with the CD46 molecule (also called membrane cofactor protein, or MCP), whereas protein F mediates adherence to epidermal Langerhans cells, which are located in the basal layer of the epidermis.229,230 Thus both M protein and protein F contribute to group A streptococcal adherence to the skin, but each protein directs interaction with a different population of epidermal cells. Early studies demonstrated that human immunodeficiency virus type 1 (HIV-1) infects CD4+ cells and interacts with the CD4 molecule but that CD4 alone is not sufficient to permit infection. More recent observations have established that a number of host cell chemokine receptors, especially CCR5 and CXCR4, serve as coreceptors for HIV-1 and are required for viral entry into CD4+ target cells. These coreceptors appear to influence the cellular tropism displayed by different HIV-1 variants.62 All HIV variants are able to replicate in primary T cells, but only some can also replicate in primary macrophages or in immortalized T-cell lines. Asymptomatic HIV-infected individuals carry strains that generally use CCR5 as a coreceptor (termed M5 strains) and are non–syncytium-inducing in vitro. Such strains have classically been described as macrophage tropic (M-tropic), but recent experiments have demonstrated that these M5 strains can also infect CD4+ T cells and peripheral blood mononuclear cells.245 Rapid viral mutation due to the error-prone HIV polymerase and HIV reverse transcriptase leads to the production within the host of syncytium-inducing, T-cell–tropic (T-tropic) HIV-1 strains, which predominate in the circulation of patients with acquired immunodeficiency syndrome.62 These variants are generally restricted to CXCR4 (expressed on T cells) as a coreceptor, although some primary syncytium-inducing variants can use both CCR5 and CXCR4.71,79,276 T-tropic, syncytium-inducing strains are characterized by positively charged residues at fixed positions of the V3 loop and changes in charge and length of the V2 region of the viral envelope glycoprotein gp120, which binds to CD4 and coreceptors before viral entry into host cells.86,87,106 Thus cellular tropism is closely aligned, but not synonymous, with HIV coreceptor usage. New HIV-1 infection is selectively established by M-tropic HIV-1 strains, even if the transmitting host harbors more pathogenic non–Mtropic strains as well.317,352 CCR5 is also expressed on the surface of rectal and vaginal epithelial cells, which may be sites of initial encounter between HIV-1 and the human host.349 The importance of CCR5 in HIV-1 binding to CD4+ cells is underscored by the observation that individuals homozygous for a 32-bp deletion in CCR5 (the Δ32 allele) are resistant to infection with HIV-1.137,184 The Δ32 heterozygous state does not necessarily protect against HIV-1 acquisition, although HIV disease in heterozygous patients may follow an attenuated course. This allele is surprisingly frequent (10%–14%) in white populations, leading to speculation that it provided a survival advantage during one or more historical epidemics of infectious diseases.225 However, more recent data suggest that the Δ32 allele may actually confer immune deficiency in the presence of challenge with certain viral pathogens, such as West Nile virus.100,101 Of note, CCR5 may have a role in controlling the development of malignancy, including lymphoma, raising some concern about developing anti-HIV pharmacologic agents that target CCR5 function.178 Finally, co-evolution of viral determinants and host cell receptors may determine the spectrum of tissue and organ involvement within the host. For example, the chemokine receptor CCR8 may facilitate the entry of neurotropic HIV-1 strains into brain cells,152 and envelopes derived from brain isolates of HIV are adapted to infect cells with low-level CD4/CCR5 expression, such as neuroglia and brain macrophages.244 Other viruses also demonstrate tropism for specific cells or tissues within the host. Hepatitis C virus (HCV) has been demonstrated to use multiple cell surface molecules in sequence to locate and gain entry into target cells. HCV is bound to low-density lipoprotein (LDL) in serum and first binds to scavenger-receptor B1 (SR-B1), which is enriched on liver cells and serves to bind lipoprotein molecules.34 After this initial binding event, HCV E2 protein interacts with the CD81 molecule, the

7

critical receptor for free virus.159,321,351 Once virus has bound to CD81, this virus-receptor complex traffics to the gap junction, where the virus interacts with two key gap junction proteins, claudin-1 and occludin-1, to enter cells.78,114,172 Human occludin-1 recently has been shown to be necessary for HCV entry into mouse cells, an advance that will facilitate disease modeling in the laboratory.248 Although the liver does not exclusively express any of these four molecules, the combination of these four, the structural organization of liver cells, and other yetundetermined intracellular factors account for the tropism of HCV for the liver.246 Similar observations have been made for coxsackievirus isolates, which bind to the coxsackie-adenovirus receptor (CAR) molecule located in the tight junction for entry into cells.12,42,53,158 Brain, heart, and muscle cells are enriched for CAR in the fetal and neonatal period, whereas adult cells from these tissues express significantly lower levels of the receptor.131,147 This developmental difference in CAR density is the likely explanation for severe coxsackievirus infections that are disproportionately seen in infants and young children compared with adults. CAR then allows for an interaction with the tight junction that is mediated by occludin-1, which allows for viral co-opting of host trafficking pathways.53 Among eukaryotic pathogens, tissue tropism can also be a major determinant of virulence. Cerebral malaria is a life-threatening consequence of infection with the protozoan parasite Plasmodium falciparum and results from adherence of parasite-infected erythrocytes to cerebral vascular endothelium.209 During erythrocyte infection, the malaria parasite exports a variety of surface receptors to the host plasma membrane. The P. falciparum erythrocyte membrane protein 1 (PfEMP1) multigene family represents a highly variable set of such receptors, only one variant of which is expressed at any given time. A substantial body of work has established that different forms of PfEMP1 possess distinct tissue adherence patterns.171 Specific classes of PfEMP1 types (Group A DC8 and DC13) are associated with cerebral vascular adherence in vitro and are correlated with severe malaria in clinical populations.7,38,177 More recent studies suggest that these PfEMP1 forms mediate adherence through interaction with the endothelial protein C receptor.314

BIOFILMS After attachment to a particular surface, a number of pathogens are capable of forming biofilms, which can be defined as structured communities of microbial cells enclosed in a self-produced exopolysaccharide matrix. Although most studies of biofilms have involved a single species, it is likely that biofilms relevant to human infection often involve multiple species sharing the advantages of biofilm existence. Human infections associated with biofilms include dental caries, lower airway infection with P. aeruginosa and other organisms in patients with cystic fibrosis, and foreign body infections in patients with prostheses and implanted devices. In addition, biofilm formation likely occurs during osteomyelitis and endocarditis.49 P. aeruginosa is a model organism for the study of biofilms and forms pillars of stationary (sessile) bacteria held together by an extracellular polysaccharide called alginate. Interposed among these pillars are channels that facilitate the flow of nutrients and provide pathways for motile (planktonic) organisms to move about (Fig. 1.6A). In experiments directed at defining the early steps of P. aeruginosa biofilm formation, O’Toole and Kolter established that flagella are required for initial bacterial attachment, presumably because these appendages promote movement toward the relevant surface. After attachment, type 4 pili and pilus-mediated twitching motility promote formation of microcolonies227 in which transcription of algC, algD, and algU is activated, resulting in synthesis of alginate.59 Pulmonary isolates from patients with cystic fibrosis often form highly mucoid colonies (reflecting expression of alginate) or can form tiny colonies on agar plates, the so-called small-colony variant (SCV) phenotype associated with biofilm formation and increased antibiotic resistance.115,116,291 Development of the complex community present within a biofilm requires intercellular communication to coordinate the metabolic and other activities of members of the community. P. aeruginosa employs several identified quorum-sensing systems, which involve the production

8

PART I  Host-Parasite Relationships and the Pathogenesis of Infectious Diseases

1) Attachment and EPS production

2) Early development of biofilm

3) Maturation of biofilm

4) Dispersion

A

Reservoir and recurrence 1) Colonization and invasion

2) Early IBC: rapid intracellular growth

3) Mid IBC: change to biofilmlike properties

4) Late IBC: fluxing out and filamentation

B FIG. 1.6  In vitro Pseudomonas biofilm formation and parallel stages of formation of uropathogenic Escherichia coli intracellular bacterial communities (IBCs). (A) Dynamics of P. aeruginosa biofilm formation on an inert surface. Keys to the formation of the biofilm include flagella-mediated attachment, production of exopolysaccharide (EPS), type 4 pilus–based twitching motility, and a quorum sensing system. (B) Composite representation of the stages of IBC formation and maturation. (A, From Costerton JW, Stewart PS, Greenberg EP. Bacterial biofilms: a common cause of persistent infections. Science. 1999;284:1318–22, copyright 1999 American Association for the Advancement of Science. B, From Kau AL, Hunstad DA, Hultgren SJ. Interaction of uropathogenic Escherichia coli with host uroepithelium. Curr Opin Microbiol. 2005;8:54–9.)

of small molecules that are sensed by neighboring organisms and regulate gene expression in these neighbors. One well-studied system is based on the acyl-homoserine lactone called N-(3-oxododecanoyl)L-homoserine lactone (3OC12-HSL).60,236 3OC12-HSL is synthesized in a reaction catalyzed by LasI and accumulates with increases in population density. Ultimately, 3OC12-HSL reaches a critical concentration and then interacts with LasR, serving to activate transcription of a number of genes. Host inflammatory pathways are also induced directly by accumulated 3OC12-HSL.279 Organisms with a mutation in lasI are capable of attachment and microcolony formation, but the resulting microcolonies remain thin, undifferentiated, and sensitive to dispersion by detergents. Addition of the missing lactone signal to the lasI mutant restores development into structured, thick, biocide-resistant biofilms, as are observed with wild-type organisms.60 In vivo, mutation in lasI impedes establishment of pulmonary infection in mice.242,340 Biofilms also play a prominent role in human infections with Candida species, with examples including oral thrush and catheter-associated infections. Although several pathogenic Candida species can form biofilms

in the host, the ultrastructure and the molecular strategies underlying biofilm formation vary from one species to another. C. albicans is the best studied Candida species and relies on the expression of certain cell wall proteins (including Hwp1),219 a regulated yeast-to-hyphal switch described earlier, and quorum-sensing molecules such as E,E-farnesol, which represses filamentation and can suppress the growth of other nearby bacterial and fungal species.63,133,275 Biofilms constitute a protected mode of growth that allows survival in a hostile environment—for example, in the presence of host immune mechanisms or antimicrobial agents.49 Based on studies of P. aeruginosa, sessile bacteria release antigens and stimulate production of antibodies, but these antibodies are ineffective in killing organisms within biofilms.41 Similarly, sessile P. aeruginosa stimulate a diminished oxidative burst and are relatively refractory to phagocytic uptake. In addition, fungi and bacteria within biofilms are resistant to the effects of a number of antimicrobial agents, in part because these agents are unable to diffuse into the biofilm and in part because these organisms may exist in a slow-growing or otherwise protected phenotypic state.49 Biofilm-like

CHAPTER 1  Molecular Determinants of Microbial Pathogenesis microbial communities have also been described within host epithelial cells, as with uropathogenic E. coli in the mammalian bladder.6 Recently, new approaches to antimicrobial therapy include novel natural products and other small molecules that inhibit quorum-sensing and biofilm formation.36,96

CELL ENTRY AND INTRACELLULAR LIFE After adherence to a host surface, many pathogenic bacteria are able to invade and survive inside epithelial cells and other nonprofessional phagocytes (i.e., M cells in intestinal Peyer’s patches). In addition, some pathogens are able to survive inside professional phagocytes (macrophages and neutrophils). Invasion may represent a mechanism to breach host mucosal barriers and gain access to deeper or more distant tissues. Alternatively, invasion may provide the organism with a special niche (e.g., protecting it from host immune mechanisms). In the case of viruses, cell entry ensures access to the cell machinery required for viral replication. Generally the process of bacterial invasion involves a class of molecules called invasins that mediate adherence and entry. For many bacteria, invasion is an active event that relies on underlying host cell functions and is associated with rearrangement of the host cell cytoskeleton. Once inside the host cell, the invading or internalized organism usually is localized within a membrane-bound vacuole that contains lysosomal enzymes. In some cases the pathogen escapes from this vacuole and enters the cytoplasm, a more permissive environment. In other cases, the pathogen remains in the vacuole and neutralizes lysosomal enzymatic activity. The processes of invasion into cells, survival within cells, cellto-cell spread, and entry into the circulation define the extent of infection and dissemination.

Invasion In considering the molecular mechanism of bacterial invasion, perhaps best characterized are the enteropathogenic Yersinia species—namely, Y. pseudotuberculosis and Y. enterocolitica. These organisms are usually acquired by ingestion of contaminated food or water and typically cause self-limited enteritis or mesenteric adenitis. In infants and other individuals with compromised immunity, they sometimes produce systemic disease. The primary determinant of Y. pseudotuberculosis and Y. enterocolitica invasion is an adhesive outer membrane protein called invasin, which is encoded by a chromosomal locus called inv and binds tightly to a family of β1 integrins expressed on host cells, including α3β1 integrin on the surface of intestinal M cells.145 The interaction between invasin and β1 integrins initiates a cascade of signaling steps in the host cell, resulting in actin rearrangement and formation of large complexes of cytoskeletal elements (talin, vinculin, α-actinin, and others) termed focal adhesions.144 Bacterial entry into the host cell occurs via a “zipper-like” mechanism, with the plasma membrane zippering around the invading organism. Beyond invasin, two additional proteins called YadA and Ail also influence invasion by enteropathogenic Yersinia species. YadA is a 45-kDa surface protein that is encoded by the 70-kb Yersinia virulence plasmid. It is highly expressed under environmental conditions (e.g., temperature of 37°C) in which invasin is repressed.75 YadA reaches the bacterial surface via the autotransporter pathway and exists in a trimeric form that is essential for its adhesive activity.51 Like invasin, YadA promotes invasion through binding to β1 integrins on the host cell surface, but its binding occurs indirectly via extracellular matrix molecules, including collagens, laminin, and fibronectin.76 Based on studies using a mouse oral infection model, in Y. enterocolitica YadA is essential for survival and multiplication in Peyer’s patches, whereas in Y. pseudotuberculosis YadA is dispensable for full virulence.22 Ail is a 17-kDa outer membrane protein that also is encoded by a chromosomal locus (ail) and mediates high levels of adherence and low levels of invasion in assays with cultured epithelial cells. In addition, Ail mediates resistance to complementmediated serum killing, independent of an effect on invasion.19 Similar to these pathogenic Yersinia species, Listeria monocytogenes invades epithelial cells via a zipper-like mechanism. Invasion is mediated by proteins called internalin A (InlA) and internalin B (InlB), which are required for virulence in animal models. InlA interacts with

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E-cadherin, a host cell transmembrane protein with an intracellular domain that interacts with the cytoskeleton.205 InlB interacts with C1q on host cells and promotes invasion by activating the PI-3 kinase pathway.24 Uropathogenic strains of E. coli also invade epithelial cells via a zipper-like mechanism mediated by the FimH adhesin expressed on the tip of type 1 pili. In experiments with cultured bladder epithelial cells, FimH is both necessary and sufficient for entry, as demonstrated by examination of a fimH− mutant and of latex beads coated with purified FimH.194 In vitro experiments further suggest that FimHmediated bacterial binding to a mannose-coated surface may be strengthened by shear forces, such as fluid flow over the surface.307,308 After FimH-dependent invasion into superficial epithelial cells of the murine bladder, UPEC multiply rapidly to form intracellular bacterial communities, which display some features of biofilms, including community behavior, differential gene expression, and protection from antimicrobial agents (see Fig. 1.6B).6,156,160 A subset of internalized bacteria ultimately form a quiescent bacterial reservoir within the uroepithelium that resists immune clearance and antibiotic therapy and may serve as a seed for recurrent infections.139,213,214 Salmonella enterica serovar typhimurium (S. typhimurium) is an example of a pathogen that invades cells by a mechanism distinct from zippering. On contact with the epithelial cell surface, S. typhimurium triggers a dramatic host cell response characterized by actin rearrangement, calcium and inositol phosphate fluxes, and a “splash” of membrane ruffling surrounding the point of entry. Bacterial internalization into the cell occurs rapidly, with organisms appearing in membrane-bound vacuoles within a few minutes of initial contact with the host cell. The determinants of S. typhimurium invasion are encoded by a pathogenicity island called SPI-1, located at centisome 63 on the bacterial chromosome.92 Especially important in this region is a prototypical type III secretion system, which forms a needle-like complex on the bacterial surface that breaches the host cell membrane and serves to translocate bacterial proteins directly into the host cell, altering the host cell cytoskeleton43,186 and influencing immune responses. The base of the needle complex spans both the inner and outer membranes and is about 40 nm in diameter, whereas the needle itself is 8 nm in width and approximately 80 nm in length (Fig. 1.7).45,93 The proteins secreted through the S. typhimurium needle complex (and other type III secretion systems) and into the host cell are referred to as effector proteins. SopE is an effector protein that mediates the initial rearrangement of actin and ruffling of the host cell membrane. It functions as a guanyl-nucleotide exchange factor (GEF) and activates two host cell Rho GTPase proteins called Rac and Cdc42.35,111,113 SptP is an effector protein that functions as an antagonist of SopE, mediating reversal of actin rearrangement by converting Rac and Cdc42 to the inactive forms (GDP forms). Consistent with these functions, SopE and SptP directly antagonize each other when coinjected into cells.91 Other effector proteins secreted by the S. typhimurium SPI-1 type III secretion system include the inositol phosphate phosphorylase SopB, which disrupts normal host cell signaling mechanisms,224 and AvrA, which interferes with the nuclear factor κB (NF-κB) signaling pathway in host cells, thereby downregulating host inflammatory responses.44 Important accessory and regulatory genes are also present within SPI-1. As an example, the sicA gene is just upstream of the sipB and sipC genes and encodes an accessory protein with chaperone activity essential for stabilization and translocation of SipB, SipC, and SopE.313 Other chaperones encoded by SPI-1 are involved in the stabilization and translocation of other effector proteins. The genetic and environmental factors that regulate the expression of type III secretion machinery and secreted proteins represent an area of ongoing study.5 In Plasmodium falciparum, the mechanisms of both host erythrocyte invasion and immune evasion are tightly linked. A mature parasite may release as many as 32 daughter parasites, called merozoites, into the bloodstream. In less than 30 seconds, merozoites attach to and invade new erythrocytes. High-titer antibodies to invasion proteins, as are present in the serum of semi-immune individuals living in endemic areas, can block these processes. For this reason, the molecular invasion machinery of P. falciparum is of considerable interest for vaccine development.240,303 The initial contact between Plasmodium merozoites and host erythrocytes is weak and is thought to be mediated through

10

PART I  Host-Parasite Relationships and the Pathogenesis of Infectious Diseases

A C Needle

Outer rings Neck

Inner rod Socket

Inner rings

Cup

B FIG. 1.7  General structure of the gram-negative type III secretion system, according to electron micrographic and other data. Represented are (A) electron micrographs of isolated needle complexes, (B) cross-sectional schematic of the components of the needle complex, and (C) surface views of the assembly. (From Galan JE, Wolf-Watz H. Protein delivery into eukaryotic cells by type III secretion machines. Nature. 2006;444:567–73.)

merozoite surface proteins (MSPs) present along the entire merozoite surface. Stronger interactions are mediated by several additional receptors, notably the erythrocyte binding antigens EBA-175 and EBA-140, which engage the erythrocyte-specific receptors glycophorin A and glycophorin B, respectively. Recently, an additional parasite protein called PfRH5 was recognized as an indispensible mediator of parasite invasion via interaction with the human receptor basigin.54 Anti-RH5 antisera have potent invasion-inhibiting activities,312 and an RH5-based vaccine showed efficacy in an Aotus monkey infection model.72 On the basis of these data, PfRH5 has emerged as a strong candidate vaccine antigen to prevent severe malaria.

Intracellular Survival Once an organism invades a nonprofessional phagocyte or is ingested by a professional phagocyte, several potential outcomes exist. Often, the organism is killed. However, some pathogens have developed strategies to survive and replicate inside host cells, in some cases within a vacuole and in others by escaping from the vacuole. There is general agreement that S. typhimurium resides within a membrane-bound vacuole in both professional and nonprofessional phagocytes. However, the vacuole lacks several lysosomal markers typical of the main endocytic pathway (the mannose-6-phosphate receptor pathway) and appears to be distinct from this pathway. Insight into the molecular determinants of intravacuolar survival came when two independent groups reported the discovery of a second Salmonella pathogenicity island, now called SPI-2.122,228 This island maps to centisome 31 and encodes another type III secretion system, including structural proteins (ssa locus),122 effector proteins (sse locus), and accessory proteins (ssc locus). In addition, this region encodes a two-component regulatory system consisting of a membrane-located sensor kinase (SsrA) and a

transcriptional regulator (SsrB).228 Mutations in SPI-2 result in reduced survival inside macrophages, with no effect on adherence and invasion in assays with intestinal epithelial cells.228 Salmonella SPI-2 mutants demonstrate reduced virulence in experimental mice (up to a 104-fold reduction in 50% lethal dose), suggesting that survival inside macrophages is a key factor in the pathogenesis of disease.273 Expression of SPI-2 genes within the macrophage vacuole depends at least in part on the acidic intravacuolar environment. Inhibition of macrophage vacuolar acidification using bafilomycin A1 (an inhibitor of the vacuolar proton ATPase) results in a sharp attenuation in transcription of SPI-2 genes. This effect is not reproduced by low pH alone outside the vacuole, suggesting that other environmental effects within the vacuole influence SPI-2 expression.37 Recent work indicates that Salmonella SPI-2 transcription is activated before invasion, apparently preparing the pathogen for the hostile intracellular environment.26 As a group, the SPI-2 genes appear to modulate host endocytic and exocytic transport mechanisms and inflammatory signaling.1,142 A third Salmonella pathogenicity island called SPI-3 also promotes survival inside macrophages. This island is located at centisome 82 and was discovered by examining the Salmonella selC locus, a tRNA gene where pathogenicity islands reside in some strains of E. coli.15,17 SPI-3 contains the mgtBC operon, which permits S. typhimurium growth in environments with low concentrations of Mg2+, including macrophages. In particular, mutation of the mgtBC operon abolishes the ability of S. typhimurium to replicate in low-Mg2+ liquid media and in macrophages, and addition of Mg2+ to the medium after phagocytosis restores the ability to survive intracellularly. Homologous mgtBC genes have been found in other organisms with intracellular lifestyles, such as Brucella melitensis and Yersinia pestis.16 In Salmonella, the mgtBC genes are expressed after internalization into host cells under control of the

CHAPTER 1  Molecular Determinants of Microbial Pathogenesis PhoP-PhoQ two-component regulatory system, a complex that directs expression of a number of virulence determinants.191 The ability to survive within phagocytic cells may provide Salmonella with a means to exploit an intrinsic host pathway and disseminate to distant sites. In particular, certain phagocytes express the β2 integrin CD18, which mediates leukocyte migration in response to various stimuli. During S. typhimurium infection, CD18-expressing phagocytes carry organisms from the intestine to the spleen. Indeed, bacterial loads in the liver and spleen are reduced after oral inoculation in CD18-deficient mice when compared with infection in wild-type mice.318 On the one hand, this function of CD18 facilitates initiation of a systemic immune response and benefits the host. However, at the same time, it provides bacteria with a mechanism of transit from the gut to organs of the reticuloendothelial system and elsewhere. Mycobacterium tuberculosis is another intracellular pathogen, and it uses an array of mechanisms to ensure intracellular survival. The M. tuberculosis vacuole lacks the usual amounts of the vesicular proton ATPase responsible for mediating acidification and fails to acidify to normal levels.298 In addition, M. tuberculosis blocks fusion of the vacuole with acidic lysosomes, further preventing acidification.268 Similar to intracellular gram-negative bacterial pathogens, M. tuberculosis contains an mgtC gene, and mutation of this gene results in impaired virulence in cultured human macrophages and in mouse spleen and lung. Low Mg2+ concentration and mildly acidic pH inhibit the growth of the mgtC mutant, suggesting that the gene is important for survival in the phagosome, where such conditions may exist.28 Another factor that influences M. tuberculosis survival within macrophages is isocitrate lyase, an enzyme of the glycolytic shunt that is essential for metabolism of fatty acids. Expression of isocitrate lyase is upregulated during infection of activated macrophages and is required for full virulence in a murine model of infection, independent of an effect on bacterial growth.198 The crystal structure of M. tuberculosis isocitrate lyase has been solved and may provide a target for new drug therapies against persistent infection because this enzyme is absent from vertebrates.271,282 During the course of interaction with macrophages, M. tuberculosis (at a low to moderate multiplicity of infection) is capable of stimulating caspase-1 and inducing macrophage apoptosis. Interestingly, less virulent strains of M. tuberculosis are more potent inducers of apoptosis, perhaps resulting in benefit to the host by preventing systemic spread of infection.163 At the same time M. tuberculosis possesses at least two antiapoptotic mechanisms that further influence the outcome of macrophage encounters. First, M. tuberculosis infection enhances host macrophage production of soluble TNFR2, a protein that binds to tumor necrosis factor alpha (TNFα) and interferes with apoptosis.8 Second, M. tuberculosis infection activates production of NF-κB, a transcriptional regulator that activates anti-apoptotic pathways within the host cell.97 Of note, higher multiplicities of infection with virulent strains of M. tuberculosis can induce caspase-independent cell death in macrophages, a mechanism proposed to contribute to the formation of necrotic lesions during tuberculous disease.179 L. monocytogenes is an example of an organism that escapes from the phagocytic vacuole in macrophages and epithelial cells and moves into the cytoplasm. This organism causes meningitis and focal brain abscesses in humans and exhibits tropism for the fetoplacental unit. In pregnant women, listeriosis results in fetal loss in 30% of cases. Intravacuolar replication and escape from the vacuole are dependent on listeriolysin O, a hemolysin encoded by the hly gene.13 Listeriolysin O interacts with cholesterol in host cell membranes and forms pores, leading to lysis of the phagosome.90 Host enzymatic activities may also contribute to Listeria escape from the phagosome. In human epithelial cells the contributions of a broad-range phospholipase C (called PC-PLC) and a metalloproteinase called Mpl are most important for vacuolar escape in the absence of listeriolysin O.107,192,281 Intracellular survival of the protozoan parasite Toxoplasma gondii is thought to rely on parasite virulence factors that directly counter innate host defenses. In mice, interferon gamma (IFNγ) production is required to limit replication of T. gondii, in part through induction of immunity-related GTPases (IRGs). In mammalian cells, successful T. gondii strains replicate within a protected parasitophorous vacuole (PV) that does not fuse to the host lysosome. During infection with relatively

11

nonpathogenic parasites, recruitment of IRGs to the PV results in disruption of the PV and parasite death. In contrast, highly pathogenic T. gondii express an active serine-threonine kinase called ROP18, which is exported into the host cytoplasm and prevents the recruitment of IRGs.140,301 The ROP kinase family is highly expanded in T. gondii, comprising 44 other proteins, many of which lack critical catalytic residues and are thought to function as regulatory “pseudokinases.” Interestingly, ROP kinases are absent from the related apicomplexan Plasmodium spp., presumably because prevention of IRG recruitment is unnecessary within the protected niche of the host erythrocyte.

Viral Cell Entry Viruses have developed a specialized family of proteins that specifically function to engage host cell proteins and fuse with cell membranes and that allow for transfer of viral genetic material. The details regarding structure and function of these proteins are reviewed elsewhere.168 There are two known classes of viral fusion proteins: class I proteins form a hairpin structure with a known α-helix domain (e.g., HIV gp41, influenza HA2), and class II proteins exist in β-sheets and transition from a moderately stable dimeric form to a very stable trimer (e.g., dengue E protein). These fusion proteins undergo conformational changes when transitioning from the prefusion to the postfusion state, resulting in a more stable form that favors the process of viral fusion and entry.

Cell-to-Cell Spread Movement from one cell to another may help an organism gain a stronger foothold in host tissues. L. monocytogenes is one example of a pathogen capable of cell-to-cell spread. Once this organism is free in the cytoplasm, actin begins to polymerize on the bacterial surface. Eventually the condensed actin forms a polar tail or comet, which propels the organism through the cytoplasm and into adjacent cells. The rate of bacterial movement within a cell correlates with actin tail length.305 Actin accumulation and condensation is mediated by the L. monocytogenes ActA protein, which is tightly anchored to the bacterial surface and is expressed asymmetrically over the length of the organism.283,304 ActA is the sole Listeria factor required for actin polymerization because actin tails form in Xenopus cytoplasmic extracts containing ActA-coated beads. However, in these experiments, motility occurs only when ActA is distributed asymmetrically on the beads.30 ActA appears to interact directly with actin and also with a variety of other host cytoskeletal proteins.90,306 Cytochalasin D is an inhibitor of actin polymerization and inhibits the cell-to-cell spread of L. monocytogenes in epithelial monolayers.58,210 On reaching the plasma membrane, bacteria protrude from the cell in filopodium-like structures (called listeriopods), which are then engulfed by neighboring cells. This engulfment may be part of a normal host process because MDCK cells demonstrate low-level endocytosis of adjacent cell membrane fragments even in the absence of bacteria.261 The formation of listeriopods and the engulfment of these structures by neighboring cells are independent of listeriolysin O, PI-PLC, and PC-PLC.98 Once inside a nascently infected cell, Listeria escapes from the double-membrane vacuole via the action of PI-PLC, PC-PLC, and Mpl.90 On arrival in the cytosol, bacteria can enter another cycle of actin-based motility and cell-to-cell spread, although one or two bacterial generations may be necessary to regain motility.261 A second pathogen capable of actin-based motility and cell-to-cell spread is Shigella flexneri. In Shigella, a single protein called IcsA is sufficient to induce formation of an actin tail, similar to that observed in L. monocytogenes. IcsA is an autotransporter protein that is encoded on the Shigella virulence plasmid and is distributed on the bacterial surface in a polarized fashion, possibly as a result of specialized machinery for autotransporter protein secretion near the poles of some gramnegative bacteria.151 Initially, IcsA is distributed over the whole bacterial surface, with a predominance at one pole. However, over time a secreted bacterial protease called IcsP cleaves roughly half of the surface IcsA, mostly at the opposite pole, further polarizing distribution.74,292 Elimination of expression of IcsP leads to increased quantities of IcsA and increased actin-based motility, suggesting that IcsA (rather than host factors) is rate limiting in the motility process.274 Like ActA, IcsA is necessary and sufficient to induce polymerization of the actin tail, and

12

PART I  Host-Parasite Relationships and the Pathogenesis of Infectious Diseases

the tail forms at the end where IcsA concentration is highest.102 Despite the functional similarities between IcsA and ActA, there is no significant sequence homology between the two proteins. In contrast to ActA, no direct interaction between IcsA and actin has been demonstrated, and IcsA is found throughout the actin tail, not only at the bacterial pole–actin tail junction. When considering cell-to-cell spread of viruses, it is helpful to return to the example of HCV. Claudin-1 and occludin-1 are the gap junction proteins that serve as the final entry point for this virus.78,248 It has been demonstrated that HCV can infect neighboring liver cells directly via these gap junction proteins, likely bypassing the extracellular release of virus and subsequent SR-B1 and CD81 binding steps.309 Experiments have demonstrated that antibodies blocking the E2–CD81 interaction inhibit infection from virus-infected media but do not affect infection of naïve cells when co-cultured with previously HCV-infected cells.309 It has also been shown that after infecting a liver cell, HCV promotes breakdown of typical apical to basal organization of liver cells, exposing the gap junction complexes and presumably facilitating cell-to-cell spread.199,200

DAMAGE TO THE HOST Damage to host cells and host tissues represents a fundamental mechanism by which a pathogen is able to survive at a given site and then spread within a host. Generally, damage is induced by microbial toxins. Most toxins are released extracellularly and are capable of inducing damage at very low concentrations (exotoxins). Microbial attachment and invasion facilitate toxin delivery to target cells and target tissues and serve to enhance toxicity. Historically, microbial toxins have been classified according to a variety of criteria, including cellular target of action (e.g., enterotoxins, leukotoxins, neurotoxins), mechanism of action (e.g., adenosine diphosphate [ADP]–ribosylating toxins, adenylate cyclase toxins, poreforming toxins, proteolytic toxins), and major biologic effect (e.g., hemolytic toxins, edema-producing toxins). In recent years the term toxin has been applied more broadly to include enzymes that mediate damaging effects via phospholipase or hyaluronidase activity.

Bordetella pertussis Toxins Whooping cough (B. pertussis infection) is a classic example of a toxinmediated disease and involves the interplay of multiple toxins.165 The pathogenesis of whooping cough begins with B. pertussis colonization of the trachea, which is facilitated by a molecule called tracheal cytotoxin (TCT). TCT is a naturally occurring disaccharide-tetrapeptide fragment of peptidoglycan and belongs to the family of muramyl peptides.103 Many gram-negative organisms produce an analogous fragment during normal turnover of cell wall components, but significant extracellular release appears to occur only in Bordetella species and gonococci. In most other species an inner membrane protein called AmpG recycles this fragment back into the bacterial cell.50 TCT is toxic to tracheal epithelial cells in vitro, stimulating nitric oxide synthase and local production of interleukin-1 and causing inhibition of ciliary motility, inhibition of DNA synthesis, and cell death.117–119,124 During natural infection, TCT is thought to paralyze the mucociliary escalator and thereby interfere with clearance of B. pertussis and respiratory mucus. Pertussis toxin is believed to be a key determinant of the clinical manifestations of whooping cough. This toxin belongs to a family of bacterial ADP-ribosyltransferase enzymes. The target of pertussis toxin is host cell G proteins, resulting in disruption of normal signaling processes. A number of biologic effects have been ascribed to pertussis toxin, including induction of lymphocytosis, stimulation of insulin release, sensitization to histamine, and disruption of phagocytic cell function; however, the specific relationship between the effects of pertussis toxin and the symptoms of whooping cough remains unclear.125 Of note, B. parapertussis is closely related to B. pertussis and produces a similar cough illness but fails to produce pertussis toxin because of mutations in the ptx promoter region.218 B. pertussis also elaborates a toxin called adenylate cyclase toxin (CyaA), a member of the RTX (repeat-in-toxin) family of bacterial cytolysins whose prototype is the E. coli hemolysin HlyA.50 These toxins

cause target cell lysis by creating pores in the host cell plasma membrane, but at sublytic concentrations many of these toxins also manipulate host enzymatic and signaling pathways within the host cell. In the case of B. pertussis, CyaA inhibits host adenylate cyclase, resulting in accumulation of cyclic adenosine monophosphate (cAMP); elevated levels of cAMP within phagocytic cells inhibit oxidative activity and induce apoptosis, thus disabling this arm of the immune system.166,167,243 In respiratory epithelial cells, elevated cAMP may result in increased fluid and mucus secretion, further impairing mucociliary function. Among other examples of these dual-function RTX toxins, the prototypic HlyA of uropathogenic E. coli induces the degradation of host actin-associated proteins, resulting in exfoliation of the superficial epithelial layer in the bladder.64 The α-hemolysin of contemporary community-associated S. aureus strains activates a host epithelial cell surface molecule called ADAM10, which cleaves E-cadherin at cell–cell junctions to permit access of the pathogen across the epithelial layer.143,332

Hemolytic-Uremic Syndrome and Shiga Toxins A number of intestinal pathogens produce Shiga toxins, including Shigella dysenteriae, enterohemorrhagic E. coli (including E. coli O157:H7), and Citrobacter freundii, among others. Shiga toxins are classic A-B toxins, consisting of an A subunit that has toxic activity and five B subunits arranged in a pentameric ring-like structure that promotes binding to host cells and delivery of the A subunit. The B subunits interact with host cell globoseries glycolipids, especially the Pk trisaccharide moiety of globotriaosylceramide (GbO3). The A subunit is endocytosed by the host cell and traverses the cytoplasm in membrane-bound vesicles. Some of these vesicles travel in a retrograde fashion to the Golgi apparatus and then to the endoplasmic reticulum.269 Shiga toxin then co-opts the function of the endoplasmic reticulum proteins HEDJ and BiP to enter the cytosol, where it enzymatically inhibits host 28S ribosomal RNA by cleaving a single adenine residue, resulting in inhibition of protein synthesis and cell death.269,347 In humans, E. coli O157:H7 is an important cause of hemorrhagic colitis and sometimes produces hemolytic-uremic syndrome. Infection begins with adherence to epithelial cells via intimin and other proteins encoded by the locus of enterocyte effacement (LEE), resulting in formation of attaching and effacing lesions analogous to those observed in EPEC infection.196 After adherence, the organism releases Shiga toxin, which traverses the intestinal epithelial cell and enters the bloodstream.2 Toxin circulates to distant organs and mediates damage via toxicity to endothelium. Diarrhea likely results from damage to endothelium in small mesenteric vessels, leading to ischemia and sloughing of the intestinal mucosa. The renal effects observed in human hemolytic-uremic syndrome arise from microvascular and glomerular damage with luminal occlusion by fibrin and platelets.353 Hemolysis and thrombocytopenia likely develop as a consequence of microangiopathy.

Tissue-Degrading Toxins A number of toxins have enzymatic activity and are capable of degrading tissue components. One example is hyaluronidase, which degrades hyaluronic acid, a repeating disaccharide glycosaminoglycan involved in cell motility, adhesion, and proliferation in normal hosts. Hyaluronic acid contains alternating N-acetylglucosamine and glucuronic acid moieties, connected by β linkages. It is prominent in extracellular matrix when cell turnover and tissue repair are prominent—for example, in embryogenesis, wound healing, and carcinogenesis.55 The primary host receptor for hyaluronic acid is CD44, which undergoes post-translational modification that varies according to host cell type. Interactions between hyaluronic acid and CD44 are critical to T- and B-cell stimulation, growth of certain lymphoid malignancies, and propagation of certain inflammatory responses.207 In S. pyogenes, hyaluronidase is a 96-kDa protein that is encoded by the hylA gene and is released extracellularly. It is proposed to promote invasion through cell layers and tissue planes and is considered one of several S. pyogenes spreading factors.141 Interestingly, S. pyogenes also produces a thick “capsule” of hyaluronic acid that can interact with other host cellular and extracellular matrix proteins to contribute to tissue invasion by the organism. Other pathogens that produce a hyaluronidase include S. agalactiae (group B streptococcus),

CHAPTER 1  Molecular Determinants of Microbial Pathogenesis Treponema pallidum, Candida spp., Entamoeba histolytica, and Ancylostoma braziliense.55

EVASION OF IMMUNITY To survive and replicate within the host, a pathogen must evade the host immune system. Initially the organism must circumvent innate immune mechanisms, including mechanical forces, resident phagocytes, and complement activity. Over time the organism must overcome adaptive immunity as well, including the presence of specific antibodies.

Antiphagocytic Factors As described earlier in this chapter, invasin-mediated entry into M cells plays an important role in the early stages of Yersinia infection. At the same time, evasion of phagocytosis is critical to the pathogenesis of Yersinia disease. The ability to avoid phagocytosis is dependent on the Yersinia virulence plasmid, which encodes a number of proteins called Yops.48,295 Both YopE and YopH interfere with ingestion by macrophages and neutrophils via slightly different mechanisms. YopE shares sequence homology with the Salmonella typhimurium SptP protein and downregulates all three of the Rho GTPases (Rho, Cdc42, and Rac), thus inhibiting actin rearrangement and blocking formation of membrane ruffles (lamellipodia) and spikes (filopodia).3,19 YopH is a protein tyrosine phosphorylase that appears to act on a host cell cytosolic protein called Cas, interfering with recruitment of Rho, Cdc42, and Rac and preventing formation of actin stress fibers, focal complexes, and focal adhesions.14,18 YopJ is an acetyltransferase that covalently modifies and inactivates intermediate kinases in the mitogen-activated protein kinase and NF-κB signaling pathways, leading to host cell apoptosis.212,345 Importantly some Yop effectors also represent important immunogens; for example, the immunodominant epitope of YopE represents a major CD8+ T-cell antigen in experimental plague and may facilitate a new direction in Yersinia vaccine development.182,350 Shigella employs another strategy to induce apoptosis in phagocytic cells. This pathogen produces hemorrhagic enterocolitis and is an important cause of bloody diarrhea in children. Infection begins with ingestion of organisms, which attach to intestinal M cells and then cross the intestinal epithelium.356 On entry into the subepithelial space, organisms are engulfed by resident macrophages and contained in membrane-bound vacuoles. However, they quickly escape from macrophage vacuoles and move to the cytosol of the cell, where they induce apoptosis.355 The mechanism of apoptosis involves a protein called IpaB, which is encoded by the Shigella virulence plasmid and is injected into host cell membranes via the Shigella type III secretion system.20 Work by Zychlinsky and coworkers showed that IpaB binds to cytosolic interleukin-1β converting enzyme (caspase-1), a cysteine protease that cleaves IL-1β to its active form.126 Of note, the S. typhimurium SipB protein shares homology with IpaB and also induces apoptosis by interacting with caspase-1.123 Interestingly, recent work has shown that IpaB has contrasting effects in epithelial cells, binding to the cell-cycle regulator Mad2L2 to inhibit epithelial turnover and promoting epithelial colonization with Shigella.148

Evasion of Complement Activity S. pyogenes expresses at least three factors that interfere with host complement activity. Perhaps best known is M protein, which inhibits activation of the alternative complement pathway. This effect is mediated at least in part by the ability of M protein to bind complement factor H, a regulatory protein that inhibits assembly and accelerates decay of C3bBb. Recent studies indicate that serotype M1 and M57 strains express an extracellular protein called Sic (streptococcal inhibitor of complementmediated lysis), which associates with human plasma proteins called clusterin and histidine-rich glycoprotein (HRG) and apparently blocks formation of the membrane attack complex (C5b-C9).4 Studies of epidemic waves of M1 infection demonstrate that Sic undergoes significant variation over time, perhaps in response to the selective pressure associated with specific antibodies.129,130,201 Of note, nonpolar inactivation of sic results in reduced mucosal colonization of mice.185 In addition, S. pyogenes produces a serine protease called C5a peptidase,

13

which cleaves and inactivates C5a.330 C5a is a cleavage product of C5 and serves as a powerful chemoattractant for neutrophils; thus, streptococcal C5a peptidase serves to attenuate the neutrophil response to infection. N. gonorrhoeae is a common cause of cervicitis, urethritis, and pelvic inflammatory disease and is also capable of producing disseminated disease. Recent spread of antibiotic resistance in this pathogen highlights the need for understanding its pathogenic mechanisms to develop new mitigating strategies. Resistance to complement-mediated killing is important in gonococcal pathogenesis and is due in part to sialylation of lipo-oligosaccharide (LOS), which involves addition of host-derived cytidine monophospho-N-acetylneuraminic acid (CMP-NANA) by a bacterial sialyltransferase. Given the requirement for CMP-NANA, subcultivation in the absence of human serum or human neutrophils is associated with loss of sialylation and loss of resistance. Sialylated LOS binds factor H, resulting in downregulation of activity of the alternative pathway C3 convertase. In addition, sialylated LOS interferes with neutrophil phagocytosis and with the normal oxidative burst in neutrophils.260,329 A second determinant of resistance to complementmediated killing is Por1, an outer membrane porin protein that binds both factor H and C4b binding protein (C4b BP).255 C4b BP binds C4b and serves to inhibit assembly and accelerate decay of C4b2a, the classical pathway C3 convertase. Gonococci also produce a third factor that influences resistance to complement—namely, an outer membraneexpressed nitrite reductase called AniA.21,31

Evasion of Humoral Immunity A number of pathogens have evolved mechanisms to vary surface-exposed immunogenic molecules, thus facilitating evasion of a specific antibody response. Antigenic variation represents one such mechanism and is characterized by the emergence of modified molecules with novel antigenic properties. Phase variation represents a second such mechanism and is typified by the reversible loss or gain of a given molecule or structure. N. gonorrhoeae is capable of producing recurrent infection, reflecting the fact that the antibody response to infection fails to provide lasting immunity. In this context, it is noteworthy that N. gonorrhoeae pili are an important target of serum antibody and undergo frequent antigenic variation. Gonococcal pilin expression is controlled by the pilE locus (the expression locus), which contains an intact pilin gene along with promoter sequences. In addition to pilE, the gonococcal chromosome contains numerous copies of variant pil sequences, called pilS loci.110 These loci are transcriptionally inactive because they lack a promoter and 5′ coding sequence. However, they can be introduced into the expression locus by RecA-dependent recombination, resulting in an altered structural subunit and antigenically variant pili.136 Because N. gonorrhoeae is naturally transformable, horizontal exchange of speciesspecific DNA may also give rise to new pil sequences. The African trypanosomes (including Trypanosoma brucei) are parasites that cause sleeping sickness in sub-Saharan Africa and account for more than 50,000 deaths per year. These organisms are able to avoid humoral immunity by antigenic variation of a large family of proteins called variable surface glycoproteins (VSGs), which coat the entire surface of the trypanosome. VSGs are highly immunogenic and stimulate antibodies that lead to efficient and rapid clearing of parasites from the bloodstream. However, at any given point in time, the organism is able to express a new VSG, allowing some organisms to escape the antibody response against the previous VSG. Each parasite can express more than 100 different VSGs, with variation in expression occurring spontaneously at a rate of up to 10–2 per cell per generation. Overall, the genome of T. brucei contains more than 1000 vsg genes, including so-called expression sites (ESs) located near telomeres on minichromosomes and silent loci in nontelomeric sites on large chromosomes.241,310 In general, VSG antigenic variation occurs by two different mechanisms. The first is called in situ activation and involves the simultaneous activation of a new ES and inactivation of the old ES, occurring independently of DNA rearrangement. The second involves DNA recombination, either between the expressed vsg and another telomeric ES (reciprocal recombination) or between the expressed vsg and a silent vsg locus (gene conversion).310

14

PART I  Host-Parasite Relationships and the Pathogenesis of Infectious Diseases

In the case of H. influenzae, lipopolysaccharide (LPS) is likely a key factor in facilitating colonization and is also a major target of the antibody response to infection. Interestingly, H. influenzae LPS undergoes phase variation. LPS biosynthesis involves multiple enzymatic steps and a number of genes. Among these genes, lic1A, lic2A, lic3A, lex-2, lgtC, and an oafA-like gene contain long stretches of tandem four-base pair repeats within their 5′ coding region. In studies of the lic loci, Weiser and coworkers observed that the number of repeats varies spontaneously, generating translational frameshifts with different ATG start codons falling in or out of frame.324 Such frameshifts result in synthesis of a protein with a different N terminus or eliminate protein production altogether (when no in-frame start codon exists). The mechanism of variation in repeat number is presumed to be slipped-strand mispairing, which occurs during DNA replication and involves a single repeat looping out on either the template or the replicating strand. Changes in lic2A and lic3A influence glycotransferase activity and alter reactivity with monoclonal antibodies directed against specific LPS oligosaccharide epitopes.108 The lic2A gene product is responsible for the addition of a Gal-α1,4-Gal moiety, which resembles the globoseries glycolipids and protects H. influenzae from antibody-mediated killing, possibly by molecular mimicry.325 lgtC may be involved in formation of a Galβ1,4-Glu moiety.132 Variation in the lic1A gene affects production of a choline kinase responsible for addition of phosphorylcholine to the LPS molecule, a physical change that enhances binding of C-reactive protein and results in susceptibility to serum bactericidal activity.187,326,327 Expression of lex2 results in addition of a tetrasaccharide (Gal-α1,4-Galβ1,4-Glc-β1,4-Glc) to the proximal heptose in LPS and increases resistance to complement-mediated serum killing.105 Similarly, expression of the oafA-like gene results in LPS O-acetylation, which facilitates resistance to serum killing.88 Recent studies of hepatitis A virus (HAV) have identified a novel mechanism by which viruses can evade humoral responses. HAV was long considered to be nonenveloped, a characteristic that seemed well suited to promote fecal-oral transmission. However, elegant centrifugation studies demonstrated that HAV features an envelope as it exits an infected cell.80 The enveloped HAV particle (eHAV) is fully infectious. Formation of eHAV requires proteins involved in host cell exosome formation (VPS4B and ALIX), suggesting that HAV has co-opted these pathways to facilitate spread. While temporary, this enveloped form of HAV is fully protected from neutralizing antibodies and likely facilitates cellto-cell spread in the liver. Following these studies of HAV, additional viruses have been observed to generate a temporary envelope, indicating an established strategy for viruses to evade humoral responses.253

Encapsulation Expression of an extracellular capsule represents a common strategy to evade phagocytosis, complement activity, and humoral immunity among pathogenic bacteria, fungi, and parasites. One example is H. influenzae, a common cause of childhood bacteremia and meningitis in underdeveloped countries. Among isolates of H. influenzae, six structurally and antigenically distinct capsular types are recognized, designated serotypes a to f. Historically, serotype b isolates accounted for more than 95% of all H. influenzae invasive disease, reflecting the distinct virulence properties of the type b capsule, which is a polymer of ribose and ribitol-5-phosphate (PRP) and is encoded by the capb locus.211 In animal studies comparing derivatives of H. influenzae strain Rd expressing type a, b, c, d, e, or f capsule, the strain expressing the type b capsule was associated with the highest incidence of bacteremia after intranasal inoculation of infant rats. Similarly, this strain was associated with the highest magnitude of bacteremia and incidence of meningitis after intraperitoneal inoculation of experimental rats.354 In considering the mechanism by which the type b capsule promotes intravascular survival and invasive disease, in vitro studies using mouse peritoneal macrophages and human peripheral blood monocytes provide some insights. The type b capsule inhibits bacterial binding to macrophages in the absence of complement and a source of C3.223 In addition, the type b capsule interferes with ingestion by macrophages when anti-PRP antibody is lacking.223,222 Furthermore the type b capsule blocks complement deposition on the bacterial surface and resultant

complement-mediated bacteriolysis. In almost all isolates of H. influenzae type b, the capb locus is a tandem repeat of 18-kb capb gene sequences.221 As a consequence of this arrangement, the capb locus serves as a template for further amplification of capsule gene sequences in vivo, resulting in increased capsule production. In a study by Corn and colleagues, 23 of 66 minimally passaged invasive isolates had between three and five copies of the 18-kb repeat.47 Further analysis demonstrated that amplification of the repeat results in augmented resistance to phagocytosis and complement-mediated bacterial killing.221 The importance of the type b capsule in disease pathogenesis was recognized in vaccine development efforts, and the routine implementation of the Hib polysaccharideconjugate vaccine in many countries has sharply curtailed the incidence of invasive Hib disease. Capsule production is also a critical virulence determinant for a number of disease-causing fungi, including the opportunistic pathogen Cryptococcus neoformans, which causes infections primarily in HIVinfected and other immunocompromised hosts. C. neoformans elaborates a thick polysaccharide capsule that is the basis for the classic “halo” appearance of the organism upon India ink staining of cerebrospinal fluid in patients with cryptococcal meningitis. The capsule comprises a complex polymer with a galactose backbone modified by xylose, mannose, and glucuronic acid. The enzymes responsible for assembly have begun to be identified, suggesting new possible targets for new antifungal development.170,257 However, several elements required for capsule biosynthesis remain to be elucidated, and major questions persist regarding the spatial organization of capsule components and the basis for interstrain variation in the chemical structure and antibody reactivity of the galactoxylomannan backbone.68

Viral Immune Suppression and Latency Infection with HCV is a potent inducer of interferon-stimulated gene expression (as with other viruses).331 However, HCV has evolved several mechanisms to evade host innate immune responses. The viral protease NS3-NS4A interferes with nuclear localization of interferon regulatory factor-3 (IRF-3) in response to interferon in HCV-infected hepatocytes.89 This disruption of IRF-3 signaling, which prevents cells from activating antiviral genes downstream of IRF-3, results from specific cleavage of the molecule IPS-1.181 Similar observations regarding evasion of innate immunity have been made with the influenzavirus NS1 protein and with West Nile virus and HIV.67,69,334 Among some other viral pathogens, latency represents an important mechanism for persistence in the presence of host immunity, especially in the case of viruses belonging to the herpesvirus family. Herpes simplex viruses (HSV types 1 and 2) commonly establish latency after either gingivostomatitis or genital tract infection. After infection of a host cell, HSV replication begins. Eventually cell death occurs, resulting in cell lysis and release of viral particles, which can then infect adjacent cells. This so-called lytic replication cycle is under control of a small number of immediate early (IE) genes, which must be transcribed in moderate amounts to allow expression of the remainder of the viral genome. IE gene expression is activated by VP16, a viral protein that binds to a sequence common to IE gene promoters.252 After lysis of the host cell, new virions enter local nerve termini and travel up the long axon to sensory ganglia, where latency is established within days. In the latent state, viral DNA can be detected in the neuron, but infectious virions cannot be isolated. During latency,217 IE genes are repressed and only one fragment of viral DNA is actively transcribed, yielding several latency-associated transcripts (LATs) via alternative splicing.348 No protein product has been definitively attributed to the LAT; instead, recent work has demonstrated HSV-1 production of microRNAs, transcribed from LAT exons, that promote latency by inhibiting transforming growth factor-β signaling, favoring survival of infected cells and regulating the expression of activation-associated viral genes.56,109,315 LAT-deficient mutants are still able to establish initial latency, suggesting that IE gene expression may be under multiple controls.320 The mechanism by which HSV is reactivated is an area of intense study and some controversy. Host cellular mechanisms may provide the inciting signals, and the actions of viral thymidine kinase and the protein ICP0 are required for a return to lytic replication.217

CONCLUSION With the proliferation of molecular techniques in recent years, our understanding of the specific microbial and host factors involved in the pathogenesis of a variety of infectious diseases continues to expand remarkably. As a consequence of this understanding, we have witnessed the development of new vaccines and potential targets for antivirulence therapeutics. In the coming years, it is likely that advances in immunology and microbial pathogenesis will inform novel approaches for treating and preventing human infections. Examples might include inhibitors of type III protein secretion systems,149 antagonists of periplasmic chaperones, analogs of important host cell receptors, and vaccine adjuvants that direct polarization of T-cell responses. However, given the impressive adaptability of human pathogens, as new therapeutic agents become available, we must remain vigilant for new microbial strategies allowing evasion of our interventions. NEW REFERENCES SINCE THE SEVENTH EDITION 7. Avril M, Tripathi AK, Brazier AJ, et al. A restricted subset of var genes mediates adherence of Plasmodium falciparum-infected erythrocytes to brain endothelial cells. Proc Natl Acad Sci USA. 2012;109:E1782-E1790. 11. Barocchi MA, Ries J, Zogaj X, et al. A pneumococcal pilus influences virulence and host inflammatory responses. Proc Natl Acad Sci USA. 2006;103:2857-2862. 32. Carruthers MD, Tracy EN, Dickson AC, et al. Biological roles of nontypeable Haemophilus influenzae type IV pilus proteins encoded by the pil and com operons. J Bacteriol. 2012;194:1927-1933. 38. Claessens A, Adams Y, Ghumra A, et al. A subset of group A-like var genes encodes the malaria parasite ligands for binding to human brain endothelial cells. Proc Natl Acad Sci USA. 2012;109:E1772-E1781. 54. Crosnier C, Bustamante LY, Bartholdson SJ, et al. Basigin is a receptor essential for erythrocyte invasion by Plasmodium falciparum. Nature. 2011;480:534-537.

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PART I  Host-Parasite Relationships and the Pathogenesis of Infectious Diseases

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Timpe JM, Stamataki Z, Jennings A, et al. Hepatitis C virus cell-cell transmission in hepatoma cells in the presence of neutralizing antibodies. Hepatology. 2008; 47:17-24. 310. Tomlinson S, Raper J. The lysis of Trypanosoma brucei brucei by human serum. Nat Biotechnol. 1996;14:717-721. 311. Touze T, Hayward RD, Eswaran J, et al. Self-association of EPEC intimin mediated by the β-barrel–containing anchor domain: a role in clustering of the Tir receptor. Mol Microbiol. 2004;51:73-87. 312. Tran TM, Ongoiba A, Coursen J, et al. Naturally acquired antibodies specific for Plasmodium falciparum reticulocyte-binding protein homologue 5 inhibit parasite growth and predict protection from malaria. J Infect Dis. 2014;209:789-798. 313. Tucker SC, Galan JE. Complex function for SicA, a Salmonella enterica serovar typhimurium type III secretion-associated chaperone. J Bacteriol. 2000;182: 2262-2268. 314. Turner L, Lavstsen T, Berger SS, et al. Severe malaria is associated with parasite binding to endothelial protein C receptor. Nature. 2013;498:502-505. 315. Umbach JL, Kramer MF, Jurak I, et al. MicroRNAs expressed by herpes simplex virus 1 during latent infection regulate viral mRNAs. Nature. 2008;454: 780-783. 316. Uphoff TS, Welch RA. Nucleotide sequencing of the Proteus mirabilis calciumindependent hemolysin genes (hpmA and hpmB) reveals sequence similarity with the Serratia marcescens hemolysin genes (shlA and shlB). J Bacteriol. 1990;172:1206-1216. 317. van’t Wout AB, Kootstra NA, Mulder-Kampinga GA, et al. Macrophage-tropic variants initiate human immunodeficiency virus type 1 infection after sexual, parenteral, and vertical transmission. J Clin Invest. 1994;94:2060-2067. 318. Vazquez-Torres A, Jones-Carson J, Baumler AJ, et al. Extraintestinal dissemination of Salmonella by CD18-expressing phagocytes. Nature. 1999;401:804-808. 319. Virji M, Stimson E, Makepeace K, et al. Posttranslational modifications of meningococcal pili: identification of a common trisaccharide substitution on variant pilins of strain C311. Ann N Y Acad Sci. 1996;797:53-64. 320. Wagner EK, Bloom DC. Experimental investigation of herpes simplex virus latency. Clin Microbiol Rev. 1997;10:419-443.

321. Wakita T, Pietschmann T, Kato T, et al. Production of infectious hepatitis C virus in tissue culture from a cloned viral genome. Nat Med. 2005;11:791-796. 322. Wann ER, Gurusiddappa S, Höök M. The fibronectin-binding MSCRAMM FnbpA of Staphylococcus aureus is a bifunctional protein that also binds to fibrinogen. J Biol Chem. 2000;275:13863-13871. 323. Weir S, Marrs CF. Identification of type 4 pili in Kingella denitrificans. Infect Immun. 1992;60:3437-3441. 324. Weiser JN, Maskell DJ, Butler PD, et al. Characterization of repetitive sequences controlling phase variation of Haemophilus influenzae lipopolysaccharide. J Bacteriol. 1990;172:3304-3309. 325. Weiser JN, Pan N. Adaptation of Haemophilus influenzae to acquired and innate humoral immunity based on phase variation of lipopolysaccharide. Mol Microbiol. 1998;30:767-775. 326. Weiser JN, Pan N, McGowan KL, et al. Phosphorylcholine on the lipopolysaccharide of Haemophilus influenzae contributes to persistence in the respiratory tract and sensitivity to serum killing mediated by C-reactive protein. J Exp Med. 1998;187:631-640. 327. Weiser JN, Shchepetov M, Chong ST. Decoration of lipopolysaccharide with phosphorylcholine: a phase-variable characteristic of Haemophilus influenzae. Infect Immun. 1997;65:943-950. 328. Weiss SM, Ladwein M, Schmidt D, et al. IRSp53 links the enterohemorrhagic E. coli effectors Tir and EspFU for actin pedestal formation. Cell Host Microbe. 2009;5:244-258. 329. Wetzler LM, Barry K, Blake MS, et al. Gonococcal lipooligosaccharide sialylation prevents complement-dependent killing by immune sera. Infect Immun. 1992;60:39-43. 330. Wexler DE, Chenoweth DE, Cleary PP. Mechanism of action of the group A streptococcal C5a inactivator. Proc Natl Acad Sci USA. 1985;82:8144-8148. 331. Wieland SF, Chisari FV. Stealth and cunning: hepatitis B and hepatitis C viruses. J Virol. 2005;79:9369-9380. 332. Wilke GA, Bubeck Wardenburg J. Role of a disintegrin and metalloprotease 10 in Staphylococcus aureus α-hemolysin-mediated cellular injury. Proc Natl Acad Sci USA. 2010;107:13473-13478. 333. Willems RJ, Geuijen C, van der Heide HG, et al. Mutational analysis of the Bordetella pertussis fim/fha gene cluster: identification of a gene with sequence similarities to haemolysin accessory genes involved in export of FHA. Mol Microbiol. 1994;11:337-347. 334. Wilson JR, de Sessions PF, Leon MA, et al. West Nile virus nonstructural protein 1 inhibits TLR3 signal transduction. J Virol. 2008;82:8262-8271. 335. Wolff C, Nisan I, Hanski E, et al. Protein translocation into host epithelial cells by infecting enteropathogenic Escherichia coli. Mol Microbiol. 1998;28: 143-155. 336. Wright SD, Silverstein SC. Receptors for C3b and C3bi promote phagocytosis but not the release of toxic oxygen from human phagocytes. J Exp Med. 1983;158:2016-2023. 337. Wu H, Bu S, Newell P, et al. Two gene determinants are differentially involved in the biogenesis of Fap1 precursors in Streptococcus parasanguis. J Bacteriol. 2007;189:1390-1398. 338. Wu H, Fives-Taylor PM. Identification of dipeptide repeats and a cell wall sorting signal in the fimbriae-associated adhesin, Fap1, of Streptococcus parasanguis. Mol Microbiol. 1999;34:1070-1081. 339. Wu H, Mintz KP, Ladha M, et al. Isolation and characterization of Fap1, a fimbriaeassociated adhesin of Streptococcus parasanguis FW213. Mol Microbiol. 1998;28:487-500. 340. Wu H, Song Z, Givskov M, et al. Pseudomonas aeruginosa mutations in lasI and rhlI quorum sensing systems result in milder chronic lung infection. Microbiology. 2001;147:1105-1113. 341. Xu H, Storch T, Yu M, et al. Characterization of the human Forssman synthetase gene: an evolving association between glycolipid synthesis and host-microbial interactions. J Biol Chem. 1999;274:29390-29398. 342. Yanagishita M, Hascall VC. Cell surface heparan sulfate proteoglycans. J Biol Chem. 1992;267:9451-9454. 343. Yeo HJ, Cotter SE, Laarmann S, et al. Structural basis for host recognition by the Haemophilus influenzae Hia autotransporter. EMBO J. 2004;23:1245-1256. 344. Yi Y, Ma Y, Gao F, et al. Crystal structure of EHEC intimin: insights into the complementarity between EPEC and EHEC. PLoS ONE. 2010;5:e15285. 345. Yoon S, Liu Z, Eyobo Y, et al. Yersinia effector YopJ inhibits yeast MAPK signaling pathways by an evolutionarily conserved mechanism. J Biol Chem. 2003;278:2131-2135. 346. Yu L, Lee KK, Sheth HB, et al. Fimbria-mediated adherence of Candida albicans to glycosphingolipid receptors on human buccal epithelial cells. Infect Immun. 1994;62:2843-2848. 347. Yu M, Haslam DB. Shiga toxin is transported from the endoplasmic reticulum following interaction with the luminal chaperone HEDJ/ERdj3. Infect Immun. 2005;73:2524-2532. 348. Zabolotny JM, Krummenacher C, Fraser NW. The herpes simplex virus type 1 2.0-kilobase latency-associated transcript is a stable intron which branches at a guanosine. J Virol. 1997;71:4199-4208.

CHAPTER 1  Molecular Determinants of Microbial Pathogenesis 349. Zhang L, He T, Talal A, et al. In vivo distribution of the human immunodeficiency virus/simian immunodeficiency virus coreceptors: CXCR4, CCR3, and CCR5. J Virol. 1998;72:5035-5045. 350. Zhang Y, Mena P, Romanov G, et al. A protective epitope in type III effector YopE is a major CD8 T cell antigen during primary infection with Yersinia pseudotuberculosis. Infect Immun. 2012;80:206-214. 351. Zhang J, Randall G, Higginbottom A, et al. CD81 is required for hepatitis C virus glycoprotein-mediated viral infection. J Virol. 2004;78:1448-1455. 352. Zhu T, Mo H, Wang N, et al. Genotypic and phenotypic characterization of HIV-1 patients with primary infection. Science. 1993;261:1179-1181. 353. Zoja A, Remuzzi G. The pivotal role of the endothelial cell in the pathogenesis of HUS. In: Kaplan BS, Trompeter RS, Moake JL, eds. Hemolytic Uremic Syndrome

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CHAPTER 2  Normal and Impaired Immunologic Responses to Infection

Normal and Impaired Immunologic Responses to Infection

15

2 

Michael F. Tosi This chapter provides an overview of immunologic responses to infection and considers host interactions with different classes of pathogens, normal innate and adaptive immune mechanisms, the developing host responses of neonates, specific primary and secondary immunodeficiencies, and approaches to the evaluation of children suspected of having impaired immunity. Human immunodeficiency virus (HIV) and acquired immunodeficiency syndrome (AIDS) are not considered here because they are addressed fully in Chapter 192B. This chapter is intended to supply a basic understanding of mechanisms involved in normal host responses to infection, an appreciation of the underlying basis and clinical presentation of important immunodeficiencies, and familiarity with general principles of evaluation and management of patients with suspected or documented disorders of immunity.

HOST-PATHOGEN INTERACTIONS General Features of Host-Pathogen Interactions Humans are constantly exposed to a daunting number and diversity of microorganisms that can cause infection. Many organisms that usually coexist harmoniously with the human host on the skin or on mucous membranes of the oral cavity, upper airways, or lower gastrointestinal tract may invade and become pathogens only if the balance of the commensal relationship is disrupted. Other organisms are more virulent, and they overtly challenge the host’s normal surface barriers and internal defense mechanisms. The human host has evolved a complex array of

protective mechanisms designed to defend itself against these continuous microbial challenges.592 To understand the pathogenesis, pathology, and natural history of infectious diseases, familiarity with the features of infectious agents that confer virulence is necessary; these topics are addressed elsewhere in this book. However, it is equally important to understand the elements of the host’s response that contribute to containment, elimination, and protection against subsequent infection with these agents. Furthermore, it is important to recognize that host responses to infections also may contribute to the pathophysiology of infectious diseases and may injure the host in other ways. The characteristic features of specific infectious diseases are determined by the interactions of structural components and released products of microbial pathogens with host tissue, cells, and their products. Virulence tactics commonly employed by organisms include adherence to host cell surfaces, internalization within or invasion of host cells, production of toxins, elaboration of surface barriers such as bacterial polysaccharide capsules, usurpation of host synthetic mechanisms, and direct inhibition of specific defense mechanisms within host cells. The successful evolution of host strategies to protect against microbial attack has resulted in defenses designed to interfere with or to counteract many of these modes of microbial virulence.592 In recent decades, some of humanity’s oldest microbial adversaries (e.g., smallpox, poliomyelitis, measles) systematically have been, or are being, eradicated with aggressive implementation of immunization programs. In the meantime, previously unrecognized human pathogens such as human immunodeficiency

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PART I  Host-Parasite Relationships and the Pathogenesis of Infectious Diseases

virus–1 (HIV-1) and Ebola virus have emerged as new adversaries. Moreover, many of our oldest nemeses (e.g., tuberculosis, malaria) continue to elude our efforts to bring them under control, and they remain serious problems worldwide. Continued research at the interface between microbial pathogenesis and immunologic mechanisms is essential for the development of innovative approaches that can support and augment human immune responses to both old and new infectious diseases.

Main Features of Host Responses to Specific Classes of Infectious Agents Viruses Viruses are obligate intracellular parasites that consist of genetic material in the form of either DNA or RNA that usually is surrounded by a protein coat and may or may not be bound by a lipid envelope.372 Diseases caused by viruses are remarkably diverse, ranging from mild and merely inconvenient to rapidly fatal, and from acute or brief to chronic or lifelong. However, certain features are common to the pathogenesis of most viral infections. First, viruses must enter host cells to replicate. Viral entry ordinarily is initiated by attachment of a viral surface protein to a specific receptor molecule on the host cell. The specific viral ligands or their corresponding host cell receptors have been identified for some viruses. For example, rhinovirus has evolved a capsid protein that binds to human intercellular adhesion molecule–1 (ICAM-1) on respiratory epithelium245; the envelope glycoproteins of HIV-1 interact with CD4 on T lymphocytes and distinct chemokine receptors on lymphocytes or macrophages154,308,589; and internalization of adenoviruses depends on interaction between a specific peptide sequence in the penton base complex of the viral capsid and αV integrins on host cell surfaces.584 After the virus has entered the host cell, the cellular synthetic machinery is redirected to the synthesis of viral components. As with many native proteins synthesized by the host cell, a portion of newly synthesized viral protein is processed into peptides and presented on the infected cell surface by major histocompatibility complex (MHC) class I molecules (see later discussion). The host mechanisms most important in defense against the majority of viral pathogens include the production of specific neutralizing antibodies against viral surface proteins, the development of specific CD8+ cytotoxic T-cell responses that eliminate infected cells, and the production by different immune cells of type 1 interferons (IFNs) that disrupt viral replication.38,345,347,476,536 Natural killer (NK) cells appear to mediate the destruction of some virus-infected host cells,120,513 and antibodydependent cellular cytotoxicity (ADCC) may ensue after immunoglobulin (Ig)G antibodies bind to viral antigens on the infected cell, permitting subsequent attachment of either NK cells or cytotoxic T cells via IgG Fc receptors.200 IFNs and other cytokines may enhance NK and ADCC activity, and cytokines such as tumor necrosis factor-α (TNF-α) may exert cytotoxic actions on cells infected with certain viruses.347 Additionally, opsonic complement components bound to viral surfaces can interfere with cell attachment, and the complement-derived membrane attack complex can lyse enveloped viruses.60 Bacteria The human host is colonized with a large variety of bacteria at skin and mucous membrane surfaces.108,404 The integrity of these mechanical barriers ordinarily prevents systemic invasion of local commensal bacteria.89 The epithelial cells that constitute these barriers, on recognition of an organism as a pathogen, also can release defensins and other microbicidal molecules.225 In healthy hosts, circulating polymorphonuclear leukocytes (PMNs) help keep the resident flora in check by leaving the bloodstream at the mucosal sites containing the highest bacterial burdens, such as the lower intestine and the gingival crevices of the oral cavity.28 This phenomenon helps account for the increased risk for local and systemic infection caused by oral and intestinal organisms in patients with severe neutropenia, including those who receive prolonged chemotherapy for malignancies, and in patients with phagocyte migration disorders such as leukocyte adhesion deficiency syndromes.28 Important host defenses against most bacteria that invade the human host systemically include the complement system, specific

antibodies that promote both the opsonic and the bacteriolytic functions of complement, and phagocytes.1,28,60,293 Fungi Host mechanisms critical for defense against fungi are less well understood than those directed at bacteria and viruses, but phagocytes and cell-mediated immunity appear to be most important.187,215 The relative importance of these factors appears to depend on the specific organisms involved, as is demonstrated by clinical observations in patients with isolated defects of one or the other. Severe mucosal infections caused by Candida spp. are common in patients with acquired or primary cell-mediated immune deficits, such as HIV infection, thymic aplasia (see later discussion), chronic mucocutaneous candidiasis, and some forms of severe combined immunodeficiency, as well as in patients with disorders of leukocyte migration.28,187 In contrast to Candida, Aspergillus infections are not as great a problem for patients with cell-mediated immune defects as they are for patients with defects in phagocytic host defenses, such as neutropenia associated with cancer chemotherapy or stem cell transplantation, or genetic defects in phagocyte killing such as chronic granulomatous disease.58,588 Fungi such as Histoplasma and Cryptococcus, like Candida, tend to cause severe infections in patients with defects in cell-mediated immunity, although phagocytes clearly are required for optimal clearance of these organisms.170,290,582 The main role of antibodies and complement in protection from fungi probably is to provide opsonic activity to enhance phagocyte function.172 Parasites Parasites such as protozoa and helminths comprise such a widely varying group of pathogenic organisms that it is difficult to generalize about mechanisms of immunity to these organisms as a group. However, the importance of specific host mechanisms in defense against certain parasites may be appreciated by considering the characteristic host responses mobilized by parasitic infection or infestations. Some helminths induce production by host cells of chemokines that recruit eosinophils and stimulate their production. This suggests a likely role for these cells in antiparasitic defenses, and eosinophils have been shown to be important in protection against helminths such as Strongyloides and other parasites in this group that can invade tissues. IgE, among the immunoglobulins, appears to play a special role, often in concert with eosinophils, in anthelmintic defenses. IgG also may be important based on the susceptibility of individuals with hypogammaglobulinemia to hyperinfection with Strongyloides. Patients with hypogammaglobulinemia also are at risk for chronic or severe infestations with the flagellate intestinal parasite Giardia lamblia, suggesting a role for some degree of antibody-mediated protection in normal hosts. Patients with primary or acquired disorders of cell-mediated immunity are prone to development of serious central nervous system and ocular manifestations of infection with the protozoan Toxoplasma gondii, an obligate intracellular parasite, as well as hyperinfection with Strongyloides.299,429

FEATURES OF NORMAL IMMUNE FUNCTION The immune system can be viewed as consisting of two broad response categories: innate immunity and adaptive immunity. The former encompasses the more rapid and phylogenetically primitive, nonspecific responses to infection, such as surface defenses, cytokine elaboration, complement activation, and phagocytic responses. The latter involves more slowly developing, persistent, and highly evolved antigenspecific responses, such as cell-mediated immunity and antibody production that exhibit extraordinarily diverse ranges of specificities. The various arms of the immune system engage in a wide range of interactions that may enhance or regulate functions of other components of immunity, adding to the already remarkable complexity of the human immune response, and numerous examples of such interactions will be provided.

Innate Immune Responses Epithelia, Defensins, and Other Antimicrobial Peptides The epithelium of skin and mucosal tissue functions as a mechanical barrier to the invasion of microbial pathogens. In recent decades, it has

CHAPTER 2  Normal and Impaired Immunologic Responses to Infection become clear that epithelial cells also are a major source of antimicrobial peptides that play important roles in local host defense.48,224,223,421 Studies of their structure, sources, expression, and actions also have revealed an unexpected range of immunologic activities for these molecules whose functions once were considered mainly antimicrobial in nature.2,33 Epithelial cells of mucous membranes of the airways and intestines, as well as keratinocytes, express the human β-defensins (HBD)-1, HBD-2, HBD-3, and HBD-4. These small cationic peptides are similar to the α-defensins stored in the azurophilic granules of neutrophils, and they display antimicrobial activity against a broad range of bacteria, fungi, chlamydiae, and enveloped viruses.48,223,225,421 Their production by epithelial cells may be constitutive, as for HBD-1, or inducible as for HBD-2, HBD-3, and HBD-4. For example, recent evidence indicates that epithelial cells of the airway or intestine can produce HBD-2 in response to activation by bacterial products via the Toll-like receptors TLR2 or TLR4 (see later discussion) on the epithelial cells.263,568,574 Stimulation of epithelium by cytokines, including interleukin (IL)-1 or TNF-α also can induce defensin production.48,225 Defensins have been reported to exert their antimicrobial action either by the creation of membrane pores or by membrane disruption resulting from electrostatic interaction with the polar head groups of membrane lipids, with more evidence now favoring the latter mechanism.48,275 Some microorganisms have evolved mechanisms for evading the action of defensins. For example, bacterial polysaccharide capsules may limit access of microbial peptides to the cell membrane,112 and an exoprotein of Staphylococcus aureus, staphylokinase, neutralizes the microbicidal action of neutrophil α-defensins.288 Several immunoregulatory properties of defensins and related peptides, distinct from their antimicrobial actions, have been documented.223 Several such peptides have been shown to facilitate posttranslational processing of IL-1β.439 Some of the β defensins have been shown to function as chemoattractants for neutrophils, memory T cells, and immature dendritic cells by binding to the chemokine receptor CCR-6.274,403,421 Separately, HBD-2 has been shown to act, via a mechanism that requires TLR4, to activate immature dendritic cells and promote their maturation.69,591 The β-defensins also act as chemoattractants for mast cells and can induce mast cell degranulation.402 HBD-2 and several other antimicrobial peptides can interfere with binding between bacterial lipopolysaccharide (LPS) and LPS-binding protein (LBP), a process important in activating inflammatory cells via TLR4 (see later discussion).493 Additional antimicrobial peptides of epithelial cells include lysozyme and cathelicidin. Lysozyme, an antimicrobial peptide also found in neutrophil granules, attacks the peptidoglycan cell walls of bacteria and may be released from cells by mechanisms that involve TLR activation.431 Cathelicidin, or LL37, like lysozyme, is released from both neutrophils and epithelial cells. It exhibits broad antimicrobial activity and can inhibit lentiviral replication.274,527 Cathelicidin also exhibits chemotactic activity for neutrophils, monocytes, and T lymphocytes. This activity is mediated via a formyl peptide receptor–like molecule (FPRL-1), rather than the chemokine receptor (CCR)6 bound by β-defensins.590

17

The release of defensins in response to activation of TLRs and the various actions of these peptides, including their direct antimicrobial activities, their chemoattractant actions for a wide range of immune cells, and their activation of dendritic cell maturation, already suggest a highly complex and regulatory role in the development of host defense and immunity. Genomic evidence for the possible existence of many additional human defensins that have not yet been characterized suggests that current knowledge describes but a small sample of the overall contribution of these peptides to immune responses.48,490 Toll-Like Receptors Mononuclear phagocytes, including circulating monocytes and tissue macrophages, other phagocytic cells, and many epithelial cells, express a family of receptors that is highly homologous to the Drosophila receptor called Toll.95,263,370,568,574 These receptors mediate a phylogenetically primitive, nonclonal mechanism of pathogen recognition based on binding, not to specific antigens, but to structurally conserved pathogenassociated molecular patterns.8,412,413,595 At least 10 human TLRs with a range of microbial ligands have been identified, such as gram-negative bacterial LPS, bacterial lipoproteins, lipoteichoic acids of gram-positive bacteria, bacterial cell wall peptidoglycans, cell wall components of yeast and mycobacteria, unmethylated CpG dinucleotide motifs in bacterial DNA, some viral particles, and viral RNA.8,412,413,595 Gram-positive cell wall components bind mainly to TLR2, and TLR2 also can bind components of herpes simplex virus.323,538 TLR2 forms dimers with either TLR1 or TLR6 when bound jointly by their ligands.288,342 Gramnegative LPS activates TLR4 indirectly by first binding to LBP, which transfers the LPS to the host accessory protein CD14 at the cell surface. The bound CD14 has no transmembrane domain but associates directly with an extracellular domain of TLR4.413,538 MD-2, an additional accessory protein associated with TLR4, also plays a role in binding LPS.434 TLR5 has been identified as the receptor for bacterial flagellin, TLR9 recognizes CpG motifs of bacterial and viral DNA, and TLR3 has been shown to bind synthetic and viral double-stranded RNA.56,255,319,323 A listing of known human TLRs with their major ligands and cellular distribution is summarized in Table 2.1. Signaling by TLRs occurs via a well-described pathway in which receptor binding generates a signal via an adaptor molecule, myeloid differentiation factor 88 (MyD88), that leads to intracellular association with IL-1 receptor–associated kinase (IRAK). In turn, this leads to activation of TNF receptor–associated factor–6 (TRAF-6), which results in nuclear translocation of nuclear factor-κB (NF-κB).133 NF-κB is an important transcription factor that activates the promoters of the genes for a broad range of cytokines and other proinflammatory products, such as TNF-α, IL-1, IL-6, and IL-8. This signaling pathway, based on studies with TLR4, is similar but not identical to the signaling pathways activated by other TLRs.133 The activation of cytokine production by TLRs plays an important role in recruiting other components of innate host defense against bacterial pathogens. However, with large-scale cytokine release, the deleterious effects of sepsis or other forms of the systemic inflammatory response syndrome demonstrate that these

TABLE 2.1  Human Toll-Like Receptors: Their Ligands and Cellular Distribution TLR

Ligands

Cellular Distribution

TLR1 (+TLR2) TLR2 (+TLR6) TLR3 TLR4 (+CD14, MD-2) TLR5 TLR7 TLR8 TLR9 TLR10

Mycobacterial lipoarabinomannans, bacterial lipoproteins, bacterial lipoteichoic acids, bacterial and fungal β-glucans Viral double-stranded RNA Bacterial lipopolysaccharide Bacterial flagellin Viral single-stranded RNA Viral single-stranded RNA Unmethylated CpG dinucleotides Unknown ligands

Mo, DC, MC, Eos, Bas, AEC NK cell MΦ, DC, MC, Eos, AEC AEC, IEC PDC, NK, Eos, BL NK cell PDC, Eos, BL, Bas (bacteria, herpesvirus) PDC, Eos, BL, Bas

AEC, Airway epithelial cell; Bas, basophil; BL, B lymphocyte; DC, dendritic cell; Eos, eosinophil; IEC, intestinal epithelial cell; MΦ, macrophage; MC, mast cell; Mo, monocyte; NK, natural killer; PDC, plasmacytoid dendritic cell; TLR, Toll-like receptor.

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PART I  Host-Parasite Relationships and the Pathogenesis of Infectious Diseases

pathways have both beneficial and potentially harmful effects for the host.133 Genetic polymorphisms in TLRs may play a role in determining the balance of these effects in certain individuals responding to the challenge of systemic infection.133,352,353 In addition to their “first responder” roles in generating an inflammatory response to invading pathogens, TLRs may network with other components of innate and adaptive immunity. TLR4 function is suppressed by activation of cells via the chemokine receptor CXCR4.307 Activation of some TLRs also can induce expression of the costimulatory molecule B7 on antigen-presenting cells, which is required for activation of naïve T cells.370 Cytokines A heterogeneous group of soluble small polypeptide or glycoprotein mediators, often collectively called cytokines, forms part of a complex network that helps regulate immune and inflammatory responses. Included in this group of mediators, whose molecular weights range from about 8 to about 45 kDa, are the ILs, IFNs, growth factors, and chemokines (see separate discussions later). Most cells of the immune system and many other host cell types release cytokines, respond to cytokines via specific cytokine receptors, or both. A list of cytokines and related molecules that play a role in immune function, with selected characteristics, is provided in Table 2.2.322,422,443 Excellent general reviews are available,321,322,347,422,443 and the use of cytokines as immunomodulating

agents is discussed in Chapter 242. However, two cytokines, IL-1 and TNF-α, are of such fundamental importance in acute host responses to infection that they warrant specific attention here. IL-1 and TNF-α are small polypeptides, each with a molecular weight of approximately 17 kDa, that exhibit a broad range of effects on immunologic responses, inflammation, metabolism, and hematopoiesis.66,422 IL-1 originally was described as “endogenous pyrogen,” referring to its ability to produce fever in experimental animals, and TNF-α, which produces some of the same effects produced by IL-1, was originally named “cachectin” after the wasting syndrome it produced when injected chronically in mice.66,422 Many of the physiologic changes associated with gram-negative sepsis can be reproduced by injecting experimental animals with these cytokines, including fever, hypotension, and either neutrophilia or leukopenia.66,422 In the development of endotoxic shock resulting from gram-negative sepsis, IL-1 and TNF-α are produced by mononuclear phagocytes in response to activation of TLRs by bacterial LPS. They in turn activate the production of other cytokines and chemokines, lipid mediators such as platelet-activating factor and prostaglandins, and reactive oxygen species. They also induce expression of adhesion molecules of both endothelial cells and leukocytes, stimulating recruitment of leukocytes by inducing release of the chemokine IL-8 and activating neutrophils for phagocytosis, degranulation, and oxidative burst activity.66,133 These are all important, usually beneficial host responses to infection. However, at very high levels of activation,

TABLE 2.2  Features of Selected Human Cytokines and Growth Factors Cytokines and Growth Factors

Main Cellular Sources

Biologic Effects

IL-1 IL-2 IL-3 IL-4

Mo, TL, BL, NK, PMN, others TL, BL, NK TL TL, BL, Mast, Mo

IL-5 IL-6 IL-7 IL-8 IL-9 IL-10

TL TL, BL, Mo Marrow and thymus stromal cells Mac, Mo, Endo, Epi, PMN, Eos TL TL, BL, Mast, Mac

IL-11 IL-12

Marrow stromal cells BL, Mo

IL-13

TL

IL-14 IL-15 IL-17 IL-18 IL-21 IL-23 IL-25 IL-27 IFN-α IFN-β IFN-γ TNF-α

TL, malignant BL Epi, Endo, Mo, Mac, marrow stromal cells TL Kupffer cells, Epi, spleen, Mac TL Dendritic cells, Mac TL (TH2), Mast Dendritic cells, Mac Mo, TL Epi, Fibro TL, NK Mo, Mac, TL, NK

GM-CSF G-CSF M-CSF

TL, BL, Mo, PMN, Eos, Fibro, Mast, Endo Mo, Epi, Fibro Mo, TL, BL, Endo, Fibro

Broad range of cellular activation in inflammatory and immune responses TL, BL proliferation and activation; enhances TL and NK cytotoxicity General stimulation of hematopoiesis TL, BL proliferation; BL isotype switching; stimulates IgE synthesis; enhances MHC class II expression Stimulation of Eos production Broad inflammatory activity; stimulates BL differentiation and megakaryocyte production TL, BL growth and differentiation Activation and chemotaxis of PMN, Eos Mast growth and differentiation; growth of activated TL Broad antiinflammatory actions; inhibits synthesis of several other cytokines (TNF, IL-2, IL-3, IFN-γ) General stimulation of hematopoiesis; BL growth and differentiation Stimulation of TL growth; induction of IFN-γ production; enhancement of TL and NK cytotoxicity BL proliferation and isotype switching; enhances MHC class II expression; inhibits production of cytokines by Mac Induces BL growth Enhances NK growth, development, function; enhances TL growth and migration Enhances TL growth; induces Mac cytokine release Promotes TL, BL, NK cytokine release; promotes TL, BL cytotoxicity Promotes BL, TL proliferation; NK cytoxicity Similar to IL-12 TL, Mac TH2 cytokine secretion TL responsiveness to IL-12 Interference with viral replication; increases MHC class I expression Similar to IFN-α Similar to IFN-α, IFN-β; stimulates Mac inflammatory functions Broad inflammatory effects; fever; cachexia; stimulates catabolism; activation of leukocytes and Endo Growth of PMN, Eos, Mo, and Mac precursors; enhances leukocyte function Enhances production and function of granulocytes Promotes Mo production; stimulates Mo and Mac function

BL, B lymphocyte; Endo, endothelial cell; Eos, eosinophil; Epi, epithelial cell; Fibro, fibroblast; G-CSF, granulocyte colony-stimulating factor; GM-CSF, granulocyte-macrophage colonystimulating factor; IFN, interferon; IL, interleukin; Mac, macrophage; Mast, mast cell; M-CSF, macrophage colony-stimulating factor; MHC, major histocompatibility complex; Mo, monocyte; NK, natural killer cell; PMN, polymorphonuclear leukocyte; TL, T lymphocyte; TNF, tumor necrosis factor.

CHAPTER 2  Normal and Impaired Immunologic Responses to Infection pathologic effects of this proinflammatory cascade may occur, including vascular instability, decreased myocardial contractility, capillary leak, tissue hypoperfusion, coagulopathy, and multiple organ failure.133,569 For some systemic actions, notably the production of hemodynamic shock, IL-1 and TNF-α are synergistic. Both IL-1 and TNF-α also induce production of IL-6, a somewhat less potent cytokine that exhibits some of the actions of IL-1 and TNF-α.422 The human host produces several soluble antagonists of IL-1 and TNF-α that can modulate their effects, including IL-1 receptor antagonist (IL-1ra), soluble TNF-α receptor (sTNF-αR), and antiinflammatory cytokines, especially IL-10.133 The importance of effects mediated by IL-1 and TNF-α in the pathophysiology of septic shock has prompted much active research aimed at blocking their direct and downstream effects to reduce sepsis morbidity and mortality. To date, despite promise and progress, clinical strategies to interfere with the cytokine-induced cascade that leads to endotoxin shock have continued, overall, to meet with limited success.29,43,96,133,212,422,456,562,572 Chemokines A specialized group of small cytokine-like polypeptides, chemokines, which all share the feature of being ligands for G-protein–coupled, seven-transmembrane-segment receptors, play a complex role in the immune response as cellular activators that induce directed cell migration mainly of immune and inflammatory cells.44,285,304,363,393,472 The chemokines and their receptors have been classified into four families based on the motif displayed by the first two cysteine residues of the respective chemokine peptide sequence. Each of at least 16 CXC chemokines binds to one or more of the CXCRs, CXCR1 to -6. Examples of CXC chemokines include IL-8 and Gro-α. Similarly, at least 28 CC chemokines, such as macrophage inflammatory protein (MIP)-1α; regulated and normal T cell expressed and secreted (RANTES); and eotaxin-1, -2, and -3 bind to one or more of the CCRs, CCR1 to -10. The sole CX3C chemokine, fractalkine (neurotaxin), binds to CX3CR1, currently the only receptor in its family. The two XC chemokines, including lymphotaxin, bind to the sole receptor in this family, XCR1. A chemokine nomenclature currently designates each of the chemokines as a numbered ligand for its respective receptor family. In this system, Gro-α is CXC ligand (L)-1 (or CXCL-1), and IL-8 now becomes CXCL-8. Similarly, RANTES becomes CCL-5, fractalkine is CX3CL-1, and lymphotactin is XCL-1.285,472 A review of this nomenclature system tabulates the members of each family with their respective ligands and receptors, as well as with the traditional names in both human and murine systems.285 Virtually every cell type of the immune system expresses receptors for one or more of the chemokines. The cells of virtually any inflamed tissue can release a range of chemokines, and tissues infected with different bacteria or viruses release chemokines that recruit characteristic sets of immune cells.235,304 For example, whereas rhinoviruses induce the release of chemokines that result mainly in recruitment of neutrophils (early in the course of infection), Epstein-Barr virus induces a set of chemokines that result in recruitment of B cells, NK cells, and both CD4+ and CD8+ T cells.235 It is of interest that almost mutually exclusive sets of chemokines are induced by cytokines associated with TH1 (IFN-γ) versus TH2 (IL-4, IL-13) versus TH17 (IL-17) immune responses (see later discussion), indicating a tight interplay between cytokines and chemokines in determining the type of immune response to specific infectious challenges generated under differing conditions.71 The specificity of such responses is strongly influenced by the type of chemokines released by specific tissues, the vascular adhesion molecules expressed in those tissues, the chemokine receptors expressed by different leukocyte populations, and the specific adhesion molecules expressed by leukocytes.71,235,304 Modulation of chemokine functions may occur by several mechanisms. Chemokines themselves may be potentiated or inactivated by tissue proteases including tissue peptidases and matrix metalloproteases.369 Heparin sulfate–related proteoglycans on endothelial cell surfaces tether chemokines locally, where they can most efficiently activate circulating leukocytes for adhesion (see later discussion). However, similar proteoglycans free in the extracellular environment may act to bind and sequester chemokines, keeping them from interacting with their cellular receptors.136,324 Finally, in addition to the well-described use of chemokine

19

receptors as coreceptors for viral entry by HIV-1, other viruses, especially members of the herpesvirus family, encode soluble decoy receptors that compete with native host receptors for chemokine binding, thereby disrupting normal host responses.136,469 Natural Killer Cells NK cells are an important cellular component of innate immunity. They are lymphoid cells found in the peripheral circulation, spleen, and bone marrow that do not express clonally distributed receptors, such as T-cell receptors or surface immunoglobulin, for specific antigens.387,388,513 They respond in an antigen-independent manner to aid in the control of malignant tumors and to help contain viral infections, especially those caused by members of the herpesvirus family, before the development of adaptive immune responses.513,514 Activated NK cells are an important source of IFN-γ, which limits tumor angiogenesis and promotes the development of specific protective immune responses.387,388,513,514 Regulation of NK cell activity involves a complex balance between activating and inhibitory signals. Several cytokines can activate NK cell proliferation, cytotoxicity, or IFN-γ production, including IL-12, IL-15, IL-18, IL-21, and IFN-αβ.514 Activating signals via other receptors on NK cells, such as NKG2D, may lead either to cytotoxicity or cytokine production or both, depending on the receptor’s association with distinct intracellular adaptor proteins that signal via different kinases.514,566 Other molecules on NK cells may act as either costimulatory or adhesion receptors, including CD27, CD28, CD154 (CD40 ligand), and lymphocyte function–associated (LFA)-1 (CD11a/CD18).50,514 Additionally, FcγRIII (CD16) can contribute to NK cell–mediated antibody-dependent cell cytotoxicity.200,387 NK cells are able to distinguish normal cells of selforigin via receptors that recognize specific MHC class I molecules. Activation of such receptors provides an inhibitory signal that protects healthy host cells from NK cell–mediated lysis. Virus-infected cells and malignant cells may express MHC class I molecules at reduced levels, rendering them more susceptible to attack by NK cells.120,513 NK cell inhibitory receptors, some of which have been characterized, appear to contain intracytoplasmic tyrosine-based inhibition motifs and antagonize NK cell activation pathways via protein tyrosine phosphatases.454,514 NK cells kill virus-infected or malignant cells by the release of perforin and granzymes from granular storage compartments and by binding of the death receptors Fas and TRAIL-R on target cells via their respective NK cell ligands.485,513,514 The mechanisms by which perforin and granzymes mediate target cell death are not fully understood. One or more of the granzymes appear to activate intracellular pathways leading to target cell apoptosis via pathways that involve the mitochondria or caspases or both.300,553 Separately, binding of the death receptors also activates caspases, causing target cell apoptosis.494,514 NK cells engage in several kinds of interactions with other cells of the immune system, including dendritic cells and other antigen-presenting cells. Dendritic cells can influence the proliferation and activation of NK cells both by release of cytokines, including IL-12, and by cell surface interactions, including CD40/CD40L, LFA-1/ICAM-1, and CD27/CD70.164 In return, NK cells can provide signals that result in either dendritic cell maturation or apoptosis.120,513 Complement System The complement system consists of more than 30 different free and membrane-bound activation and regulatory proteins. It has multiple key roles in the clearance of invading microbes, including opsonization, recruitment of phagocytic cells, and lytic destruction of pathogens.59,168,169,188,189,208,290,289,292,392 Approximately 90% of complement proteins are synthesized in the liver, but some components can be produced locally at sites of infection by tissue mononuclear phagocytes and fibroblasts.134,438 In healthy persons the majority of complement is found in the circulation. Circulating complement levels vary over time, particularly in the presence of inflammation. The inflammatory response may lead to increases in levels of those complement components such as C3 that are acute-phase reactants or to decreases in individual components and total complement activity as a result of consumption.

20

PART I  Host-Parasite Relationships and the Pathogenesis of Infectious Diseases CLASSICAL PATHWAY Ag-Ab complex

MBL PATHWAY Microbial carbohydrate

ALTERNATIVE PATHWAY Activating microbial surface

C1q C1r C1s

MBL MASP-1 MASP-2

C3b  B

C4, C2

C3 C3bB

C3

D

C4b2a

C3bBb(P) C3a

Amplification loop

C3(H2O)Bb (fluid phase)

C3b opsonization C4b2a3b

C5

C5a leukocyte recruitment

C5b

C3bBb3b(P)

C6, C7

C5b67

C5b6789 lysis

C8, C9

FIG. 2.1  The complement cascade. The initial binding events of the classical, mannan-binding lectin (MBL) and alternative pathways are indicated by a starburst. These pathways intersect at the conversion of C3 to C3b. This is followed by activation of the terminal components, beginning with the binding and cleavage of C5, releasing C5a and leaving bound C5b to initiate assembly of the remaining components to form the membrane attack complex (C5b6789). Enzymatically active proteases of the classical and alternative pathways that cleave and activate subsequent components are, by convention, shown with an overbar. The alternative pathway C3 and C5 convertases are shown associated with properdin (P), which increases their stability. B, Complement factor B; D, complement factor D; MASP, MBL-associated serine proteases.

The importance of normal complement component levels and activity in host defense has been well established and is based primarily on the increased susceptibility of patients with specific complement component deficiencies to recurrent or severe bacterial infections.166,168,188,289,290 Although the complement response to infection usually is beneficial to the host, it also may be associated with adverse clinical manifestations such as septic shock and acute respiratory distress syndrome.158,203,576 Complement activation.  Complement proteins are activated in a specific sequence or “cascade” via one or more of three pathways: the classical pathway, the alternative pathway, and the more recently described MBL pathway, as shown in Fig. 2.1. These pathways converge at C3, and the complement cascade downstream from C3 proceeds identically, irrespective of the pathway by which activation occurs. The C3 convertases, C4b2a for the classical and MBL pathways and C3bBb for the alternative pathway, cleave the C3 molecule at exactly the same location, producing C3b, which binds to the target surface, and C3a, which is released into the fluid phase. Cleavage and activation of C3 lead to a conformational change in C3b that transiently renders its reactive thioester group capable of forming covalent ester or amide bonds with acceptor molecules on the target surface.276,331 Surface-bound C3b can act as an opsonin to promote phagocytosis, or it can bind with the classical and alternative pathway C3 convertases to form the C5 convertases C4b2a3b and C3bBb3b, respectively.452 C5 convertases bind and then cleave C5, with release of the chemoattractant C5a fragment into the fluid phase. The bound C5b fragment then can initiate formation of the membrane attack complex by the sequential incorporation of the remaining terminal components, C6, C7, C8, and multiple molecules of C9. The membrane attack complex can insert into the outer membrane of target cells, such as erythrocytes or gram-negative bacteria, and cause cell lysis and death.292

Classical pathway.  Ordinarily the classical pathway is activated by IgM or IgG bound to microbial antigenic targets or by other kinds of antigen-antibody complexes.169 IgM activates complement more efficiently than IgG because only one molecule of polymeric IgM is required in contrast to at least two molecules of IgG.141 Activation typically is initiated when C1q binds directly to an immunoglobulin molecule on the surface of an organism. C1r and C1s are activated and bound to C1q sequentially, forming C1qrs. The enzymatic activity of this complex, which resides in the C1s molecule, can cleave multiple molecules of C4 and C2 into two fragments each. The C4a and C2b fragments are released into the environment, whereas C4b and C2a remain bound to each other on the target surface to form the classical pathway C3 convertase, C4b2a. C4bC2a can cleave and activate C3 and localize C3b binding to nearby sites on the target surface. As noted earlier, some C3b binds with C4b2a to form the classical pathway C5 convertase, C4b2a3b. Alternative pathway.  Alternative pathway activation of C3 is the principal means by which a nonimmune host can activate the effector functions of complement until a specific antibody response can be mounted.167,205 A spontaneous low level of hydrolysis of the thioester of C3 in the fluid phase results in an activated form of C3, C3(H2O). This activated form of C3 can bind factor B, and the latter is then cleaved by factor D to form the fluid phase C3 convertase C3(H2O)Bb. The constitutive presence of small amounts of this convertase in the fluid phase ensures that a small amount of C3b always is available to bind to microbial surfaces and initiate the alternative pathway.432 The alternative pathway protein factor B can bind to surface-bound C3b, after which factor B undergoes proteolytic cleavage by factor D to release a small soluble fragment, Ba, while the larger fragment, Bb, remains associated with

CHAPTER 2  Normal and Impaired Immunologic Responses to Infection C3b. C3bBb, the alternative pathway C3 convertase, is analogous to the classical pathway C3 convertase, C4b2a. Properdin stabilizes the C3 convertase C3bBb, permitting more efficient activation of C3 to form more C3b, creating the C3 amplification loop (see Fig. 2.1).202,205 The most important factor in determining whether a specific microbial pathogen will activate the alternative pathway is the biochemical nature of its surface. On surfaces rich in sialic acid, bound C3b is less able to bind factor B because another molecule, factor H, has a strong competitive advantage over factor B under these conditions. When bound by factor H, C3b becomes highly susceptible to further cleavage by factor I (C3b inactivator), resulting in C3bi (or iC3b). Although C3bi is an effective opsonin, it cannot bind factor B. Thus no alternative pathway convertases can be formed, and no amplification loop is established.59,325,392 Organisms whose surfaces do not support activation of the alternative pathway, such as K1 Escherichia coli, groups A and B streptococci, Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae type b, and some salmonellae are some of the most successful pathogens in infants and young children who lack specific protective antibodies.115,292 Mannan-binding lectin pathway. The most recently described complement activation pathway is the MBL pathway. It is similar to the classical pathway but does not involve antibodies. MBL is a serum protein of the collectin family that has structural and functional similarities to those of C1q. However, it does not require antigen-antibody complexes to initiate its complement-activating function. MBL binds to mannose-containing carbohydrates on microbial surfaces, leading to its association at the microbial surface with activated MBL-associated serine proteases (MASP-1 and -2). These latter proteases have structural and functional similarities to C1r and C1s, respectively, and result in activation of C4, with sequential binding of C4b and C2a and formation of C4b2a, the C3 convertase of the classical pathway. C3 is activated, and the cascade proceeds as described. A more detailed characterization of the MBL pathway and its role in immune responses to infection may be found in an excellent review.440 Effector functions of complement in host defense.  The principal complement effector functions in host defense include opsonization via bound fragments of C3; phagocyte recruitment, especially via release of C5a; lysis of microorganisms, especially gram-negative bacteria, via the membrane attack complex (C5b–C9); and immune regulation via interactions with host cells involved in adaptive immunity. Complement sometimes may be activated and bound to microbial surfaces but unable to carry out these functions if it is bound at a disadvantageous location; for example, C3b bound to a pneumococcal cell wall beneath a thick polysaccharide capsule or C5b–C9 bound to long lipopolysaccharide molecules distant from the gram-negative bacterial outer membrane.93,240,277,292 Opsonic activity. Complement opsonic activity is essential for effective phagocytic removal of organisms from the circulation by macrophages in the liver and spleen and from other sites by local macrophages and neutrophils.78 Opsonins facilitate recognition, binding, ingestion, and killing of microorganisms by phagocytes. Opsonization particularly is important for protection against gram-positive bacteria and fungi because their thick cell walls prevent them from being killed by the membrane attack complex. The major complement-derived opsonins are the C3 fragments C3b and iC3b. Surface-bound C3b and iC3b permit microbes to be recognized by circulating and tissue phagocytes by interacting with the phagocyte surface complement receptors CR1 (CD35) and CR3 (CD11b/CD18), respectively. These interactions lead to binding, ingestion, and intracellular killing of the organisms.117,240,277,276,331 Antibodies, especially of the IgG class, are important opsonins in their own right, but they also facilitate more rapid complement activation via the classical pathway and more effective localization of C3b binding to the surface of encapsulated organisms, where it is accessible to phagocyte receptors.93,277,294 Inflammation.  The cleavage products of several complement proteins contribute to the development of inflammatory responses. C3a stimulates an increase in the number of circulating granulocytes, and C5a serves as a potent stimulus for monocyte, neutrophil, and eosinophil migration toward the source of C5a gradients being produced at infected tissue sites. C5a also upregulates phagocyte expression of CR1 and CR3 and

21

stimulates these cells to release granule contents that also are important mediators of inflammation and microbicidal activity. C5a-induced neutrophil aggregation and stasis in the pulmonary circulation can be an important feature of the respiratory distress syndrome associated with sepsis.576 The anaphylatoxins, C4a, C3a, and especially C5a, induce release of histamine from mast cells and basophils, causing increased vascular dilation and permeability, which, in turn, permit local diffusion of other inflammatory mediators.279,576 When large quantities of anaphylatoxins are produced rapidly, they can contribute to septic shock.203 Microbicidal activity. As noted earlier, C5b and the terminal complement proteins C6, C7, C8, and C9 form the membrane attack complex, which can lyse gram-negative bacteria by penetrating their outer membranes.292 The C5b-C8 complex serves as a polymerization site for several molecules of C9, which increases the efficiency of lysis.68,539 As has been noted, the membrane attack complex cannot penetrate the thick cell walls of gram-positive bacteria and fungi and therefore cannot kill these organisms directly. The membrane attack complex can lyse some virus-infected host cells and some enveloped viruses themselves.143 Immune regulation.  Complement components and fragments can modulate immune responses, both directly by binding to CR1, CR2, and CR3 on the surfaces of T cells, B cells, and other cells involved in antigen recognition and indirectly by stimulating the synthesis and release of cytokines.195 For example, the C3b cleavage product, C3dg, when covalently bound to antigen, brings the antigen close to B cells by binding to B-cell CR2 (CD21).70,84,113 C3 influences antigenic localization within germinal centers, and it is involved in anamnestic responses and isotype switching. Additionally, C1-, C2-, C4-, and C3-deficient animals have decreased antibody responses that can be restored by providing the missing protein,70,84,113 and C2 deficiency in humans also has been associated with antibody deficiencies.15,113 Phagocytes PMNs, the most abundant circulating phagocytes in the human host, will serve as a model for discussing phagocyte functions. These cells constitute a major line of defense against invading bacteria and fungi. The proliferation of myeloid marrow progenitors and their differentiation into mature progeny are regulated by specific growth factors and cytokines.45,345,346,547 The normal half-life of circulating PMNs is approximately 8 to 12 hours.365,570 In the absence of active infection, most PMNs leave the circulation via the gingival crevices and the lower gastrointestinal tract, where the resident flora stimulate ongoing local extravasation of PMNs, a process that helps maintain the integrity of these tissues.29 In response to invasive bacterial infection, circulating PMNs engage in three major functions: (1) migration to the site of infection, (2) recognition and ingestion of invading microorganisms, and (3) killing and digestion of these organisms. Phagocyte recruitment to infected sites.  Activation of endothelial cells that line the microvessels of acutely infected tissue occurs via locally produced cytokines, eicosanoid compounds, and microbial products.110,505 As a result, the endothelial cells rapidly upregulate their surface expression of P-selectin from preformed intracellular storage pools and, subsequently, of E-selectin by new synthesis.344,509 These selectins interact with the fucosylated tetrasaccharide moiety sialyl Lewis X, which is presented on constitutively expressed glycoproteins on PMNs including L-selectin and P-selectin glycoprotein ligand–1 (PSGL-1).328,344,598 These early interactions slow the PMNs in this first adhesive phase of leukocyte recruitment, sometimes described as “slow rolling.”67,110,505 Within several hours, newly synthesized ICAM-1 is expressed at the endothelial surface.110,505,508 The slowly rolling PMNs are activated by transient selectin-mediated interactions and locally produced mediators, especially endothelium-derived chemokines such as IL-8.343 These chemokines are most effective in PMN activation when they are bound by complex proteoglycans at the endothelial cell surface.324,573 The activated PMNs then signal the conformational activation of binding function of their surface β2 integrins LFA-1 and Mac-1,171,563 as well as translocating an additional large quantity of Mac-1 from intracellular storage pools to the cell surface.60,80,82 This newly translocated Mac-1 also may undergo conformational activation as the PMN is exposed to increasing

22

PART I  Host-Parasite Relationships and the Pathogenesis of Infectious Diseases

Blood flow

Rolling

Activation

Firm adhesion

Emigration

Bacterial infection FIG. 2.2  Events during leukocyte (polymorphonuclear leukocytes [PMNs]) recruitment to infected sites. Interactions between microorganisms in infected tissue and host cells and proteins result in elaboration of mediators that diffuse to the local microcirculation and stimulate the endothelial cells. This induces new surface expression of P-selectin and E-selectin, release of interleukin-8 and other chemokines, and new surface expression of intercellular adhesion molecule 1 (ICAM-1). The endothelial selectins bind to constitutively expressed carbohydrate ligands on circulating PMNs and slow the passage of the PMNs through the microvessels. As the PMNs slow further, they become activated by interaction with chemokines bound to complex glycopeptides on the endothelial surface. This activation of PMNs increases their expression and binding activity of the β2 (CD11/CD18) integrins, Mac-1 and lymphocyte function–associated antigen–1 (LFA-1). Interactions between these integrins and ICAM-1 (and ICAM-2 in the case of LFA-1) lead to tight adhesion and spreading on the endothelial surface. These latter adhesive interactions also are used for migration between endothelial cells and through the subjacent extracellular matrix in response to the gradient of chemoattractants, such as C5a, chemokines, and bacterial peptides, released at the infected site. Homophilic interactions between PECAM-1 on the PMNs and endothelial cells (not diagrammed) also appear to contribute to transendothelial migration. (Courtesy Scott Seo, MD.)

concentrations of mediators.171,269 These activated β2 integrins interact with the endothelial cell ICAM-1 in this second, firm adhesion phase, which is necessary for transendothelial migration of the PMNs.60,110,170,343,496,505,508 Other chemoattractants, such as C5a, N-formyl bacterial oligopeptides, and leukotrienes (e.g., LTB4) that diffuse from the site of infection further activate PMNs and provide a chemotactic gradient for PMN migration into tissue.177,232,393 The receptors for these chemoattractants, like the chemokine receptors, are G-protein coupled and have a seven-transmembrane-domain structure.232,393 They constitute important sensory mechanisms of the PMNs for activating adhesion, directional orientation, and the contractile protein-dependent lateral movement of adhesion sites in the PMN membrane necessary for cell locomotion.24,232,393,531 A scheme for PMN recruitment from the microcirculation into infected tissue is presented in Fig. 2.2. Although the specific stimuli and adhesion molecules may vary, this general scheme applies to the local recruitment of virtually all circulating cells of the immune system.71,235,304 Phagocytosis.  After PMNs reach the site of infection, they must recognize and ingest, or phagocytose, the invading bacteria. Opsonization, especially with IgG and fragments of C3, greatly enhances phagocytosis.277,293 Although nonopsonic phagocytosis may occur, only opsoninmediated phagocytosis is considered here.483,546 CR1 and CR3 are the main phagocytic receptors for opsonic C3b and iC3b, respectively.60–62,204 When PMNs are activated by chemoattractants or other stimuli, CR1 and CR3 are rapidly translocated to the cell surface from intracellular storage compartments, thus increasing surface expression up to 10-fold.60,204 Note that CR3 is identical to the adhesion-mediating integrin Mac-1.35,60 CR1 and CR3 act synergistically with receptors for the Fc portion of antibodies, especially IgG.34,293 Phagocytic cells may express up to three different types of IgG Fc receptors, or FcγRs, all of which can mediate phagocytosis.200,556 FcγRI (CD64) is a high-affinity receptor that is expressed mainly on mononuclear phagocytes.556 The two FcγRs

ordinarily expressed on circulating PMN are FcγRII (CD32) and FcγRIII (CD16).547,556 FcγRII is conventionally anchored in the cell membrane, exhibits polymorphisms that determine preferences for binding of certain IgG subclasses, and can directly activate PMN oxidative burst activity.547,556,557 FcγRIII is expressed on PMNs as a glycolipid-anchored protein, although it is anchored conventionally on NK cells and macrophages.482,549,556 Many phagocytes also express IgA FcRs, which promote phagocytosis and killing of IgA-opsonized bacteria.278,385 The engagement of phagocyte receptors with microbial opsonins on microbes locally activates cytoskeletal contractile elements, leading to engulfment of the microbe within a sealed phagosome.530 This is followed by fusion of the phagosome with lysosomal compartments containing the phagocyte’s array of microbicidal products. Phagocyte microbicidal mechanisms.  Intracellular killing by phagocytes, usually within the fused phagolysosome, involves microbicidal weapons that can be categorized as either oxygen-dependent or oxygenindependent.466 The oxygen-dependent microbicidal mechanisms of phagocytes depend on a complex enzyme, reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, which catalyzes the conversion of molecular oxygen (O2) to superoxide anion (O2−), the reaction that is deficient in chronic granulomatous disease (see later discussion).39,40,129 As the name suggests, the reaction catalyzed by this enzyme requires a supply of NADPH, which is supplied in turn by reactions of enzymes of the hexose monophosphate shunt. The NADPH oxidase is assembled at the plasma or phagolysosomal membrane of activated cells from six known components that include a cytochrome (α- and β-subunits, designated gp91phox and p22phox, respectively) and at least three cytosolic proteins, p40phox, p47phox, and p67phox (“phox” refers to phagocyte oxidase), along with a Rac-1 GTPase, which assemble with the membrane-associated components to form the active enzyme complex (Fig. 2.3).40,80,129 Each of the main oxidant products derived from this enzyme’s activity exhibits microbicidal activity, including the earliest

CHAPTER 2  Normal and Impaired Immunologic Responses to Infection

HMP shunt enzymes (G6PD, others)

PMN (cytoplasm)

P67

23

p40

P47

NADPH NADP

Rac

Extracellular space or within phagosome

P91 p22

O2

CGD

O2 H2O2

The NADPH oxidase complex and phagocyte oxidative microbicidal reactions

MPO  CI

OCI

RNH2CI

RNH2

FIG. 2.3  The phagocyte reduced nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase enzyme complex and the major reactions in the evolution of oxygen-dependent PMN microbicidal activity. The diagram depicts the six main components of the NADPH oxidase complex: the 91-kDa and 22-kDa subunits of the membrane-bound cytochrome; the 40-kDa, 47-kDa, and 67-kDa cytosolic components; and a Rac-1 signaling molecule. After assembly at the plasma or phagolysosome membrane, the enzyme catalyzes the conversion of molecular oxygen (O2) to superoxide anion (O2−), the initial step in the sequence of production of oxidant antimicrobial products. This reaction requires a supply of NADPH, most of which is derived from activity of enzymes of the hexose monophosphate shunt (not shown). Shown in sequence are subsequent reactions for the spontaneous formation of hydrogen peroxide (H2O2), the myeloperoxidase-catalyzed formation of hypochlorite (OCl−), and formation of chloramines (RNH2Cl).

products, O2− and H2O2, and the more potent downstream products hypochlorite (OCl−) and chloramines (NH3Cl, RNH2Cl), with chloramines being the most stable.248,466 The oxygen-independent microbicidal activity of PMNs resides mainly in a group of proteins and peptides stored within their primary (azurophilic) granules and, to a lesser extent, in their secondary (specific) granules.80,81,83,225 Lysozyme is contained in both the primary and the secondary (specific) granules of PMN.522 It cleaves important linkages in the peptidoglycan of bacterial cell walls and is most effective when it can act in concert with the complement MAC.293 The primary granules contain several cationic proteins with important microbicidal activity. A 59-kDa protein, bactericidal/permeability-increasing protein, is active against only gram-negative bacteria.578 Smaller arginine- and cysteine-rich peptides, the α-defensins, similar to the β-defensins of epithelial cells, are active against a range of bacteria, fungi, chlamydiae, and enveloped viruses; other related molecules include cathelicidin and a group of peptides called p15s.221,224,225,337,341 Some of these PMN proteins and peptides interact with each other synergistically to enhance overall antimicrobial activity.340 Important Interactions Among Innate Immune Mechanisms A schematic overview of many of the main features of innate immunity discussed earlier, along with some of their important interactions, is diagrammed in Fig. 2.4. Several levels of interactions are depicted, from initial host-pathogen contact, through a variety of activating signals, to the attack by host effector mechanisms on their respective pathogenic targets.545

Adaptive Immune Responses Adaptive immunity involves the host’s antigen-specific responses to infectious challenges that can provide specific protection against subsequent challenges by the same infectious agent. The major steps in the development of adaptive immunity include the processing and presentation of specific antigens to T lymphocytes (T cells) by antigen-presenting cells (APCs); the activation and differentiation of T cells for specific cytotoxic T-cell activity, T-cell cytokine production, and T-cell help in

activating antigen-specific B cells; and the differentiation of activated B cells into plasma cells for the production of specific antibodies. Whereas the innate immune responses described earlier often occur in a matter of minutes to hours and may activate early cellular responses that are essential for the development of adaptive immunity, the full development of most adaptive immune responses requires days to weeks. Once developed, however, the latter often can provide durable protection. A summary of the major events in the adaptive immune response to infection is diagrammed in Fig. 2.5. Antigen Presentation and Specific Cell-Mediated Immunity Specific cell-mediated immunity provides T-cell help for antibody production by B cells, cytokine production for the stimulation and regulation of a range of immune responses, and cytotoxic T-cell activity against host cells infected with viruses.175,391,436 The development of cell-mediated immunity requires complex interactions between T cells and APCs via several types of surface molecules on the respective cell surfaces. These include binding of an antigen-specific T-cell receptor on the T lymphocyte to a peptide antigen presented on the class I or II MHC by the APCs, with concurrent binding of the class I or class II MHC by CD8 or CD4, respectively,144,543 as represented in Fig. 2.6. Other respective pairs of cell-surface molecules that enhance interactions between T cells and APCs include CD40 ligand/CD40, LFA-1/ICAM-1, and CD28/B7. An additional molecule, cytotoxic T lymphocyte antigen–4 (CTLA-4), expressed on activated T cells, also can bind to B7 molecules on APCs to generate a suppressive signal that may terminate T-cell activation.543 The sustained physical interface between T cells and APCs at which these molecular interactions take place has been characterized as the “immunologic synapse.”32,92,242 Class I major histocompatibility complex.  Virtually all human cells except neurons express class I MHC.152,153 The class I MHC molecule presents antigenic peptides to CD8+ cytotoxic T lymphocytes.67,407 It consists of a heavy chain that contains both the peptide-binding domain and a transmembrane domain and a smaller extracellular subunit,

24

PART I  Host-Parasite Relationships and the Pathogenesis of Infectious Diseases Microbes and products

Initial contact

Viral RNA, DNA, protein

Virus

Virusinfected cell

IL-12 Activation signals

TNF-α IL-1

TLR

TLR

MΦ

Epith. cell

Target

Complement (AP, MBLP)

Endoth. cell C3b Chemokines

Effector

Bacterial and fungal components

NK cell

Virus-infected cell

C5a

Circulating phagocyte

Antimicrobial peptides

MAC (C5b-C9)

Bacteria, fungi

Bacteria, fungi, chlamydiae, enveloped viruses

Gram-negative bacteria, enveloped viruses

FIG. 2.4  Innate immunity: first contact, intermediate signals, and effector mechanisms. Diagrammed are important host responses to infection that are independent of specific cell-mediated immunity or antibodies. Initial contact between the host and microbes or their products may result in viral infection of cells, activation of Toll-like receptors (TLR) on macrophages (MΦ) and epithelial cells, and activation of the alternative pathway (AP) or mannose-binding lectin pathway (MBLP) of complement. The resulting activation signals, including cytokines (e.g., interleukin [IL]-12, tumor necrosis factor α [TNF-α], IL-1), chemokines, and products of the complement cascade mobilize both cellular (natural killer [NK] cells, phagocytes) and humoral (antimicrobial peptides, membrane attack complex [MAC]) effectors that attack their respective microbial targets. (From Tosi MF. Innate immune responses to infection. J Allergy Clin Immunol 2005;116:241–9.)

β2-microglobulin.73,462 The three major types of class I MHC heavy chains in humans, human leukocyte antigen (HLA)-A, HLA-B, and HLA-C, have at least 22, 31, and 12 different alleles, respectively.597 This polymorphism permits a great diversity in the peptide-binding repertoire in individuals and within populations. A restricted degree of MHC genetic polymorphism has been invoked as a possible explanation for the predisposition of certain populations to develop infections.74 Class I MHC molecules within the cell ordinarily bind peptides derived from recently synthesized proteins, either of self-origin or of infecting viruses.198,199 A portion of newly synthesized proteins is processed into peptides at a cytoplasmic site, the proteasome.236 These peptides are actively transported into the endoplasmic reticulum, where they are bound in the peptide-binding cleft of MHC class I. Suitable peptides usually are restricted to 8 to 10 amino acids in length, and they must contain certain amino acids at specific “anchor” positions on the peptide to bind.280 Allelic variants of MHC class I may require different amino acids at these anchor positions.218 The other amino acids of the peptide constitute the specific antigenic determinant. After trafficking of the MHC-peptide complex to the cell surface, the peptide antigen is recognized and bound by a specific T-cell receptor on CD8+ cytotoxic T cells, which concurrently bind the heavy chain of MHC class I via CD8.67,218,280,551 Class II major histocompatibility complex.  Mononuclear phagocytes, B lymphocytes, and dendritic cells, including specialized tissue-specific dendritic cells, such as the Langerhans cells of the skin, serve the immune system as “professional” APCs.565 Dendritic cells, the most efficient APCs

for primary activation of naïve T cells, are macrophage-like cells of a distinct lineage that take up and process antigens in tissues and migrate to local lymph nodes or to the spleen, where they are likely to encounter T cells specific for the presented antigens.182,183,253,463 A defining feature of these professional APCs is their expression of class II MHC molecules in addition to class I MHC.153 Class II MHC molecules consist of an α and a β chain, which together form a peptide-binding cleft.94,475 Class II MHC molecules present peptides, 13 to 17 amino acids in length, derived from proteins that are internalized by endocytosis or during phagocytosis of microorganisms.251,281,475 The three major types of class II MHC α and β chains are HLA-DR, HLA-DP, and HLA-DQ, each exhibiting a high degree of polymorphism.460 MHC class II, bound to a separate smaller molecule known as the “invariant chain,” traffics via the Golgi to endosomal/lysosomal compartments, where it must dissociate from the invariant chain to bind antigenic peptides derived from internalized proteins.461,541,542 The class II MHC–peptide complexes then move to the cell surface, where the peptide antigens are bound by specific T-cell receptors of CD4+ T cells, which concurrently bind class II MHC via CD4.183,351 Fig. 2.7 depicts the essential features of the conventional antigen presentation pathways that involve class I and class II MHC molecules, as described earlier. Alternative mechanisms have been documented by which class I MHC can present peptides derived from internalized exogenous proteins, and class II MHC may present peptides derived from newly synthesized proteins. The importance of these unconventional pathways of antigen presentation in the immune response is not fully

CHAPTER 2  Normal and Impaired Immunologic Responses to Infection Encounter with antigen in tissues Viral infection DC

Bacterial infection Foreign protein

Into spleen, lymph node

Naïve T cell

T

Activated B cells

B

CD4+ helper function

Mature DC

Plasma cells To tissues CD4+ cytokine production CD8+ cytotoxicity

Immunoglobulins

Neutralize viruses Activate complement Block attachment Opsonize microbes

FIG. 2.5  A simplified scheme of major events in the development of adaptive immune responses. When antigen-presenting cells (APCs) such as dendritic cells (DCs) encounter and internalize microbes or their protein antigens in peripheral tissues, they process the microbial proteins and present the resulting antigenic peptides on either class I or class II MHC molecules. The activated APCs migrate to lymphoid tissue, where they undergo maturation. When mature dendritic cells encounter CD4+ or CD8+ T cells expressing T-cell receptors specific for the peptides presented in the appropriate major histocompatibility complex (MHC) context (CD4/MHC-II; CD8/MHC-I), binding between the cells occurs via TCR-peptide, MHC-CD4/8, and other pairs of accessory molecules, all necessary for stimulating the T cells to become effector cells. Cytotoxic effector CD8+ T cells migrate into the periphery and kill virus-infected cells that present viral peptides via MHC class I. Effector CD4+ cells either migrate to the periphery where they produce cytokines and otherwise regulate immune responses or remain in the lymphoid tissue to provide help to antigen-specific B cells, promoting their proliferation, differentiation, and eventual production by their progeny plasma cells of specific antibodies that can neutralize viruses, prevent microbial attachment, opsonize microorganisms, or activate complement.

CD8+ T-cell TCR

CD3 complex (ζζεδγε)

α

CD4+ T-cell CD4

CD8

β Peptide antigen

Peptide antigen

α

β2 microglobulin APC

Class I MHC heavy chain

β

Class II MHC APC

FIG. 2.6  Principal cell surface interactions between CD8 and CD4 T lymphocytes and peptide antigens complexed with major histocompatibility complex (MHC) class I and class II molecules, respectively. CD3 (composed of six subunits, ζ, ζ, ε, δ, γ, ε) is associated closely with the T-cell receptor (TCR), which recognizes a specific peptide presented on MHC molecules. Class I and class II MHC determinants are recognized by CD8 and CD4, respectively. Additional or accessory interactions are discussed in the text. APC, Antigen-presenting cell. (Modified from Lewis DB, Wilson CB. Developmental immunology and role of host defenses in neonatal susceptibility to infection. In: Remington JS, Klein JO, editors. Infectious Diseases of the Fetus and Newborn Infant. 6th ed. Philadelphia: WB Saunders; 2006:92.)

25

26

PART I  Host-Parasite Relationships and the Pathogenesis of Infectious Diseases P Class II MHC/peptide P Class I MHC/peptide

Internalized protein Lysosomal fusion P

Golgi

P Inv. chain unbound

P

Transport PP P P P Peptides

Inv. chain bound

P P

P

Class I MHC

ER

Class II MHC

“Proteasome”

New protein

Ribosome

Antigen-presenting cell FIG. 2.7  Conventional pathways for peptide antigen presentation by class I and class II major histocompatibility complex (MHC) molecules. In the antigen-presenting cell, a proportion of newly synthesized proteins, whether of viral or host origin, undergo proteolysis into peptides by enzymes that constitute the “proteasome.” The peptides are transported actively into the endoplasmic reticulum (ER), where those with the appropriate length and sequence bind to MHC class I molecules. MHC class II cannot bind peptides in the ER because of interference by the associated “invariant (inv.) chain.” The class I MHC/peptide complex is transported via the Golgi to the cell surface, where it may be recognized by CD8+ lymphocytes. Class II MHC molecules pass via the Golgi to a lysosomal compartment, where conditions favor the release of the invariant chain. This permits class II MHC to bind peptides derived from internalized proteins that have entered the lysosomal compartment via fusion of endosomes or phagosomes with the lysosome. The lysosome translocates to the cell surface, where the class II MHC/peptide complex may be recognized by CD4+ lymphocytes.

understood, but evidence indicates that such “cross-presentation” may be important for generation of CD8+ cytotoxic T-cell response against some viruses or fungi taken up via endocytosis by antigen-presenting cells.36,348 CD1 family of antigen-presenting molecules.  The CD1 family includes proteins with significant homology and structural similarity to that of the MHC class I heavy chain but that present lipid and glycolipid antigens. All mammalian species express one or more members of the CD1 family, principally on professional antigen-presenting cells. Four human CD1 proteins, CD1a, CD1b, CD1c, and CD1d, have been identified, each tightly associated with a β2-microglobulin subunit. Mycolic acid, lipoarabinomannans, and other related components of mycobacteria are the best-documented foreign antigens presented by CD1 molecules, and both internalized antigens and antigens synthesized within the antigen-presenting cells by ingested mycobacteria may be presented via distinct trafficking patterns of the CD1-antigen complexes. Antigens presented on antigen-presenting cells by CD1 molecules are recognized by a specialized subset of CD1-restricted T cells that usually lack CD4 and CD8; these are known as NK T cells. These cells share characteristics of both NK cells and T cells and exhibit a limited range of T-cell receptor specificity. Greater detail regarding the structure, function, phylogeny, trafficking, expression, and T-cell interactions for members of the CD1 family may be found in a recent review.489 Plasmacytoid dendritic cells.  A specialized class of dendritic cells known as “plasmacytoid” dendritic cells plays a multifactorial role in both innate and adaptive immune responses. These cells are early responders to viral infections by virtue of their expression of TLR7/9 and their

ability to produce large amounts of type 1 interferons that disrupt viral replication.38,536 Additionally they can play an auxiliary role in the adaptive immune response by providing help to conventional dendritic cells during antigen presentation, apparently by helping to sustain IL-12 production by the latter in response to IFN-γ released by interacting T cells.38,536 T Lymphocytes The development of T lymphocytes, or T cells, begins when prothymocytes leave the marrow and enter the subcapsular region of the thymus.181 By mechanisms that are poorly understood, the thymic environment induces the rearrangement of T-cell receptor V (variable), D (diversity), and J (joining) gene segments with the eventual expression of mature α-β T-cell receptors complexed with CD3. The T cells, now coexpressing CD4 and CD8, migrate to the thymic cortex, where they undergo screening for T-cell receptor specificity both to optimize the repertoire for distinguishing self from nonself and to eliminate T-cell receptor rearrangements that result in undesirably high self-reactivity. Thymocytes that do not pass this dual screening procedure receive signals that induce programmed cell death (apoptosis).373,394,567 Only about 5% of the original thymocytes pass this screening, after which they express either CD4 or CD8 but not both.373,394,458,567 Mature thymocytes are released into the periphery, where the CD4+ cells serve as the main source of IL-2 and provide help for B-cell antibody production, and the CD8+ cells engage in specific cytotoxic activity.231,391 This discussion of T cells and T-cell receptors specifically relates to T cells that express T-cell receptors composed of α and β chains, or α-β T cells. T

CHAPTER 2  Normal and Impaired Immunologic Responses to Infection cells of a distinct type, γ-δ T cells, are far less numerous in most tissues (intestinal epithelium is a notable exception), exhibit much less T-cell receptor diversity than do α-β T cells, may not require an intact thymus for development, and play a role in host responses to certain intracellular bacterial pathogens, including Listeria and mycobacteria.106,254 Antigen specificity of α-β T cells resides in their T-cell receptors, which are integral membrane proteins that exhibit structural homology with immunoglobulins. T-cell receptor diversity results from a rearrangement of V, (D), and J segments.226 There are up to 100 different V segments, one (D) segment, and as many as 100 different J segments in the complete germline configuration of the T-cell receptor genes. Rearrangement of these gene segments into a mature VDJ sequence occurs by the action of a recombinase enzyme complex formed by two proteins, RAG-1 and RAG-2.417,488 T-cell receptor diversity is generated by several factors, including the range of possible combinations of V, (D), and J segments; the imprecise action of the recombinase complex; the variability in the number of nucleotides deleted during rearrangement; and the action of another enzyme, terminal deoxytransferase, which appears to add nucleotides at random to extend segments during rearrangement.206,504 The actions of Artemis and DNA ligase IV, two enzymes critical for the processing and joining of DNA ends, introduce additional sources of variability.99,191,355,585 It has been estimated that as many as 1015 different T-cell receptor specificities theoretically could result from the preceding mechanisms.159 Stimulation of naïve CD4+ or CD8+ T cells occurs as they circulate through peripheral lymphoid tissue and encounter dendritic cells and other professional APCs. Localized T-cell migration is highly regulated by specific chemokines and adhesive interactions with local endothelium and involves mechanisms similar to those discussed earlier for circulating phagocytes.185,320 When T cells engage APCs presenting specific peptide antigens on the appropriate MHC molecules, they are activated via their T-cell receptor and several costimulatory molecules, especially CD28, to produce IL-2 and proliferate and differentiate into effector T cells.128,284 Effector CD4+ T cells may be of the TH1 or TH2 type, and this type is influenced by several factors, including the specific cytokines elicited by a particular microbial pathogen.395 Naïve T cells activated in the presence of IL-12 and IFN-γ are likely to develop into TH1 cells, whereas IL-4 and IL-6 tend to drive development in the direction of TH2 cells.390,395,397 Preferential development of TH1 effector cells leads mainly to macrophage activation and cell-mediated immunity, whereas TH2 effector cells help drive certain aspects of humoral immunity, including immunoglobulin class switching to IgE in allergic responses.395 Until recently, before the identification of the TFH subset (see later discussion), TH2 cells were thought to be the principal cell in providing T-cell help for B-cell antibody production. A third major subset of effector CD4 T cells are TH17 cells, whose main function appears to involve protection against extracellular bacteria and fungi by stimulating phagocytic cell responses to these pathogens.272,349,382 Their development is favored by the presence of IL-6 and TGF-β and by the absence of IL-4 and IL-12. They are distinguished by their ability to produce IL-17 cytokines, which in turn stimulate local tissues to produce chemokines, such as IL-8, that recruit neutrophils and other phagocytic cells to tissue sites.272,349,382 Development of TH17 cells involves production of IL-21, which acts in an autocrine fashion to activate signal transducer and activator of transcription 3 (STAT3), a transcription factor that drives TH17 cell development.272,382 In contrast to TH1, TH2, and TH17 CD4 T cells, which exert their main effector functions in the periphery, a fourth T-cell subset, T follicular helper cells, or TFH cells, appears to account for most of the CD4 T cells that provide help to B cells in the lymphoid follicles for antibody production.306,411 TFH cells are characterized by their location in lymphoid follicles, expression of the CXCR5 chemokine receptor, and their ability to secrete cytokines typical of both TH1 and TH2 cells.306,411 The developmental origins of these cells in humans and their relationships and interactions with the other T-cell subsets are subjects of current research. Activation of naïve CD8+ T cells by antigen binding, costimulation by accessory binding molecules on antigen-presenting cells, and exposure to cytokines, including IL-2, all lead to clonal proliferation of specific CD8+ cells and their differentiation into cytotoxic effector cells. Effector

27

CD4+ T cells bound in common to an APC may play a role in activating naïve CD8+ T cells, either by releasing IL-2 or by activating the antigenpresenting cell to provide greater costimulation to the CD8+ T cell to make its own IL-2.31 Antigenically experienced effector CD8+ T cells respond to specific antigenic peptides and costimulatory molecules on infected host cells by activating cytotoxic mechanisms similar to those described earlier for NK cells, including the release of both perforin and granzymes and the generation of receptor-mediated signals for target cell apoptosis.345,476,552 Regulatory T cells.  The existence of T suppressor cells was long a subject of debate among immunologists. Within the past decade solid evidence has been developed to support the existence of suppressor T cells, now referred to as regulatory T cells, or T-regs. These cells were discovered when thymectomized mice were noted to develop autoimmune disease. Transfer of T cells that expressed CD25, the α chain of the IL-2 receptor, from normal adult mice to thymectomized mice prevented autoimmune disease. This population of CD4+CD25+ T-regs can suppress the activity of other immune cells and has been shown to prevent graft-versus-host disease and allograft rejection.449 The mechanism of suppression by T-regs is uncertain but may involve direct contact with other cells or secretion of inhibitory cytokines, including IL-10.349,484 These inhibitory cytokines can interfere with T-cell proliferation and inhibit the ability of antigen-presenting dendritic cells to promote T-cell activation.349,484 The role of T-regs in immunity to infection is only beginning to be studied, but some current evidence suggests that the action of T-regs with specificity for microbial antigens may suppress protective immune responses to some infections but may also suppress excessive or injurious host responses.449 T-cell memory.  Some proportion of activated CD4+ and CD8+ T cells become endowed with the capacity for long-term antigenic memory and can rapidly become effectors on re-exposure to specific antigen. Whether these cells develop directly from naïve T cells or previously have been effector cells, or both, is uncertain, and the mechanisms by which they become memory T cells are poorly understood. Among the features of memory T cells are high-level expression of CD45RO, the ability to suppress activation of naïve T cells of the same specificity, and a homeostatic level of ongoing proliferation in bone marrow and peripheral lymphoid organs.296,357,481,599 T-cell activation by superantigens.  The term superantigen describes a class of proteins, mainly microbial exotoxins, including most staphylococcal enterotoxins, staphylococcal toxic shock syndrome toxin–1 (TSST-1), and related streptococcal TSST-1–like toxins. These bacterial toxins are potent pyrogens, can induce a potentially lethal toxic shock syndrome, and contain binding domains for both T-cell receptor V regions and MHC class II molecules. Superantigens bypass normal antigen-processing and presentation pathways by binding directly to class II MHC molecules on antigen-presenting cells and to specific variable regions on the β-chain of the T-cell antigen receptor. Through these interactions, superantigens induce a polyclonal activation of T cells at orders of magnitude above levels induced by antigen-specific activation, resulting in massive release of cytokines from T cells and antigen-presenting cells, including TNF-α and TNF-β, IL-1, IL-2, and IFN-γ, that are believed to be responsible for the most severe features of toxic shock syndromes.14,450 B Lymphocytes and Immunoglobulins B lymphocytes.  B lymphocytes (B cells) are the source of humoral immunity in the form of specific immunoglobulin. The earliest recognizable marrow precursors of B cells are pro-B cells whose surfaces bear the pan-B marker CD19. Further differentiation produces pre-B cells and then mature B cells, the latter expressing cell-surface immunoglobulin by which they recognize and bind antigen. B lymphocytes constitute approximately 20% of the lymphocytes in the circulation and peripheral lymphoid tissues, including the lymph nodes, spleen, bone marrow, tonsils, and intestines, and they are identified by the presence of surface immunoglobulin and the pan-B differentiation markers CD19 and CD20.109,371 B-cell activation is initiated by recognition and binding of specific antigens to B-cell surface immunoglobulins. Early activation leads to increased expression of receptors that either bind cytokines (e.g., IL-2, IL-4, and IL-6) or interact with T cells,327 leading in turn to clonal

28

PART I  Host-Parasite Relationships and the Pathogenesis of Infectious Diseases

proliferation and differentiation into memory B cells and plasma cells in the germinal centers of peripheral lymphoid tissue.302 Some data suggest that B-cell differentiation into memory B cells is favored by exposure to the CD40 ligand on dendritic cells in lymphoid organs, whereas differentiation into plasma cells is favored by exposure to CD23, IL-1α, IL-6, and IL-10.302,540 The plasma cells, later found in bone marrow and liver as well as peripheral lymphoid tissue, are responsible for most free immunoglobulin production.540 The B-cell response to protein antigens depends on T-cell help. B cells can process and present antigen to CD4+ TFH cells they encounter in the lymph nodes and spleen.301,302,540 In the typical sequence of events, B-cell surface immunoglobulin binds to a protein antigen, which is internalized, processed, and presented to the T cell via class II MHC molecules. B cell–mediated activation of T cells during antigen presentation is much more effective for memory T cells, whereas naïve T cells are more likely to be turned off or rendered tolerant.197,220 T-cell help is provided for B-cell proliferation and production of antibody against the specific protein antigen. This is mediated by signaling via CD40-ligand interactions with CD40 on the B cell and by the release of cytokines, which also can induce isotype switching.163,405,526 Most B-lymphocyte responses to polysaccharide antigens proceed largely without formal T-cell help, although antibody responses to some such antigens may be enhanced in the presence of T cells.384 Immunoglobulin.  Immunoglobulin molecules may be bound at the surface of B cells or free in the circulation, mucosal secretions, or tissues. Free immunoglobulins function in host defense against infection by binding to microbial surfaces to prevent microbial attachment, activating complement via the classical pathway, neutralizing viruses and toxins, and participating in the formation of immune complexes.128 Ig molecules are composed of two identical heavy and two identical light chains, as diagrammed in Fig. 2.8.186,430 The carboxyl terminus of the immunoglobulin molecule is the heavy chain constant, or Fc, region. The amino acid sequence of this region determines the immunoglobulin isotype. The heavy chain is encoded by V, (D), J, and constant (C) regions on chromosome 14.63,571 Each immunoglobulin molecule has a pair of either κ or λ light chains, defined by distinct constant regions.

Antigen-binding sites

VL

VH

VH

CH1

CH1

S

S

CL

VL

CL S

S S S S

CH2

CH2

CH3

CH3

S

FIG. 2.8  Structure of an immunoglobulin molecule. The schematic structure of immunoglobulin G (IgG) is shown, depicting the variable (V) and constant (C) regions of both the heavy (H) and light (L) chains, the disulfide bonds that link the two heavy chains at the hinge region and the CL region with CH1, and the antigen-binding sites formed by the complementarity-determining regions of VH and VL.

The variable region of the immunoglobulin molecule contains the antigen-binding site. Like the T-cell receptor, the Fab region consists of two identical heavy and light chain pairs; similarly, broadly diverse antigen specificity results from the variable nature of recombinasemediated DNA rearrangements of the three hypervariable, or complementarity-determining, regions (CDR1, CDR2, and CDR3) and the four framework regions during B-cell development.201,334,359 The imprecision inherent in this rearrangement, involving mechanisms similar to those described for the T-cell receptor, leads to the generation of more than 1012 potential antigenic specificities. Somatic hypermutation of variable regions after gene rearrangement adds to the repertoire, and further diversity results from differences in approximation of the three CDRs in relation to each other, affecting the three-dimensional structure of the antigen recognition site.408,433 Thus unlike most T-cell receptors, which recognize specific peptide sequences, the antigen-binding domain of an immunoglobulin molecule recognizes the three-dimensional structure of its respective antigen.43,156 All immunoglobulin is derived from B cells expressing surface IgM. B cells may change immunoglobulin isotype when they differentiate into plasma cells, which produce only one class or subclass of immunoglobulin each. Isotypes other than IgM are the result of isotype switching by replacing a part of the constant region of the immunoglobulin heavy chain with another isotype-specific segment.447,526 As already noted, isotype switching primarily depends on specific B-cell interactions with cytokines and T cells. The variable region remains unchanged during isotype switching; thus there is no change in antigen specificity. However, important features of immunoglobulins, including half-life, localization in tissues, ability to activate complement, and interactions with cellular IgG receptors, are directly determined by isotype.91,287,556 In addition to isotype switching, immunoglobulins undergo the process of “affinity maturation.” As B cells proliferate in lymphoid tissue in response to persistent or repeated antigen exposure and T-cell help, they undergo V-region somatic hypermutation. When this mutation results in a reduced or absent affinity for antigen, B cells are less able to become activated and elicit T-cell help. Such B cells die by apoptosis, removing lower affinity immunoglobulin from the repertoire. Alternatively, B cells that undergo a mutation resulting in increased affinity for antigen are better able to bind antigen, present antigenic peptides to T cells, receive T-cell help, and survive to give rise to plasma cells, which in turn will produce immunoglobulin with higher affinity. This is a process that occurs as a result of booster doses of vaccines or during persistent infections, as with cytomegalovirus, for example.26,444 Immunoglobulin isotypes.  IgG accounts for about 80% of circulating immunoglobulin and includes the subclasses IgG1, IgG2, IgG3, and IgG4.64 The half-life of IgG ordinarily is about 21 days (7 days for IgG3).287 Initial exposure to most microbial protein antigens first induces IgM and then an IgG response consisting of IgG1 and IgG3. IgG2 and IgG4 usually are produced during the secondary immune response. IgG1 usually is made in response to protein antigens.287 In adults, the main antibody response to polysaccharides is IgG2, whereas in infants IgG1 predominates.6,17 The functions of IgG in host defense include blocking microbial attachment, opsonization, complement activation, toxin and virus neutralization, and promoting antibodydependent cell cytotoxicity. IgG1, IgG2, and IgG3, but not IgG4, can trigger complement activation via the classical pathway by binding to C1q.91 Free IgM usually exists as an immunoglobulin pentamer that has a molecular weight of approximately 950,000 and is stabilized by a single J chain.186,314,374,433 Present mainly in the circulation, its half-life is approximately 8 to 10 days. The IgM response is the earliest of the isotype responses, appearing within the first few days of infection, but it is transient. The formation of an IgM response in the absence of an IgG response to infection is not associated with the formation of memory B cells. The main direct action of IgM in host defense is the activation of complement via the classical pathway.374 IgA exists in monomeric circulating and polymeric secretory forms and has a half-life of about 7 days.287 Both forms are produced mainly by plasma cells that have migrated to mucosal sites. Secretory IgA is made up of two or three IgA molecules joined by a stabilizing J segment

CHAPTER 2  Normal and Impaired Immunologic Responses to Infection that is secreted by plasma cells and a secretory component produced by mucosal epithelial cells.303,314 The secretory component permits delivery of IgA to mucosal surfaces.406 There are two subclasses, IgA1 and IgA2, that differ in the composition of their heavy chains. Most IgA in the circulation is IgA1, whereas most IgA in secretions is IgA2. IgA1 may be cleaved at mucosal sites by bacterial proteases.313 IgA neutralizes viruses at mucosal sites, may block bacterial adhesion, and can act directly as an opsonin to promote phagocytosis and via Fcα receptors.278,303 The IgE molecule has a molecular weight of 200,000 and a half-life of only 2.3 days.287 Most IgE is produced by plasma cells in lymphoid tissue near gastrointestinal and respiratory mucosal surfaces and released into the circulation.286,534 IgE acts via Fcε receptors to trigger activation and degranulation of mast cells and basophils, leading to immediate hypersensitivity reactions.534 Persons with intestinal metazoan parasites often have elevated serum levels of IgE, and IgE may have a role in protecting against parasitic disease by stimulating mediator release from mast cells that can recruit eosinophils and cause intestinal smooth muscle contraction and expulsion of parasites.534 IgD has a molecular weight of approximately 180,000 and a half-life of 3 days.287 It is expressed along with IgM on surfaces of naïve B cells but is present in normal adult serum and secretions in very low concentrations. Some antigenic specificity for IgD has been demonstrated, and although its function in host defense is unclear, it may serve as a secondary antigen receptor on B cells, where it may regulate the development of B-cell antibody responses.76

CLINICAL CONDITIONS ASSOCIATED WITH DEFICIENT HOST RESPONSES TO INFECTION Immature Host Responses of the Newborn Infant It is well recognized that newborn infants are much more susceptible to serious infections from many types of organisms than are older children and adults. This predisposition to infection is even more profound in infants born prematurely. The basis for this special vulnerability of the neonate is complex and encompasses all arms of the immune system.332,342,583 Cell-Mediated Immunity Antigen presentation per se, via the mechanisms discussed earlier, appears to be relatively intact in the newborn infant. Expression of class I and II MHC molecules has been documented in a broad range of fetal tissues by 12 weeks’ gestation,271,419 and levels of expression are sufficient to mediate normal MHC class II–restricted antigen presentation by neonatal monocytes to maternal or paternal CD4+ T cells, as well as to induce vigorous rejection of allogeneic fetal tissue by CD8+ cytotoxic T cells.258,270 By about 20 weeks’ gestation, the fetal repertoire of diversity of T-cell receptors has developed fully.561 At the time of birth, although most basic functions of cell-mediated immunity are present, a high proportion of immature T cells are in the peripheral circulation, which can be identified by their coexpression of CD4 and CD8.342 This phenotype typifies type II thymocytes, which usually are not found in the periphery in older persons. Neonatal T cells appear to be relatively deficient in most of their major functions, including CD8+ T cell–mediated cytotoxicity, delayed hypersensitivity, T-cell help for B-cell differentiation, and diminished cytokine production. Lack of prior antigenic exposure largely explains these defects because memory T cells are much more efficient in all of these functions.256,342 B Cells and Antibody B cells.  Pre-B cells are found in the fetal liver and omentum by 8 weeks’ gestation and in the fetal bone marrow by 13 weeks’ gestation.228,342,516 Pre-B cells with surface IgM have been detected as early as 10 weeks’ gestation. After 30 weeks’ gestation and delivery, pre-B cells are seen only in the bone marrow. Mature B cells are present in the circulation by the eleventh week and have reached adult levels in the bone marrow, blood, and spleen by the twenty-second week of gestation.161,228,516

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Fetal B cells express only IgM, whereas most adult B cells express both IgM and IgD. Neonatal B cells may express three immunoglobulin isotypes (e.g., different combinations of IgG, IgA, IgM, and IgD) on their surfaces.228,250 Although germinal centers are not present in lymphoid tissue at birth, they begin to develop in the first few months of life concomitant with the infant’s exposure to antigens.544 Despite conflicting in vitro data, neonatal T-cell help for B cells probably is comparable to that of adult T cells, as is reflected by the excellent T-dependent antibody response of the newborn to immunization with protein antigens.165 In contrast to B cells of older individuals, B cells of neonates and young infants cannot respond to pure polysaccharide antigens. The recruitment of T-cell help to enhance this immature response to polysaccharides has been achieved with the advent of proteinpolysaccharide conjugate vaccines. Such vaccines elicit help from T cells specific for peptides derived from the protein component as presented by polysaccharide-specific B cells that have internalized the protein-polysaccharide complex, allowing peptide-specific T cells to activate polysaccharide-specific B cells.75 Antibody.  Maternal IgG accounts for the great majority of the newborn’s circulating immunoglobulin because almost none is made by the healthy fetus and IgG is the only isotype of maternal immunoglobulin that crosses the placenta.311,362 Maternal transport of IgG can be detected as early as 8 weeks’ gestation, and the newborn’s IgG level is directly proportional to gestational age, reaching 100 mg/dL by 17 to 20 weeks’ gestation and 50% of the maternal level by 30 weeks’ gestation (Fig. 2.9).47,90,111 Maternal IgG is transported both passively and actively via trophoblast Fc receptors. Trophoblast Fc receptors have higher affinity for IgG1 and IgG3 than for IgG2 and IgG4, and thus more of those subclasses are transported from the mother.336 The concept of passive transfer of protective IgG is the basis for development of vaccines for maternal immunization before or during pregnancy so that passive transfer of vaccine-induced antibody will result in protection during the neonatal period. Examples of organisms for which such strategies have been investigated include group B streptococcus, H. influenzae type b, meningococcus, pneumococcus, rotavirus, and respiratory syncytial virus.46,194,282 By about 2 months of chronologic age, approximately half of the term infant’s quantitative IgG is of maternal and half is of infant origin. The physiologic nadir of IgG in all infants is about 3 to 4 months of age and ranges from less than 100 mg/dL in preterm infants with verylow-birth weight to about 400 mg/dL in term infants (see Fig. 2.9).47,593 Maternal IgG usually has waned completely by about 12 months of age, at which time infant levels are approximately 60% of adult levels. Production of IgG1 and IgG3 matures more rapidly than that of IgG2 and IgG4, reaching adult levels by approximately 8 years of age, versus 10 and 12 years of age, respectively.416 Little IgM, IgA, IgE, or IgD normally is produced by the fetus, and none is transported from the mother.311,362 The presence of total IgM levels greater than 20 mg/dL at birth suggests an intrauterine infection, and documentation at birth of specific serum IgM or IgA against relevant organisms, such as T. gondii and others, would be diagnostic.192,398,418 Serum IgA levels at birth in both preterm and term infants usually are less than 5 mg/dL and consist of both IgA1 and IgA2. Secretory IgA is not detectable until after birth but usually is present within the first few weeks of life. IgM and IgA reach approximately 60% and 20% of adult levels by 1 year of age, respectively (see Fig. 2.9). Secretory IgA reaches adult levels by 6 to 8 years of age.342 It has been documented that the fetus can respond to antigenic stimulation in the form of maternal immunization with tetanus toxoid vaccine and be primed for a secondary antibody response to repeat immunization after birth.233,234 The amount of fetal antibody produced in response to intrauterine antigenic stimulation is proportional to gestational age.162,528 Maternal antibody inhibits the infants’ ability to respond to live-virus vaccines against certain organisms, such as measles, but it does not prevent them from mounting protective immune responses to most childhood vaccine antigens, such as tetanus, diphtheria, polio, hepatitis B, and protein-conjugated polysaccharide vaccines.12 In general, neonates have protective responses to T-dependent antigens even though they

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PART I  Host-Parasite Relationships and the Pathogenesis of Infectious Diseases

1200 1000 Maternal IgG contribution

mg/100 mL

800

60% of adult level

tal To IgG

600 400 300 200

60% of adult IgG level

Newborn IgG contribution

150 125 100 75 50 25 0

2

4

6

8

2

4

6

8

IgM

75% of adult IgM level

IgA

20% of adult IgA level

10

12

Birth Months FIG. 2.9  Immunoglobulin (IgG, IgM, and IgA) levels in the fetus and infant in the first year of life. The IgG of the fetus and newborn infant solely is of maternal origin. The maternal IgG disappears by 9 months of age, by which time endogenous synthesis of IgG by the infant is well established. The IgM and IgA of the neonate are synthesized entirely endogenously because maternal IgM and IgA do not cross the placenta. (From Braun J, Stiehm ER. The B-lymphocyte system. In: Stiehm ER, editor. Immunologic Disorders in Infants and Children. 4th ed. Philadelphia: WB Saunders; 1996:67.)

may produce less antibody to some antigens than do older infants and adults.11,155,165,209,506,512 The newborn infant’s response to T-independent antigens, such as polysaccharides, is poor.237 The antibody response to most such antigens, including the polysaccharide capsules of group B streptococci, pneumococci, and H. influenzae type b, is not mature until 18 to 24 months of age.510 In contrast, in the first few weeks of life, infants mount excellent antibody responses to T-independent polysaccharide antigens that have been rendered T-dependent by covalent conjugation of the polysaccharide to a protein carrier, as noted earlier.75 The response of premature infants to most routine childhood vaccines by 2 months of age, including diphtheria, tetanus, pertussis, and oral and inactivated polio, is comparable to that of 2-month-old term infants.7,65,116,512 However, premature infants may not respond as well to hepatitis B vaccine for reasons that are unclear.137,330 Complement Complement proteins do not cross the placenta, but there is evidence for fetal synthesis of complement beginning as early as 5.5 weeks’ gestation, and most complement proteins are present by 10 weeks’ gestation.135,311 Levels of complement activity and of individual complement components vary significantly among infants, but, in general, classical pathway hemolytic activity of term neonates ranges from 60% to 90% of normal adult values.187,594 Alternative pathway hemolytic activity is decreased to approximately 50% to 70% of normal adult values at term.5,184,409,502 Complement activity usually is lower in premature than term infants.409,502 Hemolytic activity of both the classical and alternative pathways rises rapidly and reaches adult levels by 3 to 6 months of age and by approximately 6 to 18 months of age, respectively. In addition to hemolytic activity, complement-mediated opsonic and bactericidal activity is decreased in newborn sera and generally correlates with C3 and factor B levels.187 Studies of opsonic and bactericidal activity of newborn sera have been reviewed in detail elsewhere.187,289 Levels of individual complement proteins do not always correlate with their functional activity.229,277 Zach and Hostetter594 reported not only that

total C3 levels in neonates were decreased but also that C3 thioester reactivity was decreased and that it correlated with gestational age. Phagocytes The newborn infant exhibits both quantitative and qualitative deficits in phagocytic defenses. Although the number of circulating PMNs usually does not differ greatly from that in older children and adults, under conditions of stress, including systemic infection, the availability of marrow reserves of PMNs is impaired markedly.125 Whereas the ratio of marrow neutrophil reserves to circulating cells in older persons is nearly 15 : 1, in the newborn infant this ratio is more often between 2 : 1 and 3 : 1.125 Thus, neutropenia is more likely during severe systemic infections in the newborn than in older children and adults.125 Distinct from this quantitative deficiency in marrow reserves of PMNs, functional impairments of PMNs also are important in understanding neonatal phagocytic defenses. The most important and best-documented functional impairments of neonatal PMNs are related to defective adhesion and migration.3,4,23–25,27,317,367,375,376 Specific structural, functional, and biochemical abnormalities have been documented, any or all of which may contribute to the overall impairment in adhesion and migration of these cells.267 Impaired adhesion of neonatal PMNs to endothelial cells and other biologic substrates has been linked with deficiencies in the expression or function of the β2 integrins Mac-1 (CD11b/CD18) and LFA-1 (CD11a/ CD18).3,26,95,295,367 Perhaps the best documented of these is the diminished level of surface expression of Mac-1 on activated neonatal PMNs, although expression on resting PMNs is similar to that of adults.95,295 The total cell content of Mac-1 in PMN at the time of birth is related directly to gestational age, and cell lysates of PMNs from very early premature infants (less than 30 weeks’ gestation) have been found to contain less than 20% of the Mac-1 content of an equal number of adult PMNs, increasing to about 60% by term.367 The PMN content of LFA-1, which is normal at term, appears to be reduced in infants born before 35 weeks’ gestation.367 In addition to reduced integrin expression, reduced adhesive function of the β2 integrin molecules themselves at the surface of activated PMN has been documented.26 Several other

CHAPTER 2  Normal and Impaired Immunologic Responses to Infection defects of neonatal relative to adult PMNs that might influence chemotaxis have been documented. These include defective redistribution of surface adhesion sites,24 impaired uropod formation during stimulated shape change,25 reduced cell deformability,293 impaired microtubule assembly,25 deficient F-actin polymerization,252,479 reduced lactoferrin content and release,23 reduced ability to effect membrane depolarization and intracellular calcium ion flux,478 and impaired uptake of glucose during stimulation by chemoattractants.4 Evidence suggests that the number and binding efficiencies of neonatal PMN receptors for chemoattractants are normal.24,478,532 In some studies in which assay conditions are designed to expose a potential defect (e.g., limiting concentrations of opsonins and high bacterial inocula), defects in phagocytosis and killing have been demonstrated.376,377

Primary and Heritable Immunologic Deficiencies The infant or toddler who experiences even six to eight presumed viral upper respiratory tract infections during the course of a winter season, without other complications, ordinarily would not be considered likely to have an immunodeficiency. In contrast, a child who had experienced several episodes of acute otitis media in the previous 4 months, perhaps some accompanied by sinusitis or pneumonia, has displayed reasonable cause to suspect a humoral immunodeficiency.140 For certain organisms, infection in the healthy host is so decidedly uncommon that even a single episode should prompt a high suspicion of impaired host defenses. Pneumocystis jiroveci pneumonia strongly suggests a severe defect of T-cell number or function.140 Similarly, lymphadenitis or osteomyelitis caused by gram-negative enteric bacilli suggests a defect of phagocytic killing, such as chronic granulomatous disease.291,448 The International Union of Immunological Societies, through an expert committee on primary immunodeficiency diseases, periodically publishes an updated classification of all known primary immunodeficiency disorders based on phenotypic features.85 The following discussion of specific immunologic defects, their genetic basis (if known), and their infectious consequences focuses on well-characterized prototypic disorders within most major classes of defects but also will address other related disorders. Antibody Deficiencies Humoral immunity is provided by specific antibody and plays an important role in host defense against most pathogens, as is illustrated by the finding that patients with significant antibody deficiencies develop recurrent and sometimes life-threatening infections.139,147 They characteristically are prone to recurrent otitis media, sinusitis, pneumonia, and, less often, sepsis and meningitis. X-linked agammaglobulinemia.  X-linked agammaglobulinemia (XLA), first described by Bruton, is a primary immunodeficiency disorder of the B-cell lineage and is the most serious disorder of humoral immunity.98,335,468 It is characterized by absent or severely decreased numbers of circulating B lymphocytes and absent or extremely low levels of all classes of circulating immunoglobulins. It is caused by several different mutations in the gene encoding for a B-cell–specific tyrosine kinase, Btk, which maps to the long arm of the X chromosome at Xq22.554,564 This abnormality in kinase activity results in an arrest in the development of B cells, usually at the pre-B stage, and thus few B cells or their progeny (e.g., plasma cells) are in the circulation or lymphoid tissues.239 Most persons with XLA develop chronic or recurrent pyogenic bacterial respiratory or gastrointestinal tract infections, and some may have recurrent skin infections.98,335 Sepsis and serious focal infections resulting from bacteremia do not occur as frequently but are more common and more severe than in normal hosts. The causative agents of most of these infections are Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis, but Staphylococcus aureus and Pseudomonas aeruginosa, as well as other gram-negative organisms, may be implicated. The most troublesome gastrointestinal tract infections in XLA are caused by Salmonella, Campylobacter, and chronic infestation with G. lamblia. These patients have been found to have unusually severe or chronic enterovirus infections that can be manifested by chronic arthritis, meningoencephalitis, dermatomyositis, hepatitis, or a combination thereof, and several patients with XLA have developed vaccine-related paralytic poliomyelitis after receiving the live oral polio vaccine.335

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The only typical abnormality on physical examination in XLA that is not related directly to infections is the absence or a paucity of normal B-cell–containing lymphoid tissues, such as tonsils, adenoids, and peripheral lymph nodes. The diagnosis of XLA can be confirmed by studying lymphocyte markers and demonstrating a lack of circulating cells that stain for surface immunoglobulin or with B-cell–specific monoclonal antibodies against CD19, CD20, or both. The number and function of T lymphocytes are normal in XLA. It may be difficult to establish the diagnosis based on immunoglobulin levels in the newborn period because of the presence of maternally derived IgG. However, if suspected, the diagnosis can be made in the newborn period by documenting a paucity of circulating B cells by flow cytometry. Although individuals with XLA ordinarily are thought of as having a “pure” B-cell disorder, recent evidence reveals that the absence of B cells in XLA is associated with a contracted T-cell receptor repertoire and that mice that lack B cells are unable to prime CD4+ T cells for their effector function in clearing Pneumocystis infection, findings that are consistent with the important role of B cells in presenting antigen to CD4+ T cells.420,451 In contrast to carriers of some other X-linked diseases examined later (see discussion of chronic granulomatous disease), circulating B lymphocytes of XLA carriers express only one population of B cells, those with the normal allele on the X chromosome, presumably because B cells with the mutant allele are at a selective disadvantage and do not develop. Advances in genetic techniques have enabled detection of maternal carriers of XLA.139 Prenatal diagnosis can be made by genetic studies of amniotic fluid cells or quantitation of fetal circulating B cells.139 The prognosis for patients with XLA has improved markedly with earlier diagnosis, high-dose intravenous immunoglobulin (IVIG) therapy, and aggressive use of antibiotics. Before the availability of IVIG, most patients who survived to the third decade of life had chronic lung disease from recurrent pulmonary infections and hearing loss from recurrent otitis media.335 IgG subclass deficiency.  Persons with IgG subclass deficiencies have levels of one or more IgG subclass that are more than two standard deviations below normal for age, normal to slightly decreased total IgG, normal levels of other immunoglobulin isotypes, and, often, a poor antibody response to certain antigens.* Patients with IgG subclass deficiency who also have IgM and IgA deficiency may have another immunodeficiency disorder such as common variable immunodeficiency (CVID). The most common kinds of infections in patients with any clinically significant IgG subclass deficiency include otitis media, sinusitis, and pneumonia. Ordinarily, these patients do not have life-threatening systemic infections. Deficiency of IgG1 is likely to be associated with subnormal levels of total IgG because this subclass accounts for about 60% of total IgG, and it often is associated with other subclass deficiencies.16,17,492,498–500 IgG2 deficiency usually is associated with normal total serum IgG levels and is more likely to be clinically significant if accompanied by IgG4 or IgA deficiency. Patients with IgG2 deficiency typically have poor antibody responses to polysaccharide antigens but normal responses to protein antigens. Like most patients with deficiencies of humoral immunity, their infections primarily are due to encapsulated bacteria and are localized to the respiratory tract.498,500 IgG3 deficiency has been associated with low total levels of serum IgG and recurrent respiratory infections, which also may lead to chronic pulmonary disease.415 IgG4 deficiency is difficult to diagnose because many normal persons have low serum levels of IgG4, and most normal infants have no detectable IgG4.416 IgG4 deficiency appears to be of clinical significance, however, if it is associated with IgG2 and IgA deficiency. The treatment for children with IgG subclass deficiency typically is individualized according to the frequency and severity of symptoms. Noninvasive infections usually can be treated successfully with appropriate antibiotics. Patients with more severe presentations may benefit from *References 260–262, 386, 416, 425, 426, 491, 492, 497–501.

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PART I  Host-Parasite Relationships and the Pathogenesis of Infectious Diseases

regular IVIG therapy, but those who also are completely IgA-deficient should be treated only with IgA-depleted IVIG preparations. IgA deficiency.  IgA deficiency is the most common immunodeficiency, occurring as frequently as 1/400. This disorder appears to occur sporadically, but familial cases have been described.22,147 Most of the functions of serum IgA can be performed by IgG and IgM.147,416 Thus, although deficiencies of secretory IgA may lead to recurrent respiratory or gastrointestinal tract infections, deficiency of serum IgA alone usually is not associated with increased susceptibility to systemic infections.22 IgA deficiency has been associated with many other conditions, including recurrent infections, IgG2 deficiency, autoimmune disorders, and malignancy.21 Recurrent infections are most likely to occur in the subset of IgA-deficient patients who also have IgG2 deficiency.147,425 The infections usually are relatively mild and involve the upper respiratory and gastrointestinal tracts. Chronic gastrointestinal tract disease in these patients can be caused by G. lamblia infestations, nodular lymphoid hyperplasia, lactose intolerance, malabsorption, or inflammatory bowel disease. Other autoimmune diseases associated with IgA deficiency include rheumatoid arthritis, systemic lupus erythematosus, thyroiditis, myasthenia gravis, and vitiligo.147 About 20% of IgA-deficient patients have allergy, and many have elevated levels of IgE.147 Food allergy is common and may be the result of abnormal processing of antigen at mucosal surfaces. Rare patients with serum IgA levels less than 5 mg/dL who receive transfusions may make antibody against donor IgA and have severe reactions when transfused again. IVIG reactions also may occur because IVIG preparations contain varying amounts of IgA. IgA-depleted preparations are available and usually are well tolerated.150 Transient hypogammaglobulinemia of infancy.  The syndrome of transient hypogammaglobulinemia of infancy can be differentiated from the physiologic hypogammaglobulinemia in infants because immunoglobulin levels of normal infants begin to rise by about 6 months of age, whereas those of infants with transient hypogammaglobulinemia of infancy do not begin to increase until between 18 and 36 months of age.416 Infants suspected of having this syndrome should be evaluated for XLA and CVID (see later discussion) and followed closely until their immunoglobulin levels normalize for age. Antibody deficiency with normal or elevated levels of immunoglobulins.  Some persons with normal levels of all circulating immunoglobulin

isotypes are at increased risk for infections similar to those seen in specific deficiencies of immunoglobulin levels described earlier.16,18,416 As in other forms of humoral immunodeficiency, the most common infections in these patients are recurrent bacterial respiratory tract infections, although a few patients have developed pneumococcal sepsis.18 Such persons can be identified by their inability to make antibody in response to stimulation with specific antigens. A good way to test for this disorder is to immunize with protein antigens, such as tetanus and diphtheria toxoids, and with polysaccharide antigens, such as pneumococcal and H. influenzae type b capsular polysaccharide vaccines. Patients who can respond to protein but not to polysaccharide antigens usually will respond to protein-polysaccharide conjugates. Treatment with IVIG may help prevent recurrent infections in these patients, although their normal overall levels of immunoglobulin can pose difficulties in determining the appropriate doses of IVIG and intervals between infusions. Defects of Cell-Mediated Immunity: DiGeorge Syndrome The prototypic pure T-cell defect, DiGeorge syndrome, is characterized clinically by congenital heart disease (usually involving the aortic arch), hypocalcemic tetany, unusual facial features, and recurrent infections.173 The classical, or complete, form of this disorder has absence or hypoplasia of the thymus and parathyroid glands, cardiac or aortic arch deformities, and a stereotypical constellation of abnormal facial features, most notably micrognathia and hypertelorism, all associated with malformation of the 4th and 5th branchial arches during embryogenesis.173,318,350,537 Although the condition usually is considered to be associated with immunodeficiency because of the thymic hypoplasia, only about 25% of patients actually exhibit an immunologic defect.55 The term partial DiGeorge syndrome sometimes has been used to describe patients with the typical constellation of anatomic findings but without

immunodeficiency or similar patients with mild immunologic impairment.273 Some sources designate this disorder as an “anomaly” or “sequence” rather than a syndrome because of confusion about its relationship to 22q11 deletion syndrome (del22q11) or the more recently defined microdeletion, del22p11.2, a deletion also associated with velocardiofacial syndrome.97 Robin and Shprintzen459 hold that the findings in DiGeorge sequence, although often associated with del22q11.2, are etiologically heterogeneous and have been associated with other chromosomal deletions such as del10p and del17p or del10q13. Moreover, some individuals with del22p11.2 exhibit abnormalities quite distinct from those of the DiGeorge sequence.243,244,273,326,437,459 One candidate gene, TBX1, encoding a T-box transcription factor and located in 22q.11.2, has been a recent focus of research into the underlying genetic defect in DiGeorge syndrome. Although mice with mutations in TBX1 exhibit some features consistent with DiGeorge syndrome, data remain insufficient to confirm the precise role of TBX1 in human patients with this disorder.249 Because of the serious nature of the cardiovascular defect, many patients with DiGeorge syndrome in earlier decades have not survived long enough for the immune defect to become a clinical problem.273 However, with improvements in surgical treatment of the heart defects, more of these infants now survive long enough to display manifestations of the immunodeficiency that results in an increased frequency or severity of viral and fungal infections, as well as Pneumocystis pneumonia. In such patients, management often has included prophylaxis against Pneumocystis, avoidance of live virus vaccines, and, because antibody production is poor as a result of lack of T-cell help, periodic IVIG infusions.273 HLA-matched bone marrow transplantation has been successful in some cases.83,238,273 Earlier work with transplantation of fetal or postnatal thymic tissue provided some long-term success in correcting the immunologic defect.238,273 Recently, a highly promising large series of cases of transplantation with postnatal cultured thymic tissue in patients with complete DiGeorge syndrome yielded immune reconstitution with 73% survival at 2 years.361 Combined Defects of Cellular and Humoral Immunity Severe combined immunodeficiency disease.  Severe combined immunodeficiency (SCID) describes a heterogeneous group of heritable immunodeficiencies that involve serious impairments of both cellular and humoral immunity, thus leading to recurrent severe infections by a wide range of viral, bacterial, and fungal organisms. SCID has multiple forms, which have been reviewed in greater detail elsewhere.102,103,123 At this writing, at least 10 genes have been identified with abnormalities known to result in SCID. X-linked SCID, the most common form, is due to a mutation in the common γ chain of the receptor for IL-2 and several other cytokines (γc).103,339 The other known forms of SCID are either known or presumed to be autosomal recessive. These include a deficiency of adenosine deaminase, a purine salvage pathway enzyme; a deficiency in Janus kinase 3 (Jak3), a cytokine receptor signaling molecule; and a defect in the α chain of the IL-7 receptor, IL-7Rα.103,297,555 Mutation of one of at least six different genes whose products play a role in T-cell receptor or immunoglobulin gene recombination or T-cell receptor signaling, including RAG1, RAG2, Artemis, DNA ligase IV, CD3-δ, and CD3-ε, also results in SCID.103,123,191,210,297,356,457 Additionally, SCID is caused by a mutation in CD45, a phosphatase that regulates signaling thresholds in immune cells.297 Flow cytometry analysis of lymphocyte markers reveals very low to absent B- and T-cell numbers in patients with most forms of SCID. Long-term management of patients with SCID involves modalities employed in both B- and T-cell disorders, including prophylaxis against P. jiroveci pneumonia, avoidance of live viral vaccines, and immunoglobulin replacement therapy.103 Bone marrow transplantation from HLA-matched siblings has corrected the defect successfully in some cases and is considered the current treatment of choice.101 Adenosine deaminase deficiency is of historical interest in that it is the first heritable disorder for which gene therapy was attempted, although early success was limited.101 Approaches using retroviral-based gene therapy for X-linked SCID initially appeared to be successful. However, at least three patients developed lymphoproliferative disorders similar to lymphocytic leukemia, with malignant cells demonstrating insertion

CHAPTER 2  Normal and Impaired Immunologic Responses to Infection of the vector into the promoter or first intron of a proto-oncogene, LMO2.79,102,118,211,446 Because the earliest possible treatment with stem cell transplantation often is the key to meaningful survival in patients with SCID, newborn screening programs for SCID based on assays of bloodspots have been introduced in several states and in some countries. These assays are based on quantitation of T-cell receptor excision circles—circular fragments of DNA that are a by-product of T-cell receptor rearrangement during fetal development.46,121,445 Common variable immunodeficiency.  CVID is a heterogeneous group of combined immunodeficiencies that differ from most other primary immunodeficiencies in that they often present in the second or third decade of life, although they may present at any age.146,148 Patients with CVID characteristically have normal or only modestly decreased numbers of circulating B cells; low, but not absent, levels of IgG, IgM, and IgA; poor responsiveness to antigens; and abnormal T-lymphocyte function.149 Although both T- and B-cell abnormalities often can be demonstrated, the clinical presentation usually is most like that in patients with humoral or B-cell defects (i.e., recurrent bacterial otitis media and sinopulmonary infections).146,259,468 Occasionally, these patients also have infections with organisms more common in persons with T-lymphocyte abnormalities, such as Pneumocystis, recurrent herpes simplex virus, and herpes zoster virus infections. Chronic gastrointestinal problems may be due to G. lamblia or other intestinal pathogens. CVID patients are prone to nodular lymphoid hyperplasia, autoimmune diseases, and malignancies. Several gene mutations have been found in patients with CVID. These include the genes encoding for CD19, transmembrane activator and CAML interactor (TACI), receptor for B-cell activating factor of the TNF receptor family (BAFF-R), and inducible costimulatory molecule (ICOS).114,487,596 Patients with CVID usually can benefit from therapy with IVIG, which reduces the incidence of acute infections. However, most patients with CVID, even some of those who undergo long-term treatment with IVIG, develop chronic sinopulmonary disease.148,424 Hyper–immunoglobulin M syndrome.  Immunoglobulin deficiency with increased IgM is characterized by low levels of IgG, IgA, and IgE but normal to increased levels of IgM in the circulation and normal numbers of circulating B cells.12,37,157 The disorder is caused by an intrinsic T-cell abnormality that impairs class switching from IgM to other isotypes. The basis for the various genetic forms of this defect is in one of several possible defects that involve interactions between CD40 on B cells and CD40 ligand (CD40L) on T cells. B cells from patients with the hyper-IgM syndrome only make IgM antibody, and their B cells only express surface IgM and IgD. The originally described and most common form of the defect is X-linked recessive and results from a mutation in the gene encoding CD40L, a protein expressed transiently on activated T cells.12,37,157 More recently described autosomal recessive forms of this disorder involve mutations either in CD40 itself157,207 or in a CD40activated RNA editing enzyme, activation-induced cytidine deaminase.455 Other cells express surface CD40, thus neutropenia and the increased incidence of infections caused by Pneumocystis and of malignancies in patients with hyper-IgM syndrome also may be the result of impaired cell interactions via CD40. Clinically, hyper-IgM syndrome is manifested by recurrent bacterial infections, especially of the respiratory tract.157 Such persons are susceptible to the same kinds of recurrent pyogenic infections associated with other immunoglobulin deficiencies, as well as to infections with organisms more commonly encountered in patients with T-cell defects (e.g., P. jiroveci).49 Some patients with this syndrome have recurrent diarrhea as a result of G. lamblia and Cryptosporidium infection that is severe enough to require parenteral nutrition. About half of patients have persistent or recurrent neutropenia. Those with autoantibodies may have thrombocytopenia, hemolytic anemia, nephritis, hypothyroidism, or arthritis. The diagnosis of X-linked hyper-IgM syndrome may be established by using immunofluorescence to document absent expression of CD40L on activated T cells, absent CD40 expression on B cells, or demonstrating a mutation in one of the genes encoding CD40, CD40L, or the enzyme activation-induced cytidine deaminase.

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Treatment of patients with the hyper-IgM syndrome with IVIG usually results in significant clinical benefit.49 Wiskott-Aldrich syndrome.  Wiskott-Aldrich syndrome is a rare X-linked disorder characterized by thrombocytopenia, small platelets, eczema, recurrent infections, autoimmune disease, and hematologic malignancy. Although both T- and B-cell compartments are affected, it presents phenotypically more like a B-cell or humoral deficiency, with recurrent otitis media, sinusitis, and pneumonia. The defect involves a mutation in the gene encoding a signaling molecule, Wiskott-Aldrich syndrome protein, which regulates “immune synapse” formation and IL-2 production.414,415 Ataxia-telangiectasia.  Ataxia-telangiectasia is a rare autosomal recessive disorder characterized by progressive cerebellar dysfunction with ataxia, oculocutaneous telangiectasias, recurrent bacterial respiratory infections such as those seen in humoral deficiencies, and a predilection to hematologic malignancy and breast cancer. Serum immunoglobulins often are low, as are lymphocyte counts. The disorder is due to a mutation in the ATM gene, located on chromosome 11. This gene encodes a serine-threonine kinase that is important in cell cycle regulation and double-stranded DNA repair, and it influences expression of BRCA1 genes associated with breast cancer. The risk for breast cancer in patients with ataxia-telangiectasia is increased 15- to 20-fold over that in the general population. Heterozygotes for missense mutations of the ATM gene can be affected because copies of the abnormal protein can interfere with function of the wild-type protein.368,410 Defects of the Interferon-Gamma (IFN-γ) and Interleukin-12 (IL-12) Pathways Macrophages infected by intracellular pathogens, especially Mycobacterium or Salmonella spp., are stimulated via a TLR4-dependent mechanism to release IL-12, along with IL-18, IL-23, and IL-27. These cytokines stimulate T and NK cells to produce IFN-γ via interactions with cellular receptors for the aforementioned cytokines. The released IFN-γ, in turn, further stimulates the macrophage to release more IL-12 and to activate killing. The mechanism by which this intracellular killing occurs is unknown. This cycle of mutual activation is essential for normal defense against mycobacterial pathogens, and some genetic defects of these cytokines, their cellular receptors, or related molecules critical for receptor-mediated signaling have been associated with increased susceptibility to mycobacterial infections. Deficiencies in this system have resulted from mutations in either of the two receptors for IFN-γ, IFN-γR1 and IFN-γR2, as well as mutations in STAT1, a molecule critical for transducing signals from both IFN-γ receptors. Mutations also have been described in the 40-kDa subunit of IL-12, IL-12p40, and the IL-12 receptor, IL-12Rβ1. These disorders are rather uncommon, all involving fewer than 100 known patients.423,470 Mutation of either of the IFN-γRs is associated with increased risk for mycobacterial infections. Deficiencies of IFN-γR1 may be either autosomal recessive or dominant and either complete or partial. Most recessive defects are complete and result in absent IFN-γ responsiveness. Dominant IFN-γR1 deficiency results from heterozygous truncations of the cytoplasmic domain of the receptor with excessive accumulation of nonfunctional receptors at the cell surface. Patients with the recessive complete form of this deficiency have a much more severe clinical phenotype than those with the dominant partial form, although the latter have a fivefold greater frequency of nontuberculous mycobacterial osteomyelitis. Defects in IFN-γR2, much less common, also may be recessive or dominant in inheritance and either complete or partial. Rare deficiencies in the receptor signaling molecule STAT1 have led to increased mycobacterial infections in a partial deficiency or, in two patients with a recessive complete form, to postvaccination disseminated bacille Calmette-Guérin (BCG) disease followed later by death from severe viral infections. The latter probably relates to the additional role of STAT1 in development of IFN-α/β-mediated antiviral activity.470 Deficiencies of IL-12p40 or its receptor IL-12Rβ1 are associated with disseminated nontuberculous mycobacterial infections, tuberculosis, and Salmonella infections. The receptor deficiency results in unresponsiveness to IL-12. This defect is apparently autosomal recessive with variable clinical penetrance. Deficiency of IL-12p40 also is variable in its clinical phenotype and has resulted in deaths from severe mycobacterial infections.427,470,525

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PART I  Host-Parasite Relationships and the Pathogenesis of Infectious Diseases

The approach to specific diagnosis of defects of the IFN-γ pathway has been well systematized, but such studies should be undertaken only in a highly specialized reference laboratory.470 Complement Deficiencies Approximately 0.03% of the general population have complement deficiencies resulting from acquired or congenital abnormalities of single or multiple complement components or regulatory proteins. Excellent reviews of complement deficiencies are available elsewhere.166,167,169,176,265,289,471,580 Congenital or hereditary deficiencies of complement more often are manifested by abnormality or complete absence of a single complement protein, and most of these have been well documented to predispose to potentially life-threatening infections. Most primary complement abnormalities (C1q dysfunction and C1rs, C4, C2, C3, C5, C6, C7, C8, and C9 deficiencies) are inherited as autosomal codominant traits.166 Patients with homozygous or heterozygous deficiency of the early classical pathway proteins C1, C2, and C4 are more prone to develop autoimmune disease than difficulty with infections. However, approximately 20% of patients with homozygous deficiency of early components have problems with recurrent or severe infections that are similar to those seen in C3 deficiency.166,208,471 Their predilection for autoimmune disease probably is due, at least in part, to abnormal solubilization and removal of immune complexes. C2 deficiency has been associated with antibody deficiencies in individuals with recurrent infections.15,113 Deficiencies of alternative pathway proteins predispose to serious, often fatal, infections because of the lack of ability to respond promptly to organisms not previously encountered.167 Properdin deficiency, the only X-linked complement deficiency, has been associated with fulminant, usually fatal, meningococcal infection.167 Factor D deficiency is rare and appears to predispose to recurrent neisserial infection.309 Mutations or variants in the gene for MBL, the initiator of the MBL pathway (see earlier discussion), have been associated with an increased risk for recurrent infections.176,265 In particular, homozygosity for such mutations or variants was found to be associated with an increased risk for systemic meningococcal disease.214 Because all three complement activation pathways converge at the activation of C3, patients who are deficient in C3 are unable to mobilize any of the three main effector functions of complement in host defense—opsonization, phagocyte recruitment, or bacteriolysis. Thus it is not surprising that the most serious complement deficiency state is the rare total absence of C3.166,208,471 Patients with deficiencies or mutations of factors H and I have low but detectable levels of C3 because absence of either of these regulatory factors allows continuous activation of the alternative pathway and uncontrolled C3 consumption. Patients with C3 deficiency caused by any of these mechanisms have increased susceptibility to infections caused by encapsulated bacteria such as S. pneumoniae, N. meningitidis, and H. influenzae type b. Most of these infections involve the respiratory tract (otitis, sinusitis, bronchitis, and pneumonia), but C3-deficient patients also are predisposed to sepsis and meningitis.166,208,471 In addition, some C3-deficient persons develop autoimmune diseases.166,208,471 Deficiencies of terminal complement proteins C5, C6, C7, and C8 greatly increase the risk for developing systemic infections with N. meningitidis or Neisseria gonorrheae.72 C9 deficiency increases the risk for infection to a lesser degree than do deficiencies of other terminal components. In one study, the risk for meningococcal disease was increased 5000-fold in C7-deficient persons and about 700-fold in C9-deficient persons.396 The risk for infection is higher in patients with C5 deficiency than in those with deficiencies of other terminal proteins because, in addition to the role of C5 in initiating assembly of the membrane attack complex, the free C5 fragment, C5a, is important for leukocyte recruitment to sites of microbial invasion.15,53 At least one episode of meningococcal disease occurs in approximately 60% of persons who have been identified as having C5, C6, C7, C8, or properdin deficiency, and 75% to 85% of documented bacterial infections in complement-deficient persons are meningococcal.166,208,471 Conversely, approximately 14% of patients presenting with sporadic meningococcal disease have a defect in one of the late complement components, and

this percentage rises to about one third among individuals with two or more meningococcal infections. The mortality due to meningococcal infection in such patients is lower than in normal persons, probably because patients with these deficiencies often have antibodies to meningococci that can activate the classical pathway leading to normal opsonization and phagocyte activation, which are effector functions upstream in the cascade from the membrane attack complex. In contrast, individuals with normal complement levels who develop meningococcal infection usually do so because they do not have specific antibodies with which to mobilize any effector functions via the classical pathway, and, as noted earlier, meningococci are poor activators of the alternative pathway. Currently no specific treatment exists for patients with hereditary complement deficiencies. Replacement of missing complement proteins is not practical because of the short half-life of most of the components.52,329,474 Immunization of complement-deficient patients and their close household contacts against encapsulated organisms, especially N. meningitidis, is important. Disorders of Phagocyte Function General features of phagocyte disorders. The most frequently encountered reminder of the importance of an adequate supply of well-functioning phagocytes comes from patients who develop chemotherapy-associated neutropenia and are thus at high risk for bacterial and fungal infections.442 The qualitative disorders of phagocyte function discussed in this section result in similar susceptibilities to these infections, either because the circulating cells are unable to migrate to an infected site or because, once having migrated to the infected tissue, they are unable to effect normal microbicidal activity. There is some overlap among the types of infectious complications associated with disorders of migration versus killing. However, as a rule, defects of neutrophil migration tend to be associated with infections at skin, subcutaneous tissue, and mucous membrane sites. In contrast, killing defects are more likely to result in infections of deeper soft tissues and internal organs, although skin infections are not uncommon. Intrinsic disorders of cell migration

Type 1 leukocyte adhesion deficiency.  In the late 1970s and the first half of the ensuing decade, several reports described patients with recurrent bacterial infections, diminished neutrophil motility, and delayed separation of the umbilical cord.1,28–30,34,145,213,257 The neutrophils of these patients were discovered to be markedly deficient in adherence to both natural and artificial surfaces, response to complement-opsonized particles, and expression of members of a family of heterodimeric glycoproteins: LFA-1, Mac-1, and pl50,95, each defined by its own unique α subunit, CD11a, CD11b, and CD11c, respectively, but sharing a common 95-kDa β subunit designated CD18.29,30,34,35,523 A fourth α subunit, CD11d, whose importance remains poorly understood, has been described more recently. The defective expression of these proteins, also called the β2 leukocyte integrins, appeared to be directly responsible for the striking adherence-dependent defects that characterized the function of leukocytes from patients with this disorder.28–30,34,35,523 Variously called Mac-1 deficiency, MO1 deficiency, LFA-1 deficiency, CD11/ CD18 deficiency, or CR3 deficiency, this disorder, now usually called type 1 leukocyte adhesion deficiency (LAD-1), is an autosomal recessive disorder with one of numerous mutations in the β2 integrin subunit, CD18, localized to chromosome 21.30,35,523,524 It has been identified in more than 150 persons worldwide and encompasses a broad ethnic diversity.30,35 Patients may exhibit a moderate or severe phenotype, depending on the extent of the defect in protein expression.29,30 The documented mutations of the β2 subunit (CD18) range from complete absence of the protein to extensions of the molecule, truncations of the extracellular portion or of the cytoplasmic domain of the molecule, small deletions, and point mutations.31,35,269 Patients with LAD-1 develop recurrent necrotic skin and soft tissue infections with poor or absent pus formation, and they exhibit poor wound healing.20,29 They develop severe periodontitis, often losing their primary and secondary dentition along with alveolar bone.29,30,558 They may develop enterocolitis much like that seen in neutropenic patients.26,29 Delayed separation of the umbilical cord, presumably resulting from an impaired inflammatory response, is a common feature of the more

CHAPTER 2  Normal and Impaired Immunologic Responses to Infection severe phenotype of this disorder,29,30 but this finding alone in infants without infectious complications or other characteristic features is of doubtful significance.586 Pronounced leukocytosis is a common feature of LAD-1, even in the absence of active infection.29,30 Recent studies in CD18-null LAD-1 mice reveal abnormally high circulating granulocyte colony-stimulating factor (G-CSF) levels and suggest the absence of a negative feedback mechanism on G-CSF production that occurs during normal transendothelial migration of leukocytes and involves IL-17. Absent ongoing transendothelial migration results in failure of this putative feedback mechanism, resulting in elevated G-CSF levels and higher circulating granulocyte counts.216 Functional studies of neutrophils from patients with LAD-1 reveal a marked impairment of all adherence-dependent functions that require the β2 integrins.28–30,107,227,269 PMNs and NK cells from patients with LAD-1 exhibit impaired ADCC for virus-infected target cells, suggesting that CD11/CD18-mediated cell-cell adhesion is essential for normal killing of virus-infected cells by this mechanism310 and that the increased severity of viral infections in a few of the most severely affected patients could be related to defective ADCC. Currently the diagnosis of LAD usually is made by demonstrating absent or markedly deficient expression of the CD11/CD18 family of glycoproteins on circulating leukocytes by immunofluorescence flow cytometry.28–30,35 Careful attention to skin and oral hygiene, aggressive management of infections, and meticulous local care of wound sites are important in the care of patients with LAD-1 or any serious disorder of neutrophil migration. The efficacy of prophylactic antibiotics has not been well established. Bone marrow transplantation with HLA-matched allogeneic marrow has had mixed results, from complete correction of the phagocytic defect to death 9 months after transplantation from graft-versus-host disease.30,213 The human CD18 gene has been cloned and sequenced, and human LAD-1 cells have been corrected successfully in vitro with the normal CD18 complementary DNA carried by retrovirus vectors, hinting at the future promise of gene therapy for patients with LAD-1.26,30,316 Type 2 leukocyte adhesion deficiency.  In 1992, two unrelated patients were reported, both products of consanguineous matings, who exhibited clinical characteristics virtually identical to those described for LAD-1.219 However, expression of the β2 (CD18) integrins on leukocytes was normal. In addition to defects in neutrophil motility, these children exhibited short stature, psychomotor retardation, and the Bombay (hh) erythrocyte phenotype (homozygous for absence of the H antigen). Phagocytosis by PMNs was normal. Recently it has been documented that this defect is due to one or more mutations of a specific guanosine diphosphate (GDP)-fucose transporter,354 resulting in the absence of fucosyl residues on sialyl Lewis X, the tetrasaccharide moiety that serves as the principal ligand for members of the selectin family of adhesion molecules.219,328,567 In vivo and in vitro studies comparing the adhesive functions of PMNs from LAD-1 and this new disorder, now called LAD-2, provided elegant validation of the distinct roles of selectins and integrins in the recruitment of leukocytes in vivo, with the initial selectin-mediated “rolling” stage (deficient in LAD-2) required first for the second integrin-mediated “firm adhesion and extravasation” stage (deficient in LAD-1) to occur (see Fig. 2.2).567 The other somatic and neurologic features of LAD-2 may be related to more widespread consequences of the generalized defect in fucosylation of glycoproteins.354 Type 3 leukocyte adhesion deficiency (integrin activation defect).  During the past decade, several patients have been reported who have a clinical phenotype that includes features of both type 1 LAD and Glanzmann thrombasthenia, a bleeding disorder associated with mutations in the αIIbβ3 integrin on platelets. Laboratory studies of these patients revealed markedly deficient integrin-mediated adhesive functions of both leukocytes and platelets despite normal surface expression of both leukocyte and platelet integrins. Further studies led to the conclusion that this defect in integrin function was the result of defective “inside-out” signaling pathways that normally lead to integrin activation.196,305,366 Recent data on several kindreds with this disorder, studied in different laboratories, confirmed the presence of mutations in the gene encoding Kindlin-3, a molecule that, during cell activation, forms a critical bridge between the actin cytoskeleton and the cytoplasmic domain of the β

35

subunit of multiple classes of integrins expressed by cells of hematopoietic lineages.266,358,389,535 This bridging by Kindlin-3 is essential for normal integrin activation in both leukocytes and platelets. Specific granule deficiency.  Rare patients with hereditary specific granule deficiency have been reported, beginning with Spitznagel’s original description in 1972.86,222,521 These persons exhibited recurrent and severe infections, primarily of the skin and mucous membranes, sometimes involving the lung and, in one patient, the mastoid. Neutrophils from patients with this disorder exhibit absent specific granules on Wright-stained blood smears. Lactoferrin released from specific granules reduces the negative surface charge of the plasma membrane, contributing to nonspecific adhesiveness of the cell.222 The specific granule membrane also contains some of the intracellular store of the important adhesion molecule Mac-1 (CD11b/CD18) that is mobilized to the plasma membrane upon cell activation.60,81 Recurrent skin and mucous membrane infections resulting from S. aureus, gram-negative bacilli, and Candida spp. characterize the natural history of patients with this disorder.86,222,521 Neutrophils in this disorder also exhibit diminished microbicidal activity, presumably because of diminished amounts of the cytochrome component of NADPH oxidase that normally reside in the membrane of specific granules. In this rare disorder, males and females are represented equally. A few patients with specific granule deficiency have a deletion in the gene encoding the myeloid cell transcription factor known as CCAAT/enhancer binding protein epsilon (C/ EBPε) with absent expression of this transcription factor, although not all patients with this disorder have a mutation of this gene.174,338 Chédiak-Higashi syndrome. Chédiak-Higashi syndrome is a complex, rare autosomal recessive disorder characterized by partial oculocutaneous albinism, recurrent pyogenic infections, peripheral neuropathy, and neutropenia.77 The illness also may involve an accelerated lymphoproliferative phase.77 Granular cells, including neutrophils, contain giant lysosomal granules that are the apparent result of spontaneous intracellular fusion of azurophilic granules and, to a lesser extent, specific granules.77 Corresponding disorders of intracellular pigment granules and vesicle trafficking in axons account for the albinism and other manifestations of this disease.77 The genetic basis of the defect is now known to involve either a mutation in the gene encoding a large protein called the lysosomal trafficking regulator (LYST), homologous to the “beige” gene in mice, with all mutations studied so far resulting in a truncated protein.51,119 Patients with Chédiak-Higashi syndrome develop recurrent skin and mucosal infections, most often caused by S. aureus.30,77 A cell migration defect appears to be related to abnormal regulation of microtubule polymerization upon cell activation.77 The possible role of intracellular levels of cyclic adenosine monophosphate and guanylic acid in this microtubule abnormality has been suggested.89 Studies of two brothers with Chédiak-Higashi syndrome demonstrated abnormally increased tyrosinylation of the α subunit of tubulin.77,399 The diagnosis of Chédiak-Higashi syndrome usually is suspected clinically on the basis of partial oculocutaneous albinism and recurrent pyogenic infections. A Wright stain demonstrating giant lysosomal granules and laboratory studies showing defective cell migration are confirmatory, and genetic confirmation is now possible. Neutrophil actin dysfunction.  Filamentous actin constitutes the main contractile mechanism of neutrophils for migration and phagocytosis.530 An extremely rare and apparently heterogeneous disorder, neutrophil actin dysfunction has been characterized by recurrent skin infections caused by S. aureus and Candida albicans. In vivo and in vitro studies revealed severely impaired neutrophil chemotaxis and phagocytosis.87 The capacity for polymerization of actin from cell extracts also was diminished markedly. It is of interest that PMNs from family members of this patient also were found to be variably deficient in the CD11/CD18 family of glycoproteins that are the basis of LAD-1.518 One similarly affected infant was found to have abnormally high levels of a 47-kDa protein, now identified as lymphocyte-specific protein–1 (LSP-1), which exhibits actin-binding activity.132 Glycogen storage disease type 1B. Beaudet and colleagues57 first reported the association of recurrent infection, neutropenia, and impaired neutrophil migration with glycogen storage disease type 1B, a metabolic disorder characterized by defective microsomal transport of glucose-6-phosphate. In 1985, Ambruso and coworkers19 reviewed

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PART I  Host-Parasite Relationships and the Pathogenesis of Infectious Diseases

the features of 21 patients with glycogen storage disease type 1B, 15 of whom suffered from frequent infections, especially of the skin and subcutaneous tissues. Impaired neutrophil motility was found in 8 of 11 patients in whom this was evaluated. A specific relationship between the underlying metabolic defect in glycogen storage disease type 1B and the mechanism of impaired cell motility has not been established. However, exogenous glucose is an important energy source for chemotaxis,577 and it is interesting to note that the uptake of glucose by PMNs in response to chemoattractant stimulation is impaired in glycogen storage disease type 1B, as well as in neonates, both examples of patients with impaired PMN migration.4,53 Extrinsic or secondary defects of polymorphonuclear leukocyte migration

Defective neutrophil chemotaxis associated with serum inhibitors of cell function.  Investigators have reported the presence of inhibitors of PMN chemotaxis in the serum of patients with recurrent infection.315,507,517,559,575 In each case, the patient’s neutrophils exhibited diminished chemotaxis in the presence of autologous serum or plasma, whereas identical assays in the presence of control serum or plasma resulted in a normal chemotactic response. Most such inhibitors appear to be immunoglobulins or immunoglobulin-like molecules. Hyper-immunoglobulin E syndrome. In 1966, Davis and colleagues160 described two young girls with coarse facial features, reddish hair, fair skin, severe eczema, dystrophic nails, “cold” staphylococcal skin abscesses, and recurrent sinopulmonary infections. The term Job syndrome was suggested, referring to the similar biblical affliction. Additional patients were described with a similar disorder, first associated by Buckley and associates105 with very high serum IgE levels, including a patient who exhibited a defect in neutrophil chemotaxis reported in 1973 by Clark and associates.131 Features common to all of the patients with the disease now termed hyper-IgE syndrome include a history of staphylococcal infections of the skin and sinopulmonary tract beginning in infancy or early childhood and serum levels of IgE that are greater than 2000 IU/mL.100,105,179 Based on extensive reviews, other characteristic but variable features of this disorder include coarse facies, cold abscesses of the skin and subcutaneous tissues, a chronic eczematoid rash, eosinophilia, and mucocutaneous candidiasis.100,179,217 Consistent abnormalities of cell-mediated immune functions in patients with hyper-IgE syndrome suggest that the pathogenic basis involves a defect of T-cell regulation.104,126,179,230 An extensive study of 19 kindreds revealed autosomal dominant inheritance with a genetic locus for hyper-IgE syndrome on chromosome 4, in the proximal 4q region.246,247 In 2007, it ultimately was determined that this disorder can be attributed to dominant negative mutations in STAT3, a factor critical for signal transduction by at least 10 different cytokines, some with proinflammatory and others with antiinflammatory functions.272,381,519 The immunologic defect is characterized further by a paucity of TH17 lymphocytes, which normally promote protective leukocyte responses to bacteria and fungi.382 Recently a rare and clinically distinct autosomal recessive form of hyper-IgE syndrome has been described, resulting from a mutation in DOCK8, a member of a family of atypical guanine nucleoside exchange factors highly expressed in lymphocytes.533 Patients with this form of hyper-IgE syndrome have developed chronic viral infections, severe allergies, and early-onset malignancies.79,246,519,533 Although hyper-IgE syndrome might more properly belong in discussions of defective T-cell regulation, some patients with hyper-IgE syndrome may have a defect in neutrophil chemotaxis.179 The defect sometimes has been intermittent, and, in several cases, the presence of a serum inhibitor of chemotaxis has been recognized.178,179 Recent data suggest that keratinocytes and other epithelial cells from patients with hyper-IgE syndrome may produce reduced amounts of neutrophilattracting chemokines, and neutrophils of these patients exhibit reduced expression of chemoattractant receptors.382,383 Other secondary or poorly defined disorders of polymorphonuclear leukocyte migration.  Patients with protein-calorie malnutrition have defective PMN chemotaxis that appears to be based on systemic preactivation of circulating cells resulting from chronic low-level endotoxemia from impaired intestinal mucosal integrity.122,484 Shwachman-Diamond syndrome, in addition to pancreatic insufficiency, neutropenia, and growth retardation, also is associated with defective PMN migration.10

Two kindreds with congenital ichthyosis and an associated defect of PMN migration have been described.380 Patients with severe thermal injuries develop an acquired form of specific granule deficiency with impaired PMN migration beginning about 14 days after injury.222 Several reports have been published of a poorly defined disorder of neutrophil migration referred to as lazy leukocyte syndrome,9,378,379 marked by recurrent staphylococcal skin infections, rhinitis, gingivitis, stomatitis, neutropenia despite adequate marrow precursors, and diminished in vivo and in vitro migration of neutrophils. Defects in phagocyte microbicidal activity.  As described earlier, the broad array of available phagocyte microbicidal mechanisms may be divided into oxygen-dependent and oxygen-independent mechanisms. To date, no specific deficiency of any oxygen-independent microbicidal mechanism has been described. Thus this section is concerned mainly with the known deficiencies of oxygen-dependent microbicidal mechanisms of phagocytes, especially chronic granulomatous disease, the prototypical defect in this group. PMNs, monocytes, and the fixed phagocytes of the reticuloendothelial system generally share in the deficient microbicidal activity observed. Chronic granulomatous disease.  Chronic granulomatous disease (CGD) was one of the earliest syndromes of phagocyte dysfunction to be characterized.448 It is recognized now to be a family of biochemically and genetically heterogeneous disorders of distinct components of the phagocyte NADPH oxidase complex (see Fig. 2.3 and related text)122,174 that result in the inability of phagocytes to generate superoxide anion and other reactive oxygen species.174 Organisms that produce catalase pose a special problem for patients with this disease.174,180,291,333 This encompasses a broad range of pathogens, including staphylococci, gram-negative enteric bacteria, Pseudomonas spp., yeast, fungi, Nocardia spp., and numerous other pathogenic species.180,289,333,588 Most microorganisms produce H2O2, which might be used, even by the CGD phagocyte, as an effective microbicidal weapon because it feeds into the sequence of oxidant reactions downstream from the defective oxidase enzyme (see Fig. 2.3).465 Organisms that produce catalase are able to survive within these deficient cells because catalase is an enzyme that degrades H2O2 to oxygen and water.291,466 Infections with catalase-negative bacteria, such as Streptococcus, Haemophilus, and Neisseria spp., do not occur with increased frequency in CGD patients,588 and these organisms are killed normally in vitro by CGD phagocytes. Phagocyte functions not directly related to oxidative mechanisms of intracellular killing, including adherence, chemotaxis, phagocytosis, and degranulation, usually are normal.42,381,448,515 The genetic defect in CGD may be inherited by either X-linked recessive or autosomal recessive mechanisms.83,130,151 In the report of a registry of 368 patients with CGD in the United States,588 more than two-thirds of the patients had the X-linked recessive form with absent gp91phox, the larger subunit of the cytochrome b558; about 12% had an autosomal recessive form with absent cytosolic p47phox; and fewer than 5% each had autosomal recessive disease with absent cytosolic p67phox or absence of p22phox, the smaller subunit of the cytochrome b558. Approximately 12% had an unknown genetic form of the disease. A single individual with an autosomal recessive form of CGD due to mutations in the cytosolic p40phox has been reported.364 About 5% of patients with CGD have normal levels of an abnormal protein that is inactive, and at least 410 different mutations have been reported to result in CGD.264 These genetically diverse defects all result in defective function of the oxidase and the characteristic CGD phenotype. In the female obligate carriers of X-linked CGD, the proportion of cells that express the defect usually is between 35% and 65%, depending on the proportion of cells in which random inactivation of the normal versus the affected X chromosome occurs.355,588 Overall, patients with X-linked disease have more severe courses and experience higher yearly death rates than patients with autosomal recessive forms of the disease.588 Patients with CGD experience recurrent serious bacterial and fungal infections, usually beginning in the first few months of life. S. aureus and gram-negative bacilli, especially Serratia marcescens and Burkholderia cepacia, are the most common causes of infection in patients with CGD. Fungi, especially Aspergillus spp., also are prominent etiologic agents,333,453,588 and infections caused by Aspergillus are the most common cause of death in these patients.588 Granuloma formation at infected

CHAPTER 2  Normal and Impaired Immunologic Responses to Infection sites is one of the histologic hallmarks of this disorder.290,453 Pulmonary infections and their complications have been the reported cause of death in up to 50% of these patients in some series, and Aspergillus predominates.588 These infections often are protracted and respond slowly to appropriate antibiotic therapy.291,453 Progression to lung abscess, empyema, or both occurs in about 20% of patients with CGD with pneumonia.291 Liver abscesses occur in about half of patients and may be recurrent.59,127 The hepatosplenomegaly common in CGD may result from these infections but more likely results from chronic infections at various sites with systemic lymphoid hyperplasia.45,291 Osteomyelitis occurs in about one third of patients.291,453,588 In contrast to normal children, in whom this infection usually involves the metaphyseal area of long bones, patients with CGD more often develop infections of the small bones of the hands and feet. In normal children, S. aureus is the most common etiologic agent and causes a significant proportion of cases in CGD. However, gram-negative bacilli and Aspergillus appear to be the predominant etiologies, and other agents, including Nocardia, also may be important etiologic agents of bone infection in CGD.437,588 Skin infections in this disorder may include pyoderma, purulent dermatitis, and cutaneous or subcutaneous abscesses and often are preceded by a chronic eczematoid skin rash.453 Although localized infections are the rule in patients with CGD, these patients also may develop septicemia.291,453,588 The most common cause of septicemia in most series has been Salmonella, but other gram-negative enteric bacilli also have been prominent.290,333 Of note, S. aureus is a proportionally less common cause of septicemia in these patients.453,588 Granuloma formation adjacent to hollow viscera in patients with CGD can produce clinically significant obstruction, including obstruction of the gastric outlet, esophagus, small intestine, and ureters. This complication usually responds to treatment with corticosteroids.20,180,588 CGD should be suspected in patients with a history of recurrent indolent infections caused by catalase-positive organisms such as those

described earlier, especially if granulomas are found in biopsy specimens of lymph nodes or other tissues. Confirmation of the diagnosis usually rests on the demonstration of an absent or nearly absent oxidative metabolic burst in the patient’s phagocytes. This can be detected classically by the slide NBT test or by various other measurements of oxidative burst activity, most recently by flow cytometry of PMNs loaded with oxidant-sensitive fluorescent dyes.13,40,54,465,548 Fig. 2.10A is an example of the slide NBT test in an X-linked carrier; Fig. 2.10B is an idealized set of flow cytometry histograms with typical patterns for a normal control, a patient with CGD, and both X-linked and autosomal recessive carriers. Prenatal diagnosis has been achieved by the use of the slide NBT test with blood from placental vessels obtained at fetoscopy.401 The management of patients with CGD includes antibiotic prophylaxis, usually with trimethoprim-sulfamethoxazole, and an aggressive approach to the specific diagnosis and treatment of acute infections.453 Antifungal prophylaxis with itraconazole or voriconazole that has activity against Aspergillus also has become standard. Bone marrow transplantation met with early limited success,241,298,581 but allogeneic peripheral blood stem cell transplantation from HLA-identical sibling donors, with prior myeloablative conditioning, has been considerably more promising, as suggested by the European experience from 1985 to 2000, with 22 of 23 patients “cured” at median follow-up of 12 years.495 A multicenter study reported that daily subcutaneous injections of IFN-γ reduced the requirement for hospitalization of CGD patients for serious infections by about two-thirds.283 The mechanism by which IFN-γ exerts its beneficial effect in CGD has not been determined. Despite some systemic side effects, such as fever, fatigue, and myalgia,283 it generally has been well tolerated,360 and it continues to be used in the management of many patients with this disorder.588 Deficiencies of glucose-6-phosphate dehydrogenase, glutathione peroxidase, and glutathione synthetase.  The normal activity of the NADPH oxidase enzyme complex depends on the continued availability of NADPH to reduce molecular oxygen to form superoxide anion.129,465 The primary source of NADPH for this enzyme is the hexose

Number of PMNs

CGD diagnosis and carrier screening by fluorescence flow cytometry Unactivated cells and activated CGD cells

Activated A.R. carrier cells

B

Activated normal cells

~50% of activated X-L carrier cells

~50% of activated X-L carrier cells

A

37

Increasing fluorescence

FIG. 2.10  (A) Photomicrograph of a slide nitroblue tetrazolium (NBT) test of polymorphonuclear leukocytes (PMNs) isolated from the blood of a maternal carrier of X-linked recessive chronic granulomatous disease (CGD). Because of random inactivation of either the normal or the affected X chromosome in maternal carriers of this disorder, approximately half of the PMNs exhibit the granular blue-black staining characteristic of the oxidative reduction of NBT by normal PMNs. In contrast, the remaining PMNs, which express the reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase defect of CGD, are visible only by their nuclear counterstain. (B) Flow cytometry in CGD diagnosis and carrier testing. These idealized flow cytometry histograms demonstrate the oxidative burst activity of populations of PMNs that have been loaded with an agent such as dihydrorhodamine that becomes fluorescent when it reacts with products formed during the oxidative burst. The taller curve on the far left represents the fluorescence typical of both inactivated normal PMNs and activated PMNs from a patient with CGD with an absent oxidative burst. The taller histogram on the far right demonstrates the increased level of fluorescence exhibited by activated normal PMNs. The two smaller curves on the left and the right represent the two populations of activated PMNs from a typical maternal carrier of X-linked CGD, indicating about 50% normal PMNs and 50% expressing the defect. The taller histogram in the middle represents typical results for the cells of a carrier of autosomal recessive CGD, with all cells exhibiting an intermediate level of fluorescence.

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PART I  Host-Parasite Relationships and the Pathogenesis of Infectious Diseases

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Host Response to Infections: The “-omics” Revolution

3 

Asuncion Mejias • Octavio Ramilo INTRODUCTION There has been tremendous progress in our attempt to discern the molecular basis of infectious diseases, yet several gaps remain both in the understanding of disease processes and in the development of optimal strategies that would allow early diagnosis and targeted treatment. In addition, despite major advances in the development and implementation of vaccines and antimicrobial agents, infectious diseases continue to represent a major cause of morbidity and mortality worldwide.128 Recent examples such as the 2009 H1N1 influenza pandemic,30,121 the MERS coronavirus and enterovirus-D68 outbreaks, the West Africa Ebola and the Zika virus epidemics,111,143,148,197,220 as well as the increased frequency of hospital-acquired infections caused by multiple-resistant gram-negative bacilli78 and highly virulent strains of Clostridium difficile198 highlight the challenges we encounter when managing patients with infectious diseases. In this context of outbreaks of emergent and reemergent pathogens linked to increased antimicrobial resistance, there is a clear need for improved diagnostic tools for optimal patient classification and management.142

HOST RESPONSES FOR IMPROVING THE DIAGNOSIS OF INFECTIOUS DISEASES One of the most frequent challenges that physicians face in the clinical setting is the difficulty of establishing an appropriate etiologic diagnosis or even distinguishing between bacterial or viral infections in patients presenting with an acute febrile illness. These obstacles can delay initiation of appropriate therapy, which can result in unnecessary morbidity and even mortality. On the other hand, the need to promptly start appropriate antimicrobial therapy to control the infection has to be balanced with a rational use of antibiotics. Within this context there is an obvious need for improved diagnostics tools to help with patient classification, which in turn should allow appropriate use of targeted therapies. Microbial pathogens are detected in clinically relevant specimens using a variety of assays including cultures, rapid antigen detection tests, and polymer chain reaction (PCR) assays. To date, to be able to establish causality, growing the specific pathogen (bacteria, virus, or fungus) remains the gold standard. However, this is a flawed approach, particularly if the organism is not present in the blood or from other easily accessible sites. In addition many pathogens grow slowly or require complex media, and a significant number of clinically important microbes remain unrecognized because they are resistant to cultivation in the laboratory, thus limiting clinical decision-making.45,190 The introduction of more sensitive molecular diagnostic assays has significantly improved the diagnosis of viral infections.99 Unfortunately this is not the case for bacterial pathogens. Moreover, in the clinical setting, it is not uncommon to encounter situations in which the sole identification of a pathogen is not sufficient to establish causality (e.g., the detection of respiratory viruses in patients with no respiratory symptoms or in patients with pneumonia who often also have a co-detected bacterial pathogen). In view of these limitations, for almost a century, there has been a large quest to identify host-derived biomarkers indicative of infection, such as the erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP).223,231 These tests, which are useful in certain clinical scenarios, have proved to be nonspecific and are unable to differentiate between pathogen types (i.e., viral vs. bacterial) or even between infectious and noninfectious diseases. More recently, procalcitonin (PCT), a 116-amino acid protein produced in the thyroid and lungs, has shown improved sensitivity and specificity for the diagnosis of bacterial infections.7,22,72,149 Nevertheless, there are limitations and uncertainty about

its utility because serum concentrations of PCT also increase after surgery, trauma, cancer, or severe burns, thus raising the concern of false positives.97,154 Other candidate biomarkers have been used for the diagnosis of neonates and older children with sepsis and have produced inconsistent results because data have yet to be validated in independent cohorts.207 There is a need for an alternative strategy that has sufficient sensitivity to differentiate infectious from noninfectious conditions, sufficient specificity to distinguish among the different types of pathogens, useful to monitor response to therapy, and, ideally, is able to predict clinical outcomes. An alternative approach to the pathogen-detection strategy is based on a comprehensive analysis of the host response to the infection caused by different pathogens (Fig. 3.1).34,104,141,142,186,187 A wide range of molecular and cellular profiling assays are currently available for the study of the human immune system.33 Genomics provide information about structural DNA changes and thus the probability of developing a condition, epigenetics describe the chromatin modifications that are caused by external or environmental factors and stably alter gene expression without changing the DNA sequence, transcriptomics study the overexpression or underexpression of genes (mRNA expression profiles) in a qualitative and quantitative manner in response to the infection, and metabolomics and proteomics analyze the structure, function, and interaction of posttranslational metabolites produced by a particular gene (Fig. 3.2). Thus the information provided by the “-omics” technologies is complementary, and their use for diagnostic, pathogenetic, or prognostic purposes is mainly limited by the available technology and complexity of the analyses (Fig. 3.3). Independent of the -omics approach used, four tenets must be considered when using these tools for biomarker discovery to assure that the profiles are representative of the disease process and not of a confounding event: (a) selection and definition of the cases, which should be homogeneous in terms of the disease process and with limited confounders to allow interpretation of the multidimensional data; (b) need for controls, which should be also homogeneous, free of confounders, and similar in terms of the basic characteristics (i.e., demographic parameters) with the cases; (c) type of sample, which should reflect and change because of the biologic process and should be easy to obtain, ideally in a noninvasive manner; and (d) need for validation, to confirm that the profiles identified perform well in an independent cohort of patients that is different from the one used for the discovery phase. Of all these technologies, genomics and transcriptomics are moving into the clinical laboratory and are poised to become part of routine diagnostics in the next few years. In this chapter, we will review the application of analysis of host response through genomics, epigenetics, transcriptomics, proteomics, and metabolomics for diagnosis, understanding disease pathogenesis, patient classification and management, and possibly prognosis of pediatric patients with infectious diseases.

GENOMICS The human genome, which is relatively static, is organized into 46 chromosomes consisting of 22 pairs of autosomal chromosomes shared by males and females and the sex-determining chromosomes, X and Y. One set of autosomal chromosomes is derived from each parent. Human genes are formed by exons, which are the coding regions, and introns, the noncoding regions. During transcription, the entire gene is copied into pre-mRNA, which includes exons and introns. Through the process of RNA splicing, introns are removed and exons joined to form a contiguous coding sequence. Single genes are able to generate 4 to 6 different mRNAs; thus many of the complex biological functions that characterize humans are generated by combined interactions among 41

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PART I  Host-Parasite Relationships and the Pathogenesis of Infectious Diseases

genes rather than a specific gene being responsible for a specific function. The genome and transcriptome consist entirely of deoxyribonucleic (DNA) and ribonucleic acids (RNA). Their uniform chemical properties have enabled efficient, low-cost, and high-throughput methods for amplification, synthesis, sequencing, and highly multiplexed analysis. The genome represents a rich source of information about our pathophysiology. Genome analyses provide information about structural DNA changes and thus the probability of developing a condition. These analyses do not, however, provide information about whether and when a condition will manifest. Many diseases are caused by genetic mutations, and many more manifest as a genetic predisposition. More than 3000 gene mutations (www.omim.org/) have now been identified that are associated with more than 5000 human phenotypes that cause or predispose to diseases. These numbers suggest that many diseases are caused by mutations in single genes and that many more have an inheritable genetic component. The Human Genome Project (HGP) was an international research effort originated in 1990 that culminated in the identification and public release of the completed sequence of the human genome in April 2003. In the HGP, the genome was cloned first and then larger clones were divided into shorter pieces and

Microbe A

Microbe B

sequenced. The HGP has revealed approximately 20,500 human genes. They are contained in more than 2.85 billion nucleotides covering more than 99% of the euchromatin (i.e., gene-containing DNA). Initial genome approaches were applied to the diagnosis of congenital birth defects and tumors. However, the introduction of next-generation DNA sequencing (NGS) has revolutionized biomedical research and promises to be of great value for the diagnosis of infectious diseases.118

Basics of the Genomics Approach We now have a broad arsenal of techniques for genome analysis at our disposal, which allow the detection of gross abnormalities down to single nucleotide changes. These tools are increasingly being used for

Genome

DNA

Histone modifications DNA methylation and ncRNA*

Epigenetics

Microbe C

Transcriptome

mRNA and RNA seq

Proteome

Metabolome

Immune response A

Immune response B

Immune response C

Pattern recognition receptors FIG. 3.1  Each pathogen induces a specific response in the host that can be measured. An alternative approach to the pathogen-detection strategy is based on a comprehensive analysis of the host response to the infection caused by different pathogens.

Proteins

Lipids

Sugars

ME ME ME Genomics

Lipidomics -omics

Transcriptomics

Dicer Proteomics

Nucleotides

FIG. 3.2  Types of -omics approaches. Genomics provides information about structural DNA changes and thus the probability of developing a condition; epigenetics describes the chromatin modifications that are caused by external or environmental factors and stably alter gene expression without changing the DNA; transcriptomic approaches study the overexpression or underexpression of genes (mRNA expression profiles) in a qualitative and quantitative manner in response to the infection; and metabolomics and proteomic methodology analyze the structure, function, and interaction of posttranslational metabolites produced by a particular gene.

Epigenomics

Metabolomics

Amino acids

miRNAomics

FIG. 3.3  Omics approaches are complementary. The information provided by the -omics technologies is complementary, and their use for diagnostic, pathogenesis, or prognostic purposes is mainly limited by the available technology and complexity of the analyses. ME, Methyl group.

CHAPTER 3  Host Response to Infections: The “-omics” Revolution clinical diagnostics. Within a few years the study of the human genome has dramatically changed and greatly improved, moving from the identification of abnormalities based on the morphology and number of chromosomes (karyotype) to the newly developed sequencing instruments that are able to generate millions of short sequences per run (NGS). Karyotyping was the first method used for the identification of chromosomal abnormalities. Developed in the early 1960s, it is based on the identification of the banding pattern characteristic for each chromosome visible through the light microscope. Although it only reveals crude information, such as number, shapes, and gross alterations of general chromosomal architecture, it remains a mainstay of clinical genetic analysis. Trisomy 21 and chronic myelogenous leukemia were originally identified using this technique.8,12 Comparative genome hybridization is a cytogenetic method focused on copy number variations relative to the number of chromosomes (ploidy) in the DNA. In comparative genome hybridization, the genomes of interest, which are usually a disease genome set against a normal control genome, are labeled with different fluorescent dyes and compared. Using different colored fluorescent labels, several genes can be stained simultaneously. When the technology was developed the fluorescently labeled DNAs were hybridized to a spread of normal chromosomes and evaluated by quantitative image analysis, which was able to detect chromosome regional gains or losses with greater accuracy than conventional karyotyping.59,105 Further improvements in resolution have been achieved using microarray-based comparative genome hybridization methods in which the probe DNA can be amplified by PCR, thus only minute amounts of starting material are required.62,166 The labeled DNA is then hybridized to an array that can contain millions of oligonucleotides included on chips the size of a microscope slide, achieving very high resolution. Comparative genome hybridization techniques are used in prenatal screening for the detection of chromosomal defects. However, they do not provide information about balanced changes, such as inversions or balanced translocations, because they do not change the copy number and hybridization intensity. To circumvent this issue, if the gene of interest is known, the respective recombinant DNA can be labeled and used as a probe on chromosome spreads. This method, called fluorescence in situ hybridization (FISH), can detect gene amplifications, deletions, and chromosomal translocations. DNA sequencing is the ability to identify individual genes by determining the precise order of the four nucleotides (adenine, guanine, cytosine, and thymine) within a molecule of DNA. The rapid speed of sequencing attained with modern DNA sequencing technology has been instrumental in the sequencing of the complete human genome, which culminated in 2003. Over the years different techniques have been used for DNA sequencing. Initially the Maxam-Gilbert sequencing method used chemicals to cleave specific bases. This methodology was quickly discouraged due to its complexity and the use of radioactive labeling.139 In parallel, Sanger used small concentrations of radio- or fluorescently labeled dideoxynucleoside triphosphate (dNTP) molecules and developed a relatively reliable and less cumbersome method called chain termination. Sanger’s method was soon automated and was the method used in the first generation of DNA sequencers.200 The rapid development of novel technologies, such as NGS, has revolutionized this field. There are several NGS methods using different approaches to read DNA sequences. All these novel methods share the principle of conducting millions to billions of parallel sequencing reactions in microscopic compartments on arrays or nanobeads. Among others, DNA sequencing is used for genome-wide association studies (GWAS) using single nucleotide polymorphisms (SNPs) as high-resolution markers. SNPs are variations among individuals at a single position in a DNA sequence.88 If more than 1% of a population does not carry the same nucleotide at a specific position in the DNA sequence, then this variation can be classified as an SNP. SNPs are associated with both genes and noncoding regions of DNA and represent the most common type of genetic variation among individuals. In 2012, more than 180 million SNPs were known. SNPs are useful to identify and assess disease risk, but it is not uncommon that they are found to have no impact on the phenotype (silent mutations).221 Silent mutations, along with the need for extremely large cohorts of patients and for reproducibility of the studies, are among the main limitations of GWAS.

43

Genomics in Infectious Diseases By 1950, using malaria as a prototype disease, the concept that genetic diversity within the host may influence the outcome of infection became apparent. In the clinical setting, the majority of infectious diseases are characterized by variation in both the disease pattern and severity, even during epidemics, thus highlighting the important role of host response on clinical manifestations and disease outcomes. Different inherited conditions, such as chronic granulomatous disease or interferon-γ receptor immunodeficiency, predispose to infectious diseases, and those conditions will be reviewed in another chapter. A number of SNPs in human leukocyte antigen (HLA) and non–major histocompatibility complex (MHC) have been found in response to a variety of bacterial and viral infections and have been associated with disease susceptibility, progression, or response to treatment. Table 3.1 illustrates examples of SNPs associated with a variety of uncommon and common viral or bacterial infections.* The main limitation of GWAS is that the same SNP can be protective or influence disease progression depending on the population and on the environment, making reproducibility of studies challenging.251

EPIGENETICS In 1957, Waddington developed the idea that some heritable traits are not reflected by changes in the DNA, and this change process is now known as epigenetics. Epigenetics describe a number of chromatin modifications (phenotypic trait variations) that are caused by external or environmental factors and stably alter gene expression without changing the sequence of the DNA.14 Thus epigenetics is able to alter the phenotype of a cell without changing the genotype and supports the idea that changes in gene expression derived from long-term exposure to a certain insult are imprinted, become independent of the activating stimulus, and persist even in its absence.19 Epigenetics include the study of DNA methylation as well as a variety of more transient histone modifications (such as acetylation, methylation, or phosphorylation) along with the influence of SUMOylation (the addition of small ubiquitin-like modifiers [SUMOs]), ubiquitination, adenosine diphosphate (ADP) ribosylation, and microRNA. Although the epigenome is more variable than the genome, it may hold greater information on an individual basis, which will be useful for the application of personalized medicine.

Basics of the Epigenetics Approach The methodology used to identify changes in DNA methylation are similar to that applied in genomics and include DNA sequencing of the treated versus untreated DNA, hybridization techniques, or arraybased methods. These techniques may miss some incomplete modifications; however, new NGS methods that are able to detect DNA methylation directly look promising and will accelerate the field. The main epigenetic changes include histone modifications (such as acetylation and methylation that affect chromatin structure) and DNA methylation. It is important to note that although DNA methylation silences gene expression, histone modifications can enhance or suppress gene transcription. DNA methylation patterns have been associated with diseases and can be heritable by a poorly understood process called genomic imprinting. In addition, epigenetics includes the understanding of noncoding RNAs (ncRNAs), which are transcribed molecules that do not translate into proteins. In regard to epigenetic modifications, one of the long ncRNAs more recently discovered are small ncRNAs or microRNAs (miRs).195 miRNAs are highly conserved, small noncoding RNAs that target mRNA molecules and inhibit their translation. miRNA exist intra- and extracellularly, including in blood or serum, and are resistant to boiling or repeated freezing-thawing, thus promising to be useful biomarkers in the clinical setting.74

Epigenetics in Infectious Diseases There is growing evidence that histone modifications and chromatin remodeling regulate gene expression, including host immune responses, *References 2, 5, 6, 11, 16, 17, 31, 36, 46–48, 51, 52, 57, 61, 63, 64, 70, 84–86, 95, 98, 106, 107, 114, 126, 129, 136, 138, 140, 152, 156, 159, 165, 169, 171, 179, 191, 199, 215, 226, 229, 233, 244–247.

44

PART I  Host-Parasite Relationships and the Pathogenesis of Infectious Diseases

TABLE 3.1  Single Nucleotide Polymorphisms (SNPs)/Mutations and Associated Diseases Pathogen

Disease

SNPs/Mutations

Populations

Mycobacterium leprae

Leprosy

Adults

Mycobacterium tuberculosis Streptococcus pneumoniae Staphylococcus aureus Neisseria meningitidis Helicobacter pylori HIV Norovirus, rotavirus HCV Dengue virus HSV RSV

Tuberculosis Pneumococcal disease S. aureus infection Meningococcal disease Gastric cancer AIDS Gastroenteritis Hepatitis Dengue shock syndrome Encephalitis Bronchiolitis, severe disease

Influenza Rhinovirus

Infection/severe disease Severe bronchiolitis

HLA-DR-DQ, TLR-1, NOD2, TNFSF15, 308 bp TNF, RIPK2, IL-23R, RAB32, LRRKW136,165,229,244 Mal/TIRAP, TLR-1, -2, -4, -6, -9, TNF-α, IFN-γ, IL-12RB15,6,64,191,199,226,246 MBL2, PTPN22, Mal/TIRAP31,129,156,159 HLA-DRA, -DRB151 CFH-CFHR3, TLR-416,17,48 IL-1, EPHX1169 CCR5, CCR2, RANTES, CXCL1247,85,86,95,247 FUT246,179 IL-28B (INF-λ), IL-10R, IP-1011,52,61,171 MICB, PLCE1107 TLR-3, UNC-93B114 SP-A, SP-D, TLR-4, IL-8, IL-4, IL-13, IL-10, IL-1RL1, VDR2,36,63,98,140,215,233,245 TNF, IL-6, IL-8, LTA, IL-1B, IL-1A, IL-1070,106,126,138,152 IL-10, IL-6, IFN-γ,84

Adults Children Adults Children and adults Adults Children and adults Children Adults Children and adults Children Children Adults Children

CCR, Chemokine receptor; CFH, complement factor H; CFHR3, CFH-related protein 3; CXCL12, chemokine; EPHX1, epoxide hydrolase 1, microsomal; FUT2, fucosyltransferase 2; HBV, hepatitis B virus; HCV, hepatitis C virus; HIV, human immunodeficiency virus; HLA, human leukocyte antigen; HSV, herpes simplex virus; IFN, interferon; IL-1, interleukin-1 (gene); IL-23R, interleukin-23 receptor (gene); IL-28B, interleukin-28B; LRRK2, leucine-rich repeat kinase 2 (LRRK2); LTA, lymphotoxin alpha; Mal, myeloid differentiation primary response gene 88 (MyD88) adaptor-like protein; MBL, mannose-binding lectin; MICB, major histocompatibility complex class I polypeptide–related sequence B; NOD2, nucleotide-binding oligomerization domain containing 2; PLCE1, phospholipase C, epsilon 1; PTPN22, protein tyrosine phosphatase nonreceptor, type 22; RAB32, member RAS oncogene family; RIPK2, receptor-interacting serine-threonine protein kinase 2; RSV, respiratory syncytial virus; TIRAP, Toll-interleukin-1 receptor (TIR) domain adaptor protein; TLR1, Toll-like receptor 1 gene; TNFSF15, tumor necrosis factor (ligand) superfamily member 15; VDR, vitamin D receptor.

and thus represent key targets for pathogen manipulation during infection.80 A variety of viral and bacterial effectors have been identified that enable a pathogen’s survival by either mimicking or inhibiting host cellular machinery. Mitogen-activated protein kinase (MAPK), interferon (IFN), or transcription factor NF-κB signaling pathways, among others, are common targets of pathogen-induced posttranslational modifications on histones and chromatin-associated proteins.91,192 In Vitro Studies The majority of the initial epigenetics work associated with miRNA in relation to infections was performed in vitro and mostly included viral-induced diseases. The goal of these studies was to gain a better understanding of the mechanisms of diseases or to identify markers associated with organ-specific syndromes and/or severity associated with specific pathogens. Using a laryngeal epithelial cell model of enterovirus 71, Cui and colleagues identified 64 miRNAs that target a number of genes associated with neurologic and immune responses relevant to the pathogenesis of the disease.43 Similarly, using primary human alveolar and bronchial epithelial cells infected with influenza A virus, Buggele and colleagues identified six miRNAs targeting a number of mRNAs, including receptor-associated kinase 1 (IRAK1) or MAPK3 and other components of the innate immune response to infection.25 Another provocative study showed that influenza H3N2 uses one of its nonstructural (NS) proteins to circumvent immune responses. Investigators showed that the influenza NS1 protein had a histone-like sequence (ARTK-histone mimic) that inhibited the host transcription elongation factor (hPAF1), selectively suppressing the host cell’s production of antiviral proteins.135 Within alveolar macrophages, Pennini and colleagues showed that Mycobacterium tuberculosis (TB) inhibited the expression of several interferon-γ–induced genes through histone acetylation, which appears to be a ubiquitous mechanism used by intracellular pathogens. This mechanism may help explain the protracted course and persistence of TB in some patients.180 These studies, although descriptive, are examples of how pathogens can directly induce epigenetic changes in the host. As a diagnostic tool, a study conducted in mice infected with either Escherichia coli, a gram-negative bacterium, or S. aureus, a grampositive bacterium, identified three circulating miRNAs predictive of gram-positive bacterial infections.188

In Vivo Studies miRNA expression is a novel addition to the -omics arsenal to evaluate host responses to viral and bacterial infections. A small study in patients with dengue identified in blood samples two panels of miRNAs, one composed of 12 miRNAs and specific to dengue and another formed of 14 miRNAs common in dengue and influenza infection.216 Another study was conducted with serum samples from children with handfoot-and-mouth disease caused by EV-71 or Coxsackie virus 16 and included healthy controls and other infections including TB, pertussis, varicella zoster (VZV), or mumps.44 Investigators found six miRNAs that discriminated children with EV-71 infection versus healthy controls with greater than 90% accuracy. However, only 2 of the 6 miRNAs identified were also found in their in vitro model. This emphasizes the need to perform studies in target populations because several factors, such as disease severity, age, or other parameters, may provide discordant results. A small study conducted in infants with respiratory syncytial virus (RSV) identified a distinct profile of immune-associated miRNA in respiratory samples from patients with mild or severe disease.93 Although promising, these results will need to be validated in larger patient populations. Different studies have measured miRNA profiles in whole blood, peripheral blood mononuclear cells (PBMCs), or serum from patients infected with various strains of influenza A, including H1N1/H3N2, H7N9, or 2009 H1N1.209,217,250 However, results could not be validated in other studies, suggesting that there may be methodologic differences that must be addressed.243 In regard to bacterial pathogens, the majority of epigenetic studies have focused on TB or sepsis. A study that analyzed the sputum of patients with active TB versus controls found 95 miRNAs that were differentially expressed and were subsequently validated by quantitative reverse transcription PCR (RT-qPCR).238 Other studies conducted in adult and pediatric patients, with and without HIV, found a number of whole blood miRNAs in CD4+ T cells or sera that were differentially expressed in active versus latent TB or controls and had a specific role in T-cell immunity against TB.68,108,151,184 In regard to sepsis, serum miRNAs have been used mostly as a prognostic rather than diagnostic marker in critically ill patients with negligible or no overlapping findings among studies, which may be attributed to the different levels of disease and/or the patient populations included.131,194,213,230 Studies using miRNAs as a diagnostic tool for more common bacteria

45

CHAPTER 3  Host Response to Infections: The “-omics” Revolution are ongoing. Nevertheless the value of miRNAs for the diagnosis of bacterial and viral infections, especially in patients with pneumonia, will be evident when studies are conducted and validated in the main target populations.

of noncoding RNAs that fulfill important structural and regulatory functions, including gene transcription, mRNA processing and stability, and protein translation. One type of noncoding RNAs is the so-called small interfering (si)RNAs, which were discovered in 2006.224 siRNAs are part of an enzyme complex that targets and cleaves mRNAs with high specificity. These types of RNAs have become a powerful tool to downregulate (or silence) the expression of selected mRNAs with high specificity and efficiency. Different classes of pathogens trigger specific pattern-recognition receptors (PRRs) differentially expressed on peripheral blood leukocytes.23,113,112 Blood represents both a reservoir and a migration compartment for these immune cells that become educated and implement their function by circulating between central and peripheral lymphoid organs and migrating to and from the site of infection via blood. Therefore blood leukocytes constitute an accessible source of clinically relevant information, and a comprehensive molecular phenotype of these cells can be obtained using gene expression microarrays.33 Because they provide a comprehensive assessment of all immune-related cells and pathways, genomic studies are well suited to study the host-pathogen interaction (Fig. 3.4). In fact, studies in children and adults with acute infections have shown that different classes of pathogens induce distinct gene expression profiles that can be identified by analyses of blood leukocytes (Fig. 3.5.)15,32,34,104,141,170,186,242

TRANSCRIPTOMICS Major technological breakthroughs have also occurred in the field of transcriptomics, thus creating a unique opportunity for the study of humans in health and disease where inherent heterogeneity dictates that large collections of samples need to be analyzed. Among the highthroughput molecular profiling technologies available today, transcriptomic approaches are the most scalable, have the most breadth and robustness, and therefore appear to be best suited for the study of human populations. The transcriptome represents the complement of RNAs (messenger RNA) that are transcribed from the genome. Genes encode the information to make proteins, and RNA is the messenger that transports that information (hence the name mRNA). The transcription of a gene yields an average of 4 to 6 mRNA variants, which are translated into different proteins. The translation of mRNAs into proteins is highly regulated. Protein-coding genes only constitute 1% to 2% of the human genome sequence; however, more than 80% of the genome can be transcribed. Thus the largest part of the transcriptome consists Bacterium

Virus

Bacteria Bacteria

TRUE CLASS 4.0

mRNA

Patient Genotype (DNA)

Analysis

1

PREDICTED CLASS

3.0

M1

2.5

M2

2.0 1.2

Virus

1.0

1

0.8

Expression Profile

0.7

M1

0.6

M2 35 Genes

0.5 0.4

Virus

3

4

5

6

7

8

9 10 11

3

4

5

6

7

8

9 10 11

M3

1.5

mRNA

2

0.3

2

M3

23 samples

FIG. 3.4  Viral versus bacterial host responses. Microarray technology can measure the differences in gene expression patterns present in blood immune cells as induced by various types of infectious agents (viruses vs. bacteria) with a high level of specificity. 1

2

3

4

5

6

7

8

9

1

10 11

M1

M1

M2

M2

M3

M3

2

3

4

5

6

E. COLI 1

2

3

4

5

6

7

8

9

7

8

9

Functional interpretation Plasma cells Erythrocytes

10 11

S. PNEUMONIAE

10 11

1

2

3

4

5

6

7

8

9

Platelets

T-cells

B-cells

Interferon Inflammation

Myeloid lineage

10 11

M1

M1

Ribosomal proteins

Undetermined

M2

M2

Cytotoxic cells

No Module

M3

M3

Neutrophils

S. AUREUS 1

2

3

4

5

6

7

8

9

INFLUENZA

10 11

1

M1

M1

M2

M2

M3

M3

RSV

2

3

4

5

6

7

8

9

1

10 11

2

3

4

5

6

7

M1 M2

DENGUE

M3

FIG. 3.5  Infectious disease fingerprints. Studies in children and adults with acute infections have shown that different classes of pathogens induce distinct gene expression profiles that can be identified by analyses of blood leukocytes. Expression levels were compared between patients and appropriately matched healthy controls on a module-by-module basis. The spots represent the percentage of significantly overexpressed (red) or underexpressed (blue) transcripts within a module (i.e., a set of coordinately expressed gene). Blank spots indicate that there are no differences in the genes included in that module between patients and healthy controls. This information is displayed on a grid, with the coordinates corresponding to one of 28 module IDs (e.g., module M3.1 is at the intersection of the third row and first column). Each pathogen induces an easily identifiable disease-specific biosignature. RSV, Respiratory syncytial virus.

8

9

10

11

46

PART I  Host-Parasite Relationships and the Pathogenesis of Infectious Diseases

Basics of the Transcriptomics Approach Microarray Analyses Microarray methods for studying global mRNA expression profiles are now well established. Microarray gene chips contain several million DNA spots arranged on a small slide in a predefined order. They allow a relative quantitation of changes in transcript abundance among different conditions. Modern arrays use unique sequences of synthetic oligonucleotides to avoid ambiguity in identifying specific RNA transcripts, and several oligonucleotides are used per gene to improve accuracy. The newer high-density arrays are able to scan the transcription of all human genesm map exon content, and splice variants of mRNAs, including noncoding RNAs (such as siRNAs and miRNAs). Briefly, RNA derived from the cells or tissue analyzed is copied first to complementary cDNA using a reverse transcriptase that can synthesize DNA from RNA templates. cDNA is transcribed back into cRNA, which is labeled with fluorescent tags, such as biotin, to improve detection. cRNA is preferred to cDNA because it hybridizes more strongly to the array oligonucleotides. After hybridization, the microarray chip is scanned and the hybridization intensities are compared using different statistical software. Thanks to a common convention for reporting microarray experiments called Minimal Information for the Annotation of Microarray Experiments (MIAME), gene array databases that have been published are publicly available free of charge and represent a valuable source for further analysis in which microarray results from different experiments can be compared. Gene array analysis is already being used for clinical applications. RNA Seq Transcriptome analysis can also be performed by direct sequencing once RNAs have been converted to cDNAs. The advances in rapid and cheap DNA sequencing methods permit every transcript to be sequenced multiple times. These “deep sequencing” methods not only unambiguously identify the transcripts and splice forms but also allow the direct counting of transcripts over the whole dynamic range of RNA expression, resulting in absolute transcript numbers rather than relative comparisons. Thus the sequencing methods, called RNA seq, are quickly becoming attractive alternatives to array-based transcriptomic methods.228 Studies using RNA seq to characterize different infections are ongoing. As examples, two studies in mice, one in a model of Staphylococcus aureus infection21 and the second one in a model of H5N8 avian influenza virus,172 found transcripts associated with proinflammatory and antiinflammatory mediators, chemotaxis, cell signaling, keratins, and TH1/ TH17 cytokines.

Use of Transcriptomics in Infectious Diseases Of all the -omics technologies, transcriptomics is probably the most popular, affordable, and easiest to implement approach because it allows measuring transcript abundance in a sample on a genome-wide scale using a single assay. Several studies have been conducted over the years, initially in vitro and subsequently in samples (usually PBMCs or whole blood) from patients with a variety of infectious diseases. In Vitro Studies The initial studies supporting the hypothesis that pathogen-specific gene expression profiles can be measured in immune cells were derived from in vitro studies. The comparative analysis of a compendium of host-pathogen microarray datasets identified both a common host transcriptional response to infection and a pathogen-specific signature.20,35,94,100 Upon activation, Toll-like receptors (TLRs) trigger signaling pathways that share common components while retaining unique characteristics, accounting in part for the specificity of transcriptional responses.214 In fact, in vitro microarray studies have shown the ability of herpes simplex virus (HSV), West Nile virus, pseudorabies virus, hepatitis C viruses (HCV), VZV, and rhinovirus to limit the ability of the host to develop effective antiviral responses by a variety of mechanisms.90,185 However, the vast body of in vitro experimental data accumulated over the years suggests that hosts can mount pathogenspecific transcriptional responses to infections.

In Vivo Human Studies Initial studies tested the hypothesis that leukocytes isolated from peripheral blood of patients with acute infections carry unique transcriptional signatures, which would in turn permit pathogen discrimination and classification. In those initial studies, gene expression patterns derived from PBMCs of pediatric patients hospitalized with acute infections showed that there are pathogen-specific signatures that can be measured in the blood, and these distinguished children with influenza A from S. aureus, Streptococcus pneumoniae, and E. coli acute infections with greater than 95% accuracy.186 Analysis of PBMC samples requires processing in real time, which has limitations from a practical clinical application if there are large numbers of patients. In addition, PBMC samples do not include neutrophils, which is a relevant cell population for the pathogenesis of bacterial and viral infections. For these reasons, in recent years, there has been a shift toward whole blood samples to study transcriptional profiles in the clinical setting. Indeed whole blood signatures for several other infections have also been described from infected subjects including malaria, dengue, salmonella, melioidosis, TB, RSV, influenzavirus (including the pandemic H1N1/09), rhinovirus, adenovirus, human T-cell lymphotropic virus (HTLV-1), HIV, and neonatal sepsis (Table 3.2).* A study performed in adult volunteers experimentally infected with RSV, rhinovirus, or influenza A identified an “acute respiratory viral signature” that was independently validated using a previously published dataset of pediatric patients with pneumonia.186 Despite the technical challenges involved in such analysis and the differences in the patient populations analyzed (children naturally infected vs. adults with experimental infection), the identified “viral signature” classified pediatric patients with influenza from age-matched healthy controls with 100% accuracy.242 This is a critical observation that confirms the reproducibility and potential value of blood transcriptome analysis to study host immune responses to respiratory viruses in the clinical setting. Additional studies will be necessary to evaluate this approach in other relevant clinical situations where the application of this methodology has the potential to transform the standard of care. In this regard, two studies have already shown the utility of host gene expression profiles as a diagnostic tool when effective treatment depends on rapid identification of the infectious agent or even the need for treatment. In the first study, also using adult volunteers experimentally infected with influenza A H1N1 or H3N2,242 the authors found a blood RNA signature that was detectable more than 24 hours before the peak of clinical symptoms.235 Subsequently, the same group of investigators used the transcriptome profiles derived from the experimental influenza signature242 to develop a targeted host-based RT-PCR low-density array assay. This assay was applied to adult patients presenting with fever to the emergency department (ED) and differentiated viral versus bacterial infections with 89% sensitivity and 94% specificity,241 demonstrating that gene expression profiles identified by microarray analyses can be successfully applied to custommade platforms with the potential for a fast, point-of-care patient diagnosis and classification. It is remarkable that although in the majority of studies patient samples were collected at different time points after pathogen exposure and disease onset, robust and pathogen-specific biosignatures have been derived and validated in independent cohorts of patients in completely different settings.

Areas for Improved Diagnosis in Pediatrics Lower Respiratory Tract Infections (LRTI)/Pneumonia Acute LRTI/community-acquired pneumonia (CAP) represent the leading cause of hospitalization in the United States and is the main cause of death worldwide in children less than 5 years of age.79,119,125,128 In industrialized countries, CAP has an annual incidence of 36 to 40 per 1000 children below the age of 5 years and 11 to 16 per 1000 in children 5 to 14 years of age.103 In the United States it is second only to injuries as the most common reason for hospitalization in children less than 18 years of age.160 In current clinical practice, establishing the precise etiologic diagnosis of pneumonia, or even simply discriminating viral from bacterial respiratory infections, remains *References 4, 15, 53, 55, 83, 87, 92, 104, 141, 170, 173, 196, 208, 219, 222, 241.

CHAPTER 3  Host Response to Infections: The “-omics” Revolution

47

TABLE 3.2  Studies of Pathogens in Various Populations Country/Study Year 186

Pathogens a

US, 2007

Virus vs. bacterial

Vietnam, 2009222

Salmonella typhi

Thailand, 2009170

Burkholderia pseudomallei

Cambodia, 201053

Dengue

UK, South Africa, 201015

Mycobacterium tuberculosis (TB)

Switzerland, 2010196

HIV

West Africa, 201292

Plasmodium falciparum

US, 201210

S. aureus (invasive)

UK, 2012173

H1N1 influenza A

US, 201294

RSV, influenza

US, Finland, 2013141

RSV, influenza, HRV

UK, 201387

H1N1/09 influenza, RSV, bacteria Virus vs. bacterialb

US, 201390 South Africa Malawi, Kenya, UK, 20144

TB ± HIV

US, Australia, 2013241

Virus vs. bacterialc

UK, Australia, 2014208

Neonatal sepsis

Scotland, Ireland, 201455

Neonatal sepsis

USA, Finland, Spain, 201683

Rhinovirus

Population

Sample Type

Cohorts/Validation

Children 13 Years Chronic pulmonary disease Clubbing Abnormal glucose tolerance Diabetes mellitus Chronic intestinal obstruction Recurrent pancreatitis Focal biliary cirrhosis Portal hypertension Gallstones Aspermia From Maclusky I, Levison H. Kendig’s disorders of the respiratory tract in children. 5th ed. Philadelphia: WB Saunders; 1990:701.

A strong association between pancreatic function and genotype has been reported for individuals homozygous for p.Phe508del.24 Most patients homozygous for p.Phe508del have pancreatic insufficiency.57 Obstruction of the pancreatic duct begins in utero, resulting in fibrosis and loss of exocrine pancreatic function. Pancreatic fluid from patients with CF is low in enzyme and bicarbonate concentrations, resulting in maldigestion of fat and protein. Clinically, children can present with steatorrhea, protein-calorie malnutrition, muscle wasting, and progressive failure to thrive. A voracious appetite is characteristic, and stools are described as bulky, greasy, and foul smelling. Approximately 10% to 15% of patients have enough preservation of pancreatic function to allow for normal digestion of food (pancreatic sufficiency).75 At least five mutations from classes 3 to 5 described earlier are associated with pancreatic sufficiency, whereas almost all patients homozygous for p.Phe508del have pancreatic insufficiency.57 Failure to thrive was a common complication observed at the time of diagnosis before newborn screening was implemented; however, this complication is now rare. If malnutrition is present and severe, hypoproteinemia and edema are observed. In addition, malabsorption can lead to vitamin deficiency, especially of fat-soluble vitamins A, D, E, and K. These problems can be reversed with pancreatic enzyme replacement therapy, oral nutritional supplements, and routine vitamin supplements. Infants diagnosed by newborn screening may have normal absorption of food for several months after birth; however, with time, pancreatic function is lost and symptoms of malabsorption develop. Glucose metabolism often becomes impaired with age, because fibrosis of the pancreas occurs in patients with exocrine pancreatic insufficiency. In the 2014 CF registry, 35% of adults were reported to have impaired glucose tolerance or CF-related diabetes with and without fasting hyperglycemia.64 Decreased secretion of insulin and reductions in peripheral glucose use and hepatic insulin sensitivity are observed in patients with impaired glucose tolerance.197 CF-related diabetes has features of type 1 and type 2 diabetes. The prevalence increases with age and is associated with increased morbidity and mortality disproportionately in women.194,196 Progressive fibrosis of the pancreas causes destruction of insulin-producing β cells within the islets of Langerhans. In addition, destruction of islet α cells impairs glucagon secretion; therefore, ketoacidosis is rare. Microvascular complications have been reported in up to 20% of patients with CF-related diabetes.6 Diabetes in CF is common and strongly affected by genetic modifiers.22 Affectedtwin studies have reported that genetic modifiers were primarily responsible for the age at onset of diabetes.56 Liver disease in CF is associated with pancreatic insufficiency.216 Approximately 25% of patients with CF develop focal biliary cirrhosis, but fewer than 5% progress to multilobar biliary cirrhosis and portal hypertension. In the absence of CFTR, bile becomes inspissated and associated with periductal inflammation and fibrosis. Liver function tests frequently are abnormal, as is a small, poorly functioning gallbladder. Cholelithiasis has been reported in 12% of patients and may be related to loss of bile acids in the stool.50,97,105 Meconium ileus, the thick inspissated meconium that mechanically obstructs the distal ileum, occurs in 8% to 20% of newborns with CF. It also is associated with pancreatic insufficiency.149 Both CFTR and modifier genes are thought to play an important role in the development of meconium ileus.19,36 A similar syndrome (distal intestinal obstructive syndrome) mimicking meconium ileus can occur in older children and young adults with CF. Complete or incomplete obstruction can occur in the terminal ileum or proximal colon. Higher rates are observed in patients with pancreatic insufficiency, positive history of meconium ileus, and previous episodes of distal intestinal syndrome.49 Absence of the vas deferens with secondary aspermia renders 98% of men with CF infertile.78 Sexual potency is normal, and with microsurgical techniques for sperm aspiration, affected men can become biologic fathers.187 Men with congenital absence of the vas deferens can have abnormal CF alleles with little clinical expression of disease other than the reproductive system. Fertility in women with CF may be decreased secondary to amenorrhea (malnutrition) and dehydrated cervical mucus.287 Pregnancy in women with mild to moderate disease appears to be well tolerated and not associated with an increased risk for death.90,115,118 The live birth rate is 1.9/100.62

CHAPTER 25  Cystic Fibrosis Pulmonary disease is the primary cause of morbidity and mortality in patients with CF.318 Expression of CFTR has been localized to the airways and submucosal glands of the lung.295 Clinical studies in young children with CF have found significant inflammatory changes in the airways in bacterial-positive and bacterial-negative patients. Large-animal models of CF suggest that infection occurs first, followed by inflammation.284 Imaging studies using high-resolution computed tomography (CT) in infants with CF describe the presence of thickened airway walls and nonhomogeneous air trapping.70,166,173 Smaller airways and tracheal ring abnormalities are noted at birth in the CF porcine model.3 Human lungs are reported to be morphologically normal at birth; within weeks, they begin showing evidence of small-airway abnormalities and inflammation. Small and medium-sized airways become obstructed, and neutrophils are the inflammatory cells primarily recovered from bronchoalveolar lavage (BAL) fluid. An intense neutrophilic response leads to the release of proteases that cause chronic injury to the respiratory epithelium and supporting airway structure. The massive numbers of neutrophils subsequently release elastase, which overwhelms the antiproteases in the airway, contributing to enhanced destruction of tissue. Large amounts of neutrophil-derived DNA and cytosol proteins are released into the airway lumen, increasing sputum viscosity and worsening airway obstruction.68 Progressive bronchiectasis develops with time, leading to advanced destruction of the airways and parenchyma (Figs. 25.2 and 25.3).100 Bronchiectatic cysts are prominent, especially in the upper lobes. Death eventually occurs from respiratory failure. Progressive deterioration of pulmonary function occurs despite the routine use of antiinflammatory therapy, mucolytics, airway clearance, and antimicrobial agents. Progressive destruction of the airway and increasing obstruction lead to air trapping, hyperinflation, hemoptysis, and spontaneous pneumothorax. Many children with CF present during infancy with recurrent wheezing or persistent bronchiolitis. Most infants are asymptomatic at birth; however, many develop tachypnea, wheezing, hypoxia, and hyperinflation after having a respiratory viral infection.129 These findings often resolve with therapy. As mucopurulent secretions increase, chronic cough develops.43 Digital clubbing occurs gradually and correlates with severity of lung disease. Cough is the earliest symptom in infants and precedes persistent sputum production, crackles, or clubbing. It is present in half the infants in a prospective study of CF infants diagnosed by newborn screening.97 Predictive risk factors included the presence of pancreatic insufficiency, infection with Pseudomonas aeruginosa, socioeconomic status, and ethnicity. On examination, evidence of crackles and decreased breath sounds secondary to mucopurulent secretions is seen. Acute exacerbations may develop, requiring intravenous antibiotic therapy and frequent hospitalization. More than a third of patients with CF in the 2014 US CF patient registry64 experienced a pulmonary exacerbation requiring intravenous antibiotics. As lung disease progresses, tolerance for exercise is reduced, dyspnea increases, and respiratory failure develops. Marked heterogeneity occurs in the rate of progression of pulmonary disease. Some patients live to the sixth decade of life, whereas others die as a result of respiratory failure before their 20th birthday. Since newborn screening was instituted, patients are being treated at an earlier age, improving the health in children. In 2014, the median predicted survival for individuals with CF was 39 years. Survival for children born in 2005 is expected to increase, with the median age approaching the fifth decade of life. In the United States, 50% of people with CF are 18 years old or older,62,64 and within 5 years, half are expected to be older than 18 years.

243

FIG. 25.2  Early stages of lung disease in cystic fibrosis are visible in this lung specimen. Airway inflammation and bronchiectasis are present. The surrounding lung parenchyma is normal.

FIG. 25.3  Late stages of pulmonary disease. Epithelial ulceration of the airway, loss of smooth muscle from the airway wall, inflammation, and bronchiectasis are present in the large airway at the top of the photomicrograph. Compression of the surrounding lung parenchyma occurs as bronchiectasis increases.

DIAGNOSIS The diagnosis of CF has changed over the past 15 years. Newborn screening for CF has been adopted by the United States, Europe, Australia, New Zealand, and many Latin American countries. The CF newborn screening program identifies patients at risk for the disease by measuring values of immunoreactive trypsinogen in dried blood spots. Trypsinogen is produced in the pancreas and is released into the serum secondary to pancreatic duct dysfunction. After an abnormal immunoreactive trypsinogen value is identified, many programs perform DNA testing to identify known CFTR mutations. Other programs repeat the

immunoreactive trypsinogen testing 2 weeks after the initial test. Both programs report 90% to 95% sensitivity and identify infants with varying disease severity.96,303 After a positive screen, infants are referred for diagnostic testing (sweat test or molecular genetic testing). For most patients, the sweat test remains the best diagnostic test to establish the diagnosis of CF. If the sweat test results are in the intermediate range, then DNA analysis may help in the diagnosis. The clinical significance of all 2000 CF mutations is unknown. Many are sequence variants

244

SECTION 2  Lower Respiratory Tract Infections

without known clinical disease. Others are known to cause loss of CFTR function and are associated with clinical abnormalities in one or more organ systems. Sequence analysis of the exons, introns, and promoter regions and detection of deletions and duplications identifies 98% of CFTR mutations.285 Infants are generally asymptomatic at the time of diagnosis, although some may be underweight. Data from the 2014 US CF registry reported that newborn screening accounted for more than 60% of newly diagnosed patients.61,64 In the absence of newborn screening, an in utero diagnosis, or a family history of CF, a strong clinical suspicion is required for early recognition. Most children present with a history of recurrent lower respiratory tract disease and symptoms secondary to malabsorption. Approximately 15% to 20% of children have meconium ileus at birth, a family history of CF, or both. A consensus panel convened by the US Cystic Fibrosis panel recommended a combination of phenotypic features, family history of CF, or positive newborn screen and one or more laboratory tests to diagnose CF.95,246 A new CF consensus panel was convened in 2015, but results have not been published. Laboratory tests include identification of known CF mutations, abnormal bioelectric transepithelial membrane properties, and elevated concentrations of sweat chloride. The World Health Organization adopted similar recommendations.319 The quantitative pilocarpine iontophoresis sweat test is the primary test to establish a diagnosis of CF.246 A sweat chloride concentration greater than 60 mEq/L is consistent with a diagnosis of CF. Values between 40 and 60 mEq/L are considered borderline, and values less than 40 mEq/L are normal. Infants with a positive newborn screen and sweat chloride values between 30 and 59 mEq/L under 6 months of age are considered to have values in the intermediate range. Molecular genetic testing should be pursued in those infants with indeterminate sweat chloride values. In the presence of two CF-causing mutations, a diagnosis of CF can be made. Infants with intermediate sweat test values and one CF-causing mutation cannot be diagnosed definitively with CF and will need to be followed longitudinally. Infants with an elevated immunoreactive trypsinogen level and inconclusive CFTR functional and genetic testing should be designated CFTR-related metabolic syndrome (United States) or CF Screen Positive, Inconclusive Diagnosis (Europe). If the sweat test is positive, it should be repeated on two separate occasions. Identification of two CF mutations by genotype is highly specific but less sensitive and should be confirmed with a sweat test. Mutational analysis can be done by several different techniques, with commercial laboratories testing for the most common 30 to 87 mutations. These laboratories identify approximately 90% of CF mutations but leave more than 1000 mutations unidentified. Extensive screening for the remaining 10% of mutations is expensive. For rare mutations, gene sequencing is available.245,246 The mutational classifications in the CFTR2 project (http://www.cftr2.org/index.php) should be used to help with diagnosis. The p.Phe508del mutation is found in 89% of patients with CF in the United States and a similar number of CF patients in the United Kingdom. Because each patient has two chromosomes, however, only 50% of patients are homozygous for p.Phe508del. Nasal potential difference measurements assess the transepithelial electric potential difference that exists across nasal epithelium. Different patterns of potential difference are found in patients with CF.318 Abnormalities in chloride transport and sodium absorption alter the transepithelial electric potential difference in CF in contrast to normal epithelia. The test can be useful in individuals with mild or atypical phenotypic features of CF, but it is not readily available and requires experienced personnel to perform.245,246 Newborn screening programs are associated with long-term benefits in children with CF diagnosed shortly after birth. Improved nutritional status as a result of newborn screening has been reported in a controlled, randomized trial in Wisconsin96 as well as in countries other than the United States.259 A total of 90% of screened infants in the Wisconsin study diagnosed with CF at birth maintained their weight greater than the 10th percentile in contrast to only 60% of unscreened controls. Children in the screened group were less likely to fall below the 10th percentile for weight and height from early childhood through 16 years of age.30,96 In addition, cognitive function improved significantly in the screened group.157,160 No long-term improvements in pulmonary status

were observed in the Wisconsin study; however, several observational studies have reported improved pulmonary outcomes, less colonization with P. aeruginosa, decreased hospitalization for complications, and improved nutrition in children diagnosed by newborn screening. In addition to improving nutritional outcomes, newborn screening may result in improved survival rates for children. A systematic literature review of mortality in children with CF reported a survival benefit for patients diagnosed by newborn screening.55,123 A survival effect also was shown in a study from Wales.81 Without screening, approximately 60% of patients are diagnosed by the time they reach 1 year of age and almost 90% by the time they are 5 years old. Early diagnosis through neonatal screening improves nutritional outcome, with increasing evidence that these programs are associated with improved pulmonary outcomes and improved long-term survival. The diagnosis of CF should be based on the presence of one or more clinical features (Box 25.2), a positive newborn screening test, and laboratory evidence of abnormal CFTR function. Laboratory tests include elevated sweat chloride concentration, two identifiable CF mutations, or abnormal in vivo nasal potential difference measurements made across the nasal epithelium.

PATHOGENESIS The CFTR protein is a cyclic adenosine monophosphate–regulated chloride channel that resides primarily in the apical membranes of epithelial cells. CFTR is highly expressed in airways; its loss of function leads to defective secretion of chloride and bicarbonate and subsequent dehydrated and acidic airway secretions.32 Sweat glands, pancreas, liver, intestinal tract, and reproductive organs are among the other organ systems affected by dysfunctional CFTR. In affected organs, the abnormal chloride and fluid secretion impairs fluid movement and leads to ductular obstruction and organ damage. Mucociliary clearance is impeded, and a destructive cycle of inflammation and chronic infection in the airways results. Chronic inflammation and resultant lung damage in CF results from failure of the innate immune system to protect the airways from invading pathogens. The complex process of CFTR dysfunction leading to inflammation in the airways is still not fully understood. In the CF lung, decreased volume of airway surface liquid (ASL) impairs mucociliary clearance (MCC), which is the body’s primary defense against inhaled particulate matter and various microbial pathogens. The ASL is composed of a gel and sol layer that function together to help trap microbial pathogens to be propelled up and out of the lungs by beating cilia. The sol or periciliary liquid layer consists of low-viscosity fluid to hydrate mucins and allows ciliary movement to occur. The periciliary liquid layer is thin, 7 µm in height, bathes the cilia, and allows them to beat freely. The gel or mucous layer floats on top of the sol and is composed of high-molecular-weight mucins with carbohydrate side chains that bind inhaled particulate matter and pathogens. The ASL and mucus layer is a dynamic structure that changes in response to the environment and host. ASL volume is regulated by the

BOX 25.2  Diagnosis of Cystic Fibrosis ≥1 Phenotypic Features Chronic sinopulmonary disease Gastrointestinal and nutritional abnormalities Salt loss syndromes: acute salt depletion Chronic metabolic alkalosis Male urogenital abnormalities resulting in obstructive azoospermia Plus Laboratory Evidence of CFTR Abnormality (≥1) Elevated sweat chloride concentrations Identification of two CFTR mutations In vivo evidence of abnormal ion transport across nasal epithelium CFTR, Cystic fibrosis transmembrane conductance regulator.

CHAPTER 25  Cystic Fibrosis respiratory epithelium through ion transport processes by CFTR. Salt concentrations can be changed to regulate the hydration of the airway lining fluid to maintain optimal mucociliary function. The absence of CFTR in the apical cellular membrane decreases the ability of cells to secrete chloride into the periciliary fluid. CFTR inhibits the epithelial sodium channel; in its absence, excessive absorption of sodium occurs. Other channels are available for secretion of chloride (i.e., calciumactivated chloride channel) in the respiratory epithelium; however, they cannot compensate for the loss of CFTR. The net effect is increased absorption of sodium, chloride, and water, which reduces the periciliary volume, alters the composition of mucins, and decreases mucociliary clearance. The reduction in the periciliary fluid impairs ciliary movement, as they are weighed down by the heavy gel layer and mucus cannot be transported and cleared. This initiates the cycle of airway obstruction, chronic infection, inflammation, and progressive lung destruction. Altered chloride channel function and fluid secretion also help to explain the presence of disease in the sweat gland, intestine, pancreas, and male genital tract. The epithelial cells affected by CFTR mutations in various organs represent different channel and regulatory activities of CFTR but result in deficient secretion of fluids. This deficiency causes accumulation of mucus, obstruction, and various degrees of organ damage. Plugging of pancreatic ducts leads to chronic fibrosis, pancreatic atrophy, and loss of digestive enzymes and islet cells. Similar obstruction in the biliary tract can cause inflammation and focal biliary cirrhosis. Glandular obstruction of the vas deferens causes involution of the Wolffian duct and infertility in more than 95% of men with CF. Women with CF produce abnormally tenacious cervical mucus, with reported rates of infertility of 20%. Human cell culture models of normal and CF epithelia have shown that the airway surface liquid is decreased in CF186,293; this remains the primary hypothesis of the impaired MCC in the disease.25,156,240 Work with large-animal models of CF has revealed that there is likely a more complex pathology for early defects in MCC. CF piglets showed abnormal MCC not due to periciliary liquid depletion but rather due to abnormal CF submucosal gland secretion. Even when periciliary fluid volume was replaced, abnormal mucins remained tethered to glandular ducts, thus preventing normal upward movement on the mucociliary ladder.131,312 Submucosal glands have high expression of CFTR.94,120 Loss of CFTR function alters the composition of mucins produced by the submucosal glands,146,151,307 leading to ductular dilation with mucus and obstruction. Mucus is tightly adhered to the respiratory epithelium and prevents normal flow of the mucociliary elevator. Failure to clear mucous plugs, continued mucin secretion, and abnormal adherent mucus to the airway surface provides the focus for infection. Pili extending from the surface of the bacterium are able to bind to mucin.272 In CF, dysfunctional bicarbonate secretion also results in ASL that is 8-fold more acidic than that of individuals without CF. This low pH can inactivate ASL and mucus antimicrobial peptides.32 Obstruction of small terminal airways and submucosal glands with thickened mucopurulent secretions are often the first signs of early disease in infants with CF. Ductular dilation, neutrophil infiltration, glandular hyperplasia, and peribronchiolar inflammation are classic findings of the disease. Thick mucus adherent to epithelial cell surface is seen in the lungs of even newborn CF pigs.285 A recent study showed that CFTR activity of bicarbonate transfer is greater in small-airway epithelial cells compared with larger airways and the effect of nonfunctioning CFTR in small airways leads to more acidic, viscous ASL with impaired bacterial killing. This may help explain the vulnerability of the small airways to bacterial infection and disease.166 Air trapping is found in infants with CF as young as a few months old even when clinically asymptomatic.273 Also, piglets with CF have been shown to have air trapping prior to the onset of infection and inflammation in the airways. These piglets were found to have a smaller trachea and proximal airways compared with non-CF piglets. These data suggest that working CFTR is necessary for normal development of early airways.3 Early and exaggerated inflammation occurs in the CF airways that begins in infancy and may precede bacterial infection.273 In CF lung disease, various immune cells migrate to the airways, contributing to the chronic unrelenting inflammation. Neutrophils predominate to fight

245

bacterial and fungal pathogens, but the activation of these cells can lead to tissue destruction through oxidant and protease release. The serine proteases released have been shown to predict the development of bronchiectasis in CF.282 Neutrophil elastase mediates killing of P. aeruginosa by degrading its outer membrane protein but also breaks down structural airway matrix proteins, cleaves proteins important for host defense, and increases mucus secretion.32,293,297 Neutrophil elastase has a clear role in the development of bronchiectasis and tissue destruction in progressive CF lung disease. Other proteases, such as cathepsins (found to be increased in BAL samples of infants and children with CF) and matrix metalloproteinases, may play a role in early CF disease. Calgranulins are proinflammatory proteins that are also increased in CF sputum and have been shown to activate key processes of CF lung inflammation.121,181 The inflammatory response in CF involves different immune pathways. Neutrophils, macrophages, TLR4-dependent responses, and T lymphocytes have all been shown to have defective functioning associated with CFTR deficiency. Lipid abnormalities, such as an accumulation of epithelial ceramide, have been suggested in CF to increase cell death, increase bacterial binding to extracellular DNA, and release inflammatory chemokines. Other investigators highlight the importance of ceramides in lipid rafts needed to clear infection. CF cell membranes are also reported to have increased arachidonic acid compared to docosahexaenoic acid. Docosahexaenoic acid has important antiinflammatory properties.121,181 Chronic infection, with retention of the by-products of inflammation, ultimately leads to the severe bronchiectatic changes and derangements of gas exchange characteristic of end-stage CF. A hypoxic environment develops within the thickened mucous plugs that form in the airways, which may hinder host defenses and favor bacterial growth and inflammation. Pseudomonas aeruginosa, after binding to mucin, is able to penetrate the thickened mucus and grow in an anaerobic environment. P. aeruginosa is able to grow in anaerobic conditions because of the production of nitrate reductase, which allows it to cleave oxygen from nitrate (Fig. 25.4).270,323 When it is in the anaerobic environment, an alginate polysaccharide is formed. Biofilm-containing macrocolonies of P. aeruginosa are then established. The established macrocolonies remain within the airway lumen. These macrocolonies are very resistant to antibiotics and host defense and allow chronic infection, inflammation, and airway destruction to occur.134,221,323 Several in vivo studies have assessed the location of bacterial adherence within the lung of CF patients and the attachment of bacteria to CF and non-CF cells in vitro.17,302 P. aeruginosa is found within the lumen of airways of patients with CF obtained from autopsy specimens.17 These organisms are observed within the inflammatory exudates of the airway and not within epithelial cells lining the lung or in alveolar spaces. In vitro studies have shown adherence of P. aeruginosa in areas of epithelial cell destruction.223,228,302 No adherence to the apical membrane of intact epithelial cells has been noted, however. In contrast, evidence in cell culture models indicates that defects in CFTR enhance bacterial binding to immortalized airway epithelial cells.254 A tetrasaccharide (asialo GM1) is expressed more on CF than on non-CF cells and promotes P. aeruginosa binding to the epithelial membrane. Pseudomonal exoproducts, such as neuraminidase, increase the amount of asialo GM1 available for bacterial binding and facilitate bacterial adherence to airway epithelial cells.29,255,259 CFTR itself can act as a receptor for P. aeruginosa and initiate an effective innate immune response in the initial stages of infection to clear Pseudomonas from the airway.31 CFTR binding to P. aeruginosa induces release of IL-1β, nuclear translocation of nuclear factor-κB (NF-κB), and neutrophil influx. Endocytosis of Pseudomonas by the epithelial cells and subsequent clearance of infected epithelial cells by desquamation has been reported.224,226 In the absence of CFTR, clearance of infection with P. aeruginosa is impaired. Mucins also are important in binding bacteria within the airway. Sialylated and neutral forms of mucins bind P. aeruginosa.235 Removal of sialylic acid from mucin by neuraminidase reduces adherence of P. aeruginosa. Mucus dehydration can lead to increased concentration of mucins, decreased pH, and a reduction in glutathione, which decreases mucus viscoelasticity.249 Decreased bicarbonate secretion results in mucin cross-linking by calcium.99 Polymeric macromolecules within the gel

246

SECTION 2  Lower Respiratory Tract Infections

FIG. 25.4  Schematic model of the pathogenic events hypothesized to lead to chronic Pseudomonas aeruginosa infection in airways of patients with cystic fibrosis (CF). (A) On normal airway epithelia (NL), a thin mucous layer (light gray) resides atop the periciliary liquid (PCL; clear). The presence of the low-viscosity PCL facilitates efficient mucociliary clearance (vector). A normal rate of epithelial oxygen (O2) consumption ( QO2 ; left) produces no O2 gradients within this thin airway surface liquid (ASL). (B–F) CF airway epithelia. (B) Excessive CF volume depletion (vertical arrows) removes the PCL, mucus becomes adherent to epithelial surfaces, and mucus transport slows or stops (bidirectional vector). The increased O2 consumption (left) associated with accelerated CF ion transport does not generate gradients in thin films of ASL. (C) Persistent mucus hypersecretion (denoted as mucus secretory gland/goblet cell units; dark gray) with time increases the height of luminal mucus masses and plugs. The increased CF epithelial QO2 generates steep hypoxic gradients in thickened mucus masses. (D) P. aeruginosa bacteria deposited on mucus surfaces penetrate actively or passively or both (as a result of mucus turbulence) into hypoxic zones within the mucus masses. (E) P. aeruginosa adapts to hypoxic niches within mucus masses with increased alginate formation and the creation of macrocolonies. (F) Macrocolonies resist secondary defenses, including neutrophils, setting the stage for chronic infection. The presence of increased macrocolony density and, to a lesser extent, neutrophils renders the now mucopurulent mass hypoxic. (From Worlitzsch D, Tarran R, Ulrich M, et al. Effects of reduced mucus oxygen concentration in airway Pseudomonas infections of cystic fibrosis patients. J Clin Invest. 2002;109:317–25.)

NL 60 µm/s PO2 QO2 = NL

A CF 0 µm/s

PO2 QO2 =

B

Na+

CI−

H2O

PO2

matrix reduce pore size from 500 to 150 nm, immobilizing bacteria within the mucus and inhibiting neutrophil migration and clearance.52 The concentrated mucus impairs neutrophil migration, promotes an anaerobic environment, and reduces mucociliary transport. Mucin, a component of mucus, is decreased in CF; its decreased content may promote development of infection.252 The balance between oxidants and antioxidants is known as redox balance. Imbalance can lead to acute or long-term oxidative or reductive stress. Chronic redox imbalance favoring an oxidative environment is hypothesized to contribute to the disease state in CF.329 Increased oxidant production by neutrophils has been proposed as a mechanism of airway injury in CF. Evidence of the effects of oxidative damage in airway epithelial cells and extracellular fluids can be seen in the peroxidation of lipids and modifications of proteins.153 Markers of reactive oxygen species increase during acute pulmonary exacerbations and improve with treatment but do not normalize.192,295 An intracellular imbalance in oxidant metabolism has been proposed for airway epithelial cells in CF.267 ASL in CF is characterized by lower levels of glutathione (GSH) and nitric oxide.17 Mucins, reduced glutathione, α-tocopherol, and metal-binding proteins function in the airway as antioxidants. The cysteine residues and carbohydrates of mucin account for its antioxidant properties.58 Secretion of mucins is increased with oxidative stress; however, dehydration of mucins may impair its ability to scavenge reactive oxidative metabolites. Glutathione is important in regulating inflammation related to oxidative stress. GSH is reduced in ASL either from increased consumption or secondary to CFTR dysfunction.172 GSH is found in large amounts in airway lung fluid from normal patients33; however, it is reduced in patients with CF.288 CFTR may alter glutathione transport, impairing defense to oxidant injury. High-throughput metabolomic analyses of human primary airway epithelia measured decreases in GSH, glutathione disulfide, and a metabolite of S-nitroglutathione in CF versus non-CF cells. Also, the GSH/glutathione disulfide ratio was diminished in CF cells, suggesting oxidative stress.313,329 Reduced intracellular concentrations of GSH affect hydrogen peroxide content of airway cells and increase NF-κB production, contributing to airway inflammation. GSH acts to scavenge free radicals in epithelial lining. GSH is also important in the immune response with chemotaxis, phagocytosis, and oxidative burst. Impaired absorption of antioxidants

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CHAPTER 25  Cystic Fibrosis from the gut in CF may contribute as well. Thus, increased production of reactive oxygen species from neutrophils and impaired antioxidant biosynthesis associated with mutant CFTR create an environment within the airway for excessive inflammation and cellular injury.329 There are repeated descriptions of abnormalities in oxidants and antioxidants in CF plasma, cells, and ASL. However, several studies failed to show significant clinical benefit of antioxidant therapies in CF.121,329 Further studies using omics technology may help us to better understand redox in CF and potential therapies. Production of cell adherence molecules and inflammatory cytokines is intact in patients with CF.80,150 Defects in bacterial opsonization, reduction in antiinflammatory cytokines, and proinflammatory effects of bacterial DNA have been reported. Impaired phagolysosomal function and decreased respiratory burst have been found in neutrophils in CF with upregulation of Toll-like receptor 4 (TLR4) and downregulation in TLR2. These abnormalities would be expected to reduce the ability of neutrophils to clear bacteria.18,199 Inflammation and infection can increase intracellular Ca2+ and affect the immune response mediated by airway epithelial cells and T-helper cells. Increased intracellular Ca2+ in CF mice helper T-cells affect gene expression and favor a Th2 differentiation rather than the Th1 needed for bacterial clearance.203 Altered T-helper lymphocytes impair macrophage activation for bacterial killing. Humoral antibody responses are normal; however, increased elastase in the CF airway can alter opsonic receptors, impairing phagocytosis. Large amounts of elastase are present in lavage fluid from airways of patients with CF, overwhelming the normal antiprotease activity. This condition can lead to local impairment in phagocytosis of bacteria within the airway lumen, contributing to bacterial persistence. Proinflammatory mediators are elevated in BAL fluid from young patients with CF, as are macrophages expressing intracellular cytokines.148,204,325 Increased numbers of neutrophils and interleukin 8 (IL-8) in BAL fluid are seen in bacterial culture–negative and bacterial culture– positive infants with CF in contrast to controls.136,314 Proinflammatory mediators IL-1, IL-2, tumor necrosis factor-α, and IL-8 are markedly elevated in children with advanced disease.128,136,314 In contrast, some antiinflammatory cytokines (e.g., IL-10) are found in reduced amounts in BAL from patients with CF. These observations have prompted some investigators to assess production of IL-10 from bronchial epithelial cells in normal subjects and subjects with CF.23 Bronchial epithelial cells from normal individuals produce significantly greater amounts of IL-10 than cells of subjects with CF. NF-κB is a transcription factor for several proinflammatory mediators and is activated persistently in CF. Inhibitors to NF-κB, including IL-10, are downregulated.76,265,304,311 Enhanced intracellular Ca2+ signaling in response to infection and inflammation in both airway epithelial and immunomodular cells may account for the hyperinflammatory response noted in CF.237,239 Both phases of Ca2+ release, either by Ca2+ influx or endoplasmic reticulum release, can upregulate NF-κB and production of proinflammatory cytokines. Chronic airway inflammation and infection increase endoplasmic reticulum Ca2+ stores, enhancing the inflammatory response. Therefore, the CF gene defect may result in an inability to control airway inflammation after exposure to repeated infections, altering the innate and immune responses to specific pathogens. Although the understanding of this disease pathogenesis is incomplete, airway damage that occurs from excessive inflammation and chronic infection remains a target for new therapeutic modalities. The range of severity of disease is related to the production of functioning CFTR. Patients with at least one “mild” mutation in CFTR have some low level of CFTR expression. They retain some degree of pancreatic function, have less severe lung disease, and have sweat chloride concentrations that are borderline normal.55,70,318 Male patients with congenital bilateral absence of the vas deferens are pancreatic sufficient, exhibit little or no lung disease, can have normal sweat chloride concentrations, and are thought to have CFTR expression that is 10% of normal.13 Carriers for CFTR who are heterozygotes expressing half the expected amount of CFTR are at increased risk for developing pancreatitis, allergic bronchopulmonary aspergillosis (ABPA), and sinusitis.40,45,84,229 As we begin to see the clinical effects of pharmacologic therapies that correct and potentiate CFTR function, we are learning more about the direct effect of CFTR on the symptoms of CF. The

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potentiator ivacaftor has been able to show that improvement in CFTR function, evidenced by dramatic improvement in sweat chloride tests, leads to improvement in multiple clinical factors. Lung function assessed by forced expiratory volume in 1 second and MCC improved and rates of P. aeruginosa infection dropped by 18% in 6 months after initiation of the drug in one study.74,217,248 Variation in phenotype also exists in individuals with the same genotype, indicating that other factors—including modifier genes and epigenetic and environmental factors—influence the disease process.28

SPECIFIC CYSTIC FIBROSIS PATHOGENS Viral Pathogens Numerous studies have evaluated the role of nonbacterial infections with pulmonary exacerbations in CF. A clear correlation between respiratory viral infection and exacerbations of lung disease has been shown in most of these reports. Viral lower respiratory tract infections occur more often in younger children with CF and are associated with increased pulmonary disease in 40% of cases.1,298 Respiratory syncytial virus (RSV) has been identified most often with CF pulmonary exacerbations; however, influenza, adenovirus, parainfluenza virus, rhinovirus, picornavirus, and human metapneumovirus also have been reported.298 Respiratory viruses are isolated from patients with CF requiring hospitalization, and infection is associated with increased morbidity rates. Infants with CF infected with RSV can experience prolonged hospitalizations, mechanical ventilation, and supplemental oxygen at hospital discharge.1 Severe viral infections in infants with CF were reported in 31 of 80 children diagnosed by newborn screening. Half of the children hospitalized had a respiratory virus identified at the time of hospitalization, and RSV infection accounted for hospitalization in 7 of the 31 children.8 Two studies have reported prolonged bronchiolitis-like syndromes in infants younger than 6 months of age.106,170 These infants required intensive respiratory therapy, including bronchodilators, chest physiotherapy, and mechanical ventilation. Increased hospitalization was observed for children with CF who were infected with RSV in another study of children younger than 3 years of age.128 Although prolonged hypoxia and respiratory failure were not observed, pulmonary function was markedly decreased after hospitalization and persisted for several months after infection.128 Studies in older children with CF have reported reduction in pulmonary function, clinical scores, and radiographic scores and increased hospitalization after viral infection.47,211,277,308,315 These studies show that infection with respiratory viruses results in clinical deterioration, hospitalization, and decreases in lung function. Mechanisms to explain the enhanced disease observed with respiratory viral infections are being investigated. Normal airway epithelia use an adenosine-regulated pathway to maintain periciliary fluid volume by regulation of sodium absorption and chloride secretion. In a CF model, this regulation can be normalized by phasic motion simulating movement of the lung. Periciliary volume is restored to normal by release of adenosine triphosphate into the periciliary liquid and activation of alternative chloride channels. Viral infections, such as RSV, upregulate the extracellular adenosine triphosphatase activity, reducing periciliary fluid volume. Reduction in periciliary liquid volume promotes mucous stasis and plugging.293 Other investigators have shown impaired innate defense manifested by reduced production of nitric oxide and impaired interferon-γ signaling pathway.326,327 Synergism between bacteria and respiratory virus infection was suggested by Przyklenk and coworkers227 after an increase in the number of bacterial colony-forming units was found in sputum of subjects with CF. Hordvik and associates133 and Efthimiou and coworkers86 noted that patients with CF and severe pulmonary disease recovered slowly from viral infection. The underlying severity of lung disease was crucial in predicting response to viral respiratory infection. The interrelationship between the acquisition of P. aeruginosa and viral respiratory infection is unclear. Increased colonization with P. aeruginosa has been observed during the respiratory viral season,141 and infection with P. aeruginosa has been associated with hospitalization for viral respiratory illness. Antipseudomonal antibodies have been reported to increase after RSV infection, and new infection with

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P. aeruginosa has been observed during an acute respiratory illness.47,220 Other investigators have not observed any change in bacterial infection or change in colonization associated with viral respiratory infection.210 In cell culture models, RSV acts as a coupling agent between P. aeruginosa and enhances attachment to respiratory epithelial cells.299 Petersen and colleagues220 and Ong and associates211 reported more severe pulmonary disease with viral infection in the presence of P. aeruginosa colonization, but Przyklenk and coworkers227 found no correlation. Nontypeable Haemophilus influenzae Haemophilus influenzae is frequently the earliest pathogen isolated from patients with CF, most prevalent in the CF population during the first 5 years of life. The advent of the H. influenzae type b vaccine has not had an impact on the prevalence of this organism because patients with CF harbor nontypeable strains. Generally, H. influenzae is susceptible to a wide variety of agents and is amenable to treatment. However, recent studies suggest that more than 20% of young patients with CF are infected with H. influenzae, with some antibiotic resistance detected in current strains.34 Despite the frequent recovery of this organism from infants and children, the impact of this organism on the clinical course of CF has been difficult to assess because of the frequent occurrence of coinfection with other pathogens. Staphylococcus aureus Staphylococcus aureus is the bacterium cultured most commonly from the respiratory tracts of children with CF; the earliest descriptions of CF lung infections focused on this species.74 Subsequently, P. aeruginosa was increasingly isolated from children with CF, and studies established an association between P. aeruginosa and CF lung disease,89,159 largely shifting the focus of CF microbiologic research and therapy. Recently, increases in S. aureus prevalence, both methicillin-susceptible (MSSA) and methicillin-resistant (MRSA), have been described in CF. Data from the Cystic Fibrosis Patient Registry shows that the overall prevalence of MSSA increased from 37% in 1995 to 54% in 2015.62 Similarly, MRSA prevalence increased from 0.1% in 1995 to 26% in 2015, although it varied substantially from center to center (range per center, 5–48%). Causes for this variability are unclear but could reflect different laboratory practices and clinical practices or regional differences in communityacquired MRSA. Although MRSA generally infects older patients, it is associated with deterioration in both pediatric and adult patients.193,294 Methicillin resistance is conferred by the mecA gene located within the staphylococcal cassette chromosome (SCC). Several SCCmec types have been described and may also carry the putative virulence factor PantonValentine leukocidin (PVL), which is commonly detected in the USA300 epidemic strain in the United States. A six-center observational study in the United States (STARCF) examined the clinical impact of different MRSA strains characterized by molecular typing. Of the over 200 isolates obtained from pediatric patients with chronic MRSA infection, 69.5% were SCCmec II- PVL negative, consistent with hospital associated-MRSA. The remaining isolates were 13% SCCmec IV-PVL negative and 17% SCCmec IV-PVL positive. Ongoing studies are evaluating chronic MRSA infection in CF with different SCCmec types and PVL status to determine their roles in clinical and disease outcomes.68,87,127,144,202 Recent studies of children with CF noted similar inflammation and lung function decline during infection with S. aureus compared with P. aeruginosa, and the pathologic consequences of MRSA infection in patients with CF have been recently determined. Chronic MRSA infection in patients with CF is associated with increased rate of lung function decline, failure to recover lung function after a pulmonary exacerbation, and decreased survival. These observations have led to a reexamination of S. aureus and its role in CF lung disease.65,66,225,236,250,258 Slow-growing, antibiotic-resistant mutants of S. aureus known as small-colony variants (SCVs) have been isolated from respiratory secretions in both adults and children with CF with specific but infrequently used culture techniques. Distinction of SCVs is based on colony size on the agar plate, slower growth, nonpigmentation, reduced production of alpha-toxin, and thymidine dependence. There is evidence that exoproducts of P. aeruginosa enhance SCV formation; conversely, SCV growth provides a survival advantage for S. aureus in the presence of P. aeruginosa infection.130 Clinically, SCVs are associated with higher

rates of antimicrobial resistance and more advanced lung disease in CF.114 The rarity of clinical laboratory culture for SCVs indicates that physicians are frequently unaware of these highly antibiotic-resistant infections in selecting treatments for their CF patients, underestimating the presence both of all S. aureus and of a subtype that correlates with worse respiratory disease. Therefore, routine S. aureus SCV surveillance would provide more complete information to guide treatment.316 Pseudomonas aeruginosa P. aeruginosa is the most common and important pathogen in patients with CF. Initial strains are nonmucoid, antibiotic-susceptible strains that express pili, flagella, and a more highly acylated lipid A component of lipopolysaccharide. P. aeruginosa also produces virulence factors, including exotoxin A, exoenzyme S, leukocidin, phospholipase C, elastase, and alkaline protease, which contribute to the pathogenesis of sepsis, acute lung infections, and bacteremia.35,279,292 These factors may be chemotactic stimuli for neutrophils, and exotoxins may increase the viscosity of secretions, impair ciliary clearance, and cause small airway obstruction, thus ultimately lung destruction. Over time, P. aeruginosa adapts to the CF lung and undergoes genetic and phenotypic alterations. P. aeruginosa initially attaches to solid surfaces (e.g., mucin or respiratory epithelial cells), using flagella and type IV pili.53 Attachment activates genes that synthesize extracellular polysaccharide (alginate),73 which confers the mucoid phenotype of P. aeruginosa unique to chronic infections in CF.117 Strains associated with chronic infections lack pili, lack flagella, and undergo structural changes in lipopolysaccharide. These changes may render P. aeruginosa more resistant to host defenses, including defensins and the innate inflammatory response. The lasR-lasI system (quorum-sensing genes) promotes the initial formation of microcolonies, which differentiate into alginateencased mature biofilms.53 Bacteria in biofilms avoid ciliary clearance, evade phagocytosis, and are antibiotic resistant.271 Biofilms are the proposed mechanism by which P. aeruginosa is able to infect the CF airway chronically and avoid eradication by host defenses and by antimicrobial agents. The CF lung can harbor very high concentrations of P. aeruginosa—108 to 109 organisms per gram of sputum may be present.317 In 2015, the CF Registry reported that 30.4% of patients with CF younger than 18 years of age were infected with P. aeruginosa.61 Infection with P. aeruginosa is associated with increased morbidity and mortality rates caused by recurrent pulmonary exacerbations and a gradual deterioration in lung function.147,214 Children who are infected with P. aeruginosa are more likely to have cough and lower chest radiograph scores than are uninfected children. Investigators have shown that infants younger than 2 years of age infected with S. aureus and P. aeruginosa have worse pulmonary function, chest radiograph scores, and 10-year survival rates than do uninfected children.2,89,159,244 In a recent large, multicenter cohort of US children with CF, there was no detectable association between early acquisition of P. aeruginosa and more rapid decline in lung function or change in growth parameters. P. aeruginosa detection/acquisition was associated with an increased rate of pulmonary exacerbations, more frequent detection of crackles or wheeze on examination and increased emergence of MRSA, S. maltophilia and Achromobacter xylosoxidans on respiratory cultures.324 The mucoid phenotype of P. aeruginosa is associated with a more rapid decline in lung function.215 Multidrug-resistant P. aeruginosa (MRPA) was identified in 8.6% of all patients with CF in 2014.61 MRPA isolates are defined as resistant to all antibiotics evaluated in two or more of the following groups: aminoglycosides, fluoroquinolones, and β-lactams.163 Infection with MRPA as opposed to P. aeruginosa has been shown to cause more rapid decline in pulmonary function220 and increase in the likelihood of death or lung transplantation.164 Additional studies have linked poor patient prognosis to a specific MRPA strain, as in the cases of the Liverpool epidemic strain and the Australian epidemic strains.4,85,208,209 Burkholderia cepacia Complex Infection with Burkholderia cepacia complex (Bcc) and the associated cepacia syndrome was reported first in 1979 among adolescent Canadian patients with CF.138,290 The cepacia syndrome is characterized by a virulent

CHAPTER 25  Cystic Fibrosis course, high fevers, bacteremia, rapid deterioration in lung function, and early death. Generally, patients with CF do not have bacteremia caused by other pathogens. Different clinical courses can be associated with Bcc, including transient colonization, a gradual decline in lung function, or the virulent cepacia syndrome. Through a series of genetic and phenotypic studies, researchers have discovered that B. cepacia is actually a complex of several different species, previously called genomovars, which are indistinguishable phenotypically but distinguishable genotypically.44 Additional genomovars are likely to be described.44,300,301,305 Several international investigators have described the epidemiology and clinical courses associated with different genomovars, although these studies usually involved a single strain and might not be generalizable to all strains of a given genomovar.167,177,281 Most CF isolates are Burkholderia cenocepacia (genomovar III) or Burkholderia multivorans (genomovar II). The former may be associated with a more rapidly progressive clinical course,169 whereas B. multivorans is more likely to be associated with transient colonization.177 However, patient-to-patient transmission and clinical deterioration has been associated with B. multivorans.167 An outbreak of Burkholderia dolosa (genomovar VI) associated with increased morbidity and mortality rates in the patients following acquisition of this bacterium has also been reported.145 Virulence factors for Burkholderia spp. include multidrug resistance, the ability to form biofilms, the ability to reside intracellularly, and the ability to spread from patient to patient.177 Studies are ongoing to unravel potential environmental reservoirs of Burkholderia spp. Stenotrophomonas maltophilia Stenotrophomonas maltophilia, an intrinsically multidrug-resistant, gram-negative bacillus, is a well-known hospital-acquired pathogen in non-CF patients and is isolated with increasing frequency from the respiratory tract of patients with CF. The overall prevalence of this organism in patients with CF is 13.5% (range 0–40% in individual centers).61,71 There is evidence that many clinical laboratories fail to identify this potential pathogen. Transient colonization also seems to be a common occurrence; Demko and colleagues71 reported that 50% of patients with CF at their center had only a single positive culture for this microorganism. Increased use of antibiotics has been shown to be a potential risk factor for acquisition of S. maltophilia,180,291 and the role of S. maltophilia as a pathogen in CF is still being investigated. Case-control studies have shown that S. maltophilia has not had a significant impact on lung function or mortality.114,180 In contrast, Demko and colleagues71 found that the 5-year survival of patients with S. maltophilia (n = 211) was 40% in contrast to patients without S. maltophilia (n = 471), whose 5-year survival was 70%. Achromobacter xylosoxidans The clinical significance of A. xylosoxidans in CF also is unclear; this organism was reported to the CF patient registry in 1996 when 2.7% of patients harbored this multidrug-resistant, gram-negative bacillus.60 In 2014, A. xylosoxidans was found in 6.1% of patients.61 The nationally reported prevalence most likely is underestimated; 8.7% of participants in the aerosolized tobramycin trial had positive cultures for A. xylosoxidans.27 Further complicating the epidemiology of this potentially emerging pathogen is the observation that A. xylosoxidans may be misidentified as another nonlactose-fermenting, gram-negative bacillus, and that P. aeruginosa, B. cepacia complex, and S. maltophilia may be misidentified as A. xylosoxidans.253 In addition, the impact of this organism is difficult to assess fully because A. xylosoxidans generally is cultured from patients concomitantly infected with other CF pathogens, especially P. aeruginosa.162 A. xylosoxidans is associated with an increase in pulmonary exacerbations.82,93

ANAEROBIC BACTERIA Anaerobes are organisms that do not require oxygen for growth. Steep oxygen gradients exist within CF mucus such that even at relatively shallow depths within mucus, the environment is considered to be hypoxic or even frankly anaerobic. Conventional culture-dependent approaches are not optimized for identifying anaerobes. Specific anaerobic

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culture methods, or culture-independent techniques, may be more appropriate.176 Several studies on tracheal aspirates, sputum, or BAL fluid have confirmed the presence of anaerobes in the lower airways in CF in up to 80% of samples and at bacterial densities of between 107 and 109 cfu/mL in sputum. The most common genera identified were Prevotella, Veillonella, Propionibacterium, Actinomyces, Staphylococcus saccharolyticus, Peptostreptococcus, and Clostridium. No data linking anaerobes to inflammation or clinical outcomes in CF are available. Longitudinal studies are also lacking, although a comprehensive longitudinal study conducted in a single patient suggested that anaerobes of the Streptococcus milleri group contributed to the development of pulmonary exacerbations. Ulrich and colleagues297 reported that 16 of 17 patients with CF produced antibodies against two immunoreactive antigens of Prevotella intermedia compared with 0 of 30 controls, suggesting that anaerobes are, indeed, immunogenic in CF. In studies in which anaerobes were specifically targeted during treatment for pulmonary exacerbations, the results have been conflicting. Worlitzsch and colleagues320 did not identify any significant reduction in the density of anaerobes in sputum after treatment with antibiotics despite an increase in pulmonary function during the period of treatment. Similarly, Tunney and colleagues296a identified only limited reduction in the density of anaerobes at the end of 2 weeks of treatment. An important factor to consider when treating anaerobic infections is that anaerobic organisms are often resistant to the commonly administered antibiotics.41

Fungal Species Oral and aerosolized antimicrobial agents are risk factors for colonization with Aspergillus spp.,14,232 with 19.7% of patients with CF in the CF Registry having at least one positive culture for this mold in 2014.61 Recent findings also confirmed the formation of biofilms and increased antifungal drug resistance by A. fumigatus.268 Although Aspergillus spp. do not normally invade the parenchyma, the airways can become impacted with mucus-containing fibrin, eosinophils, and mononuclear cells, which can cause airway obstruction and bronchiectasis.88 The role of Aspergillus colonization is unclear, and most experts do not recommend treatment. Scedosporium spp. can be isolated from the lungs of patients with CF, but the clinical significance of this microorganism is also unknown. In the aerosolized tobramycin trial, 2.4% of patients harbored saprophytic fungi,27 and in a single center, 8.6% of 128 patients followed for more than 5 years were colonized or infected with Scedosporium apiospermum.42 Additional selective media beyond routine culture methods are necessary to recover most Scedosporium spp. and obtain more accurate infection rates.21 Candida albicans and other Candida spp. are frequently isolated from CF sputum; colonization rates are best predicted by features of advanced CF pulmonary disease. At present, the clinical role of C. albicans, if any, is unclear and there is no evidence to suggest treatment benefit.41 ABPA is an allergic reaction to colonization of the lungs, with the fungus Aspergillus fumigatus affecting approximately 5% of people with CF in 2014.61 Several studies have also implicated S. apiospermum in ABPA-like reactions.42 ABPA is associated with an accelerated decline in lung function. Of patients with CF, 2% to 10% develop APBA, which can be associated with a dramatic loss of lung function.88,107,182,201 The diagnosis of ABPA can be difficult to establish because of variability in the application of standardized diagnostic criteria, confusion regarding these criteria, and limited recognition by physicians. This immunologically mediated syndrome is marked by a brisk immunoglobulin E (IgE) response, specific antibody to Aspergillus fumigatus, peripheral eosinophilia, and symptoms of reactive airway disease. Short-lived pulmonary infiltrates may be noted on chest radiograph. A workshop sponsored by the Cystic Fibrosis Foundation sought to further the understanding of the diagnostic criteria needed for ABPA in CF.238,283 This committee established minimum criteria for the diagnosis, which include (1) new clinical deterioration not attributable to another cause; (2) asthma; (3) chest roentgenographic infiltrates—current or in the past—may be detectable on CT when chest radiography is unremarkable; (4) immediate cutaneous reactivity to Aspergillus species; (5) elevated total serum IgE (>417 IU/mL or >1000 ng/mL); (6) serum precipitating antibodies to

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A. fumigatus; (7) central bronchiectasis on chest CT; (8) peripheral blood eosinophilia; and (9) elevated serum IgE and/or IgG to A. fumigatus.

Nontuberculous Mycobacteria Since the early 1990s, appreciation has been increasing that nontuberculous mycobacteria (NTM) may be pathogens in patients with CF. Estimates of the prevalence of NTM in the CF population have ranged from 1.3% in the earliest study reported in 1984275 to 32.7% in a review of patients with CF over the age of 40 years in Colorado.242 In a nested case-control study from 2006 to 2010 in France, data suggested that azithromycin may be a primary prophylaxis for NTM in CF adults.51 The NTM species most commonly identified in individuals with CF from North America and Europe are the slow-growing Mycobacterium avium complex (including M. avium, M. intracellulare, and M. chimaera), which can be found in up to 72% of NTM-positive sputum cultures, and the rapid-growing M. abscessus complex (comprising the subspecies M. abscessus subsp. abscessus [M. a. abscessus], M. a. bolletii, and M. a. massiliense [the latter currently classified as part of M. a. bolletii]), which in many centers has now become the most common NTM isolated from individuals with CF. Other less commonly isolated species include M. simiae, M. kansasii, and M. fortuitum. There are geographic differences in both the prevalence of NTM-positive cultures and the relative frequency of different species seen between but also within countries.102,205 In an individual patient, determining if NTM is colonizing the lung or causing disease can be difficult. Signs and symptoms of mycobacterial disease are nonspecific and may be consistent with CF pulmonary exacerbations. Making the diagnosis of NTM does not, per se, necessitate the institution of therapy, which is a decision based on potential risks and benefits of therapy for individual patients.104 The CF Foundation and the European Cystic Fibrosis Society recommend that (1) cultures for NTM be performed annually in spontaneously expectorating individuals with a stable clinical course, with oropharyngeal swabs not used; (2) individuals receiving azithromycin as part of their CF medical regimen who have a positive NTM culture should not continue azithromycin treatment while evaluation for NTM disease is under way, as azithromycin monotherapy may lead to resistance; (3) American Thoracic Society/Infectious Diseases Society of America diagnostic criteria,104 which include a combination of clinical, radiographic, and microbiologic elements, be used; and (4) the potential for cross-infection of NTM (especially M. abscessus complex) between individuals with CF should be minimized by following national infection control guidelines. Expert consultation should be obtained when NTM is encountered or when isolates usually representing environmental contamination are recovered.102 Recent studies focusing on M. abscessus have also failed to identify risk factors for infection,306 highlighting the need to determine if NTM causes progressive deterioration in lung function and, if so, the optimal therapy.

TREATMENT OF PATHOGENS IN CYSTIC FIBROSIS PATIENTS Airway infections are a key component of CF lung disease. Whereas the approach to common pathogens such as P. aeruginosa is guided by a significant body of evidence, other infections often pose a considerable challenge to the treating clinicians. A cornerstone of CF care is the aggressive use of oral, intravenous, and aerosolized antibiotics. The increasing longevity of patients with CF has paralleled the development of effective antibiotics. Antibiotics may be used during several stages of CF lung disease (1) to prevent acquisition of pathogens, most commonly MSSA; (2) to eradicate initial acquisition of pathogens, most commonly P. aeruginosa and MRSA, in efforts to prevent or delay chronic infection; (3) to treat pulmonary exacerbations caused by classic CF pathogens; (4) to treat patients infected with P. aeruginosa, as long-term suppressive therapy; and (5) to treat emerging multidrug-resistant pathogens. Newer molecular techniques have demonstrated that the airway microbiome consists of a large number of microbes, and the balance between microbes, rather than the mere presence of a single species, may be relevant for disease pathogenesis. A better understanding of this complex environment could help define optimal treatment

regimens that target pathogens without affecting others. The recognition that there is a diverse microbiota in sputum samples from people with CF raises questions about how we approach antibiotic therapy. Conventional bacterial culture in aerobic conditions allows isolation of a limited number of organisms. Extended culture methods identify a much wider range of bacteria, which include more difficult to culture bacteria, such as anaerobic bacteria.176 At present, there is no readily available methodology to identify all of these organisms in a way that makes this information valuable for clinical treatment. Studies are under way to develop technologies to allow molecular identification without prior culture.

Prophylaxis to Prevent Acquisition of Staphylococcus aureus Few studies have been conducted on antibiotic prophylaxis in patients with CF, and these studies have focused exclusively on S. aureus. The rationale for this strategy is to prevent S. aureus infection and to delay acquisition of P. aeruginosa.229,231 From 1985 to 1992, British investigators studied 42 newly diagnosed infants randomly assigned to 12 months of flucloxacillin versus standard care.16,269 Infants treated with flucloxacillin had fewer infections with S. aureus and fewer hospitalizations, but both groups had similar pulmonary function. In a placebo-controlled trial conducted in the United States, 119 patients newly diagnosed with CF (mean age, 16 months) were randomly assigned to receive cephalexin or placebo for 5 to 7 years.240 No significant differences were found in pulmonary function, the number of pulmonary exacerbations, nutritional status, or chest radiograph scores in the two groups. In contrast, subjects treated with cephalexin had decreased incidence of infection with S. aureus but increased incidence of infection with P. aeruginosa. Similarly, an analysis of the German national database showed that patients receiving antistaphylococcal agents had increased acquisition of P. aeruginosa and no improvement in lung function.203,171 Antistaphylococcal prophylaxis, although practiced in the United Kingdom in infants, has not been widely endorsed in the United States because of concerns about the emergence of resistance, the increased risk of acquiring P. aeruginosa, and the lack of impact on lung function. The different findings in these studies may reflect the different agents studied because cephalexin is broader spectrum than is flucloxacillin or the different durations of therapy, or both. In an era of increasing prevalence of MRSA, strategies to prevent MSSA may prove to be less useful. To date, no studies have been done to assess antibiotic prophylaxis for other pathogens in CF.

Early Eradication of Methicillin-Resistant Staphylococcus aureus Eradication of initial S. aureus infection in CF represents a different approach than outlined earlier (chronic suppressive therapy). One of the earliest reports of attempts to eradicate S. aureus (MSSA) from the CF airways was a retrospective cohort study of a Danish CF center following 191 CF patients treated with 2349 courses of antistaphylococcal chemotherapy from 1965 to 1979. They reported eradication of S. aureus in 74% of these subjects after a single course of therapy and, with further treatment, only 9% of subjects were chronically infected with S. aureus.289 Based on these data, the European CF Consensus group evaluating early intervention in CF lung disease has recommended an initial 2 to 4 weeks of antistaphylococcal treatment with new S. aureus infection and an additional 1- to 3-month course of antibiotics if the initial course fails.79 The long-term sequelae of this treatment approach are not known and warrant further investigation. Researchers in the United Kingdom reported that patient segregation and aggressive antibiotic eradication therapy achieved S. aureus eradication in the majority of their patients with CF; the most successful regimens were those that included two oral antibiotics (one of which was rifampin) and nebulized vancomycin.77 Currently, there are two ongoing studies investigating the use of inhaled vancomycin, including one accessing a novel dry powder formulation.26,126,262 The results of these trials will help to delineate the risks and benefits of treating chronic MRSA infection.

Early Eradication of Pseudomonas aeruginosa An increasingly practiced therapeutic strategy is to use antibiotics to eradicate initial acquisition of P. aeruginosa and prevent or delay chronic

CHAPTER 25  Cystic Fibrosis infection. This strategy was described first in Europe at the Danish Cystic Fibrosis Center.86,121,244,260,266 The rationale for this approach is that antibiotics may be effective at eradicating initial infection and colonization with P. aeruginosa because the organism burden is low, organisms are largely susceptible, and a biofilm has not yet been established. Evidence for the optimal regimen for successful eradication is emerging. In some CF centers in Europe, colistin and ciprofloxacin are administered every 3 months after the initial isolation of P. aeruginosa has occurred.86 Compared with historical controls, patients treated with this approach had improved lung function, improved survival rates, decreased prevalence of P. aeruginosa, and increased resistance to the therapeutic regimen.244 In Australia, investigators used intravenous antibiotics followed by ciprofloxacin or aerosolized agents and found that six of 24 children no longer had P. aeruginosa isolated for 12 months or longer.7 Compared with children treated with placebo, children treated with inhaled tobramycin within 7 to 12 weeks of initial infection and colonization with P. aeruginosa had shorter time to conversion from a positive to negative culture.276 All eight subjects treated with inhaled tobramycin compared with 1 of 13 subjects treated with placebo had successful eradication of P. aeruginosa.92 Despite the concerns about the potential emergence of antimicrobial resistance and lack of long-term studies that show the durability of eradication or an improvement in lung function, the growing consensus has been that early eradication for P. aeruginosa has merit. The Early Pseudomonal Infection Control randomized trial rigorously evaluated the efficacy of different antibiotic regimens for eradication of newly identified Pseudomonas in children with CF. Protocol-based therapy in the trial was provided based on culture positivity independent of symptoms and resulted in a lower rate of Pseudomonas recurrence but comparable hospitalization rates as compared to a historical control cohort less aggressively treated with antibiotics for new-onset Pseudomonas.183 The Cystic Fibrosis Foundation clinical care guidelines for the prevention of P. aeruginosa infection recommend (1) use of inhaled antibiotic therapy for the treatment of initial or new growth of P. aeruginosa from an airway culture, with a regimen of inhaled tobramycin (300 mg twice daily) for 28 days as the favored antibiotic; (2) against the use of prophylactic antipseudomonal antibiotics to prevent the acquisition of P. aeruginosa; and (3) routine oropharyngeal cultures rather than cultures obtained by bronchoscopy in individuals with CF who cannot expectorate sputum to determine if they are infected with P. aeruginosa.195

TREATMENT OF PULMONARY EXACERBATIONS Pseudomonas aeruginosa Much effort has been put into standardizing and validating the definition of a pulmonary exacerbation in CF. No currently accepted definition has been adopted universally, however, for use clinically, in quality improvement initiatives, or in clinical research. A combination of clinical signs and symptoms is used to define a pulmonary exacerbation in research trials; similar factors are used in the clinical setting. Mild exacerbations often are treated with oral ciprofloxacin35,110 with or without an inhaled agent. Treatment trials supporting the use of inhaled antibiotics for management of an exacerbation are lacking, however. Several pivotal trials have led to widely accepted principles for intravenous treatment of more severe pulmonary exacerbations. During the 1970s and early 1980s, placebo-controlled trials showed that participants in the placebo group had increased morbidity and mortality rates compared with participants treated with intravenous antibiotics.97,113,274 Hospitalized participants treated with bronchodilators and chest physiotherapy alone had less improvement in lung function and less reduction in bacterial density compared with patients treated with these interventions plus a β-lactam and an aminoglycoside agent.204 Treatment with a β-lactam and an aminoglycoside agent led to a significant reduction in bacterial density and a longer time to readmission for a new exacerbation compared with treatment with a β-lactam agent alone.227 Most studies comparing various agents, singly or in combination, enrolled small numbers of patients and concluded that the comparative treatment regimens were equivalent in efficacy, but the studies were

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insufficiently powered to detect differences.20,38,98,119,136,157,189,219,222 Many studies showed the emergence of resistance to study drug at the completion of therapy, which did not correlate with clinical response to treatment.122,185 No specific antibiotic combination can be considered to be superior to another, and neither is there evidence showing that the intravenous route is superior to the inhaled or oral routes. There remains a need to understand host-bacteria interactions and, in particular, to understand why many people fail to fully respond to treatment.135 Accepted treatment of a pulmonary exacerbation caused by P. aeruginosa consists of two parenteral agents from different antibiotic classes to potentially provide synergy and to delay the emergence of resistance.91,164,200,214 A number of different oral and intravenous antibiotics may be combined to best tailor antibiotic therapy to particular combinations of positive bacterial culture results. The choice is largely empiric and based on the experience of the physician, patient, and previous occurrence of drug allergy. In addition, there are no data to suggest that this also applies to other bacteria cultured in CF sputum. Treatment trials for pulmonary exacerbations caused by other CF pathogens are unavailable, however. Antibiotic dosages must be higher or more frequent (or both) in patients with CF because the volume of distribution and clearance is increased in CF.54 Treatment is administered for 10 to 21 days; treatment outcomes include improved lung function, improved well-being or quality of life or both, and a reduction in organism burden. Examination of the safety and efficacy of single daily dosing of tobramycin versus multiple daily dosing during a pulmonary exacerbation showed that single daily dosing was associated with the same efficacy and reduced nephrotoxicity; in children, the mean percentage change in creatinine in the single daily dosing group was less than the mean change in the three-times-daily dosing group (3.7% vs. 4.5%).230 Data from the CF Patient Registry reports that the total median duration of intravenous antibiotic treatment for a pulmonary exacerbation in children in 2015 was 13.0 days. The Epidemiologic Study of Cystic Fibrosis analyzed the relationship between pulmonary function and treatment strategies for pulmonary exacerbations; centers with patients in the upper quartile of pulmonary function treated pulmonary exacerbations more frequently than did centers in the lower quartile.163 It is well recognized that eradication of most pathogens does not occur.184 Inevitably, P. aeruginosa develops increasing resistance to antibiotics. Molecular studies have confirmed that resistance generally develops in the infecting strains rather than the acquisition of more resistant strains.178 Previously, much interest existed in optimizing the treatment of pulmonary exacerbations caused by multidrug-resistant P. aeruginosa using in vitro synergy testing. No clinical benefits have been demonstrated from synergy testing, leading guidelines to recommend against such testing.139,214 CF experts have not arrived yet at a consensus regarding the efficacy of inpatient versus outpatient management of pulmonary exacerbations. Outpatient management has advantages; it is less costly, is less disruptive to patients and their families, and involves less risk of acquiring nosocomial pathogens. Patients treated at home were shown, however, to have longer treatment courses and less improvement in lung function.168 Patients may improve more with hospitalization as a result of better compliance with antibiotics, bed rest, chest physiotherapy, and bronchodilator treatments.22,41

Staphylococcus aureus and Methicillin-Resistant Staphylococcus aureus The clinical utility of antistaphyloccocal agents is best shown by early studies of infants with CF treated with penicillin before the nearly universal acquisition of β-lactamases by S. aureus.5,158 Infants treated during that antibiotic era had markedly improved survival rates. Experts advocate the use of a first-generation cephalosporin (e.g., cephazolin) or semisynthetic penicillin (e.g., oxacillin) for treatment of a pulmonary exacerbation associated with MSSA.91 Treatment trials justifying this approach are lacking, however. Vancomycin generally is advocated for treatment of MRSA when this organism is considered a pathogen. Although no treatment trials in CF patients using linezolid have been conducted, a case series showed that adults with CF required 600 mg every 8 hours to provide desired

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pharmacokinetics.21,218 Linezolid-resistant MRSA has been reported with frequent or prolonged use.88,322

Burkholderia cepacia Complex Management of Burkholderia cepacia complex is more problematic because of higher levels of intrinsic antibiotic resistance and a paucity of clinical trials for this pathogen. Initial isolates may be susceptible to ciprofloxacin, β-lactam antibiotics, chloramphenicol, trimethoprimsulfamethoxazole, meropenem, and minocycline, but with the exception of Burkholderia gladioli, all Burkholderia spp. are resistant to aminoglycosides. Temocillin has been used in Europe to treat pulmonary exacerbation caused by B. cepacia.251 Resistance has developed, however, limiting therapeutic options. As described for the management of P. aeruginosa, combinations of two or three agents are used to treat a pulmonary exacerbation. Even more prolonged courses may be required to improve lung function. One of the new inhalation antibiotics available is tobramycin inhalation powder (TIP) delivered by the podhaler device. TIP has been shown to result in comparable increases in forced expiratory volume in 1 second and decreases in hospitalization as tobramycin inhalation solution (TIS) in the treatment of chronic P. aeruginosa in patients with CF. However, TIP can achieve up to 1.5- to 2-fold higher sputum tobramycin concentrations (up to 2000 mg/g) than TIS. In vitro studies of 180 Bcc and 103 S. maltophilia isolates demonstrated a minimum inhibitory concentration at which 50% of isolates were susceptible (MIC50) of 100 mg/mL, tested by planktonic and biofilm growth. This suggests that a maximum serum concentration/MIC ratio of up to 20 may be achievable with TIP treatment of these pathogens. Clinical trials of TIP in patients with CF with Bcc and S. maltophilia infection to decrease sputum bacterial densities are planned.234

Stenotrophomonas maltophilia and Achromobacter xylosoxidans There are no published treatment trials for patients with CF who are harboring S. maltophilia or A. xylosoxidans undergoing an exacerbation. Although definitive data confirming that these organisms are pathogens in CF are unavailable, clinicians target these multidrug-resistant, gramnegative bacilli if they are consistently recovered from the respiratory tract of an individual patient. At present, the Clinical and Laboratory Standards Institute recommends testing ticarcillin-clavulanate, ceftazidime, minocycline, chloramphenicol, trimethoprim-sulfamethoxazole, and levofloxacin against S. maltophilia,39 but CF strains frequently are resistant to these agents.216 Nonetheless, similar strategies are used to treat these organisms as described for P. aeruginosa or Bcc; two or more parenteral agents are chosen based on susceptibility testing and given for 10 days to 3 weeks. In a survey of 263 isolates of S. maltophilia from 218 patients with CF, doxycycline, ticarcillin-clavulanate, piperacillin-tazobactam, and trimethoprim-sulfamethoxazole were most active and inhibited 78%, 39%, 18%, and 13% of isolates, respectively.216,286 A survey of 94 A. xylosoxidans isolates from 77 patients showed that meropenem and imipenem, or piperacillin with or without tazobactam, were most active.212 In an in vitro study of a large number of clinical S. maltophilia CF isolates, levofloxacin, at levels achievable by inhalation, was the most active antibiotic alone and in combination against S. maltophilia grown as a biofilm or planktonically. In addition to achieving high levels of drug in the lung (4000 mg/g), levofloxacin demonstrated an antiinflammatory effect.296,321 Inhaled levofloxacin may thus be an effective chronic suppressive antimicrobial therapy in patients with CF with chronic S. maltophilia infection and warrants further investigation of this multidrugresistant organism.

Allergic Bronchopulmonary Aspergillosis Treatment of ABPA also may be very challenging. Steroids are the treatment of choice because ABPA is immunologically mediated, although the response to steroids is varied and may have the undesirable consequence of diabetes in this vulnerable patient population. The oral antifungal therapies voriconazole109 and itraconazole169 have been used with reported response and toxicity, but no controlled trials have been performed.164 Monitoring serum levels of itraconazole is desirable because this agent may be malabsorbed if the gastric pH is nonacidic.

Nontuberculous Mycobacteria Treatment of NTM in patients with CF is challenging and guided by the clinical presentation and the mycobacterial species. Before therapy for NTM is initiated, patients should be treated aggressively for the classic CF pathogens they harbor to determine if they clinically improve without the need for specific NTM treatment. If NTM treatment is initiated, a careful history, physical examination, and pulmonary function tests should be done to determine the baseline status of the patient in efforts to monitor response to therapy. Susceptibility testing for NTM is not done routinely for patients who do not have CF. Given the increased antibiotic exposure in CF and the potential for the emergence of resistance, NTM strains isolated from patients with CF should undergo susceptibility testing at a reference laboratory. Treatment can be guided by the initial susceptibility profile. The US Cystic Fibrosis Foundation and the European Cystic Fibrosis Society published consensus recommendations for the management and treatment of NTM in CF102; a lack of treatment trials have been published for NTM in CF. Treatment of NTM pulmonary disease should involve an intensive phase followed by a continuation phase and should be managed in collaboration with experts in the treatment of NTM and CF, as drug intolerance and drug-related toxicity occur frequently. Monotherapy or intermittent (three times per week) oral antibiotic therapy should never be used in the treatment of NTM. Serum levels should be monitored in patients receiving intravenous amikacin or streptomycin; serum levels of other antimycobacterial drugs are not routinely recommended. An initial course of intravenous amikacin as part of the intensive phase may be changed to inhaled amikacin in the continuation phase. Patients should be followed closely and have monthly sputum testing done for acid-fast bacillus smear and culture, and NTM antibiotic therapy should be prescribed for 12 months beyond culture conversion. Cure for M. abscessus is less likely; the therapeutic goal may be long-term suppression.41,102

Long-Term Suppressive Therapy Inhaled Antibiotics Long-term suppressive antibiotic therapy has been used increasingly to treat patients with CF and infected with P. aeruginosa to prolong the time between pulmonary exacerbations and to slow the progression of lung deterioration. The use of long-term oral antibiotics is discouraged; no clinical trials support this practice, which may contribute to antibiotic resistance. Inhaled antibiotics are standard of care for treating chronic pseudomonal respiratory infections in CF patients; three antimicrobial agents are currently approved for intermittent management of chronic Pseudomonas infection in the United States: TIS and TIP, aztreonam-lysine (AZLI), and colistimethate (COL) as inhalation solution (also available as licensed dry powder in Europe).179,195 The aerosol route delivers 100-fold higher concentrations of antibiotic without toxicity; the median concentration of tobramycin in the phase III trial was 1200 µg/g of sputum.201 However, TIP can achieve up to 1.5- to 2-fold higher sputum tobramycin concentrations (up to 2000 mg/g) than TIS.321 The outcomes desired from use of inhaled antibiotics in treated patients include a reduction in bacterial density, fewer days of hospitalization, and fewer days of intravenous antibiotics, with minimal systemic absorption of the drug. Although initially approved for intermittent administration, the use of continuous alternating inhaled antibiotic regimens of differing combinations is growing. A recent double-blind trial compared continuous alternating therapy of AZLI/TIS to placebo/TIS in an intermittent treatment regimen. The AZLI/TIS treatment reduced exacerbation rates by 25.7% and rates of respiratory hospitalizations by 35.8% compared with placebo/TIS.103 New antibiotics are in development (inhaled levofloxacin, liposomal ciprofloxacin, and liposomal amikacin), although recently two did not meet primary outcomes in large clinical trials. Although inhaled antibiotics have the advantage of being able to deliver high intrapulmonary concentrations of drug, antimicrobial resistance can still develop and is a concern in CF. Of particular interest is the development of nonantibiotic antimicrobials, which may allow treatment of intrinsically antibiotic-resistant organisms and perhaps even mitigate antimicrobial resistance. Examples

CHAPTER 25  Cystic Fibrosis of nonantibiotic treatments being investigated in patients with CF include antibiotic adjuvants, which have activity against bacteria, such as gallium, antimicrobial peptides, anti-biofilm compounds such as alginate oligosaccharides (OligoG), and garlic. Vaccination strategies and antibody therapy (IgY) against P. aeruginosa have also been attempted to prevent initial infection with this organism in CF. Although aggressive and long-term use of antibiotics has been crucial in slowing lung function decline and improving survival in people with CF, it has added a significant burden of care and associated toxicities in these individuals. Careful surveillance and the use of preventive strategies for antibiotic-related toxicity (such as nephrotoxicity and ototoxicity) are essential. Continued development of effective antimicrobial agents that can function against bacterial biofilm growth and under anaerobic conditions in the conditions encountered in the CF lung is needed.309 Macrolide Antibiotics Much interest has been generated in the use of macrolide agents in CF112 as long-term suppressive therapy. The rationale for macrolide therapy in CF stems from the successful treatment of diffuse panbronchiolitis with erythromycin, azithromycin, and clarithromycin.131,137 Diffuse panbronchiolitis is a chronic lung disease, diagnosed primarily in Asian adults, with several clinical features similar to those found in CF, including progressive lung disease caused by mucoid and nonmucoid strains of P. aeruginosa.243 Long-term administration of low-dose macrolide agents to patients with diffuse panbronchiolitis has reduced morbidity and mortality rates. In vitro studies have provided the scientific rationale for this clinical efficacy. Although macrolides are not cidal for P. aeruginosa, subinhibitory concentrations of macrolide agents reduce the production of several virulence factors by P. aeruginosa,161,162 including the formation of biofilm.117,133 Macrolide antibiotics also may have an antiinflammatory effect and decrease cytokine production by neutrophils, monocytes, and bronchial epithelial cells.116,280 Four azithromycin trials have been conducted in patients with CF,37,74,213,278 with three trials in patients chronically infected with P. aeruginosa.74,213,278 All showed improvement in lung function using similar treatment regimens of azithromycin. Improvements in secondary outcomes, such as decreased hospitalization, decreased antibiotic use, and increased weight gain, also were noted. In a study performed in 82 children and adolescents, most (63 of 82; 77%) with negative cultures for P. aeruginosa,37 participants in the azithromycin-treated group had fewer pulmonary exacerbations and less oral antibiotic use, with no differences in lung function or intravenous antibiotic usage. A Cochrane review concluded that short-term (i.e., 3 to 6 months) azithromycin seemed effective in CF, but long-term safety and efficacy remain unknown.235 Patients treated with azithromycin should be screened for NTM before initiating therapy and annually thereafter because of concern about macrolide resistance in these microorganisms. A secondary analysis of a cohort of 263 subjects with CF enrolled in a recent clinical trial comparing inhaled TIS with AZLI noted that concomitant oral azithromycin may antagonize the therapeutic benefits of inhaled tobramycin in subjects, with significantly greater improvement in outcome measures noted in the AZLI-treated group. Further studies are needed to determine if this antagonism can be replicated.206

Lung Transplantation Lung transplantation currently is considered a viable therapy for selected patients with end-stage pulmonary disease of CF.281 Bilateral lung, heart-lung, and living donor lobar lung transplantation all have been performed in patients with CF, but most operations in recent years have used the bilateral lung transplant approach with lungs from deceased donors. The survival of lung transplant recipients with CF exceeds that of any other diagnostic group for all ages, with projected survival half-life of 6.2 years.256 Patients with CF nonetheless present special challenges for successful lung transplantation. The life-threatening manifestations of CF generally are limited to the lungs except for patients with advanced liver disease with portal hypertension. Advantages of a lung transplant recipient with CF include relative young age, giving the potential of many years of productive life ahead. In addition, patients with CF have experience with complex medical regimens.

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The optimal time to refer potential candidates for evaluation for lung transplant is difficult to determine because the natural history of CF cannot be predicted precisely. Although transplanted lungs do not develop CF, they can become infected with the pretransplant pathogens because the trachea and paranasal sinuses continue to manifest the pathophysiology of CF. Lung transplant recipients with CF are at risk for development of infection via pretransplant microbial flora or newly acquired pathogens.125,143,233,237 Controversy has ensued about whether microbiologic criteria, specifically pretransplant infection with fungi, NTM, or multidrug-resistant pathogens, should be considered contraindications to performing lung transplantation in patients with CF. Several centers have published their experiences with infections that developed from lung transplantation pathogens; they include invasive aspergillosis; sepsis with S. maltophilia, Bcc organisms, and B. gladioli; and sternal wound infection.125 Other centers have reported that morbidity and mortality caused by P. aeruginosa infections posttransplant are not higher in patients with CF than in patients who do not have CF.85,175 Patients with CF are at risk of developing invasive aspergillosis after transplant but at lower rates than patients without CF.175,188 Many of these patients with CF were colonized with Aspergillus spp. or Scedosporium spp. before undergoing transplantations. Treatment with antifungal therapy after surgery should be considered. The decision to transplant patients infected with NTM, Bcc, or multidrug-resistant P. aeruginosa, or colonized with Aspergillus spp. or Scedosporium spp., should be made on a case-by-case basis. Potentially, an understanding of the microbial species infecting a patient may be a useful predictor of mortality.

Antiinflammatory Therapy Inflammation associated with chronic bacterial colonization plays a crucial role in CF lung disease. Nonsteroidal agents and glucocorticoids have been used as potential medications for antiinflammatory therapy. A randomized trial using oral prednisone (1–2 mg/kg every other day) showed a reduction in the rate of decline in pulmonary function of patients with CF but was associated with significant steroid-related side effects.9 Three short-term trials using inhaled steroids have led to mixed results and no clear direction for long-term use.11,172,264 A systematic review of inhaled steroids for CF was equivocal with respect to efficacy.10 A multicenter randomized trial of withdrawal of inhaled steroids in CF did not find a difference in pulmonary exacerbations, infection with P. aeruginosa, or pulmonary function after inhaled steroids were discontinued.12 High-dose ibuprofen (20–30 mg/kg twice per day) used over a 4-year period showed a decreased rate of decline in pulmonary function with few reported side effects.134 Macrolide antibiotics decrease inflammation by modulation of inflammatory signaling pathways and decreased cytokine production from inflammatory cells.72 Several antiinflammatory agents—including antiproteases, statins, and antioxidants—have been proposed as potential therapies, but they remain under investigation and are not a part of routine clinical practice.

CFTR Modulators A great deal of progress has been made over the past few years in the field of small molecule therapies targeting CFTR, the protein defective in patients with CF. Until recently, modulating CFTR dysfunction was only a research aspiration. However, greater focus placed on addressing the primary defect of CF has developed several clinical therapeutic strategies in this area to modulate CFTR and restore robust functional protein to the cell surface. This approach has now led to the licensing of two CFTR potentiator/corrector medications, which have been shown to have significant clinical improvements in a subset of CF patients. This success represents the beginning for CFTR modulation, and further research is ongoing that aims to broaden the applicability of these techniques. Ivacaftor (Kalydeco) is the first drug licensed for clinical use in patients with a class 3 CFTR mutation, a number of mutations resulting in defective gating. For patients homozygous for delta F508, the class 2 mutation characterized by misfolding, a combination approach is required; the recently approved lumicaftor/ivacaftor (Orkambi) allows the protein to correctly localize and potentiates improved protein

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function. A number of other CFTR modulators are at earlier stages of clinical development. Clinicians should be aware that lumicaftor/ivacaftor has many potential drug-drug interactions. With the advent of such precision medicine, patient genotype is now highly relevant. Areas of current unmet need include drugs to cover all mutation classes, increasing access to younger children with the design of rational and tailored clinical trials, and ensuring equality of access globally.15,67 With the approval of ivacaftor to reverse protein defects in patients with the class 3 gating mutation, there is evidence that P. aeruginosa culture positivity is significantly reduced following ivacaftor treatment in persons with the G551D-CFTR mutation.126

Prevention Immunizations The use of currently available routine childhood and adolescent vaccines is strongly advocated for patients with CF. Although patients with CF are not at increased risk of developing Streptococcus pneumoniae infections, they should receive the pneumococcal vaccine, 13-valent (Prevnar). Annual influenza vaccination is recommended for patients with CF and household members.78,82 One randomized controlled study comparing palivizumab (Synagis) prophylaxis against RSV infection in infants with CF failed to draw conclusions about its efficacy.241 Most CF experts, however, agree that RSV prevention may be warranted, since viral lower respiratory disease in infants with CF puts them at risk for severe bronchiolitis and hospitalization. The results of a phase III multicenter study of a P. aeruginosa vaccine were published.63 Although this bivalent antiflagella vaccine was immunogenic and was found to reduce the incidence of P. aeruginosa infection and serum antibody titers, it did not prevent chronic P. aeruginosa infection, and it did not affect lung function.

Infection Control Precautions Although the sources of most pathogens in patients with CF are unknown, it is increasingly recognized that patient-to-patient spread and acquisition from the contaminated health care environment can occur. To date, reports of transmission of bacterial pathogens occurring between individuals with and without CF are rare.96,111,155 Direct contact, indirect contact, and spread of droplets with infectious secretions all have been implicated as modes of transmission of CF pathogens. Risk factors for transmission were described first for Bcc.30,101,142,190,191,252 Perhaps of most concern have been several reports of clonal spread of P. aeruginosa among patients with CF.154,221,263 These examples have involved obvious phenotypes that triggered an investigation of possible patient-to-patient spread, including an increase in ceftazidime-resistant P. aeruginosa32 or initial colonization of young children with mucoid strains of P. aeruginosa.7,174 These reports have led CF centers in Europe to segregate all patients, regardless of their P. aeruginosa or Bcc status, in hospital and clinic settings.86,132,154 Occasional cases of patient-to-patient spread of other potential pathogens, including NTM, S. maltophilia, and A. xylosoxidans, have been reported in patients with CF.207,261 The U.S. Cystic Fibrosis Foundation convened an expert panel to develop revised recommendations for infection control that addressed inpatient, outpatient (i.e., CF clinic and pulmonary function test laboratories), and non–health care settings, as so much CF care is delivered in the home.257 These recommendations have implications for treatment, transplantation, and the psychosocial well-being of patients, families, and staff (Box 25.3). The guidelines emphasized that all patients with CF could harbor potentially transmissible respiratory tract pathogens, and containing respiratory tract secretions is of paramount importance. The consensus is that all patients should be cared for apart from other patients with CF; patients are hospitalized in single rooms and seen in outpatient settings geographically or temporally apart from other patients with CF. Similarly, patients with CF should be placed in private rooms without access to common areas.

CONCLUSION The microbiology of patients with CF is complex and changing. Although the pathogenesis of lung infections is still under active investigation, the current hypothesis suggests multiple etiologies. Appropriate microbiologic

BOX 25.3  Infection Control Strategies for Cystic Fibrosis Guideline All patients placed into contact isolation (outpatient and inpatient settings) Quarterly cultures of respiratory tract Appropriate processing of CF respiratory tract cultures Educate patients and families about proper hand hygiene Implement contact precautions for MDROs, including MRSA Hospitalize all patients in single-patient room Consider all patients at risk for organisms with potential spread to/from other CF patients including, but not limited to, those with B. cepacia complex Clean and disinfect respiratory therapy equipment Avoid socialization among CF patients Maintain at least 6 ft between CF patients to prevent droplet transmission CF, Cystic fibrosis; MDROs, multidrug-resistant organisms; MRSA, methicillin-resistant Staphylococcus aureus.

processing of respiratory tract specimens is crucial to ensure an accurate understanding of the epidemiology of CF lung disease and to provide appropriate treatment and infection control. Current treatment strategies are directed largely at management of deteriorations of pulmonary function, but increasingly strategies are directed at prevention and preservation of lung function. This success from CFTR modulation and further research holds promise for a shift in outcome of this chronic progressive disease. NEW REFERENCES SINCE THE SEVENTH EDITION 3. Adam RJ, Michalski AS, Bauer C, et al. Air trapping and airflow obstruction in newborn cystic fibrosis piglets. Am J Respir Crit Care Med. 2013;188:1434-1441. 15. Barry PJ, Ronan N, Plant BJ. Cystic fibrosis transmembrane conductance regulator modulators: the end of the beginning. Semin Respir Crit Care Med. 2015;36(2):287-298. 25. Boucher RC. Evidence for airway surface dehydration as the initiating event in CF airway disease. J Intern Med. 2007;261:5-16. 26. Boyle MP. Persistent methicillin resistant Staphylococcus aureus eradication protocol (PMEP). Clinicaltrials.Gov. NLM identifier: NCT01594827. Bethesda, MD: National Library of Medicine (US). 31. Cantin AM, Hartl D, Konstan MW, et al. Inflammation in cystic fibrosis lung disease: pathogenesis and therapy. J Cyst Fibros. 2015;14(4):419-430. 36. Castellani C, Cuppens H, Macek M Jr, et al. Consensus on the use and interpretation of cystic fibrosis mutation analysis in clinical practice. J Cyst Fibros. 2008;7(3):179-196. 41. Chmiel JF, Aksamit TR, Chotirmall SH, et al. Antibiotic management of lung infections in cystic fibrosis. II. Nontuberculous mycobacteria, anaerobic bacteria, and fungi. Ann Am Thorac Soc. 2014;11(8):1298-1306. 43. Clunes MT, Boucher RC. Cystic Fibrosis: the mechanisms of pathogenesis of an inherited lung disorder. Drug Discov Today Dis Mech. 2007;4(2):63-72. 51. Coolen N, Morand P, Martin C, et al. Reduced risk of nontuberculous mycobacteria in cystic fibrosis adults receiving long-term azithromycin. J Cyst Fibros. 2015;14(5):594-599. 56. Cutting GR. Cystic fibrosis genetics: from molecular understanding to clinical application. Nature reviews. Genetics. 2015;16(1):45-56. 62. Cystic Fibrosis Foundation. Patient Registry 2014. Bethesda, Md. 2015. 68. Davies JC. The future of CFTR modulating therapies for cystic fibrosis. Curr Opin Pulm Med. 2015;21(6):579-584. 70. De Boeck K, Munck A, Walker S, et al. Efficacy and safety of ivacaftor in patients with cystic fibrosis and a non-G551D gating mutation. J Cyst Fibros. 2014;13(6):674-680. 102. Floto RA, Olivier KN, Saiman L, et al. US Cystic Fibrosis Foundation and European Cystic Fibrosis Society consensus recommendations for the management of non-tuberculous mycobacteria in individuals with cystic fibrosis: executive summary. Thorax. 2016;71(1):88-90. 103. Flume PA, Clancy JP, Retsch-Bogart GZ, et al. Continuous alternating inhaled antibiotics for chronic pseudomonal infection in cystic fibrosis. J Cyst Fibros. 2016;15(16):30050-30059. pii: S1569-1993. 118. Griese M, Kappler M, Eismann C, et al. Inhalation treatment with glutathione in patients with cystic fibrosis. A randomized clinical trial. Am J Respir Crit Care Med. 2013;188:83-89.

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The full reference list for this chapter is available at ExpertConsult.com.

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155. Konstan MW, Butler SM, Wohl ME, et al. Growth and nutritional indexes in early life predict pulmonary function in cystic fibrosis. J Pediatr. 2003;142:624-630. 156. Koscik RL, Farrell PM, Kosorok MR, et al. Cognitive function of children with cystic fibrosis: deleterious effect of early malnutrition. Pediatrics. 2004;113:1549-1558. 157. Koscik RL, Lai HJ, Laxova A, et al. Preventing early, prolonged vitamin E deficiency: an opportunity for better cognitive outcomes via early diagnosis through neonatal screening. J Pediatr. 2005;147:S51-S56. 158. Kosorok MR, Jalaluddin M, Farrell PM, et al. Comprehensive analysis of risk factors for acquisition of Pseudomonas aeruginosa in young children with cystic fibrosis. Pediatr Pulmonol. 1998;26:81-88. 159. Kosorok MR, Zeng L, West SE, et al. Acceleration of lung disease in children with cystic fibrosis after Pseudomonas aeruginosa acquisition. Pediatr Pulmonol. 2001;32:277-287. 160. Kunzelmann K, Schreiber R, Nitschke R, et al. 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SECTION 2  Lower Respiratory Tract Infections

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Infection control recommendations for patients with cystic fibrosis: microbiology, important pathogens, and infection control practices to prevent patient-to-patient transmission. Infect Control Hosp Epidemiol. 2003;24:S6-S52. 257. Saiman L, Siegel JD, LiPuma JJ, et al. Infection prevention and control guideline for cystic fibrosis: 2013 update. Infect Control Hosp Epidemiol. 2014;35(suppl 1):S1-S67. 258. Salsgiver EL, Fink AK, Knapp EA, et al. Changing epidemiology of the respiratory bacteriology of patients with cystic fibrosis. Chest. 2016;149(2):390-400. 259. Salvatore D, Buzzetti R, Baldo E, et al. An overview of international literature from cystic fibrosis registries 2. Neonatal screening and nutrition/growth. J Cyst Fibros. 2010;9:75-83. 260. San Gabriel P, Zhou J, Tabibi S, et al. Antimicrobial susceptibility and synergy studies of Stenotrophomonas maltophilia isolates from patients with cystic fibrosis. Antimicrob Agents Chemother. 2004;48:168-171. 261. Saralaya D, Peckham DG, Hulme B, et al. Serum and sputum concentrations following the oral administration of linezolid in adult patients with cystic fibrosis. J Antimicrob Chemother. 2004;53:325-328. 262. Savara, Inc. Efficacy and safety study of AeroVanc for the treatment of persistent MRSA lung infection in cystic fibrosis patients. Clinicaltrials.Gov. NLM identifier: NCT01746095. 263. Schaad UB, Wedgwood-Krucko J, Guenin K, et al. Antipseudomonal therapy in cystic fibrosis: aztreonam and amikacin versus ceftazidime and amikacin administered intravenously followed by oral ciprofloxacin. Eur J Clin Microbiol Infect Dis. 1989;8:858-865. 264. Schottelius AJ, Mayo MW, Sartor RB, et al. Interleukin-10 signaling blocks inhibitor of kappaB kinase activity and nuclear factor kappaB DNA binding. J Biol Chem. 1999;274:31868-31874. 265. Schwar1zer C, Illek B, Suh JH, et al. Organelle redox of CF and CFTR-corrected airway epithelia. Free Radic Biol Med. 2007;43:300-316. 266. Scott FW, Pitt TL. Identification and characterization of transmissible Pseudomonas aeruginosa strains in cystic fibrosis patients in England and Wales. J Med Microbiol. 2004;53:609-615. 267. Scott FW, Pitt TL. Pseudomonas aeruginosa: basic research. Prog Respir Res. 2006;34:138-144.

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268. Seidler MJ, Salvenmoser S, Muller FM. Aspergillus fumigatus forms biofilms with reduced antifungal drug susceptibility on bronchial epithelial cells. Antimicrob Agents Chemother. 2008;52:4130-4136. 269. Shelhamer JH, Levine SJ, Wu T, et al. NIH conference. Airway inflammation. Ann Intern Med. 1995;123:288-304. 270. Simpson DA, Ramphal R, Lory S. Genetic analysis of Pseudomonas aeruginosa adherence: distinct genetic loci control attachment to epithelial cells and mucins. Infect Immun. 1992;60:3771-3779. 271. Singh PK, Schaefer AL, Parsek MR, et al. Quorum-sensing signals indicate that cystic fibrosis lungs are infected with bacterial biofilms. Nature. 2000;407:762-764. 272. Sly PD, Brennan S, Gangell C, et al. Lung disease at diagnosis in infants with cystic fibrosis detected by newborn screening. Am J Respir Crit Care Med. 2009;180:146-152. 273. Sly PD, Gangell CL, Chen L, et al. Risk factors for bronchiectasis in children with cystic fibrosis. 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Speert DP, Campbell ME, Henry DA, et al. Epidemiology of Pseudomonas aeruginosa in cystic fibrosis in British Columbia, Canada. Am J Respir Crit Care Med. 2002;166:988-993. 281. Speert DP, Henry D, Vandamme P, et al. Epidemiology of Burkholderia cepacia complex in patients with cystic fibrosis, Canada. Emerg Infect Dis. 2002;8:181-187. 282. Stanke F, Becker T, Kumar V. Genes that determine immunology and inflammation modify the basic defect of impaired ion conductance in cystic fibrosis epithelia. J Med Genet. 2011;48:24-31. 283. Stevens DA, Moss RB, Kurup VP, et al. Allergic bronchopulmonary aspergillosis in cystic fibrosis: state of the art: Cystic Fibrosis Foundation Consensus Conference. Clin Infect Dis. 2003;37(suppl 3):S225-S264. 284. Stoltz DA, Meyerholz DK, Pezzulo AA, et al. Cystic fibrosis pigs develop lung disease and exhibit defective bacterial eradication at birth. Sci Transl Med. 2010;2(29):29ra31. 285. Strom CM, Huang D, Chen C, et al. 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Risk factors for emergence of Stenotrophomonas maltophilia in cystic fibrosis. Pediatr Pulmonol. 2000;30: 10-15. 292. Tang H, Kays M, Prince A. Role of Pseudomonas aeruginosa pili in acute pulmonary infection. Infect Immun. 1995;63:1278-1285. 293. Tarran R, Button B, Picher M, et al. Normal and cystic fibrosis airway surface liquid homeostasis: the effects of phasic shear stress and viral infections. J Biol Chem. 2005;280:35751-35759. 294. Thomas SR, Gyi KM, Gaya H, et al. Methicillin-resistant Staphylococcus aureus: impact at a national cystic fibrosis centre. J Hosp Infect. 1998;40:203-209. 295. Tomashefski JF Jr, Konstan MW, Bruce MC, et al. The pathologic characteristics of interstitial pneumonia cystic fibrosis: a retrospective autopsy study. Am J Clin Pathol. 1989;91:522-530. 296. Tsivkovskii R, Sabet M, Tarazi Z, et al. 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SECTION 2  Lower Respiratory Tract Infections

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SECTION 3  ■ Infections of the Heart

26 

Infective Endocarditis Sheldon L. Kaplan • Jesus G. Vallejo

Infective endocarditis results when microorganisms adhere to the endocardial surface of the heart. This process usually occurs on heart valves, although septal defects and mural surfaces can be affected. Most episodes of endocarditis begin on endocardium that has been altered by congenital defects, previous disease, surgery, or trauma. The clinical manifestations depend on the degree of compromise of cardiac function and the occurrence of embolic phenomena. Although bacteria are responsible for most cases, instances of infective endocarditis caused by fungi, chlamydiae, rickettsiae, and perhaps viruses have been described. Advances in the practice of general pediatrics and cardiology during the past three decades have contributed to changes in the predisposing conditions and etiologic agents of infective endocarditis. Before the 1950s, rheumatic fever was the major underlying condition, but its incidence has declined greatly since then.338,463 Improvements in the medical and surgical management of children with congenital heart disease have increased survival rates. Eighty percent to 90% of children with infective endocarditis have congenital heart disease. Many cases occur after cardiac surgery, especially for replacement of valves and creation of shunts with prosthetic materials.376 The reported incidence of infective endocarditis in neonates has been increasing, probably owing to the use of sophisticated and highly invasive techniques in neonatal intensive care nurseries.103,178,363,446 Infective endocarditis has been classified as acute or subacute based on the progression of untreated disease.489 The acute form has a fulminant course, with high fever, systemic toxicity, and death from sepsis in several days to 6 weeks. The most common etiologic agents are Staphylococcus aureus, Streptococcus pyogenes, and Streptococcus pneumoniae. Children with the acute form often have no underlying cardiac lesion.585 Subacute disease usually occurs in patients with previous valvular disease or those who have undergone cardiac surgical intervention.66 It is characterized by a more indolent course (6 weeks to several months) and with low-grade fever, vague systemic complaints, and various embolic phenomena. Viridans streptococci are the most common etiologic agents. This classification ignores the frequent overlap in clinical manifestations caused by various organisms, especially the staphylococci and fungi, which are causes of an increasing number of subacute cases in the postcardiac surgical setting. Classification based on specific etiologic agents is preferable because it has implications for the usual clinical course, predisposing factors, and appropriate medical and surgical management.23

EPIDEMIOLOGY The incidence of infective endocarditis in adults has been difficult to determine because the methods of study and criteria for diagnosis vary among series.37,135,390 Accurate figures on the incidence of infective endocarditis in children are difficult to obtain. The most common method of reporting the incidence in pediatric series expresses the number of cases of infective endocarditis as the numerator and the total number of hospital admissions during the analyzed period as the denominator. Zakrzewski and Keith609 reported an incidence of endocarditis of 1 in 4500 pediatric admissions at the Hospital for Sick Children in Toronto from 1952 to 1962, whereas Van Hare and colleagues571 at Case Western Reserve in Cleveland, Ohio, found an incidence of 1 in 1280 in the period from 1972 to 1982. In a large series from Boston Children’s Hospital spanning the period between 1933 and 1972, the incidence before 1963 was 1 in 4500 pediatric admissions, whereas that 256

for 1963 to 1972 was 1 in 1800 admissions.257 A study from a children’s hospital in Australia reported an incidence of 1 in 4500 hospital admissions between 1971 and 1983.505 One Japanese center reported an annual incidence of 0.9 cases per 1000 children seen at the cardiology clinic.175 In a report from Canada the cumulative incidence of IE occurring in children with congenital heart disease was 6.1 per 1000 through 18 years of age.468 Although differences in referral patterns at these centers may have introduced bias into these figures, the incidence of infective endocarditis in children appears to be rising. This rise may be explained by the increased survival rate of children with all forms of cardiovascular disease and an increase in the percentage of cases that occur after cardiac surgery31 (especially implantation of foreign material583) and are related to intravascular catheters.157,263,475 Early surgical correction of many types of congenital heart diseases, along with effective appropriate perioperative antibiotic prophylaxis regimens, ultimately may lower the incidence of postoperative infective endocarditis.561 However, the use of invasive therapeutic modalities, especially intravenous catheters and pacemakers, has led to an increased incidence of health care–associated endocarditis.157,163,346,447,561,584 In general children with predisposing cardiac conditions who develop infective endocarditis while hospitalized have longer hospitalizations and higher mortality than patients with communityassociated endocarditis.164,343 The average age of children with infective endocarditis is increasing, a phenomenon that may reflect the longer life expectancy created by improved therapy for children at risk.537 From 1930 to 1950, the mean age for children with infective endocarditis was close to 5 years.257 Between 1960 and the present, it increased to 8.5 and then to 13 years.175,186,291,345,475 The number of reports of infective endocarditis in children younger than 2 years of age had been small but has increased significantly since the late 1980s.46,186,363,463,593 The clinical course of infective endocarditis in these young children often is atypical, and some cases are diagnosed at autopsy.257,420 Before the 1950s, this disease was a rare event in neonates, with only eight autopsy cases reported.328 Several reports suggest a rapidly increasing rate associated with the development of intensive supportive care in neonates.54,353,363,370,404,405 Symchych and colleagues535 found a 3% incidence of bacterial endocarditis among all neonatal autopsies. Endocarditis in neonates frequently occurs on the tricuspid valve when associated with an indwelling central venous catheter.555 Congenital heart defects also predispose neonates to the development of infectious endocarditis.103 Any form of structural cardiac disease may predispose to infective endocarditis, especially disorders associated with turbulence of blood flow.182,516 In autopsy and clinical series, children with ventricular septal defect, tetralogy of Fallot, left-sided valvular disease, and systemicpulmonary arterial communication were at highest risk, whereas those with pulmonary stenosis, coarctation of the aorta, and secundum atrial septal defect were at low risk.462,475 Hypertrophic obstructive cardiomyopathy rarely is associated with infective endocarditis.85 Isolated pulmonic or tricuspid valve endocarditis can occur in “otherwise normal” children and adolescents with sepsis or focal bacterial infection,391 but usually it is associated with congenital heart disease, intravenous catheters, or intravenous drug abuse.76,388 A bicuspid aortic valve is recognized as an important risk factor for the development of infective endocarditis, especially in elderly men.354 The underlying heart diseases in 266 pediatric cases of infective endocarditis are listed in Table 26.1.263 In a large Canadian study, independent risk factors for infective endocarditis among children with congenital heart disease were cyanotic congenital

CHAPTER 26  Infective Endocarditis

TABLE 26.1  Underlying Heart Disease in 266 Children With Infective Endocarditis Underlying Heart Disease Congenital heart disease   Tetralogy of Fallot   Ventricular septal defect   Congenital aortic stenosis   Patent ductus arteriosus   Transposition of great vessel  Others Rheumatic heart disease No heart disease

Percentage Affected (%) 78 24 16 8 7 4 19 14 8

From Kaplan EL. Infective endocarditis in the pediatric age group: an overview. In: Kaplan EL, Taranta AV, eds. Infective endocarditis: an American Heart Association symposium. Dallas: American Heart Association; 1977: 51–4.

heart disease, endocardial cushion defects, left-sided heart lesions, age less than 3 years, and cardiac surgery within 6 months.468 A cooperative study on the natural history of aortic stenosis, pulmonary stenosis, and ventricular septal defect reported data from a controlled pediatric population collected over a period of 4 to 15 years.184 In patients not undergoing surgical correction, the risk of acquiring endocarditis by 30 years of age in those with ventricular septal defects was 9.7% versus 1.4% for aortic stenosis and 0.9% for pulmonic stenosis. Aortic valvotomy in children with aortic stenosis actually increases the relative risk, whereas successful repair of ventricular septal defect significantly decreases long-term susceptibility to infective endocarditis.185 Similarly endocarditis is an extremely rare occurrence after ligation of patent ductus arteriosus has been performed. At present, palliative systemic-to-pulmonary shunting is the surgical procedure most often complicated by infective endocarditis.475 In a review of 115 patients with tetralogy of Fallot, Kaplan and colleagues264 reported an 8% incidence of infective endocarditis after placement of a Pott shunt. Transcatheter placement of prosthetic pulmonary valves (TPV) (Melody valve) has been associated with an incidence of subsequent development of infective endocarditis of 2.4% per patient-year and 0.88% per patientyear for TPV-specific endocarditis.352,575 The increasing use of prosthetic valves and valved conduit repairs in children with complex heart disease may lead to a larger number of cases of infective endocarditis in the future.265,272,303,545,551 Most medical centers report an incidence of prosthetic valve endocarditis of 2% to 4% after surgery,65,187,375,470,516 with the aortic and mitral valves affected most frequently.244,330 Prosthetic material is also implanted for right ventricular outflow reconstruction. In such cases conduit endocarditis is more common for bovine jugular vein grafts compared to cryopreserved homografts. In a report from Canada reviewing conduits placed in almost 300 patients with a median follow-up of 3.4 years, conduit endocarditis occurred in 9.4% (23/244) of bovine jugular vein grafts implanted versus 0.7% (1/135) of the cryopreserved homografts (P < .001).564 Older studies arbitrarily divided prosthetic valve endocarditis into two categories—early and late—based on whether the infection occurred within 60 days of valve placement or later.39 The rationale for categorizing by time was based on apparent differences in bacteriologic, pathogenetic, and prognostic associations. So-called early cases most often were caused by coagulase-negative staphylococci (CONS), gram-negative bacilli, and fungi, whereas oral and enterococcal streptococci, along with staphylococci, predominated in late cases.269 These older reports suggested that early cases were acquired by contamination of an intraoperative valve or were secondary to postoperative extracardiac infections, whereas late cases were acquired by the same mechanisms as native-valve endocarditis. Nosocomial bacteremia that develops at any time after the patient has undergone valve placement is a significant risk factor for development of endocarditis.145,343,566 Finally the mortality rate was thought to be higher in early versus late infection. However, more recent studies have blurred this arbitrary time distinction between early and late prosthetic valve endocarditis.65,244 The risk

257

probably is highest in the first 6 to 12 months and decreases to its lowest point beyond 1 year after valve replacement. CONS are the dominant organisms both before and after the 60th postoperative day.65,268 Clinical and epidemiologic data also suggest that prosthetic valve infection caused by staphylococci within the first year after placement probably is acquired at the time of surgery.39 Identified risk factors for the development of prosthetic valve endocarditis in adults include native valve endocarditis, black race, male sex, a mechanical (vs. biologic) prosthesis, and prolonged cardiopulmonary bypass time244; no comparable information is available for children. Mitral valve endocarditis occurs frequently on an anatomically normal valve in patients with other predisposing factors.158 An association between mitral valve prolapse and infective endocarditis has been recognized in adults and children. This heart lesion is detected with increasing frequency in adolescent girls and may be only one component of a developmental syndrome.495 In adults, 40% to 50% of cases of infective endocarditis associated with isolated insufficient mitral valves occur in patients with mitral prolapse.97 In some series of native valve endocarditis, mitral valve prolapse has been the most common underlying lesion.354 The reported incidence of infective endocarditis in patients with mitral valve prolapse has varied markedly among studies, from low rates of 14 per 100,000 per year to 5 of 58 patients monitored prospectively for 9 to 22 years.221 A retrospective epidemiologic analysis involving matched cases and controls yielded an odds ratio of 8.2, indicative of a substantially higher risk for development of endocarditis in patients with mitral valve prolapse than in normal controls.94 The risk of developing infective endocarditis is not uniform for all patients with mitral valve prolapse. The risk is increased in patients with a preexisting systolic murmur (but not for those with an isolated click and no murmur), echocardiographically demonstrated regurgitation, and valvular redundancy.105,329,340 The signs and symptoms of endocarditis associated with mitral valve prolapse may be more subtle than those of other types of left-sided endocarditis.158,402 However, significant complications are relatively common occurrences and sometimes require valve replacement during the acute illness or during convalescence.21,521 Fungal endocarditis is a rare disorder in children but should be suspected in certain clinical and epidemiologic settings. It is more likely to occur after cardiac surgery and rarely occurs on native heart valves. It occurs more commonly in neonates treated in intensive care settings than in older children.103 Other predisposing factors include (1) the presence of an indwelling vascular catheter, (2) prolonged use of antibiotics, (3) intrinsic (immunodeficiency diseases, malignancy, malnutrition) or extrinsic (corticosteroids, cytotoxic drugs) immunosuppression, (4) bowel surgery resulting in transient fungemia, (5) intravenous drug use, and (6) preexisting or concomitant bacterial endocarditis. Many conditions other than structural heart disease predispose children to the development of infective endocarditis. The most important is the presence of an indwelling central venous catheter, especially in patients who are seriously ill or immunocompromised.178,186,313,558,592 The catheter acts as a foreign body and presumably causes microscopic damage by abrading endocardial and valve surfaces; such damage results in nonbacterial thrombotic vegetation.28 Infection of intracardiac pacemaker wires also can lead to endocarditis.15 Infection acquired during the placement procedure and infection of the pacemaker pouch are most common. Infective endocarditis, usually of the tricuspid valve, has developed in children with ventriculoatrial shunts placed for the treatment of hydrocephalus.263 In patients with arteriovenous fistulas created for hemodialysis, bacterial vegetations may develop in the fistula and on heart valves.305,450 Rarely, penetrating wounds or foreign bodies can initiate endocarditis.225,339 Piercings of various body parts also have been associated with endocarditis.2,443 One important group of patients with an increased risk for development of infective endocarditis is intravenous drug users.348,599 A predilection for involvement of the tricuspid valve, followed by the mitral and aortic valves, has been noted.174 Radiographic evidence of septic pulmonary emboli and signs of tricuspid insufficiency dominate the clinical findings.489 Within this group of patients, increased rates of infective endocarditis and mortality are associated with infection by human immunodeficiency virus (HIV), particularly as CD4 cell counts fall to less than 200/mm3.436

258

SECTION 3  Infections of the Heart

Several recent studies have found an apparent shift in the epidemiology of pediatric infective endocarditis toward a higher proportion of children without preexisting heart disease, which accounted for 35% to 58% of all the infective endocarditis cases.116,301,316 In these patients, S. aureus was the most common causative organism, and delay in diagnosis was common. Although the incidence of infective endocarditis in children may be rising, the prognosis has improved dramatically during the past several decades. Current mortality rates usually are close to 10%.379,475,494 Most survivors remain hemodynamically stable at long-term follow-up.161,494 However, patients who experience infective endocarditis appear to be at higher risk for developing recurrent endocarditis than are those with similar cardiac abnormalities who have not had previous endocarditis.516 The patient’s functional class before treatment appears to be most predictive of long-term functional status. In one study, 22% of children who survived infective endocarditis required surgery related to the infection, including vegetectomy, evacuation of a hematoma, atrioventricular valve replacement, and placement or replacement of a graft or intracardiac shunt.475

PATHOPHYSIOLOGY Clinical observations, autopsy studies, and work with experimental animal models have demonstrated that the occurrence of several independent events is required for the development of subacute infectious endocarditis. The endocardial surface usually is disrupted by stress or injury commonly caused by the turbulence of blood. This surface damage results in the deposition of fibrin and platelets, which form nonbacterial thrombotic vegetations. If bacteria adhere to these deposits, infective endocarditis will result. The surface of the infected vegetation becomes protected by a cover of fibrin and platelets. A tremendous proliferation of organisms (as many as 109 CFU/g) may ensue.131 The protective sheath isolates the organisms from the action of host neutrophils and antibiotics. The clinical manifestations and complications of infective endocarditis are related to both the hemodynamic changes caused by local infection and the occurrence of embolization and metastatic infection. In experimental animals, the valvular surface must be damaged, usually by an intravenous catheter, to produce infective endocarditis.22 The first step in the pathogenesis of subacute infective endocarditis in humans is the development of hemodynamic factors that favor endocardial damage. In an autopsy study of 1024 patients with infective endocarditis, Lepeschkin306 showed that the location of the endocardial lesions correlated with the impact of pressure; this finding makes a strong argument for the role of mechanical stress as a critical factor in the evolution of the lesions. When associated with valvular insufficiency, infective endocarditis usually occurs on the atrial surface of the mitral valve and the ventricular surface of the aortic valve. Injection of a bacterial aerosol into the air stream passing through a Venturi tube

demonstrates how high pressure drives an infected fluid into a lowpressure sink.457 This process establishes maximal deposition of bacteria in the low-pressure sink immediately beyond the orifice. Mitral insufficiency creates a Venturi effect when blood is driven from the highpressure left ventricle into a low-pressure atrium; maximal deposition occurs around the mitral annulus on the atrial side. Similarly, with aortic valve insufficiency, the high-pressure source is the aorta, and the low-pressure sink is the left ventricle, which leads to deposition on the ventricular surface of the valve. Lesions also are created more directly by a jet stream causing endocardial damage. For example, in a small, restrictive ventricular septal defect with a left-to-right shunt, a Venturi effect leads to the development of lesions on the right ventricular septal side of the defect, whereas secondary lesions created by the jet effect are located on the right ventricular wall opposite the defect.587 Heart defects with a surface area sufficiently large to prevent a significant pressure gradient and those in which smaller volumes minimize the gradient do not create the jet and Venturi effects. This difference helps to explain the rarity of endocarditis in patients with atrial septal defects and the increased risk of infection complicating small, but not large, ventricular septal defects. Once endocardial damage has occurred, collagen is exposed and platelet and fibrin deposition ensues in a manner analogous to formation of the primary plug of normal hemostasis after vascular injury.253,588 The sterile platelet-fibrin thrombus that is formed subsequently is referred to as a nonbacterial thrombotic vegetation.322,412 Formation of the vegetation reflects two pathogenic mechanisms: hypercoagulability and endothelial damage.489 To establish experimental infective endocarditis without initial formation of the vegetation is nearly impossible. Microscopic examination demonstrates that this lesion is the one to which microorganisms attach during the early stages of experimental endocarditis. Nonbacterial thrombotic vegetations have been found in both adults and children with malignancy, chronic wasting diseases, uremia, connective tissue diseases, and congenital heart disease and after the placement of intracardiac catheters,349,450 and they have been associated with embolism and infarction in distant organs.50 Once a nonbacterial thrombotic vegetation has been established, transient bacteremia or fungemia may result in colonization of the lesion. Transient bacteremias are common occurrences, especially with traumatization of a mucosal surface. The incidence of bacteremia in adults and children after various procedures is listed in Table 26.2.143,455 The bacteremia usually is of low grade and is proportional to the amount of trauma produced by the procedure and the number of organisms inhabiting the surface. In addition, “silent” bacteremia probably occurs frequently. Many persons have circulating antibodies to their own oral flora, as well as an increase in peripheral T cells sensitized to the flora of their dental plaque.489 Some children with congenital heart disease may be at increased risk for having gingival colonization and subsequent

TABLE 26.2  Bacteremia After Various Procedures in Adults and Children Initiating Event Dental extraction (children) Chewing gum, candy, paraffin Tooth brushing Tonsillectomy Bronchoscopy (rigid scope) Bronchoscopy (fiberoptic) Orotracheal intubation Nasotracheal intubation/suctioning Sigmoidoscopy/colonoscopy Upper gastrointestinal endoscopy Percutaneous liver biopsy Urethral catheterization Manipulation of S. aureus suppurative foci

Positive Blood Cultures (%) 30–65 0–51 0–26 28–38 15 0 0 16 0–9.5 8–12 3–14 8 54

Predominant Organisms Streptococcus, diphtheroids Streptococcus, Staphylococcus epidermidis Streptococcus Streptococcus, Haemophilus, diphtheroids Streptococcus, S. epidermidis

Streptococcus, aerobic gram-negative rods Enterococcus, aerobic gram-negative rods Streptococcus, Neisseria, S. epidermidis, diphtheroids, other Pneumococcus, aerobic gram-negative rods, Staphylococcus aureus, other Not stated

From Everett ED, Hirschmann JU. Transient bacteremia and endocarditis prophylaxis: a review. Medicine (Baltimore). 1977;56:61–77.

CHAPTER 26  Infective Endocarditis development of bacteremia with organisms associated with infectious endocarditis, such as the HACEK (Haemophilus spp., Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, Kingella kingae) microbes.517 The ability of microorganisms to adhere to the platelet-fibrin thrombus is a critical factor in the development of infective endocarditis.110,209,253 In a canine model, S. aureus and the viridans streptococci, which frequently cause infective endocarditis, adhere more readily to normal aortic leaflets than do organisms uncommon in endocarditis.197 Within isolates of S. aureus, strains devoid of microencapsulation are less capable of inducing endocarditis in an experimental model than are encapsulated strains.21 Specific products released by these organisms, including dextran, mannan, teichoic acid, and slime, may enhance their ability to colonize the vegetation.253,281 The amount of dextran produced by various viridans streptococci in broth correlates with both their adherence and their ability to produce endocarditis in the rabbit model.371,491 Candida albicans is readily adherent and produces infective endocarditis in rabbits more easily than does C. krusei, a nonadherent yeast rarely implicated in human infective endocarditis.487 In addition, endocarditis-producing strains of streptococci and staphylococci are more potent stimulators of platelet aggregation than are other bacteria that do not produce infective endocarditis.93,218,371 This action may accelerate the formation of an infected vegetation or may increase the removal of organisms from the circulation. The importance of adherence by organisms has been studied by preincubating organisms with many classes of antibiotics. After incubation at subinhibitory concentrations, adhesion of streptococcal species to fibrin-platelet matrices and damaged canine valves is decreased.492 Antibiotics may prevent development of infective endocarditis by both bacterial killing and inhibition of adherence to the vegetation.191 Host tissue factors undoubtedly play an important role in adherence of bacteria to the developing thrombus. Activation of the coagulation system ensues once bacteria become adherent to a nonbacterial thrombus. Some organisms that produce endocarditis may be able to initiate procoagulant activity through microbial enzymes. Activation of the intrinsic coagulation pathway is triggered by exposed connective tissue components and platelet aggregation.281 However, activation of the extrinsic coagulation pathway probably is the major stimulus for growth of vegetations. Elements of the extracellular matrix, including fibronectin, laminin, and collagen, have been shown to facilitate the adherence of bacteria on fibrin-platelet matrices.532,557 Fibronectin may be the host receptor for organisms within the nonbacterial thrombotic vegetation.292,324 Laminin-binding proteins have been found on the cell walls of organisms recovered from patients with endocarditis.511 The platelet-organism interaction is complex and not understood completely. Streptococcus sanguinis produces two cell surface antigens that promote platelet aggregation: a class I antigen promotes adhesion of S. sanguinis to platelets, whereas coexpression of a class II antigen promotes platelet adhesion or aggregation.219 The induced platelet aggregation appears to be an important determinant of further development of vegetation and progression of disease in experimental endocarditis. In addition, production of streptococcal exopolysaccharide inversely correlates with platelet adhesion while inhibiting aggregation, thus indicating that surface molecules may enhance endocarditis at only certain pathogenic steps.529 Platelets also may be involved in host defense within the vegetation. After exposure to thrombin, platelets may release microbicidal proteins with bactericidal activity against some gram-positive cocci; resistance to these proteins may be a virulence factor for S. aureus in the development of endocarditis.398,605 As bacterial colonization of a nonbacterial thrombotic vegetation progresses, it enlarges by further bacterial proliferation and platelet-fibrin deposition (Fig. 26.1).374 Kissane286 described three histologic zones: (1) necrotic endocardium; (2) a broad zone of bacterial colonies, pyknotic nuclear debris, and fibrin; and (3) a thin coating on the surface of fibrin and leukocytes. The location of bacterial colonies below the surface and the minimal infiltration by phagocytic cells create an environment of impaired host resistance that results in extreme bacterial proliferation. The structure of the vegetation diminishes the penetration of antibiotics into the bacterial layer. In addition, the metabolic activity of bacteria within this lesion is slowed, thus rendering antibiotics less effective.

259

FIG. 26.1  Subacute endocarditis of the mitral valve with vegetation and rupture of the papillary muscle caused by Staphylococcus aureus. (Courtesy of Dr. Edith P. Hawkins, Texas Children’s Hospital, Houston.)

The formation of vegetations and erosion of heart valves may cause valvular incompetence and thereby may result in cardiac failure. Immunopathologic factors may have important roles in both the development and sequelae of infective endocarditis.42 The susceptibility of a gram-negative bacillus to complement-mediated bactericidal activity is critical to its potential to create endocarditis.130 Gram-positive cocci are a more frequent cause of infective endocarditis than are gram-negative bacilli. Gram-positive organisms are resistant to this bactericidal activity; phagocytosis is required for killing. The frequent presence of hypergammaglobulinemia, splenomegaly, and monocytes in the blood of patients with infective endocarditis indicates stimulation of the humoral and cellular immune systems. Macroglobulins, cryoglobulins, and agglutinating, opsonic, and complement-fixing antibodies have been associated with infective endocarditis.228,300 Studies in animals preimmunized with heat-killed streptococci before aortic valve trauma and infection are induced suggest that circulating antibody has a protective role.490,567 However, antibody to S. aureus or Staphylococcus epidermidis does not prevent the development of endocarditis in immunized animals, perhaps because this antibody does not enhance opsonophagocytosis.489 The continuous antigenic challenge created by intravascular organisms leads to increased production of specific antibody (including opsonic, agglutinating, and complement-fixing antibodies), cryoglobulins, macroglobulins, and antibodies to bacterial heat shock protein,439 as well as to the subsequent formation of circulating immune complexes. These complexes are found with increased frequency in patients with a long duration of illness, hypocomplementemia, extravalvular manifestations, and right-sided disease.41 Quantitative levels of circulating immune complexes may be helpful in distinguishing endocarditic from nonendocarditic sepsis and in monitoring anti-infective therapy. Effective treatment usually leads to a prompt decrease in these levels,40 whereas relapses may be characterized by rising titers.273 The diffuse glomerulonephritis occasionally noted with infective endocarditis is caused by subepithelial deposition of immune complexes and complement.204 Immune complexes can be demonstrated in some diffuse purpuric lesions seen with endocarditis.323 Bacterial antigens have been found within these complexes.241 Further evidence of stimulation of the immune system in infective endocarditis is the development of rheumatoid factor in approximately 50% of adults with disease lasting longer than 6 weeks.594 Titers of rheumatoid factor correlate with hypergammaglobulinemia and, as with immune complex levels, decrease with therapy and increase during relapse. The role of rheumatoid factor in the disease process is unknown, but it may be involved by blocking immunoglobulin G opsonic activity, stimulating phagocytosis, or accelerating microvascular damage.489 Antinuclear, antiendocardial, antisarcolemmal, and antimyolemmal

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SECTION 3  Infections of the Heart

antibodies also have been identified in patients with infective endocarditis; their role in pathogenesis is unclear.332 The pathologic changes that occur in the heart in association with infective endocarditis are secondary to local extension of the infection. The vegetations vary from a millimeter to several centimeters; frequently they are singular, but they may be multiple. Valvular stenosis may result from large lesions. Vegetations secondary to certain organisms, especially Candida, Haemophilus, and S. aureus in acute cases, often are large and friable, with a propensity for embolization.606 Ulcerative lesions may occur and may lead to perforation of the valve and subsequent congestive heart failure. Other local complications include rupture of the chordae tendineae or papillary muscle (see Fig. 26.1), valve ring abscess with subsequent fistula formation and pericardial empyema,55,71 aneurysms of the sinus of Valsalva or ventricle,84,179,485 myocarditis, and myocardial infarction.149 Persistent fever occurring during appropriate medical therapy for infective endocarditis may reflect a persistent vegetation, especially with right-sided disease, or extension of infection into a valve ring and adjacent structures.124 In such cases, surgery frequently is required. The pathologic changes in distant organs usually are secondary to embolization with subsequent infarction or metastatic infection. In many cases of infective endocarditis, the causative organism is of low pathogenicity; infections caused by septic emboli often are low grade because of the reduced propensity of these organisms to invade tissue. However, the emboli in acute S. aureus endocarditis frequently cause severe metastatic infections and overwhelming sepsis. Emboli from right-sided heart lesions lodge in the lungs and cause pulmonary infarcts and abscesses, which usually are small and multiple. Left-sided lesions may embolize to any organ but most commonly affect the brain, kidney, spleen, and skin.287,392 Cerebral emboli have been detected in 30% of cases in adults and children and have caused infarction, abscess, mycotic aneurysm, subarachnoid hemorrhage, meningitis, and acute hemiplegia of childhood.68,199,212,260,347,477,486,573 Kidney abscess is a rare occurrence, but infarcts are noted in most patients at autopsy.366 Amyloidosis involving primarily the kidneys is a rare complication of chronic infective endocarditis.217 Splenic abscess also is a rare event but can be a fatal complication if undetected.255 The most common manifestation of embolization to the skin is petechiae. Janeway lesions are septic emboli consisting of bacteria, neutrophils, necrosis, and subcutaneous hemorrhage. Osler nodes are areas of thrombosis and necrosis. They may be related to both immune complex deposition and septic emboli.5

CLINICAL MANIFESTATIONS The signs and symptoms of infective endocarditis are determined by the extent of local cardiac disease, the continuous bacteremia, and the degree of involvement of distant organs as a result of embolization, metastatic infection, and circulating immune complexes.26 Consequently the clinical findings are highly variable and mimic those of many other diseases.82,473 Unexplained embolic phenomena in any organ should suggest the diagnosis of endocarditis, especially in children with known heart disease. Patients with acute bacterial endocarditis initially may be seen with florid sepsis; the endocarditis is diagnosed at autopsy. The indolent manifestations of subacute endocarditis may evolve for weeks or months before medical care is sought. Endocarditis frequently occurs in children with preexisting heart disease, so subtle changes in cardiac function may be difficult to detect early in the course. The frequency of the major clinical manifestations of bacterial endocarditis in infants and children is listed in Table 26.3. Fever is the most common symptom of infective endocarditis, but it is absent in 10% of cases. It usually is of low grade and has no specific pattern. Chills may accompany the fever, but they rarely are seen in children. Persistent fever during antimicrobial therapy is an uncommon occurrence. Prolonged (≥2 weeks) fever is associated with certain etiologic agents (S. aureus, gram-negative bacilli, fungi), with culture-negative endocarditis, and with complications such as embolization of major vessels, intracardiac or peripheral abscess, tissue infarction, a need for cardiac surgery, and a higher mortality rate.56,302 Nonspecific symptoms such as malaise, anorexia, weight loss, and fatigue are common findings. Arthralgia occurs in 24% of patients. The arthralgia frequently is multiple

TABLE 26.3  Clinical Manifestations of Bacterial Endocarditis in Children Symptom Fever Malaise Anorexia/weight loss Heart failure Arthralgia Neurologic findings Gastrointestinal findings Chest pain Physical Finding Splenomegaly Petechiae Embolic phenomena New or change in heart murmur Clubbing Osler nodes Roth spots Janeway lesion Splinter hemorrhages

Average (%)

Range (%)

90 55 31 30 24 18 16 9

56–100 40–79 8–83 9–47 16–38 12–21 9–36 5–20

55 33 28 24 14 7 5 5 5

36–67 10–50 14–50 9–44 2–42 7–8 0–6 0–10 0–10

Data from references 57, 98, 100, 175, 257, 291, 345, 400, 473, 505, 513, 537, 546, and 571.

and most commonly affects the large joints. Although adults initially may have synovitis,91 this finding is rare in children. Osteoarticular infection in association with infective endocarditis in adults occurs almost exclusively in intravenous drug users.484 It is seen very rarely in children except those with disseminated S. aureus infection. Gastrointestinal complaints are noted in 16% of cases and include nausea, vomiting, and abdominal pain. Chest pain occurs in approximately 10% of older children and generally is mild and nonspecific. Although chest pain usually is related to diffuse myalgias, it may be secondary to pulmonary complications or cardiac lesions, especially if the tricuspid valve is involved. Heart murmurs occur in more than 90% of children with infective endocarditis, but most patients have underlying heart disease with existing murmurs. The appearance of a new murmur or appreciation of a significant change in a previous one occurs in only 25% of cases. Significant blood flow turbulence caused by compromised valvular function must have occurred for a murmur to be detected or to change. The frequent absence of changes in the cardiac examination early in the disease contributes to the long average delay in establishing the diagnosis, especially in children with preexisting heart disease. Congestive heart failure occurs in 30% of children with infective endocarditis and is especially common in those in whom a new murmur of valvular insufficiency develops. Endocarditis should be suspected in any child who has rheumatic or congenital heart disease and unexplained deterioration in cardiac function. Although valvular regurgitation is the most common hemodynamic complication of endocarditis, significant obstruction of a valve or shunt requiring rapid surgery rarely occurs.83 Neurologic signs and symptoms are reported in approximately 20% of children with endocarditis. These signs and symptoms may dominate the clinical findings, especially in patients with endocarditis caused by S. aureus.212,477 Neurologic abnormalities also are common in children with endocarditis caused by Kingella kingae.165 The sudden development of cerebral lesions in an infant or child should suggest this diagnosis. The manifestations are those that commonly accompany a cerebral infarct or abscess—namely, acute hemiplegia of childhood, seizures, ataxia, aphasia, sensory loss, focal neurologic deficits, and alterations in mental status.68 They may be the initial features of endocarditis or may occur years after the infection has been eradicated.610 Mycotic aneurysms of the cerebral vessels occur rarely in cases of pediatric

CHAPTER 26  Infective Endocarditis endocarditis.72 They usually are single, small, and peripheral but may lead to subarachnoid hemorrhage. Whereas computed tomographic scanning of the brain is useful for delineating central nervous system involvement in patients with infective endocarditis, magnetic resonance imaging may be more sensitive for detecting small infarctions and changes secondary to cerebral edema.47 Other neurologic manifestations associated with endocarditis include cranial nerve palsies, neuropathy, visual changes, choreoathetosis, seizures, and toxic encephalopathy. Splenomegaly, a common manifestation of endocarditis in children, occurs in 55% of cases. It is found frequently in patients with longstanding disease and other evidence of immune system activation. The spleen generally is nontender and may be associated with mild hepatomegaly. Splenic infarction and abscess are rare events but should be suspected in patients with left upper quadrant abdominal pain that radiates to the left shoulder, a pleural friction rub, or left pleural effusion. Skin manifestations occur less commonly in children than in adults.323 Clubbing is found in 10% to 20% of children with endocarditis but frequently is related to underlying heart disease. Petechiae are noted in approximately one-third of patients, especially those with long-standing disease. These lesions are found most commonly on the extremities, oral mucosa, and conjunctivae. Splinter hemorrhages are linear red or brown streaks seen in the nail beds. They are present in only 5% of children with endocarditis and are associated with other conditions.283 Three other types of lesions are more specific for infective endocarditis but occur in only 5% to 7% of patients: Osler nodes, which are small (2 to 10 mm), painful nodular lesions found in the pads of the fingers or toes5; Janeway lesions, which usually are painless hemorrhagic macular plaques that frequently occur on the palms and soles147; and Roth spots, which are small, pale retinal lesions associated with areas of hemorrhage located near the optic disk. Other than fever and, perhaps, splenomegaly, no single sign or symptom occurs in more than 50% of children with endocarditis. That no classic clinical manifestation exists for this disease is obvious because the chance that even three or more signs will be present is extremely low. The appearance of any one of these clinical features in a child with predisposing heart disease should raise suspicion of infective endocarditis and should lead to an appropriate diagnostic evaluation.84 The clinical findings of infective endocarditis in infants and neonates are less specific than are those in older children. The onset more often is acute and related to overwhelming infection.258,358 Infants with heart defects undergo corrective and palliative surgery at a younger age than in the past. Infants in whom postoperative endocarditis does develop probably will have clinical findings more similar to those in older children. Infective endocarditis is an uncommon occurrence in neonates and frequently is associated with indwelling vascular catheters.178,341 It may affect the tricuspid valve and have a fairly “silent” clinical manifestation. Persistent bacteremia or fungemia should lead to a search for a cardiac focus of infection. Deterioration in pulmonary function, coagulopathies, thrombocytopenia, and low-grade murmurs often develop in neonates. Skin abscesses and hepatomegaly also are common findings. Reported series of infective endocarditis in children with prosthetic valves are scarce. In early stages of disease, fever may be the only finding because the other signs of endocarditis are masked by the medical and surgical complications occurring in the immediate postoperative period. Late infections generally produce clinical findings similar to those in native valve endocarditis. Clinical evidence of systemic embolization occurs in as many as 40% of patients.86 Neurologic complications carry a particularly poor prognosis for survival.279 A new or changing murmur often indicates valvular insufficiency caused by a paravalvular leak. Florid cardiac failure is the major manifestation if local infection or an abscess creates valve instability and acute, severe regurgitation. The signs and symptoms of infective endocarditis in intravenous drug users may be similar, but these patients have several more distinctive features of their illness. Two-thirds of these patients have no predisposing heart disease. The valve most commonly affected is the tricuspid, which leads to a predominance of pulmonary signs and symptoms resulting from pleural effusion, pulmonary infarction, and lung abscesses. Signs of tricuspid insufficiency (gallop rhythm, pulsatile liver, regurgitant

261

murmur) are found in one-third of cases.489 Many patients have extracardiac sites of infection that are helpful in establishing the diagnosis.544

LABORATORY FINDINGS The most important diagnostic procedure is the blood culture. Because many bacteria that usually are not pathogenic cause infective endocarditis, scrupulous aseptic technique must be used to distinguish causative agents from contaminants.415 The yield of organisms is not increased by obtaining blood from arterial puncture or cardiac catheterization.43 The bacteremia usually is of low grade and continuous. The first two cultures yield the organism 90% of the time; in two-thirds of cases, all blood cultures are positive.591 Therefore, isolated positive cultures generally are not significant. Previous outpatient antibiotic therapy may change the yield significantly.277 In one study, culture positivity in cases of proven endocarditis was 64% in patients who received antibiotics before blood was drawn for culture versus 100% in patients without exposure to antibiotics.416 When Candida endocarditis is suspected, several additional points should be considered. Isolation of Candida spp. may require incubation for 1 week or longer. All blood cultures from a patient with Candida endocarditis may not be positive, in contrast to the usual situation with bacterial endocarditis; several positive cultures may be interspersed among negative cultures. In patients with fungal endocarditis, Candida is isolated commonly from other infected sites, such as urine, sputum, synovial fluid, cerebrospinal fluid, lymph nodes, and bone marrow.480 Three to five samples of blood for culture should be obtained from different sites within the first 24 hours in children with suspected endocarditis. Although difficult to obtain in smaller children, 3 to 5 mL of blood per culture is desirable for optimal yield. The samples should be injected into thioglycolate and trypticase soy (or brain-heart infusion) broth and held for at least 3 weeks to detect slow-growing organisms. However, one study has shown that the method of detection and not the time of incubation is critical to detect fastidious organisms. Baron et al.33 reported evidence that the Bactec9240 system can detect the HACEK organisms within 5 days. If gram-positive cocci grow in the broth but fail to grow on subculture, nutritionally variant streptococci should be suspected and subculture should be performed on media with either L-cysteine or pyridoxal phosphate.69,519 Negative blood cultures are noted in 10% to 15% of patients with clinically diagnosed endocarditis.560 However, when patients have not received antibiotic therapy previously and blood for culture is obtained properly, these cases account for less than 5% of the total. Potential reasons for negative cultures include the following: (1) right-sided endocarditis; (2) previous administration of antibiotics; (3) fungal (especially Aspergillus) endocarditis; (4) endocarditis caused by Bartonella spp., rickettsiae, chlamydiae, or viruses; (5) mural endocarditis; (6) slow growth of organisms (Candida, Haemophilus, Brucella, nutritionally variant streptococci); (7) anaerobic infection; and (8) nonbacterial thrombotic endocarditis or an incorrect diagnosis.207,211,425,560 In some instances, intraleukocytic organisms may be seen in layered peripheral blood, even when cultures are negative.433 If surgical resection of vegetations or valve replacement is performed, a cause may be demonstrated by appropriate histologic examination and stains for bacteria and fungi.374 Molecular testing (universal bacterial, fungal, or mycobacterial (polymerase chain reaction [PCR]) for organisms in the valvular tissue may reveal the causative organism and likely will be more widely available in the future.506 Organisms also may be isolated from extracardiac sites (bone marrow, urine). Many nonspecific laboratory findings are abnormal in patients with infective endocarditis (Table 26.4). The total white blood cell count rarely is helpful, but peripheral eosinophilia may be seen with Loeffler endocarditis.227 Leukocytosis occurs in a few patients, but leukopenia is a rare finding in the absence of acute endocarditis with overwhelming sepsis. The erythrocyte sedimentation rate is elevated in 80% to 90% of cases. However, frequently it is normal or low when congestive heart failure or renal failure is present. Serum C-reactive protein levels usually are elevated initially and return to normal during the course of successful

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SECTION 3  Infections of the Heart

TABLE 26.4  Selected Laboratory Findings of Bacterial Endocarditis in Children Laboratory Finding

Average (%)

Range (%)

Positive blood culture Elevated erythrocyte sedimentation rate Low hemoglobin (anemia) Positive rheumatoid factor Hematuria

87 80

68–98 71–96

44 38 35

19–79 25–55 28–47

Data from references 56, 98, 175, 255, 291, 345, 505, 513, 546, and 571.

therapy.350 An increase during therapy may result from treatment failure, but it can also be caused by drug allergy or intercurrent infection. Rheumatoid factor rarely has been measured in a series of pediatric patients, but when measurements have been made, they have been positive in 25% to 50% of children with endocarditis. A positive test may be a diagnostic aid in cases of culture-negative endocarditis when other causes are excluded. Serial measurements may provide evidence of efficacy of therapy, although a fall in the titer of rheumatoid factor may lag behind the clinical and bacteriologic response.580 Hypocomplementemia is seen in association with glomerulonephritis. Anemia is present in approximately 40% of patients, especially those with longstanding disease. Although hemolysis may occur in the areas of turbulence in the heart, more often it is anemia of chronic disease. Because many patients with cyanotic heart disease normally have a compensatory polycythemia, a serial drop in hematocrit is of more significance than is a single measurement. Hematuria and proteinuria, present in 25% to 50% of cases, usually are secondary to microemboli in the kidneys and may be accompanied by “pyuria,” casts, and bacteriuria. Circulating immune complexes are present in most adults with subacute endocarditis, as measured by Raji cell radioimmunoassay547 or the 125I-Clq binding assay.611 These immune complexes frequently are absent in acute endocarditis. Low levels of immune complexes have been found in 32% of adults with septicemia but not endocarditis, in 10% of normal controls, and in 40% of noninfected intravenous drug users.41 However, levels higher than 100 µg/mL are correlated highly with the presence of endocarditis. Serial measurement of immune complex levels may aid in monitoring therapeutic efficacy.40 Systematic investigation of immune complexes has been reported infrequently in children with endocarditis. When immune complexes have been sought, most patients, including two of three children with culture-negative endocarditis, have had significant levels. When infective endocarditis is suspected but blood cultures remain negative, serologic testing for specific organisms may prove helpful. Antibodies to teichoic acid, major components of the S. aureus cell wall, are present in more than 85% of adults with staphylococcal endocarditis, but the false-positive rate is as high as 10%.389 False-negative results correlate with a short (60 kg) children but did not improve on the results of transthoracic echocardiography in smaller children.422 It is significantly more sensitive in the detection of vegetations and complications in infected prosthetic valves.280,417,459,522,536 TEE is particularly useful for detecting an aortic root abscess or involvement of the sinus of Valsalva in adults, and it should be considered in children with aortic valve endocarditis and changing aortic root dimensions on a standard transthoracic echocardiogram.159,355 It appears to be less helpful for detection of vegetations in right-sided endocarditis.479 Although a negative transesophageal echocardiographic study does not exclude endocarditis,510 the procedure should be considered for patients with suspected endocarditis and a negative transthoracic echocardiogram, when the transthoracic echocardiographic windows are suboptimal, and when perivalvular extension of infection is suspected.16,237 To aid in establishing the diagnosis of infective endocarditis, various sets of clinical criteria have been suggested.576 The most widely used diagnostic criteria were proposed by investigators from Duke,133 and they have been modified subsequently (Boxes 26.1 and 26.2).297,312,360 These criteria have been validated in large series of infective endocarditis in adults and children.117,133,222,453,482 In two pediatric series of clinically defined endocarditis, no cases were rejected by the Duke criteria, whereas 25% and 19% were rejected by older criteria.117,524 However, one study found that 12% of pediatric endocarditis cases were not classified as “definite” by the modified Duke criteria.549 In addition, the presence of an indwelling venous catheter causing prolonged bacteremia may cause an overestimation of the rate of infective endocarditis using the Duke criteria.45

MICROBIOLOGY Many different microorganisms are capable of causing infective endocarditis in humans.242 A list of the organisms isolated from patients in major pediatric series is presented in Table 26.5. Gram-positive cocci are the etiologic agents in 90% of cases in which an organism is isolated. Streptococci remain the bacteria isolated most frequently, although the percentage of cases caused by staphylococci and fungi has been increasing during the past two decades.170,475,571,606 In a preliminary study, Gupta

TABLE 26.5  Etiologic Agents of Bacterial Endocarditis in Children Organism Streptococci  Viridans  Enterococci  Pneumococci   β-Hemolytic  Other Staphylococci   Staphylococcus aureus  Coagulase-negative Gram-negative aerobic bacilli Fungi Miscellaneous bacteria  Culture-negative

Average (%)

Range (%)

40.3 4.0 3.3 2.7 1.1

17–72 0–12 0–21 0–8 0–16

23.8 4.7 4.0 1.1 2.4 12.6

5–40 0–15 0–15 0–12 0–10 2–32

Data from references 57, 67, 100, 253, 255, 256, 291, 358, 475, 513, 546, and 571.

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et al.203 used the Nationwide Inpatient Sample to study the incidence, pathogens, and outcomes of infective endocarditis in children admitted to hospitals in the United States from 2000 to 2010. Streptococcus spp. were most common (40.1%), followed by S. aureus in 36.6% of the 3840 patients reported.203 Polymicrobial infective endocarditis, especially in nosocomial settings, also appears to be increasing in incidence.24 The characteristics of selected organisms and the type of disease that they produce are considered next.

Streptococci Several terminologies have been used to classify streptococci. The Lancefield system defines groups (A, B, C, D, E, F, G, H) by serologic reactions. The viridans streptococci are α-hemolytic or nonhemolytic, may be Lancefield nontypeable (Streptococcus anginosus [formerly S. milleri], S. mitior, S. salivarius, most S. mutans, and S. sanguinis) or typeable (S. bovis group D, some S. sanguinis group H, some S. anginosus group F), and display similar characteristics in vivo. They are the most frequent etiologic agents in subacute infective endocarditis and cause 40% of cases in children. They may cause rapidly progressive invasive disease.229,531 Viridans streptococci are common pathogens in patients with underlying heart disease but are less common in postoperative patients. They are part of the indigenous flora of the human mouth and

BOX 26.1  Definition of Terms Used in the Modified Duke Criteria for Infective Endocarditis Major Criteria 1. Positive blood culture a. Typical microorganisms for IE from ≥2 blood cultures (1) Viridans streptococci, Streptococcus bovis, HACEK group, Staphylococcus aureus or (2) Enterococci, in the absence of another primary focus, or b. Persistently positive blood cultures, with recovery of a microorganism consistent with IE from (1) Blood cultures drawn ≥12 hours apart or (2) All of three or a majority of four or more separate blood cultures, with first and last drawn ≥1 hour apart 2. Evidence of endocardial involvement a. Positive echocardiogram for IE (1) Oscillating intracardiac mass on valve or supporting structures, in the path of regurgitant jets, or on implanted material, in the absence of an alternative anatomic explanation, or (2) Abscess or (3) New partial dehiscence of a prosthetic valve or (4) New valvular regurgitation (increase or change in preexisting murmur is not sufficient) Minor Criteria 1. Predisposing heart condition or intravenous drug use 2. Fever ≥38°C (100.4°F) 3. Vascular phenomena: major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial hemorrhage, conjunctival hemorrhages, Janeway lesions 4. Immunologic phenomena: glomerulonephritis, Osler nodes, Roth spots, rheumatoid factor 5. Microbiologic evidence: positive blood culture but not meeting major criteria as noted previouslya or serologic evidence of active infection with organism consistent with IE HACEK, Haemophilus spp., Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, Kingella kingae; IE, infective endocarditis. a Excluding single positive cultures for coagulase-negative staphylococci and organisms that do not cause IE. From Li JS, Sexton DJ, Mick N, et al. Proposed modifications to the Duke criteria for the diagnosis of infective endocarditis. Clin Infect Dis. 2000;30:633–8.

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SECTION 3  Infections of the Heart

BOX 26.2  Modified Duke Criteria for the Diagnosis of Infective Endocarditis Definite 1. Pathologic criteria a. Microorganisms: demonstrated by culture or histology in a vegetation, in a vegetation that has embolized, or in an intracardiac abscess or b. Pathologic lesions: vegetation or intracardiac abscess present and confirmed by histology showing endocarditis 2. Clinical criteria (see Box 26.1) a. Two major criteria or b. One major and three minor criteria or c. Five minor criteria Possible 1. One major criterion and one minor criterion, or 2. Three minor criteria Rejected 1. Firm alternative diagnosis explaining evidence of IE or 2. Resolution of IE syndrome with antimicrobial therapy for ≤4 days or 3. No pathologic evidence of IE at surgery or autopsy with antibiotic therapy for ≤4 days IE, Infective endocarditis. From Li JS, Sexton DJ, Mick N, et al. Proposed modifications to the Duke criteria for the diagnosis of infective endocarditis. Clin Infect Dis. 2000;30:633–8.

gastrointestinal tract, and procedures that disrupt mucosal integrity in these areas predispose patients to development of viridans streptococcal bacteremia. In the pediatric population, most blood and cerebrospinal fluid isolates of viridans and nonhemolytic streptococci are not from patients with infective endocarditis.210 Most strains are exquisitely susceptible to penicillin, although resistance has been increasing related to previous administration of antibiotics.289,308 Nutritionally variant viridans streptococci, reclassified as Abiotrophia defectiva or Granulicatella spp., are recognized as one cause of culture-negative endocarditis in children and can cause endocarditis in children without congenital heart disease.48,81,150,315,393,441,456 These organisms grow in broth but will not grow on subculture agar-based plates. Bacteriologic failure has occurred in 40% of reported cases of endocarditis caused by these organisms despite susceptibility to the antibiotics used.26,519 Most viridans streptococci have low pathogenicity; however, the S. anginosus group has a predilection for suppurative complications.385 The prognosis of endocarditis caused by nonenterococcal streptococci is excellent with good medical and surgical management; the cure rate is greater than 90%, although complications (emboli, congestive heart failure) occur in as many as 30% of cases. Enterococcal endocarditis occurs much less frequently in children than in adults357,543,545 and accounts for only 4% of pediatric cases. The organism normally inhabits the gastrointestinal and genitourinary tracts; instrumentation of these areas may cause enterococcal bacteremia. More than 40% of adult patients have no underlying heart disease.451 Endocarditis should be considered in all infants and children with unexplained enterococcal bacteremia. Although the incidence of enterococcal bacteremia appears to be increasing in some neonatal intensive care units, the incidence of associated endocarditis seems to be very low. Factors that may suggest endocarditis in patients with enterococcal bacteremia include (1) preexisting heart disease, (2) community acquisition, (3) a cryptogenic source, and (4) the absence of polymicrobial bacteremia.333 Differentiation of enterococci from other group D streptococci (S. bovis) is important because their respective therapeutic approaches are different. Endocarditis caused by β-hemolytic streptococci occurred more commonly in the preantibiotic era than today. Most cases are caused by Lancefield group B or G organisms,1,18,67,177,586 whereas group C and

A streptococci rarely cause endocarditis.53,125,193,321,444 Group A, B, or C streptococcal infection may lead to large, bulky vegetations, easily seen by echocardiography, and to embolic complications.19,369,478 Although group B streptococcal bacteremia is a common finding in neonates, endocarditis caused by this organism occurs rarely in this age group. Similarly, S. pneumoniae accounted for 10% to 15% of endocarditis cases in the preantibiotic era but currently causes less than 1%.181,247,406 Pneumococcal endocarditis may involve either the aortic or the mitral valve.139,190,553 In older studies, fewer than 50% of affected children had underlying heart disease, but in more recent series, most children have had existing heart disease.243 The clinical course often is fulminant.136,304,431 Concurrent meningitis or pneumonia (or both) occurs frequently. Valvular dysfunction and cardiac decompensation are common findings.56,64,87 Early surgical intervention may be required because the mortality rate is 75% when medical management alone is used.247

Staphylococci Staphylococci cause 20% to 30% of cases of infective endocarditis in children, but the relative incidence appears to be increasing, and in some series this organism has been more common than streptococci.6,170 S. aureus is the etiologic agent in most cases of acute endocarditis and frequently infects normal heart valves.171,342,378 The course often is fulminant when the mitral or aortic valve is involved, with frequent suppurative complications occurring both in the heart (myocardial abscess, pericarditis, valve ring abscess) and in other organs.142,261,365 S. aureus is responsible for more than 50% of cases of endocarditis in intravenous drug users, but the disease tends to be less severe in these patients.79,80 The origin of the infecting organism is the addict’s own nose or skin, not the injection paraphernalia.559 Endocarditis associated with indwelling vascular catheters or prosthetic valves frequently is caused by S. aureus.252 Endocarditis must be suspected in any patient with S. aureus bacteremia, even when a peripheral focus of infection is present.464 However, most patients with S. aureus bacteremia do not have endocarditis. A risk score may help to determine which adults with S. aureus bacteremia should have an echocardiogram due to increased likelihood of endocarditis.408 However, this risk score has not been evaluated in children and thus may or may not be useful in pediatric patients with S. aureus bacteremia. The rise of methicillin-resistant S. aureus (MRSA) has rendered treatment more difficult but has had little impact on the rate of local complications.235 CONS is a common etiologic agent of endocarditis occurring after cardiac surgery,14,278,317 and it is occurring more frequently on native valves.88,89 This organism is the leading agent in prosthetic valve endocarditis, for which it causes 25% to 67% of early cases and 25% to 33% of late cases.187,244,268 CONS endocarditis also has been associated with mitral valve prolapse and the use of intravascular catheters in premature neonates.25,401 Although metastatic infection rarely occurs, CONS can be locally invasive; the mortality rate of prosthetic valve endocarditis caused by CONS approaches 75% when valve replacement is not performed.

Gram-Negative Organisms Although gram-negative bacteria cause 4% to 5% of cases of infective endocarditis in children, the percentage of children with gram-negative enteric bacteremia in whom endocarditis develops is extremely low. Endocarditis should be suspected in patients with gram-negative infection when bacteremia persists despite administration of usually appropriate antibiotic therapy.74 Burn patients,239 immunosuppressed hosts, narcotic addicts, and patients with implanted endovascular devices373 are at an increased risk for development of gram-negative endocarditis. However, in the early postoperative period after cardiac surgery, sustained gramnegative bacillary bacteremia commonly is caused by other foci of infection and does not imply the presence of endocarditis. Many species of gram-negative enteric organisms have caused infective endocarditis in children, but no clear pattern has emerged. Among the gram-negative organisms more commonly reported are Brucella, Escherichia coli, Serratia, Klebsiella-Enterobacter, Salmonella, and Pseudomonas.119,290,325,373,533,541 Endocarditis caused by Salmonella has been reported in patients with HIV infection.156 It most often affects previously abnormal heart valves.

CHAPTER 26  Infective Endocarditis Endocarditis is a rare complication of tularemia.539 Cure of left-sided endocarditis caused by the Enterobacteriaceae seldom is achieved with medical therapy alone.489 Most information about gram-negative enteric endocarditis is limited to case reports and general medicine reviews; discussion of individual organisms is beyond the scope of this review. Other gram-negative organisms associated with infective endocarditis are the so-called HACEK coccobacilli.111,151,236 These organisms caused 57% of cases of gram-negative endocarditis seen at the Mayo Clinic in Rochester, Minnesota, from 1958 to 1979.183 Endocarditis caused by Haemophilus influenzae has been reported in only several children.106,337 Cases caused by H. parainfluenzae and H. aphrophilus occur slightly more commonly.49,90,112,236,250,327,423 They generally are seen in the setting of preexisting valvular disease and run a subacute course. However, central nervous system complications and emboli to major peripheral arteries are frequent occurrences.90 Infective endocarditis caused by other organisms of the HACEK group is an extremely rare event in children.13,152,331,377,413,440,590 Infection caused by K. kingae is being recognized more frequently due to recognition and enhanced culture techniques.127,128,226 In one study from Israel, one clone of K. kingae in particular was associated with infective endocarditis compared with other invasive phenotypes.9 All the bacteria in this group are fastidious, may require 2 to 3 weeks for primary isolation, and need subculturing onto chocolate agar in an atmosphere of 5% to 10% carbon dioxide for optimal growth. These procedures should be performed in all cases of culture-negative endocarditis. Neisseria gonorrhoeae was responsible for 10% of cases in the preantibiotic era, but fewer episodes have been reported since 1942.155,245 This pathogen frequently attacks previously normal heart valves and is manifested as an acute illness.540 Valvular destruction with a need for valve replacement occurs commonly. At present, nonpathogenic Neisseria spp. are isolated more frequently in endocarditis than are gonococci, but they usually attack abnormal or prosthetic valves.61,215,230,240,428,465,496 Although 1% of cases of infective endocarditis in adults are caused by anaerobic bacteria,153 reports of anaerobic endocarditis in children are exceedingly rare.95,394,508,527

Gram-Positive Bacilli Infective endocarditis caused by Corynebacterium spp. is an unusual finding but may occur on normal or previously abnormal valves.44,359 Both toxigenic115 and nontoxigenic201,493,509,548 strains of C. diphtheriae cause endocarditis in children, a finding demonstrating that the toxigenic and invasive properties of the organism are independent. Infection occurs most often on native valves and may be quite aggressive and lead to major vascular complications. Listeria monocytogenes endocarditis rarely occurs, has a high mortality rate, and, unlike other forms of listeriosis, usually is not associated with immunocompromised hosts.38,75 It has not been associated with listeriosis in neonates. Fewer than 40 cases of Lactobacillus endocarditis have been reported.200,238,530 Endocarditis caused by Erysipelothrix rhusiopathiae is found predominantly in adults who are farmers or are exposed to farm animals or products.195,213 Most cases of Bacillus endocarditis involve the tricuspid valve in intravenous drug users, but other patients have been affected, including those with prosthetic valves.518 Gemella morbillorum (formerly Streptococcus morbillorum) is a gram-positive coccus that normally resides in the gastrointestinal tract and is a rare cause of endocarditis.146,293,437

Other Organisms Many different bacteria, including Acinetobacter,198 Stenotrophomonas,458 Nocardia,582 Actinomyces,296 Streptobacillus,467 and Rothia,528 have been associated rarely with endocarditis.63 Mycobacterial endocarditis is an exceedingly infrequent event.176 Infective endocarditis caused by Coxiella burnetii, the causative agent of Q fever, is well documented in northern Africa, Europe, and Australia.4,62,299,311,368 Most cases are chronic (occurring over a 6- to 12-month period) and involve the aortic valve.335 Clues to establishing the diagnosis include exposure to parturient cats or rabbits, massive splenomegaly, hypergammaglobulinemia, and thrombocytopenia.426 The diagnosis usually is confirmed by measurement of antibodies against phase I and phase II antigens, but the organism has been isolated from leukocytes in a shell vial assay and has been demonstrated by immunohistologic

265

techniques.62,189 At least 20 well-documented cases of infective endocarditis caused by Chlamydia psittaci and Chlamydophila pneumoniae (formerly Chlamydia pneumoniae) have been reported.223,259,344,503 Most patients have had preexisting heart disease and a subacute course.336 Mycoplasma endocarditis is exceedingly rare.123 Legionella has been implicated in several cases of prosthetic valve endocarditis.554 Bartonella quintana and B. henselae have been identified as the cause of endocarditis in “culture-negative” cases.113,126,224,249,512 Most described cases have been in immunocompetent individuals.427 The diagnosis was established by serology, PCR, or special culture techniques.30,154,166,445,578 Although culture of bacteria remains the primary method for establishing the microbial cause of infective endocarditis, the number of organisms causing endocarditis that cannot be cultivated by standard culture methods is growing.167,232 More recently, universal and speciesspecific primers have been designed to amplify bacterial DNA directly from resected valves. Among the organisms causing endocarditis identified by these methods are Bartonella, Tropheryma whippelii, Coxiella, Mycoplasma, Haemophilus, Abiotrophia, Gemella, Cardiobacterium, and Streptococcus.180,194,232,319,438

Fungi Most cases of fungal endocarditis in children have been described as occurring after cardiovascular surgery and prolonged intravenous and antibiotic therapy.138,144,362,550 More recently, cases have been reported in neonates349 and after prosthetic valve placement.397 The most common causative organism is C. albicans, although disease has been attributed to other Candida spp., including C. krusei, C. parapsilosis, C. stellatoidea, C. tropicalis, and C. guilliermondii.435,480,498 Among intravenous drug users, Candida spp. other than C. albicans are more common causes of endocarditis.466 The clinical manifestation usually is indolent and not specific, with symptoms occurring weeks to months before the diagnosis is established. Signs and symptoms caused by emboli to large vessels, especially those supplying the brain, kidney, spleen, and extremities, should alert the physician to the possible presence of fungal endocarditis. Large, friable vegetations occur frequently and can be detected by echocardiography.525 Cutaneous and ocular manifestations of systemic Candida infection may be present.58 The prognosis of Candida endocarditis is poor and is related to the propensity for septic emboli, the tendency for invasion into the myocardium, and the poor penetration of antifungal agents into the bulky vegetation. The diagnosis frequently is delayed by the tendency for negative or intermittently positive blood cultures to occur in this disease.254 Surgical intervention usually is required. Aspergillus spp., including A. flavus, A. fumigatus, A. terreus, and A. niger, are the second most frequent causes of fungal endocarditis.34,35,399 Two-thirds of reported pediatric patients had underlying heart disease. Aspergillus endocarditis has been found in immunocompromised hosts with no previous cardiac problems.603 The most common initial manifestations are fever and embolic phenomena, especially to the central nervous system.579 Fewer than 25 cases have been diagnosed ante mortem, several by culture of peripheral emboli. Most cases occur after open heart surgery; the most likely source of the organism is airborne inoculation of the heart during the operation.34,351 Surgical removal of all infected material is recommended, although only several children have been treated successfully. Other fungi that rarely cause endocarditis include Histoplasma capsulatum, Coccidioides immitis,294 Cryptococcus neoformans, Torulopsis glabrata, Trichosporon beigelii,276 and Fusarium spp.205,233

TREATMENT In the preantibiotic era, infective endocarditis was a uniformly fatal disease. With the current improved methods of diagnosis and therapy, 80% to 90% of children with this disease can be expected to survive. Mortality rates are higher for acute staphylococcal infection, fungal endocarditis, and prosthetic valve endocarditis, although the tendency toward earlier surgical intervention for these entities may improve survival rates. The cornerstone of successful therapy is selection of antibiotics with specific activity against the causative organism. Better analysis of pharmacodynamic variables, such as bactericidal activity and the postantibiotic effects of various drugs, may assist in the selection

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of optimal therapeutic regimens.99,282,596 Although persistent infection occasionally complicates treated endocarditis,449 deterioration in cardiac function is the major cause of morbidity and mortality. Several general principles provide the basis for the current recommendations for treatment of endocarditis. Parenteral administration of antibiotics is preferred because erratic absorption of oral antibiotics, especially in infants, can lead to therapeutic failure. Although patient selection criteria for the use of outpatient parenteral antibiotic therapy for endocarditis in adults have been suggested, no data have been published about this practice for children.11 The 2015 AHA Pediatric endocarditis treatment guidelines state that home parenteral therapy can be considered after initial treatment in the hospital in selected patients who are stable, afebrile, have negative blood cultures, and are at low risk for a complication (not fungal endocarditis or young age).29 Prolonged treatment, usually 4 to 6 weeks or longer, is necessary to sterilize the vegetations and to prevent relapse. Bacteriostatic antibiotics are not effective and lead to frequent relapses or failure to eradicate the infection, or both. Antibiotic combinations may produce a rapid bactericidal effect through synergistic mechanisms of action. When synergy exists, smaller doses of each drug may be used, thereby reducing toxic side effects. Blood should be drawn for culture for several days to evaluate the effect of the antibiotics. Negative follow-up cultures do not guarantee the success of therapy, but persistent positive cultures usually require that a change or addition to the antibiotic regimen be made. Observation of the patient’s clinical course is extremely important. When fever is present initially, the temperature often returns to normal within a few days after therapy is started. However, fever can persist for weeks in patients whose eventual outcome is good. Such patients must be monitored closely for cardiac arrhythmias and congestive heart failure, which may require intensive care observation and electrocardiographic monitoring. Evidence of major embolic phenomena must be sought diligently by physical examination. Several laboratory tests may aid in monitoring therapy. In all cases of bacterial endocarditis, the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) ideally are determined for the antibiotics being used because disk susceptibility testing may not be as reliable and is not quantitative. The role of monitoring the inhibitory and bactericidal activity of the patient’s serum is highly controversial.448 Standardization of this test is poor, with laboratories using variations in inoculum size, in composition of the broth, in timing of samples (at expected peak or trough antibiotic concentrations in serum), in methods of dilution, and in determining the bactericidal end point. In the rabbit endocarditis model, peak serum bactericidal titers greater than 1 : 8 correlate with therapeutic success.73 A retrospective review of 17 reports of serum bactericidal activity in patients with endocarditis failed to show any correlation between titers greater than 1 : 8 and therapeutic success.96 A prospective study suggested adjusting antibiotic doses to achieve peak titers of 1 : 64 or greater and trough titers of 1 : 32 or greater.589 At present, no generally accepted recommendation can be made.602 Little information is available concerning optimal antibiotic therapy for infective endocarditis in children; most treatment regimens are adapted from studies of adults with endocarditis.26,597 In general, these regimens have been equally successful (and generally less toxic) in children. Recommended doses of the antibiotics commonly used are listed in Table 26.6. After performing the initial evaluation of a patient with suspected infective endocarditis, the physician must make a clinical judgment about when to initiate therapy. If the findings are strongly indicative of the diagnosis or the child is very ill, treatment should be started as soon as blood has been drawn for culture. Initial empiric therapy depends on the clinical setting in which the tentative diagnosis is made. If the infection is subacute, a combination of penicillin G and an aminoglycoside usually is recommended for its activity against viridans streptococci, enterococci, and most gram-negative organisms. If S. aureus endocarditis is a strong consideration (acute manifestation, narcotic addicts), vancomycin and a penicillinase-resistant penicillin should be added to this regimen. Patients who recently have undergone cardiac surgery, especially prosthetic valve placement, are treated best with an

TABLE 26.6  Suggested Intravenous Antibiotic Doses and Schedules for Infective Endocarditis in Children Antibiotic

Daily Dose/kg

Divided Doses Every:

Aqueous crystalline penicillin G sodium Ampicillin sodium Ampicillin-sulbactam Cefazolin Ceftriaxone

200,000–300,000 U

4–6 h

300 mg 200–300 mg 100 mg 100 mga 80 mg 20–30 mg 6 mg 12 y 60 mg 200 mg (max, 12 g) 200 mg (max, 12 g) 20 mg 40–60 mgb

4–6 h 4–6 h 8 h 12 h 24 h 12 h 24 h 24 h 12 h 8 h 6 h 8 h 12 h 8 h 4–6 h 4–6 h 8–12 h 8–12 h

Ciprofloxacin Daptomycin Doxycycline Gentamicin sulfate Imipenem/cilastatin Linezolid Meropenem Nafcillin sodium Oxacillin sodium Rifampin Vancomycin hydrochloride a

If dose is over 2 g, divide every 12 h; maximum is 4 g daily. Target trough usually 10–15 µg/mL although higher levels (15–20 µg/mL) when the MRSA isolate has vancomycin MIC >1 µg/mL. Both levels are difficult to achieve in children using the recommended vancomycin dose, and increasing the dose to achieve these levels can cause nephrotoxicity From Baltimore RS, Gewitz M, Baddour LM et al. Infective endocarditis in childhood: 2015 update. A scientific statement from the American Heart Association. Circulation. 2015;132:1487–1515. b

aminoglycoside and vancomycin to “cover” for health care–associated infection caused by MRSA or CONS; some physicians add penicillin G to this regimen to improve activity against streptococci. When culture and susceptibility data are known, antibiotic therapy can be changed as needed. Most strains of viridans streptococci, S. pyogenes, and nonenterococcal group D streptococci are exquisitely susceptible to penicillin, with an MIC of less than 0.2 µg/mL. However, 15% to 20% of viridans streptococci have an MIC of 0.2 µg/mL or greater and are defined arbitrarily as relatively resistant.234 In addition, some strains (particularly S. mutans and S. mitior) demonstrate tolerance; that is, an MIC to penicillin of less than 0.1 µg/mL but an MBC that is more than 10-fold higher (1.25 to 50 µg/mL). Most strains of nutritionally dependent streptococci are tolerant to penicillin.25 Clinical failure may occur in endocarditis caused by these tolerant organisms when penicillin alone is used for treatment.10,234 However, except for nutritionally dependent streptococci, therapy for tolerant viridans streptococci generally should be the same as for susceptible strains. Although most experts recommend that patients with endocarditis caused by relatively resistant streptococci be treated with high doses of penicillin combined with 2 to 4 weeks of an aminoglycoside, some authorities consider that penicillin alone usually is adequate therapy.52,121,334 Synergy in vitro between penicillin or vancomycin and streptomycin or gentamicin can be demonstrated against virtually all penicillinsusceptible streptococci.581 This observation correlates with a faster rate of eradication of bacteria from cardiac vegetations in the rabbit endocarditis model when synergistic combinations of antibiotics are used.131,134 However, streptomycin is not synergistic for strains with high-level streptomycin resistance; gentamicin is the preferred second drug for these rare isolates.140 In pediatric patients, gentamicin usually is substituted for streptomycin because of its lower toxicity.

CHAPTER 26  Infective Endocarditis Several regimens have been examined in adults with penicillinsusceptible viridans streptococcal native valve endocarditis (Table 26.7). A 2-week course of penicillin alone leads to an unacceptable relapse rate. However, a 2-week course of intramuscular procaine penicillin and streptomycin cured 99% of adults with penicillin-susceptible streptococcal endocarditis in one report.600 These results are similar to those obtained with β-lactams alone for 4 weeks270 or with penicillin for 4 weeks combined with streptomycin for the first 2 weeks. Gentamicin may be substituted for streptomycin. The 2-week penicillin-gentamicin regimen is the least expensive and is the preferred therapy in uncomplicated cases of penicillin-susceptible streptococcal endocarditis in young adults.489 In general, the regimen of 4 weeks of penicillin alone is preferred for patients in renal failure or at high risk for developing aminoglycoside-induced ototoxicity. Vancomycin or ceftriaxone administered for 4 weeks can be used in patients with penicillin-susceptible viridans streptococcal endocarditis who have a penicillin allergy.172,173,499,526 A 4-week regimen of penicillin plus an initial 2 weeks of gentamicin is recommended in children with infection caused by relatively penicillinresistant organisms (Table 26.8). Most nutritionally deficient streptococci are tolerant to penicillin and should be treated as for enterococci (Table 26.8).26,29,597 In patients with streptococcal infection of prosthetic valves or other prosthetic materials, a 6-week regimen of penicillin usually supplemented with an aminoglycoside is recommended (Tables 26.7 and 26.8). None of the regimens discussed has been evaluated specifically in children with endocarditis.

TABLE 26.7  Suggested Regimens for 4-Weeka Treatment of Native Valve Endocarditis Caused by Highly Penicillin-Susceptible Viridans Streptococci and Streptococcus bovis Antibiotic(s)

Comments

Aqueous crystalline penicillin G sodium Ceftriaxone sodium Cefazolin Vancomycin hydrochloride

Recommended Recommended Alternative choice Alternative choice; recommended for patients allergic to β-lactam antibiotics

Most strains of enterococci have an MIC to penicillin of 0.4 µg/mL or greater and an MBC of 6.25 µg/mL or greater.384 All β-lactam antibiotics are bacteriostatic against enterococci and cannot be used alone. However, plasmid-mediated β-lactamase production has been found in rare strains of Enterococcus faecalis. Ampicillin-sulbactam overcomes the enzyme production and may be effective as therapy.545 Although therapy with penicillin alone is ineffective, the combination of penicillin and an aminoglycoside is synergistic and produces a bactericidal effect on most enterococcal strains. Unfortunately, 20% to 50% of enterococcal strains demonstrate very high resistance (MIC >2000 µg/mL) to streptomycin, and synergy between penicillin and streptomycin does not occur.216,488 High-level resistance to gentamicin has been found in some isolates, and the incidence is increasing in certain locales.137,318,414 When these isolates are encountered, all aminoglycosides should be tested because the organism may be susceptible to one while resistant to others.587 Fortunately these strains rarely cause endocarditis.384 Although vancomycin-resistant enterococci have emerged as important nosocomial pathogens, they rarely cause endocarditis in children. Optimal therapy for these strains has not been established, but a combination of high-dose penicillin plus vancomycin and gentamicin may be effective in some cases.70 Vancomycin-resistant enterococcal endocarditis has been treated successfully with oral linezolid.12,17 The usual regimens for enterococcal endocarditis are listed in Table 26.8. Most isolates of S. aureus are resistant to penicillin, but endocarditis caused by penicillin-susceptible (MIC 0.2 µg/mL); Includes Enterococci and Less-Susceptible Viridans Streptococci Antibiotic

267

a

If prosthetic material is present, rifampin for 6 weeks and gentamicin for 2 weeks are added to the regimen. b If Staphylococcus is penicillin susceptible (minimal inhibitory concentration ≤0.1 µg/mL), aqueous crystalline penicillin G sodium can be used for 4–6 weeks instead of nafcillin or oxacillin. From Baltimore RS, Gewitz M, Baddour LM, et al. Infective endocarditis in childhood: 2015 update. A scientific statement from the American Heart Association. Circulation. 2015;132:1487–1515.

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TABLE 26.10  Suggested 4-Week Therapy for Endocarditis Caused by HACEK Organisms

TABLE 26.11  Suggested Empiric Therapy for Culture-Negative Endocarditis

Antibiotic

Comments

Antibiotic(s)

Ceftriaxone sodium or cefotaxime Ampicillin-sulbactam Ampicillin plus aminoglycosidea

Recommended Recommended Alternative choice

Native Valve Ampicillin-sulbactam plus 4–6 wk gentamicin sulfate plus ciprofloxacin Prosthetic Valve (early, ≤1 year) Vancomycin plus 6 wk

HACEK, Haemophilus species, Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, Kingella kingae. a For susceptible organisms. From Baltimore RS, Gewitz M, Baddour LM, et al. Infective endocarditis in childhood: 2015 update. A scientific statement from the American Heart Association. Circulation. 2015;132:1487–1515.

has been used, but treatment failures have occurred because of the emergence of resistance.382,542 Vancomycin for at least 6 weeks is recommended for the treatment of endocarditis caused by MRSA.29 Daptomycin and linezolid also have been used successfully to treat endocarditis caused by MRSA; only daptomycin is recommended as an alternative choice in the 2015 AHA pediatric guidelines.29,169,367 Nosocomial infections with coagulase-negative staphylococcus usually are treated with vancomycin because of the high incidence of methicillin resistance among these isolates. The addition of rifampin and gentamicin to either nafcillin or vancomycin may increase bactericidal activity and is recommended in cases of prosthetic valve endocarditis secondary to any staphylococci (see Table 26.9).26,29 Therapy for endocarditis caused by gram-negative organisms must be individualized in accordance with in vitro susceptibility studies. A regimen of 6 to 8 weeks of combination therapy with two or more drugs may be required, especially with endocarditis caused by Klebsiella or Pseudomonas.160,418 Surgical intervention frequently is necessary, especially for infection of the mitral or aortic valves. Endocarditis caused by Haemophilus and other fastidious gram-negative organisms usually is responsive to ampicillin-sulbactam or ceftriaxone alone29; the addition of an aminoglycoside is recommended if ampicillin is used as an alternative choice (Table 26.10).26,90 Anaerobic bacilli generally are susceptible to penicillin, but infection caused by resistant Bacteroides fragilis is treated best by combinations including metronidazole, piperacillin-tazobactam, or meropenem. Survival rates of only 10% to 20% in patients with fungal endocarditis are related to the poor ability of currently available antifungal agents to sterilize the vegetations. Only rare cures with medical therapy alone have been reported.480 Most investigators contend that early surgical intervention is mandatory in every patient who has conclusive evidence of intracardiac fungal infection.520,563,565 Neonates with fungal endocarditis can have an especially high mortality rate.469 Eradication of fungal prosthetic valve endocarditis has been reported rarely, even when surgery was performed.188 Although a prolonged course of antifungal therapy before surgery does not improve the outcome, chemotherapy should be given in conjunction with operative treatment. The drug of choice is usually amphotericin B or liposomal amphotericin. This antibiotic may be either fungistatic or fungicidal, depending on the infecting organism. The optimal dosage of amphotericin B is unknown; total doses of 20 to 50 mg/kg commonly are used. 5-Fluorocytosine356 may act synergistically with amphotericin B against many strains of fungi, but their roles in fungal endocarditis are unproven. Fluconazole is less effective than is amphotericin B for the prophylaxis or treatment of experimental Candida endocarditis,601 but it has been used successfully in a few patients.101,572 Some newer antifungal agents, such as caspofungin, have been used successfully to treat fungal endocarditis, but the reported experience in children is limited.538 The Infectious Diseases Society of America clinical practice guidelines recommend liposomal amphotericin B (3 to 5 mg/kg per day) with or without flucytosine (25 mg/kg every 6 hours) for treatment of Candida native valve endocarditis.410 Echinocandins are alternatives. Step-down therapy to fluconazole should be considered for stable patients with susceptible Candida isolates and with negative blood cultures.

Duration

Gentamicin sulfate plus

2 wk

Cefepime plus

6 wk

Rifampin

6 wk

Prosthetic valve (late >1 year)

6 wk

Comments Ciprofloxacin can be administered IV or oral

40 mg/kg/day in 2 or 3 divided doses 3 mg/kg/day in 3 divided doses 150 mg/kg/day in 3 divided doses 20 mg/kg PO/IV in 3 divided doses Same as for native valve endocarditis above

From Baltimore RS, Gewitz M, Baddour LM, et al. Infective endocarditis in childhood: 2015 update. A scientific statement from the American Heart Association. Circulation. 2015;132:1487–1515.

Treatment of culture-negative endocarditis is problematic.32 In general, the same criteria used to choose empiric therapy for infective endocarditis can be followed. Antibiotics usually are continued for 6 weeks, and ongoing surveillance for an etiologic agent must be performed. The suggested regimens for treating culture-negative endocarditis in children in the AHA 2015 Pediatric guidelines are shown in Table 26.11. In 52 adults with culture-negative endocarditis, survival correlated with the initial clinical response to antibiotics; most deaths were caused by systemic emboli or congestive heart failure.425 Surgery has become a valuable adjunct to medical therapy in the management of infective endocarditis.37,407,424,432,476 The general trend has been for surgical intervention to be undertaken earlier and more frequently to prevent complications of endocarditis and lower mortality.231,465,607 Several echocardiographic findings suggest a possible need for surgical intervention (Box 26.3).36,159 Among the generally accepted indications for surgical intervention during active endocarditis are (1) refractory congestive heart failure,361,552,595 (2) uncontrolled infection,336 (3) more than one serious embolic episode, (4) fungal endocarditis, (5) most cases of prosthetic valve endocarditis,7,114,141,386,474,608 and (6) local suppurative complications including perivalvular or myocardial abscess with conduction system abnormalities.51,271,387,461,500,534,604 Surgical intervention should also be considered urgently for any child with acute endocarditis caused by S. aureus.501 The usual indication for surgical intervention is congestive heart failure in left-sided lesions and persistent infection in right-sided disease.116,574 Among children with endocarditis after cardiac surgery, repair or takedown of infected graft material commonly is the reason for surgery.92,403 Recent studies have demonstrated that preservation of the child’s native valve is frequently possible despite advanced clinical disease.118,221,220,266 In general, operative mortality is low even if surgery is performed during the active infection.381,396 The hemodynamic status of the patient, rather than the activity of the infection, is the critical factor in determining the timing of cardiac surgery or valve replacement.3,267 The aortic valve is the site most often requiring surgical intervention.275,434,556 Treatment with recombinant tissue plasminogen activator has been used successfully in some cases of endocarditis when surgery could not be performed safely.202,310

PREVENTION Accepted medical practice has been to give prophylactic antibiotics to susceptible patients in an attempt to prevent infective endocarditis.129,275,507 The rationale for such treatment is based on studies indicating that antibiotics can reduce the incidence of bacteremia after various

CHAPTER 26  Infective Endocarditis

269

TABLE 26.12  Endocarditis Prophylaxis Regimens for a Dental Procedure to Be Considered in Children With High-Risk Conditions REGIMEN: SINGLE DOSE 30 TO 60 min BEFORE PROCEDURE

Situation

Agent

Adults

Children

Oral Unable to take oral

Amoxicillin Ampicillin or Cefazolin or ceftriaxone Cephalexina or Clindamycin or Azithromycin or clarithromycin Cefazolin or ceftriaxonea or Clindamycin

2 g 2 g IM or IV 1 g IM or IV 2 g 600 mg 500 mg 1 g IM or IV 600 mg IM or IV

50 mg/kg 50 mg/kg IM or IV 50 mg/kg IM or IV 50 mg/kg 20 mg/kg 15 mg/kg 50 mg/kg IM or IV 20 mg/kg IM or IV

Allergic to oral penicillins Allergic to penicillins and unable to take oral

IM, Intramuscularly; IV, intravenously. a Cephalosporins not to be used in an individual with a history of anaphylaxis, angioedema, or urticaria with penicillins. From Wilson W, Taubert KA, Gewitz M, et al. Prevention of infective endocarditis: guidelines from the American Heart Association. Circulation. 2007;116:1736–54.

BOX 26.3  Echocardiographic Features Suggesting a Possible Need for Surgical Intervention in Endocarditis Vegetation Persistent vegetation after systemic embolization Anterior mitral valve leaflet vegetation, particularly >10 mm Embolic event during first 2 weeks of therapy Increase in vegetation size after 4 weeks of therapy Valvular Dysfunction Acute aortic or mitral insufficiency with signs of ventricular failure Heart failure unresponsive to medical therapy Valve perforation or rupture Perivalvular Extension Valvular dehiscence, rupture, or fistula New heart block Large abscess or extension of abscess Data from Bayer A., Bolger A, Taubert K, et al. Diagnosis and management of infective endocarditis and its complications. Circulation. 1998;98:2936–48; and Ferrieri P, Gewitz MH, Gerber MA, et al. Unique features of infective endocarditis in children. Pediatrics. 2002;109:931–43.

procedures in humans143 and can prevent experimental endocarditis in animals.421 However, no controlled trials have documented the efficacy of endocarditis prophylaxis in humans.570 Prevention of bacterial infection is most likely to be successful and cost effective when a single antibiotic is directed against a single pathogen and when the disease occurs with high frequency in the absence of prophylaxis. Prevention of endocarditis has not met these ideals because various drugs have been used against numerous organisms, and the disease rarely occurs even if prophylaxis is not given.127 Fewer than 10% of all endocarditis cases can be attributed to bacteremia caused by previous medical, surgical, or dental procedures.568 Many cases of prophylaxis failure have been reported,132 but only 12% of such patients received antibiotic regimens recommended by the American Heart Association. For reasons that are not clear, mitral valve prolapse was the condition associated most frequently with failure of prophylaxis. The most common errors in attempted prevention of endocarditis included inadequate medical histories taken by dentists and other health care professionals to identify high-risk patients, initiation of prophylactic antibiotics too early, continuation of preventive therapy too long, the use of low-dose antibiotics, lack of prophylaxis for minor dental procedures, and confusion between prevention of rheumatic fever and prevention of infective endocarditis.162,208,214 Several studies

BOX 26.4  Heart Conditions With the Highest Risk for Adverse Outcome From Endocarditis for Which Prophylaxis With Dental Procedures Can Be Considered Prosthetic heart valve Previous infective endocarditis Congenital heart disease • Unrepaired cyanotic congenital heart disease, including palliative shunts and conduits • Completely repaired congenital heart defect with prosthetic material or device, whether placed by surgery or catheter, during the first 6 months after the procedure • Repaired congenital heart disease with residual defects at or adjacent to the site of a prosthetic patch or device Cardiac transplantation recipients who develop cardiac valvulopathy From Wilson W, Taubert KA, Gewitz M, et al. Prevention of infective endocarditis: guidelines from the American Heart Association. Circulation. 2007;116:1736–54.

have shown that adult patients at risk for development of infective endocarditis often have inadequate knowledge of their cardiac lesion, endocarditis, and recommended prophylaxis.78,288,569 Several studies demonstrated that the parents of children with heart defects have a low level of knowledge about the importance of good oral health in preventing endocarditis.27,102,206,395,442 Another study cast doubt on the cost-effectiveness of endocarditis prophylaxis for urinary catheterization in children.77 The American Heart Association published new and radically different guidelines for the prevention of infective endocarditis in 2007.598 These new guidelines eliminated many of the procedures for which prophylaxis previously was recommended.104 It is now recommended that prophylaxis be undertaken for all dental procedures that involve manipulation of gingival tissue or the periapical region of teeth or perforation of the oral mucosa. Prophylaxis also can be considered for procedures on the respiratory tract or infected skin, skin structures, or musculoskeletal tissue. Prophylaxis no longer is recommended for gastrointestinal or genitourinary tract procedures. In addition, the heart lesions for which prophylaxis is to be considered has been reduced to only those with the highest risk for adverse outcome of endocarditis (Box 26.4).598 Finally, the specific regimens for prophylaxis have been changed and simplified to encourage more judicious use (Table 26.12). Although some experts have expressed doubt about the validity of these newer recommendations,502 there is no evidence that the release of these guidelines has been associated with a significant change in admissions for infective endocarditis.411

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The full reference list for this chapter is available at ExpertConsult.com.

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SECTION 3  Infections of the Heart

65. Calderwood S, Swinski L, Waternaux C, et al. Risk factors for the development of prosthetic valve endocarditis. Circulation. 1985;72:31-37. 66. Caldwell RL, Hurwitz RA, Girod DA. Subacute bacterial endocarditis in children. Am J Dis Child. 1971;122:312-315. 67. Camarillo D, Banerjee R, Greenhow TL, et al. Group B streptococcal endocarditis after elective abortion in an adolescent. Pediatr Infect Dis J. 2009;28:67-69. 68. Canter MC, Hart RG. Neurologic complications of infective endocarditis. Neurology. 1991;41:1015. 69. Carey RB, Gross KC, Roberts RB. Vitamin B6–dependent Streptococcus mitior (mitis) isolated from patients with systemic infections. J Infect Dis. 1975;131: 722-725. 70. Caron F, Carbon C, Gutmann L. Triple-combination penicillin-vancomycingentamicin for experimental endocarditis caused by a moderately penicillin- and highly glycopeptide-resistant isolate of Enterococcus faecium. J Infect Dis. 1991;164:888-893. 71. Carpenter JL. Perivalvular extension of infection in patients with infectious endocarditis. Rev Infect Dis. 1991;13:127-138. 72. Carr P, Wright M, Handler LC. Endocarditis-related cerebral aneurysms: radiologic changes with treatment. AJNR Am J Neuroradiol. 1995;16:745. 73. Carrizosa J, Kaye D. Antibiotic concentrations in serum, serum bactericidal activity, and results of therapy of streptococcal endocarditis in rabbits. Antimicrob Agents Chemother. 1977;12:479-483. 74. Carruthers M. Endocarditis due to enteric bacilli other than salmonellae: case reports and literature review. Am J Med Sci. 1977;273:203. 75. Carvajal A, Frederiksen W. Fatal endocarditis due to Listeria monocytogenes. Rev Infect Dis. 1988;10:616-623. 76. Cassling RS, Rogler WC, McManus BM. Isolated pulmonic valve infective endocarditis: a diagnostically elusive entity. Am Heart J. 1985;109:558-567. 77. Caviness AC, Cantor SB, Allen CH, et al. 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98. Coward K, Tucker N, Darville T. Infective endocarditis in Arkansan children from 1990 through 2002. Pediatr Infect Dis J. 2003;22:1048-1052. 99. Cremieux AC, Carbon C. Pharmacokinetics and pharmacodynamic requirements for antibiotic therapy of experimental endocarditis. Antimicrob Agents Chemother. 1992;36:2069-2074. 100. Cutler JG, Ongley PA, Schwachman H, et al. Bacterial endocarditis in children with heart disease. Pediatrics. 1958;22:706-714. 101. Czwerwiec FS, Bilsker MS, Kamerman ML, et al. Long-term survival after fluconazole therapy of candidal prosthetic valve endocarditis. Am J Med. 1993;94:545-546. 102. da Silva DB, Sovza IP, Cunha MC. Knowledge, attitudes and status of oral health in children at risk for infective endocarditis. Int J Pediatr Dent. 2002;12:124-131. 103. Daher AH, Berkowitz FE. Infective endocarditis in neonates. Clin Pediatr (Phila). 1995;20:198-206. 104. Dajani AS, Taubert KA, Wilson W, et al. Prevention of bacterial endocarditis: recommendations by the American Heart Association. Clin Infect Dis. 1997;75:1448-1458. 105. Danchin N, Voiriot P, Briancon S, et al. Mitral valve prolapse as a risk factor for infective endocarditis. Lancet. 1989;1:743-745. 106. Danford DA, Kugler JD, Cheatham JP, et al. Haemophilus influenzae endocarditis: successful treatment with ampicillin and early valve replacement. Neb Med J. 1984;38:88-91. 107. Daniel WG, Erbel R, Kasper W, et al. Safety of transesophageal echocardiography: a multicenter survey of 10,419 examinations. Circulation. 1991;83:817-821. 108. Daniel WG, Mugge A, Grote J, et al. Evaluation of endocarditis and its complications by biplane and multiplane transesophageal echocardiography. Am J Card Imaging. 1995;9:100-105. 109. Daniel WG, Mugge A, Martin RP, et al. Improvement in the diagnosis of abscesses associated with endocarditis by transesophageal echocardiography. N Engl J Med. 1991;324:795-800. 110. Dankert J, Krijgsveld J, van der Werff J, et al. Platelet microbicidal activity is an important defense factor against viridans streptococcal endocarditis. J Infect Dis. 2001;184:597-605. 111. Das M, Badley AD, Cockerill FR, et al. Infective endocarditis caused by HACEK microorganisms. Annu Rev Med. 1997;48:25-33. 112. Das I, DeGiovanni JV, Gray J. Endocarditis caused by Haemophilus parainfluenzae identified by 16 S ribosomal RNA sequencing. J Clin Pathol. 1997;50:72-74. 113. Das BB, Wasser E, Bryant KA, et al. Culture negative endocarditis caused by Bartonella henselae in a child with congenital heart disease. Pediatr Infect Dis J. 2009;28:922-925. 114. David TE. The surgical treatment of patients with prosthetic valve endocarditis. Semin Thorac Cardiovasc Surg. 1995;7:47-53. 115. Davidson S, Rotem Y, Bogkowski B, et al. Corynebacterium diphtheriae endocarditis. Am J Med Sci. 1976;271:351-353. 116. Day MD, Gauvreau K, Shulman S, et al. Characteristics of children hospitalized with infective endocarditis. Circulation. 2009;119:865-870. 117. Del Pont JM, DeCicco LT, Vartalitis C, et al. Infective endocarditis in children: clinical analyses and evaluation of two diagnostic criteria. Pediatr Infect Dis J. 1995;14:1079-1086. 118. Delmo Walter EM, Musci M, Nagdyman N, et al. Mitral valve repair for infective endocarditis in children. Ann Thorac Surg. 2007;84:2059-2065. 119. Delvecchio G, Fracasetti O, Lorenzi N. Brucella endocarditis. Int J Cardiol. 1991;33:328-329. 120. Dillon T, Meyer RA, Korfhagen JC, et al. Management of infective endocarditis using echocardiography. J Pediatr. 1980;96:552-558. 121. DiNubile MJ. Treatment of endocarditis caused by relatively resistant nonenterococcal streptococci: is penicillin enough? Rev Infect Dis. 1990;12:112-117. 122. DiNubile MJ, Calderwood SB, Steinhaus DM, et al. Cardiac conduction abnormalities complicating native valve active infective endocarditis. Am J Cardiol. 1986;58:1213-1217. 123. Dominguez SR, Littlehorn C, Nyquist AC. Mycoplasma hominis endocarditis in a child with complex congenital heart disease. Pediatr Infect Dis J. 2006;25:851-852. 124. Douglas A, Moore-Gillon J, Eykyn S. Fever during treatment of infective endocarditis. Lancet. 1986;1:1341-1343. 125. Downing GJ, Spirazza C, Group C. beta-hemolytic streptococcal endocarditis. Pediatr Infect Dis J. 1986;5:703-704. 126. Drancourt M, Mainardi JL, Brouqui P, et al. Bartonella (Rochalimaea) quintana endocarditis in three homeless men. N Engl J Med. 1995;332:419-423. 127. Dubnov-Raz G, Ephros M, Garty BZ, et al. Invasive pediatric Kingella kingae infections: a nationwide collaborative study. Pediatr Infect Dis J. 2010;29:639-643. 128. Dubnov-Raz G, Scheuerman O, Chodick G, et al. Invasive Kingella kingae infections in children: clinical and laboratory characteristics. Pediatrics. 2008;122: 1305-1309. 129. Durack DT. Prevention of infective endocarditis. N Engl J Med. 1995;332: 38-44.

CHAPTER 26  Infective Endocarditis 130. Durack DT, Beeson PB. Protective role of complement in experimental Escherichia coli endocarditis. Infect Immun. 1977;16:213-214. 131. Durack DT, Beeson PB, Petersdorf RG. Experimental bacterial endocarditis, part III: production and progress of the disease in rabbits. Br J Exp Pathol. 1973;54: 142-151. 132. Durack DT, Kaplan EL, Bisno AL. Apparent failure of endocarditis prophylaxis: analysis of 52 cases submitted to a national registry. JAMA. 1983;250: 2318-2322. 133. Durack DT, Lukes AS, Bright DK, et al. New criteria for diagnosis of infective endocarditis: utilization of specific echocardiographic findings. Am J Med. 1994;96:200-209. 134. Durack DT, Pelletier LL, Petersdorf RG. Chemotherapy of experimental streptococcal endocarditis, part II: synergism between penicillin and streptomycin against penicillin-sensitive streptococci. J Clin Invest. 1974;53:829-836. 135. Durack DT, Petersdorf RG. Changes in the epidemiology of endocarditis. 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Anaerobic bacterial endocarditis. N Engl J Med. 1970;283:1188-1192. 154. Fenollar F, Lepidi H, Raoult D. Whipple’s endocarditis: review of the literature and comparisons with Q fever, Bartonella infection and blood culture-positive endocarditis. Clin Infect Dis. 2001;33:1309-1316. 155. Fernandez GC, Chapman AJ, Bolli R, et al. Gonococcal endocarditis: a case series demonstrating modern presentation of an old disease. Am Heart J. 1984;108:1326-1334. 156. Fernandez-Guerrero ML, Torres-Perea R, Gomez-Rodrigo J, et al. Infectious endocarditis due to non–typhi Salmonella in patients infected with human immunodeficiency virus: report of two cases and review. Clin Infect Dis. 1996;22:853-855. 157. Fernandez-Guerrero ML, Verdejo C, Azofra J, et al. Hospital-acquired infectious endocarditis not associated with cardiac surgery: an emerging problem. Clin Infect Dis. 1995;20:16-23. 158. Fernicola DJ, Roberts WC. 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161. Fisher RG, Moodie DS, Rice R. Pediatric bacterial endocarditis: long-term followup. Cleve Clin Q. 1985;52:41-45. 162. Fitzgerald K, Fleming P, Franklin O, et al. Dental health and management for children with congenital heart disease. Prim Dent Care. 2010;17:21-25. 163. Fitzsimmons K, Bamber AI, Smalley HB. Infective endocarditits: changing aetiology of disease. Br J Biomed Sci. 2010;67:35-41. 164. Fortún J, Centella T, Martín-Dávila P, et al. Infective endocarditis in congenital heart disease: a frequent community-acquired complication. Infection. 2013;41:167-174. 165. Foster MA, Walls M. High rates of complications following Kingella kingae infective endocarditis in children. Pediatr Infect Dis J. 2014;33:785-786. 166. Fournier PE, Lelievre H, Eykyn SJ, et al. Epidemiologic and clinical characteristics of Bartonella henselae endocarditis: a study of 48 patients. Medicine (Baltimore). 2001;80:245-251. 167. Fournier PE, Raoult D. 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SECTION 3  Infections of the Heart

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223. Hoen B, Selton-Suty C, Lacassin F, et al. Infective endocarditis in patients with negative blood cultures: analysis of 88 cases from a one-year nationwide survey in France. Clin Infect Dis. 1995;20:501-506. 224. Hoffman RM, AboulHosn J, Child JS, et al. Bartonella endocarditis in complex congenital heart disease. Congenit Heart Dis. 2007;2:79-84. 225. Holland F II, Fernandez L, Jacobs J, et al. Clostridial endocarditis following penetrating cardiac trauma. Clin Infect Dis. 1997;24:87-88. 226. Holmes AA, Hung T, Human DG, et al. Kingella kingae endocarditis: a rare case of mitral valve perforation. Ann Pediatr Cardiol. 2011;4:210-212. 227. Horenstein MS, Humes R, Epstein ML, et al. Loeffler’s endocarditis presenting in 2 children as fever with eosinophilia. Pediatrics. 2002;110:1014-1018. 228. Horwitz D, Quismorio FP, Friou GJ. Cryoglobulinemia in patients with infective endocarditis. Clin Exp Immunol. 1975;19:131-137. 229. Hosea SW. Virulent Streptococcus viridans bacterial endocarditis. Am Heart J. 1981;101:174-176. 230. Hoshimo T, Ohkusu K, Sudo F, et al. Neisseria elongata subsp. nitroreducens endocarditis in a seven year-old boy. Pediatr Infect Dis J. 2005;24:391-392. 231. Hosono M, Sasaki Y, Hirai H, et al. Considerations in timing of surgical intervention for infective endocarditis with cerebrovascular complications. J Heart Valve Dis. 2010;19:321-325. 232. Houpikian P, Raoult D. Diagnostic methods: current best practices and guidelines for identification of difficult-to-culture pathogens in infective endocarditis. Infect Dis Clin North Am. 2002;16:377-392. 233. Hsu CM, Lee PI, Chen JM, et al. Fatal Fusarium endocarditis complicated by hemolytic anemia and thrombocytopenia in an infant. Pediatr Infect Dis J. 1994;13:1146-1148. 234. Hsu RB, Lin FY. Effect of penicillin resistance on presentation and outcome of nonenterococcal streptococcal infective endocarditis. Cardiology. 2006;105: 234-239. 235. 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CHAPTER 26  Infective Endocarditis 255. Johnson JD, Raff MJ, Barnwell PA, et al. Splenic abscess complicating infectious endocarditis. Arch Intern Med. 1983;143:906-912. 256. Johnson CM, Rhodes KH. Pediatric endocarditis. Mayo Clin Proc. 1982;57: 86-94. 257. Johnson DH, Rosenthal A, Nadas A. A forty-year review of bacterial endocarditis in infancy and childhood. Circulation. 1975;51:581-588. 258. Johnson DH, Rosenthal A, Nadas A. Bacterial endocarditis in children under 2 years of age. Am J Dis Child. 1975;129:183-186. 259. Jones RB, Priest JB, Kuo C. Subacute chlamydial endocarditis. JAMA. 1982;247:655-658. 260. Jones HK, Siekert RG. Neurologic manifestations of infective endocarditis. Brain. 1989;112:1295-1315. 261. Julander I. Unfavourable prognostic factors in Staphylococcus aureus septicemia and endocarditis. Scand J InfectJ Infect Dis. 1985;17:179-187. 262. Kaell AT, Volkman DJ, Gorevic PD, et al. 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288. Knirsch W, Hassberg D, Beyer A, et al. Knowledge, compliance and practice of antibiotic endocarditis prophylaxis of patients with congenital heart disease. Pediatr Cardiol. 2003;24:344-349. 289. Knoll B, Tleyjeh IM, Steckelberg JM, et al. Infective endocarditis due to penicillinresistant viridans group streptococci. Clin Infect Dis. 2007;44:1585-1592. 290. Komshian SV, Tablan OC, Palutke W, et al. Characteristics of left-sided endocarditis due to Pseudomonas aeruginosa in the Detroit Medical Center. Rev Infect Dis. 1990;12:693-702. 291. Kramer H, Bourgeois M, Liersch R, et al. Current clinical aspects of bacterial endocarditis in infancy, childhood and adolescence. Eur J Pediatr. 1983; 140:253-259. 292. Kuypers JM, Proctor RA. Reduced adherence to traumatized rat heart valves by a low-fibronectin-binding mutant of Staphylococcus aureus. Infect Immun. 1989;57:2306-2312. 293. La Scola B, Raoult D. Molecular identification of Gemella species from three patients with endocarditis. 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CHAPTER 26  Infective Endocarditis 384. Murray BE. The life and times of the Enterococcus. Clin Microbiol Rev. 1990;3: 46-65. 385. Murray HW, Gross KC, Masur H, et al. Serious infections caused by Streptococcus milleri. Am J Med. 1978;64:759-765. 386. Musci M, Hubler M, Amiri A, et al. Surgical treatment for active infective prosthetic valve endocarditis: 22-year single-centre experience. Eur J Cardiothorac Surg. 2010;38:528-538. 387. Musci M, Weng Y, Hubler M, et al. Predictors of early mortality in patients with active infective native or prosthetic aortic root endocarditis undergoing homograft aortic root replacement. Clin Res Cardiol. 2009;98:443-450. 388. Musewe NN, Hecht BM, Hesslein PS, et al. Tricuspid valve endocarditis in two children with normal hearts: diagnosis and therapy of an unusual clinical entity. J Pediatr. 1987;110:735-738. 389. Nagel JG, Tuazon CV, Cardella TA, et al. Teichoic acid serologic diagnosis of staphylococcal endocarditis. Ann Intern Med. 1975;82:13-18. 390. Nagunuma M. Infective endocarditis in children. Jpn Circ J. 1985;49:545-552. 391. Naidoo DP. Right-sided endocarditis in the non–drug addict. Postgrad Med J. 1993;69:615-620. 392. Nakayama DK, O’Neill JA, Wagner H, et al. Management of vascular complications of bacterial endocarditis. J Pediatr Surg. 1986;21:636-639. 393. Narasimhan SL, Weinstein AJ. Infective endocarditis due to a nutritionally deficient Streptococcus. J Pediatr. 1980;96:61-62. 394. Nastro LJ, Finegold SM. Endocarditis due to anaerobic gram-negative bacilli. Am J Med. 1973;54:482-496. 395. Nath P, Kiran V, Maheshwari S. Awareness of infective endocarditis prophylaxis in parents of children with congenital heart disease: a prospective study. Ann Pediatr Cardiol. 2008;1:54-55. 396. Nelson RJ, Harley DP, French WJ, et al. Favorable ten-year experience with valve procedures for active infective endocarditis. J Thorac Cardiovasc Surg. 1984;87:493-502. 397. Nguyen MH, Nguyen ML, Yu VL, et al. Candida prosthetic valve endocarditis: prospective study of six cases and review of the literature. Clin Infect Dis. 1996;22:262-267. 398. Nicolau DP, Freeman CD, Nightingale CH, et al. Reduction of bacterial titers by low-dose aspirin in experimental aortic valve endocarditis. Infect Immun. 1993;61:1593-1595. 399. Nikolousis E, Velangi M. Two cases of Aspergillus endocarditis in non-neutropenic children on chemotherapy for acute lymphoblastic leukemia. Hematol Rep. 2011;3:e7. 400. Niwa K, Nakazawa M, Tateno S, et al. Infective endocarditis in congenital heart disease: Japanese national collaboration data. Heart. 2005;91:795-800. 401. Noel GJ, O’Loughlin JE, Edelson PJ. Neonatal Staphylococcus epidermidis right-sided endocarditis: description of five catheterized infants. Pediatrics. 1988;82: 234-239. 402. Nolan CM, Kane JJ, Grunow WA. Infective endocarditis and mitral prolapse: a comparison with other types of endocarditis. Arch Intern Med. 1981;141: 447-450. 403. Nomura F, Penny DJ, Menahem S, et al. Surgical intervention for infective endocarditis in infancy and childhood. Ann Thorac Surg. 1995;60:90-95. 404. O’Callaghan C, McDougall P. Infective endocarditis in neonates. Arch Dis Child. 1988;63:53-57. 405. Oelberg DG, Fisher DJ, Gross DM, et al. Endocarditis in high-risk neonates. Pediatrics. 1983;71:392-397. 406. Okumura A, Ito K, Kondo M, et al. Infective endocarditis caused by highly penicillin-resistant Streptococcus pneumoniae: successful treatment with cefuzonam, ampicillin and imipenem. Pediatr Infect Dis J. 1995;14:327-329. 407. Olaison L, Pettersson G. Current best practices and guidelines: indications for surgical intervention in infective endocarditis. Infect Dis Clin North Am. 2002;16:453-476. 408. Palraj BR, Baddour LM, Hess EP, et al. Predicting risk of endocarditis using a clinical tool (PREDICT): scoring system to guide use of echocardiography in the management of Staphylococcus aureus bacteremia. Clin Infect Dis. 2015;61:18-28. 409. Panidis IP, Kotler MN, Mintz GS, et al. Right heart endocarditis: clinical and echocardiographic features. Am Heart J. 1984;107:759-764. 410. Pappas PG, Kauffman CA, Andes D, et al. Clinical practice guidelines for the management of candidiasis: 2016 update by the Infectious Diseases Society of America. Clin Infect Dis. 2016;62:e1-e50. 411. Pasquali SK, He X, Mohamad Z, et al. Trends in endocarditis hospitalizations at U.S. children’s hospitals: impact of the 2007 American Heart Association Prophylaxis Guidelines. Am Heart J. 2012;163:894-899. 412. Patchell RA, White CL, Clark AW, et al. Nonbacterial thrombotic endocarditis in bone marrow transplant patients. Cancer. 1985;55:631-635. 413. Patrick WD, Brown WD, Bowmer MI, et al. Infective endocarditis due to Eikenella corrodens: case report and review of the literature. Can J InfectJ Infect Dis. 1990;1:139. 414. Patterson JE, Zervos MJ. High-level gentamicin resistance in Enterococcus: microbiology, genetic basis and epidemiology. Rev Infect Dis. 1990;12: 644-652.

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415. Pavlovsky M, Press J, Peled N, et al. Blood culture contamination in pediatric patients: young children and young doctors. Pediatr Infect Dis J. 2006; 25:611-614. 416. Pazin GJ, Saul S, Thompson ME. Blood culture positivity: suppression by outpatient antibiotic therapy in patients with bacterial endocarditis. Arch Intern Med. 1982;142:263-269. 417. Pedersen WR, Walker M, Olson JD, et al. Value of transesophageal echocardiography as an adjunct to transthoracic echocardiography in evaluation of native and prosthetic valve endocarditis. Chest. 1991;100:351-356. 418. Pefanis A, Giamarellou H, Karayiannakos P, et al. Efficacy of ceftazidime and aztreonam alone or in combination with amikacin in experimental left-sided Pseudomonas aeruginosa endocarditis. Antimicrob Agents Chemother. 1993;37: 308-313. 419. Pefanis A, Thauvin-Eliopoulos C, Eliopoulos GM, et al. 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SECTION 3  Infections of the Heart

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480. Sanchez PJ, Siegel JD, Fishbein J. Candida endocarditis: successful medical management in three preterm infants and review of the literature. Pediatr Infect Dis. 1991;10:239-243. 481. Sande MA, Courtney KB. Nafcillin-gentamicin synergism in experimental Staphylococcus endocarditis. J Lab Clin Med. 1976;88:118-124. 482. Sandre RM, Shatran SD. Infective endocarditis: review of 135 cases over 9 years. Clin Infect Dis. 1996;22:276-286. 483. Sanfilippo AJ, Picard MH, Newell JB, et al. Echocardiographic assessment of patients with infectious endocarditis: prediction of risk for complications. J Am Coll Cardiol. 1991;18:1191-1199. 484. Sapico FL, Liquete JA, Sarma RJ. Bone and joint infections in patients with infective endocarditis: review of a 4-year experience. Clin Infect Dis. 1996;22: 783-787. 485. Sapsford RN, Fitchett DH, Tarin D, et al. Aneurysm of left ventricle secondary to bacterial endocarditis. J Thorac Cardiovasc Surg. 1979;78:79-86. 486. 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542. Tebas P, Martinez R, Roman F, et al. Early resistance to rifampin and ciprofloxacin in the treatment of right-sided Staphylococcus aureus endocarditis. J Infect Dis. 1991;163:204-205. 543. Teixeira OH, Carpenter B, Vlad P. Enterococcal endocarditis in early infancy. Can Med Assoc J. 1982;127:612-613. 544. Thadelpall H, Francis CK. Diagnostic clues in metastatic lesions of endocarditis in addicts. West J Med. 1978;128:1-7. 545. Thal LA, Vazquez J, Perri MB, et al. Activity of ampicillin plus sulbactam against β-lactamase producing enterococci in experimental endocarditis. J Antimicrob Chemother. 1993;31:182. 546. Thapar MK, Rao PS, Feldman D, et al. Infective endocarditis: a review. Paediatrician. 1978;7:65-84. 547. Theofilopoulos AN, Wilson CB, Dixon FJ. The Raji cell radioimmune assay for detecting immune complexes in human sera. J Clin Invest. 1976;57:169-182. 548. Tiley SM, Kociuba KR, Heron LG, et al. Infective endocarditis due to nontoxigenic Corynebacterium diphtheriae: report of seven cases and review. Clin Infect Dis. 1993;16:271-275. 549. Tissieres P, Gervaix A, Beghetti M, et al. Value and limitation of the von Reyn, Duke and modified Duke criteria for the diagnosis of infective endocarditis in children. Pediatrics. 2003;112:e467-e471. 550. Tissieres P, Jaeggi ET, Beghetti M, et al. Increase in fungal endocarditis in children. Infection. 2005;33:267-272. 551. Tleyjeh IM, Steckelberg JM, Murad HS, et al. Temporal trends in infective endocarditis: a population-based study in Olmstead County, Minnesota. JAMA. 2005;293:3022-3028. 552. Tolan RW, Kleiman MB, Frank M, et al. Operative intervention in active endocarditis in children: report of a series of cases and review. Clin Infect Dis. 1992;14:852-862. 553. Tolaymat A, Rhatigan RM, Levin S. Pneumococcal endocarditis in infants. South Med J. 1979;72:448-451. 554. Tompkins LS, Roessler BJ, Redd SC, et al. Legionella prosthetic-valve endocarditis. N Engl J Med. 1988;318:530-535. 555. Tornos MP, Castro A, Toran N, et al. Tricuspid valve endocarditis in children with normal valves. Am Heart J. 1989;118:624-625. 556. Tornos MP, Permanyer-Miralda G, Olona M, et al. Long-term complications of native valve infective endocarditis in non-addicts: a 15-year follow-up study. Ann Intern Med. 1992;117:567-572. 557. Toy PT, Lai W, Drake TA, et al. Effect of fibronectin on adherence of Staphylococcus aureus to fibrin thrombi in vitro. Infect Immun. 1985;48:83-86. 558. Tsao MM, Katz D. Central venous catheter-induced endocarditis: human correlate of the animal experimental model of endocarditis. Rev Infect Dis. 1984;6:783-790. 559. Tuazon CV, Sheagren JW. Staphylococcal endocarditis in parenteral drug abusers: source of the organism. Ann Intern Med. 1975;82:788-790. 560. Tunkel AR, Kaye D. Endocarditis with negative blood cultures. N Engl J Med. 1992;326:1215-1217. 561. Turcotte RF, Brozovich A, Corda R, et al. Health care-associated infections in children after cardiac surgery. Pediatr Cardiol. 2014;35:1448-1455. 562. Turner SW, Wyllie JP, Hamilton JR, Bain HH. Diagnosis of infected modified Blalock-Taussig shunt by computed tomography. Ann Thorac Surg. 1995; 59:1216-1217. 563. Turnier E, Kay JH, Bernstein S, et al. Surgical treatment of Candida endocarditis. Chest. 1975;67:262-268. 564. Ugaki S, Rutledge J, Al Aklabi M, et al. An increased incidence of conduit endocarditis in patients receiving bovine jugular vein grafts compared to cryo­ preserved homograft for right ventricular outflow reconstruction. Ann Thorac Surg. 2015;99:140-147. 565. Utley JR, Mills J, Roe BB. The role of valve replacement in the treatment of fungal endocarditis. J Thorac Cardiovasc Surg. 1975;69:255-258. 566. Valente AM, Jain R, Scheurer M, et al. Frequency of infective endocarditis among infants and children with Staphylococcus aureus bacteremia. Pediatrics. 2005;115:e15-e19. 567. van de Rijn I. Analysis of cross-protection between serotypes and passively transferred immune globulin in experimental nutritionally variant streptococcal endocarditis. Infect Immun. 1988;56:117-121. 568. van der Meer JTM, Thompson J, Valkenburg HA, et al. Epidemiology of bacterial endocarditis in the Netherlands, part II: antecedent procedures and use of prophylaxis. Arch Intern Med. 1992;152:1869-1873. 569. van der Meer JTM, van Wijk W, Thompson J, et al. Awareness of need and actual use of prophylaxis: lack of patient compliance in the prevention of bacterial endocarditis. J Antimicrob Chemother. 1992;29:187-194. 570. van der Meer JTM, van Wijk W, Thompson J, et al. Efficacy of antibiotic prophylaxis for prevention of native valve endocarditis. Lancet. 1992;339:135. 571. Van Hare GF, Ben-Shacher G, Liebman J, et al. Infective endocarditis in infants and children during the past 10 years: a decade of change. Am Heart J. 1984;107:1235-1240. 572. Venditti M, De Bernardis F, Micozzi A, et al. Fluconazole treatment of catheterrelated right-sided endocarditis caused by Candida albicans and associated with endophthalmitis and folliculitis. Clin Infect Dis. 1992;14:422-426.

270.e10

SECTION 3  Infections of the Heart

573. Venkatesan C, Wainwright MS. Pediatric endocarditis and stroke: a single-center retrospective review of seven cases. Pediatr Neurol. 2008;38:243-247. 574. Vikram HR, Buenconsejo J, Hasbun R, et al. Impact of valve surgery on 6-month mortality in adults with complicated, left-sided native valve endocarditis. JAMA. 2003;290:3207-3214. 575. Villafañe J, Baker GH, Austin IIIEH, et al. Melody valve bacterial endocarditis: experience in four pediatric patients and a review of the literature. Catheter Cardiovasc Inter. 2014;84:212-218. 576. Von Reyn CF, Levy BS, Arbert RD, et al. Infective endocarditis: an analysis based on strict case definitions. Ann Intern Med. 1982;94:505-517. 577. Vuille C, Nidor FM, Weyman A, et al. Natural history of vegetations during successful medical treatment of endocarditis. Am Heart J. 1994;128: 1200-1209. 578. Walls T, Michael K, Trounce J, et al. Broad-range polymerase chain reaction for the diagnosis of Bartonella henselae endocarditis. J Paediatr Child Health. 2006;42:469-471. 579. Walsh TJ, Hutchins GM. Aspergillus mural endocarditis. Am J Clin Pathol. 1979;71:640-644. 580. Walterspiel JN, Kaplan SL. Incidence and clinical characteristics of “culture negative” infective endocarditis in a pediatric population. Pediatr Infect Dis J. 1986;5:328-332. 581. Watanakunakorn C, Glotzbecker C. Synergism with aminoglycosides of penicillin, ampicillin and vancomycin against nonenterococcal group D streptococci and viridans streptococci. J Med Microbiol. 1977;10:133-137. 582. Watson A, French P, Wilson M. Nocardia asteroides native valve endocarditis. Clin Infect Dis. 2001;32:660-661. 583. Weber R, Berger C, Balmer C, et al. Interventions using foreign material to treat congenital heart disease in children increase the risk for infective endocarditis. Pediatr Infect Dis J. 2008;27:544-550. 584. Wei HH, Wu KG, Sy LB, et al. Infectious endocarditis in pediatric patients: analysis of 19 cases presenting at a medical center. J Microbiol Immunol Infect. 2010;43:430-437. 585. Weidman DR, Al-Hashami H, Morris SK. Two cases and a review of Streptococcus pyogenes endocarditis in children. PediatricsBMC Pediatrics. 2014;14:227. 586. Weinberg AG. Group B streptococcal endocarditis detected by echocardiography. J Pediatr. 1978;92:335-336. 587. Weinstein AJ, Moellering RC. Penicillin and gentamicin therapy for enterococcal infections. JAMA. 1973;223:1030-1032. 588. Weinstein L, Schlesinger JJ. Pathoanatomic, pathophysiologic and clinical correlations in endocarditis. N Engl J Med. 1974;291:832-837, 1122-1126. 589. Weinstein MP, Stratton CW, Ackley A, et al. Multicenter collaborative evaluation of a standardized bactericidal test as a prognostic indicator in infective endocarditis. Am J Med. 1985;78:262-269. 590. Wells L, Ritter N, Donald F. Kingella kingae endocarditis in a sixteen-month-old child. Pediatr Infect Dis J. 2001;20:454-455. 591. Werner AS, Cobbs CG, Kaye D, et al. Studies on the bacteremia of bacterial endocarditis. JAMA. 1967;202:199-203. 592. Wheeler JG, Weesner KM. Staphylococcus aureus endocarditis and pericarditis in an infant with a central venous catheter. Clin Pediatr (Phila). 1984; 23:46-47.

593. White PD. The incidence of endocarditis in earliest childhood. Am J Dis Child. 1926;32:536-549. 594. Williams RC, Kunkel HG. Rheumatoid factor, complement and conglutinin aberrations in patients with subacute bacterial endocarditis. J Clin Invest. 1962;41:666-675. 595. Wilson WR, Davidson GK, Guiliani E, et al. Cardiac valve replacement in congestive heart failure due to infective endocarditis. Mayo Clin Proc. 1979;54:223-226. 596. Wilson WR, Gilbert DN, Bisno AL, et al. Evaluation of new anti-infective drugs for the treatment of infective endocarditis. Clin Infect Dis. 1992;15(suppl 1):89-95. 597. Wilson WR, Karchmer AW, Dajani AS, et al. Antibiotic treatment of adults with infective endocarditis due to streptococci, enterococci, staphylococci, and HACEK microorganisms. JAMA. 1995;274:1706-1713. 598. Wilson W, Taubert KA, Gewitz M, et al. Prevention of infective endocarditis: guidelines from the American Heart Association. Circulation. 2007;116:1736-1754. 599. Wilson LE, Thomas DL, Astemborski J, et al. Prospective study of infective endocarditis among injection drug users. J InfectJ Infect Dis. 2002;185: 1761-1766. 600. Wilson WR, Thompson RL, Wilkowske CJ, et al. Short-term therapy for streptococcal infective endocarditis. JAMA. 1981;245:360-363. 601. Witt MD, Bayer AS. Comparison of fluconazole and amphotericin B for prevention and treatment of experimental Candida endocarditis. Antimicrob Agents Chemother. 1991;35:2481-2485. 602. Wolfson JS, Swartz MN. Serum bactericidal activity as a monitor of antibiotic therapy. N Engl J Med. 1985;312:968-975. 603. Woods GL, Wood RP, Shaw BW. Aspergillus endocarditis in patients without prior cardiovascular surgery: report of a case in a liver transplant recipient and review. Rev Infect Dis. 1989;11:263-272. 604. Yankah AC, Klose H, Petzina R, et al. Surgical management of acute aortic root endocarditis with viable homograft: 13 years experience. Eur J Cardiothorac Surg. 2002;21:260-267. 605. Yeaman MR, Norman DC, Bayer AS. Staphylococcus aureus susceptibility to thrombin-induced platelet microbicidal protein is independent of platelet adherence and aggregation in vitro. Infect Immun. 1992;60:2368-2374. 606. Yokochi K, Sakamato H, Mikajima T, et al. Infective endocarditis in children: a current diagnostic trend and the embolic complications. Jpn Circ J. 1986;50:1294-1297. 607. Yoshinaga M, Niwa K, Niwa A, et al. Risk factors for in-hospital mortality during infective endocarditis in patients with congenital heart disease. Am J Cardiol. 2008;101:114-118. 608. Yu VL, Fang GD, Keys TF, et al. Prosthetic valve endocarditis: superiority of surgical valve replacement versus medical therapy alone. Ann Thorac Surg. 1994;58:1073-1077. 609. Zakrzewski T, Keith JD. Bacterial endocarditis in infants and children. J Pediatr. 1965;67:1179-1193. 610. Ziment I. Nervous system complications in bacterial endocarditis. Am J Med. 1969;47:593-607. 611. Zubler RH, Lange G, Lambert PH, et al. Detection of immune complexes in unheated sera by a modified 125I-Clq binding test. J Immunol. 1976;116: 232-239.

270

SECTION 3  Infections of the Heart

27 

Infectious Pericarditis Sheldon L. Kaplan

Purulent pericarditis generally refers to bacterial infection of the pericardium. Inflammation of the pericardium may result from numerous nonbacterial microorganisms, however, or may occur with a variety of noninfectious illnesses (Box 27.1). Regardless of the cause of pericarditis, the responses of the pericardium are limited to acute inflammation, effusion with or without tamponade, and fibrosis with or without constriction.18 Because untreated purulent pericarditis is rapidly fatal, suspecting the disease early and approaching the diagnosis aggressively are important.

poorly from the pericardial space because lymphatic channels are sparse, and drainage must occur primarily through the epicardial capillaries.70 Ainger1 summarized the function of the pericardium as follows: prevention of overdistention of the heart, protection of the heart from infection and adhesions, maintenance of the heart within a fixed geometric position within the chest, and regulation of the interaction between the stroke volumes of the two ventricles.

ANATOMY AND FUNCTION

Population and Incidence

The pericardium is composed of two loosely approximated layers: visceral and parietal. The visceral pericardium is composed of mesothelial tissue, which closely follows the contour of the heart and extends for a short distance beyond the atria and ventricles to the great vessels. The outer parietal pericardium is a more fibrous structure, composed of layers of collagen interlaced with elastic fibers. The pericardial sac is attached to the diaphragm below; to the sternum in front; and to the thoracic vertebrae, esophagus, and aorta posteriorly. It is surrounded by the lungs on either side and is related closely to the main bronchi and the mediastinal lymph nodes. The phrenic and vagus nerves supply a network of pain fibers to the parietal pericardium. The dynamics of the pericardial fluid are poorly understood. The pericardial membrane is active in the transfer of water, electrolytes, and small molecules. Molecules of large molecular weight are absorbed

Although purulent pericarditis is not a common infection in pediatric patients, it is an important one to recognize because of its life-threatening nature. In an extensive early review of the literature on purulent pericarditis, half of 425 cases occurred in children younger than 13 years of age.66 In a review of 162 reported children with pericarditis from 1950 to 1977, 67% of the children were 48 months old or younger.28 From 1962 to 1974, 67 cases were recognized at St. Louis Children’s Hospital (Table 27.1).89 During this 12-year period, pericardial disease of all causes occurred in approximately 1 of every 850 hospital admissions. Twelve (18%) of these children had purulent pericarditis. Most cases in younger children are infectious. Acute pericarditis was found in 20 children between 1987 and 1997 in a hospital in Iran.79 The causes of pericarditis were bacterial in eight (40%), collagen vascular disease in six (30%), viral in four (20%), and secondary to mediastinal

BACTERIAL PERICARDITIS

271

CHAPTER 27  Infectious Pericarditis

BOX 27.1  Causes of Pericarditis

TABLE 27.1  Pericarditis in Children, 1962–74 (St. Louis Children’s Hospital)a

Idiopathic Benign Recurrent Infectious Purulent Bacterial: Staphylococcus aureus, Haemophilus influenzae, streptococci, Neisseria meningitidis, Streptococcus pneumoniae, anaerobes, Francisella tularensis, Salmonella, enteric bacilli, Pseudomonas, Listeria, Neisseria gonorrhoeae, Actinomyces, Nocardia Tuberculosis Fungal: Histoplasma, Coccidioides, Aspergillus, Candida, Blastomyces, Cryptococcus Viral Coxsackieviruses B Other: influenza A and B, mumps, echoviruses, adenoviruses, Epstein-Barr virus, hepatitis, measles, influenza, human immunodeficiency virus, parvovirus B19, cytomegalovirus Other Rickettsial: typhus, Q fever Mycoplasmal: Mycoplasma pneumoniae Parasitic: Entamoeba histolytica, Echinococcus Spirochetal: syphilis, leptospirosis Chlamydial: psittacosis Protozoal: toxoplasmosis Noninfectious Postpericardiotomy syndrome Kawasaki disease Rheumatic fever Connective tissue disorders: juvenile rheumatoid arthritis, systemic lupus erythematosus, dermatomyositis, periarteritis nodosa Trauma: blunt or penetrating Metabolic: uremia, myxedema Hypersensitivity: serum sickness, pulmonary infiltrates with eosinophilia, Stevens-Johnson syndrome, drugs (hydralazine, procainamide, chemotherapy) Neoplasm: leukemia, metastatic After irradiation

mass invasion in two (10%). In another series from Turkey, 18 children with purulent pericarditis were encountered from 1990 to 2000.10 At the Boston Children’s Hospital, fewer than 10 patients seen among more than 1700 patients in consultation by the pediatric cardiologists had pericarditis during the period July 1, 2001, to June 30, 2002.33 Over a 21-year period, 31 children with an inflammatory large pericardial effusion requiring drainage were admitted to one tertiary care children’s hospital; 12 of the effusions were caused by bacterial infections.68 Although rare, purulent pericarditis also can occur in neonates.53 In most series, a marked male predominance has been noted.

Etiology Primary purulent pericarditis is a rare disease; it accounted for only seven of 50 cases of pericarditis reported by Gersony and McCracken.34 The disease is associated most often with infection from another site, with hematogenous or direct spread to the pericardium. Feldman28 reviewed all cases of bacterial pericarditis reported in the English language literature from 1950 to 1977. Bacteria were isolated in 146 (90%) of 162 cases. No other infection was found in 10 patients. The most common concomitant site involved was the lung, especially for Staphylococcus

Etiology Unknown Purulent Juvenile rheumatoid arthritis Acute rheumatic fever Uremia Viral Blunt chest trauma Dermatomyositis

No. Patients 28 12 9 8 5 2 2 1

a

Patients with postpericardiotomy pericarditis and patients with small exclusions at autopsy were excluded from consideration. From Strauss AW, Santa-Maria M, Goldring D. Constrictive pericarditis in children. Am J Dis Child. 1975;129:822–6.

aureus, Haemophilus influenzae, and Streptococcus pneumoniae. When septic arthritis, osteomyelitis, or skin infections were found, S. aureus usually was the cause of pericarditis. Neisseria meningitidis and H. influenzae most often were responsible for concomitant meningitis and pericarditis. Before the introduction of antibiotics, pneumococcal and streptococcal organisms were the most frequent causes of purulent pericarditis in children. Most cases were associated with pulmonary infections. Nearly half of patients with streptococcal pericarditis had associated postinfluenzal pneumonia. Hemolytic streptococci were isolated most often; 10% were nonhemolytic streptococci, and 5% were viridans streptococci. Kauffman and colleagues56 reviewed 113 cases of pneumococcal pericarditis reported since 1900. Preceding pneumonia was present in 93%, and empyema was present in 66%. Pericarditis was thought to be a late event resulting from delay in administering appropriate therapy for pneumonia. S. aureus is the organism most commonly responsible for purulent pericarditis in children.28,34,44,79 Most cases are the result of hematogenous seeding of the pericardium from staphylococcal pneumonia with empyema, acute osteomyelitis, or soft tissue abscesses. Among 117 children with S. aureus pneumonia at Texas Children’s Hospital, 13 children had an echocardiogram; one had a large pericardial effusion.14 Occasionally, the pericardium is infected during the course of staphylococcal endocarditis. S. aureus is the most frequently recovered organism when purulent pericarditis develops within 3 months after the patient has undergone open heart surgery. The clinical course of acute staphylococcal pericarditis is dominated by severe toxemia. In addition to the necrotizing infection produced by S. aureus, the organism may release exotoxins, which produce shock and contribute to the high mortality. Community-associated methicillin-resistant S. aureus isolates have been recovered from some patients with acute pericarditis.47,64 S. aureus was isolated from 73% of infants who died of purulent pericarditis in the series reported by Gersony and McCracken.34 It was responsible for 50% of cases in children 1 to 4 years old in the review by Feldman.28 In seven patients younger than 1 month of age, S. aureus was isolated from four. This finding is corroborated in literature from other countries.19,50,79 Thebaud and colleagues93 reported 19 patients with purulent pericarditis in a children’s hospital in Paris between 1979 and 1994. The mean age of the children was 3 years (range, 3 months to 10 years). The organisms isolated were S. aureus (three cases), H. influenzae (four cases), group A streptococci (three cases), S. pneumoniae (three cases), and N. meningitidis (one case). Concomitant infections included pneumonia (six cases), osteomyelitis (three cases), cellulitis (one case), and sinusitis (one case). In the series from Turkey, S. aureus was isolated from five patients, and S. pneumoniae was isolated from one patient.10 S. aureus pericarditis as a complication of varicella has been reported in several children.8 S. aureus has also caused pericarditis associated with disseminated infection in a child with IRAK-4 deficiency.17

272

SECTION 3  Infections of the Heart

In the prevaccine era, the second most frequently encountered organism was H. influenzae type b.7 It was responsible for 22% (35 of 163) of the cases in Feldman’s review.28 A single site of coexisting infection, the lung, was identified in 16 of the 35 cases. Meningitis as a single other site of infection was found in five of 35 patients, and multiple involvement was found in seven of 35. Echeverria and colleagues24 summarized 33 cases from the literature. Pulmonary infiltrates and empyema were seen in 64% of patients. In countries where the H. influenzae type b conjugate vaccine is administered to infants routinely, this organism has been eliminated as a cause of pericarditis. Pneumococcal, streptococcal, and meningococcal pericarditis have diminished in frequency since the introduction of penicillin.6 Go and coworkers35 summarized the 15 reported cases of pneumococcal pericarditis from 1980 to 1998. One was a child. Only four cases did not have an underlying risk factor. In a surveillance study of invasive pneumococcal infections in eight pediatric hospitals, only three cases of pericarditis have been observed in more than 2500 cases of systemic pneumococcal infection during the 6-year period of 1993 through 1999.54 Nevertheless, S. pneumoniae remains an important, although rare, cause of acute bacterial pericarditis.27 The routine administration of the pneumococcal conjugate vaccine to young children has likely resulted in S. pneumoniae being an even less common cause of acute pericarditis. Pericardial involvement occurs in approximately 5% of young adults with meningococcemia.21 The clinical course generally is milder than that observed with other types of purulent pericarditis. Pericardial involvement rarely is detected at the time of hospital admission. Pericarditis became apparent by the third day in 13 of 17 patients reported by Dixon and Sanford.21 In some patients, it did not occur until late in the course of therapy. In a multicenter study involving 159 children with meningococcal infections in children from 2001 through 2005, pericarditis was not encountered.55 Whether this late-onset pericardial effusion is a part of the meningococcal infection or is related to immune complexes is unclear.21,73,84 Primary meningococcal pericarditis that occurs without clinical evidence of meningococcemia, meningitis, or any other focal infection has been reported in 16 patients, including six children 18 years old or younger (range, 2 to 18 years).3 Meningococcal serogroup C was identified in 11 (79%) of 14 cases for which the serogroup was known. Cardiac tamponade developed in 88% of the patients. Pericarditis also has been reported in two children with W135 meningococcal infection.25 Occasionally, other microorganisms cause acute purulent pericarditis. Feldman28 reported that 11 (8%) of 146 cases of pericarditis in children were caused by Pseudomonas aeruginosa. P. aeruginosa caused pericarditis in an immunocompetent adult with cystic fibrosis.2 Pericarditis can occur with pneumonic tularemia, salmonellosis, sepsis from enteric bacilli, listeriosis, and disseminated gonococcal disease.6 Anaerobic bacteria should be suspected when pericarditis develops in association with lung abscess, intraabdominal infection including ruptured appendicitis,91 or a penetrating wound. Callanan and colleagues12 reported the rapid development of constrictive pericarditis after purulent pericarditis caused by anaerobic streptococcal infection. The child had a history of blunt trauma to the chest with no evidence of a penetrating wound 3 weeks before cardiac tamponade developed. The incidence of anaerobic infection may be underestimated because of improper handling of specimens for culture. Prolonged symptoms related to pericarditis can be associated with Mycoplasma pneumoniae infection.26 Mycobacterium tuberculosis, previously a common cause of acute pericarditis in the United States,5 now is responsible more often for chronic pericardial disease. This infection is a complication of miliary tuberculosis and rarely a primary infection. In the series of 2500 children with tuberculosis reported by Lincoln and Savell,62 pericarditis was diagnosed in 0.4% and found at necropsy in 5% of patients. A review of 100 cases of tuberculous pericarditis in South Africa by Desai20 revealed a marked male predominance (72%). The duration of symptoms, consisting of cough and peripheral edema, in most patients was 0 to 120 days. Most patients were febrile and had congestive heart failure. Generalized lymphadenopathy occurred in nearly 30% of patients, pulsus paradoxus occurred in 50%, and a friction rub was audible in 25%. Of the 52 patients who had pericardiocentesis, 40% yielded fluid, but none

was positive for acid-fast bacilli. Pericardial effusion was shown in 82 patients, 16 of whom died of tamponade and another 16 of whom developed constricting pericarditis. The four stages of tuberculous pericarditis have been described as dry, effusive, absorptive, and constrictive.75 Granulomas usually are found in the dry stage and heal with no sequelae. The effusive stage occurs commonly with tuberculous lymphadenitis, and 15 to 200 mL of fluid usually accumulates in the pericardial space. The absorptive stage is characterized by thickening of the pericardium with fibrin deposition. Further fibrin deposition and calcification occur during the constrictive phase. The disease may progress through all stages or remain in one stage. Latent infection in the mediastinal lymph nodes with spread directly into the pericardium is thought to be the mode of involvement with M. tuberculosis.75 The lymph nodes at the tracheal bifurcation often are the source. Histoplasma pericarditis generally occurs with pulmonary, rather than disseminated, disease.77 Coccidioidomycosis67 also may cause pericardial disease. Aspergillus and Candida are more serious considerations in patients who are immunosuppressed, have serious burns, or are receiving long-term, broad-spectrum antibiotics after undergoing cardiac surgery.81 Finally, several parasites such as Trypanosoma cruzi and Toxoplasma gondii can attack the pericardium.42

Pathology and Pathogenesis Pericarditis begins with fine deposits of fibrin adjacent to the great vessels; it causes the pericardial membrane to lose its smoothness and translucency. Numerous granulocytes may extend into the myocardium.37 Bacterial pericarditis most commonly results from direct extension of infection from involved lung and pleura. Pulmonary infections may spread to the pericardium through the bronchial circulation.41 Pericarditis also can develop through hematogenous dissemination from infection elsewhere, and it also may be the result of an immunologically induced response to a primary infection. As pericardial fluid accumulates, intrapericardial pressure increases. The rate of increase is a function of the speed of accumulation and the compliance of the pericardium. With slow accumulation of fluid, large volumes can be accommodated because of the gradual expansion of the parietal pericardium. As the compliance of the pericardium reaches its maximum, however, further accumulation of even small volumes of fluid results in an abrupt increase in intrapericardial pressure. If pericardial fluid accumulates at a rapid rate, marked elevation in intrapericardial pressure may occur with much smaller volumes of fluid. In a small child, 100 mL can cause severe tamponade, whereas 3 L may accumulate slowly in an older child and not result in tamponade.1 The most significant hemodynamic effect of pericardial effusion is restriction of ventricular filling. Ventricular end-diastolic, atrial, and venous pressures increase on the right and left sides of the heart equally. When restriction of ventricular filling becomes more pronounced, the ventricular stroke volume and cardiac output decrease. In an attempt to maintain cardiac output, tachycardia and peripheral vasoconstriction occur. Systemic arterial blood pressure and pulse pressure are reduced markedly. Tamponade occurs when these compensatory mechanisms fail to maintain adequate cardiac output.

Clinical Manifestations A diagnosis of purulent pericarditis should be suspected in any patient with septicemia who develops cardiomegaly. The classic signs and symptoms of pericarditis are precordial pain, pericardial friction rub, evidence of cardiac fluid, and muffled heart sounds.15 Chest pain is not a common symptom, especially in small children; the reported rates vary from 15% to 80%.4,6,35,45,73,77,96 However, in one study focusing on 22 children (aged 6 to 17 years old) who presented to an emergency center and ultimately were found to have acute pericarditis, 95% had chest pain.78 Acute abdominal symptoms may be the presenting complaints of some children.22 The most common symptoms and signs of pericarditis are fever, tachypnea, and tachycardia, which also are presenting features of

CHAPTER 27  Infectious Pericarditis Right Atrial and Femoral Pressures Before Pericardiocentesis

Kussmaul sign (paradoxical venous pressure)

SVC

Femoral 100 mm Hg

50

0

40

  

Inspiration

273

Expiration



Femoral

RA

100

40

50

20

20

   Inspiration

FIG. 27.1  Simultaneous recording of right atrial and femoral artery pressures. Notice the increased V wave and exaggerated decrease in the femoral artery pulse with inspiration.

A After Pericardiocentesis

associated systemic infection. If the cardiac shadow is radiographically enlarged, with or without a friction rub, and the tachypnea and tachycardia are out of proportion to the fever, myocardial dysfunction or pericarditis should be suspected. An evanescent or ubiquitous rub may be detected. The typical sound of a rub is that of a high-frequency murmur,76 which may have a toand-fro or triphasic pattern but may not have any correlation with the cardiac cycle.29 Frequently the rub is heard better with the patient leaning forward or kneeling. A rub may be differentiated from a murmur by pressing the diaphragm of the stethoscope firmly against the chest wall; this pressure amplifies the rub, and the typical scratchy quality becomes more apparent as the examiner opposes the visceral and parietal pericardium by compression of the chest. Rubs have been known to increase with inspiration.87 Although a rub is less likely to be heard in the presence of a large effusion, it still may exist.29 The heart sounds usually are muffled, and the palpable ventricular impulse generally is diminished. Both findings may be present in congestive heart failure, but they may be absent with tamponade. Cardiac tamponade may be an early complication of pericarditis associated with a systemic infection. Cardiac tamponade means that there is compression of the heart by a tense pericardial sac, usually full of fluid, resulting in a decrease in venous return to the cardiac chambers and a decrease in cardiac output. During inspiration, the intrathoracic pressure decreases and venous return to the venae cavae increases. The tense pericardial sac limits the amount of blood that can enter the right atrium because of diastolic compression; a paradoxical increase in jugular venous pressure occurs during inspiration (i.e., Kussmaul sign) (Fig. 27.1).58 During inspiration, a small decrease in systolic blood pressure and cardiac output normally occurs and is caused by an increase in pulmonary venous capacitance. It is exaggerated with pericardial tamponade (>10 mm Hg decrease in blood pressure) because of the restricted inflow into the cardiac chambers. This clinical sign has been called paradoxical pulse, but it actually is an exaggeration of the normal respiratory cycle (Fig. 27.2).36

Diagnosis The radiographic appearance of a rapidly increasing cardiothoracic ratio without increasing pulmonary vascular markings is more suggestive of pericardial effusion than of congestive heart failure caused by myocardial dysfunction (Fig. 27.3). Fluoroscopy alone generally is of little value; myocardial dysfunction and pericarditis can impair cardiac contractility. The size of the pericardial shadow does not indicate the severity of hemodynamic effects. It is a function of the rapidity of accumulation and the volume of pericardial fluid. When acute infection results in sudden cardiac tamponade, the heart size may be normal. A large, globular heart shadow with no evidence of increased pulmonary vasculature, particularly in a patient who has signs of right-sided heart failure, is strong evidence for pericardial disease. The lack of pulmonary overcirculation helps to distinguish this condition from myocarditis; however, determining whether pulmonary infiltrates also exist may be difficult.

Femoral

RA

100

40

50

20

B FIG. 27.2  Recordings of femoral artery and right atrial pressures (A) before and (B) after pericardiocentesis. (A) There is an exaggerated decrease in the fall of femoral artery pressure with inspiration and a sustained increase in right atrial pressure. (B) The recording shows a more normal variation of femoral pressure and a lower right atrial pressure.

A plain lateral chest radiograph may show findings consistent with a pericardial effusion.59 Separation of more than 2 mm between the anterior mediastinal and subepithelial “fat stripes” suggests an effusion. Obliteration of the retrosternal space without evidence of thymic or right ventricular enlargement also indicates pericarditis. The extent of electrocardiographic abnormalities may be explained by the amount of pericardial effusion and the presence of superficial myocardial injury or myocarditis. Pericardial effusion gives rise to low-voltage QRS complexes as a result of the damping effect of pericardial fluid between the chest wall and the myocardium. Accumulation of fluid and fibrin under pressure also may produce an injury pattern manifested by ST-segment deviation. More than 90% of patients have elevation of the ST segment, which occurs most frequently in leads I, II, V5, and V6. Widespread T-wave inversion indicative of epicarditis may be seen in the same leads in which ST-segment elevation occurs. Spodick86 described four stages of electrocardiographic changes in acute pericarditis. In stage I, ST-segment elevation is pronounced and the PR segment may be depressed. In stage II, the ST segment begins to return to the isoelectric line, the amplitude of the T wave diminishes, and the PR segment is depressed. By stage III, the ST segment has returned to the isoelectric line, and the T-wave inversion occurs. An incompletely inverted T wave (i.e., a diphasic wave or an upright T wave with a notched summit) sometimes is observed. In stage IV, these changes may resolve completely. T-wave abnormalities may persist for life, however, and do not indicate active disease. Electrical alternans is seen in a large pericardial effusion. Electrical alternans refers to the alternation in electric amplitude of the T wave and the QRS complex with each cardiac cycle. It is thought to result from the rotational and pendular motion of the heart suspended in pericardial fluid.

274

SECTION 3  Infections of the Heart

FIG. 27.3  In this patient with pericarditis, the first two radiographs show an enlarged cardiac shadow without an increase in pulmonary vascular markings. The third radiograph shows a marked decrease in apparent heart size after pericardiocentesis.

RV

RV IVS MV

IVS LV

MV

LV

END EPI

PE

PE

PE

PE

PE PE

ECG

A

B

END EPI

PE

PE

ECG

FIG. 27.4  Serial echocardiograms of a child (A) before pericardiocentesis and (B) after pericardiocentesis. (A) Note the large effusion anteriorly and posteriorly with the “swinging” movement of the septum and anterior and posterior walls. (B) The heart movement is normal, and there remains only a small effusion anteriorly and posteriorly. ECG, Electrocardiogram; END, endocardium; EPI, epicardium; IVS, interventricular septum; LV, left ventricle; MV, mitral valve; PE, pericardial effusion; RV, right ventricle.

Deviations from classic patterns occasionally occur, and single electrocardiographic changes are common findings. All 12 children reported by Okoroma and colleagues74 had ST-segment elevation, whereas only 3 had concomitant low voltage. Dysrhythmias with pericarditis are unusual in the absence of coexisting heart disease.88 M-mode echocardiography is the most sensitive method for diagnosing significant pericardial effusion (Fig. 27.4).40,45 With a small to moderate effusion, only a “fluid space” is seen posteriorly (Fig. 27.4B). With a larger effusion, fluid is seen anteriorly and posteriorly, and the septal motion becomes grossly abnormal. The heart may give the appearance of freely swinging (Fig. 27.4A). Newer echocardiographic techniques, such as two-dimensional sector scanning, are not more useful than the conventional M-mode. Pericarditis may be detected uncommonly by echocardiography in children with S. aureus bacteremia but without clinical evidence of pericardial or endocardial involvement.31 Computed tomography and magnetic resonance imaging of the chest are other modalities used to examine the pericardium.7 They may help to differentiate a bacterial pericarditis from other conditions involving the pericardium. Occult or unsuspected pericarditis has been discerned with radionuclide techniques in immunocompromised patients and in trauma patients.39,83 A pericardial effusion may be diagnosed by noticing a discrepancy between the position of a catheter placed adjacent to the lateral wall of the right atrium and the right cardiac border. An injection of radiopaque contrast material into the right atrium may delineate these

findings further. Pressure measurements at the time of cardiac catheterization reveal the elevated right atrial pressure and emphasize further the exaggeration of venous, systemic, and left ventricular pressures imposed by inspiration (see Fig. 27.2). Injection of carbon dioxide or air into the pericardium percutaneously may delineate further the pericardial effusion fluoroscopically and differentiate freely moving fluid from loculated areas (Fig. 27.5). The diagnosis of purulent pericarditis is established definitively only by direct examination of pericardial fluid. Purulent fluid is characterized by a predominance of polymorphonuclear leukocytes; however, it also may occur early in the course of viral and tuberculous pericarditis. Proper handling of pericardial fluid is crucial to recovery and identification of the etiologic agent, as follows: 1. Fluid should be placed directly into broth capable of supporting aerobic and anaerobic microorganisms. The fluid should be plated directly onto agar media, such as blood agar, chocolate agar, or MacConkey agar. 2. Cultures also should be submitted for identification of M. tuberculosis, fungi, and viruses. 3. Several slides should be prepared for immediate examination by Gram stain and stain for acid-fast bacilli. Unstained slides should be stored in case of controversy or the need for special histochemical stains. 4. Antigen detection for S. pneumoniae or polymerase chain reaction for other microorganisms may be useful in selected cases, particularly when the patient has received prior antimicrobial therapy.11,61

CHAPTER 27  Infectious Pericarditis

PERICARDIUM AIR APEX of HEART FLUID LEVEL PERICARDIAL CATHETER

FIG. 27.5  Chest radiograph of a patient lying on the right side with a catheter in the pericardium. Air has been injected through the catheter, outlining the pericardium and fluid within the sac.

The causative microorganism is isolated from blood cultures in many patients. When indicated, cerebrospinal fluid also should be cultured. Because purulent pericarditis often occurs after infections of the lung or pleural space, thoracentesis can reveal the etiologic agent in many cases. Documentation of empyema together with evidence of pericardial disease correlates highly with purulent pericarditis. Acid-fast bacilli are seen on stained smears of pericardial fluid from 15% to 42% of patients with tuberculous pericarditis.5 Examination of pericardial biopsy specimens by routine methods and with special stains such as the auramine O can increase the frequency of identification of M. tuberculosis.72 A negative purified protein derivative skin test does not exclude the diagnosis of tuberculous pericarditis. Grossly bloody pericardial fluid is observed frequently in patients with Histoplasma pericarditis, and an aspirate of the effusion reveals a predominance of mononuclear leukocytes. Growth of H. capsulatum from pericardial fluid rarely is successful. Showing the typical intracellular yeast forms on special stain of pericardial tissue also is helpful. Elevation of the yeast phase of the complement-fixation titer in pericardial fluid allows one to make a more rapid diagnosis.77 Detecting the polysaccharide of H. capsulatum in urine or other body fluids is a rapid and sensitive means by which to establish the diagnosis of histoplasmosis.

Differential Diagnosis Any patient with a rapidly increasing heart size in the absence of increasing pulmonary vascular markings should be suspected to have a pericardial effusion. Purulent pericarditis must be differentiated from pericardial effusion caused by collagen diseases, other infectious agents (e.g., viral, tuberculous, rickettsial, protozoan), neoplastic disorders, metabolic disorders, and congestive heart failure.15 Glycogen storage disease, congenital heart disease, primary myocardial disease, cardiac tumors, and coronary artery aberrations (i.e., anomalous origin from the pulmonary artery, medial wall necrosis, and Kawasaki disease) may be confused with pericardial effusion. Appropriate analysis of pericardial fluid usually permits differentiation of purulent pericarditis from pericarditis caused by other disorders. A high eosinophil count in the pericardial fluid suggests a parasite or a hypereosinophilic syndrome.85

Treatment Purulent pericarditis is a potentially life-threatening illness that requires pericardial decompression and open drainage, appropriate antimicrobial therapy, and intense supportive therapy. Most children with purulent pericarditis require early or emergency drainage of the pericardium for relief of critical tamponade. Although bedside needle pericardiocentesis may be lifesaving or necessary for establishing a rapid diagnosis, deaths related to pericardiocentesis performed by inexperienced physicians can occur. Complications include arrhythmias resulting from myocardial injury, laceration of the coronary arteries leading to hemopericardium and tamponade, and pneumothorax. Ledbetter60 described a 10-year-old girl with staphylococcal pericarditis who developed an aortic aneurysm

275

TABLE 27.2  Influence of Pericardial Drainage on Survival in Purulent Pericarditis in Children Treatment Antibiotics alone Antibiotics and pericardial drainage

Survived

Died

5 45

28 10

Data from references 4, 30, 56, and 71.

after undergoing multiple pericardiocentesis procedures for recurrent tamponade. Ultrasound-guided pericardiocentesis is recommended. Decompression and drainage of the pericardium are safest in a controlled environment, such as in an operating room or under fluoroscopy in the catheterization laboratory. If the patient is awake and agitated, premedication may be required. If pericardiocentesis does not relieve symptoms successfully, and evidence of tamponade continues, immediate surgical drainage is necessary. Multiple attempts may prove unsuccessful and can lead to serious complications. The pus surrounding the heart may be too thick to be aspirated.69 Surgical creation of a pericardial window with a drain occasionally is necessary for complete removal of fluid, which accumulates rapidly. In preparation for evacuation of the pericardial fluid during tamponade, adequate cardiac output can be maintained by stimulating the heart with pharmacologic agents that cause a chronotropic and an inotropic effect. Medications that tend to decrease heart rate and intravascular volume are contraindicated because they compromise the patient further.95 Wyler and colleagues95 warn against the use of halothane anesthesia because of its known depressant effect on myocardial function. Purulent pericarditis requires some type of pericardial drainage, but the optimal approach to drainage including the extent of surgery is uncertain.27,30,31,60,72,85 Some surgeons favor the creation of a pericardial “window”; however, others favor more extensive removal of pericardial tissue. This decision may be influenced by the severity of pericardial inflammation or the presence of bloody pericardial fluid because these conditions have greater potential for producing acute or chronic constriction. Video-assisted thoracoscopic approaches to managing pericarditis also have been described.65,68 For selected patients for whom surgery cannot be performed in a timely manner, the instillation of intrapericardial streptokinase or urokinase or other thrombolytic agents has been successful in draining purulent pericarditis and preventing the need for a more extensive surgical procedure.52 Antimicrobial therapy alone is insufficient for the successful treatment of purulent pericarditis. The survival of patients with purulent pericarditis is improved significantly when early pericardial drainage is performed (Table 27.2). In the preantibiotic era, draining the pericardium decreased the mortality rate from nearly 100% to 45%.66 Occasionally patients with meningococcal pericarditis have been managed successfully without pericardial drainage.18 Fyfe and colleagues32 described 73 of 79 patients with H. influenzae pericarditis seen between 1928 and 1984. The mortality rate before 1960 was 64% (7 of 11 patients), although five of seven deaths were reported before the antibiotic era. From 1960 to 1969, the mortality rate was 36 percent, and from 1970 to 1979, it decreased to 11.5%. From 1980 to 1984, 25 cases with no mortality were reported. When the etiologic agent cannot be detected rapidly, the initial antibiotic regimen should consist of two or more drugs. Because S. aureus is a major pathogen and community-associated methicillinresistant S. aureus isolates are common in almost all areas, a penicillinaseresistant penicillin, such as nafcillin or oxacillin, in a dose of 200 mg/ kg per 24 hours (maximum 12 g) plus vancomycin in a dose of 60 mg/ kg per day in four divided doses is usually recommended for initial empiric therapy. Vancomycin is also recommended when strains of S. pneumoniae resistant to the extended-spectrum cephalosporins are present or when the infection is nosocomially acquired. Cefotaxime 200 to 300 mg/kg per day in three or four divided doses or ceftriaxone 100 mg/kg per day in one or two doses should be administered to provide protection against S. pneumoniae (including penicillin-resistant

276

SECTION 3  Infections of the Heart

strains), N. meningitidis, and H. influenzae type b (for children who may be inadequately immunized). An aminoglycoside antibiotic should be added to the just-mentioned combined drug therapy when purulent pericarditis occurs after cardiac surgery, in association with genitourinary infections, or in the immunocompromised host. The antibiotics selected for empiric therapy for acute pericarditis complicating recent cardiac surgery are influenced by the hospital’s antibiogram. For patients who are allergic to penicillin, vancomycin, clindamycin, or cefazolin is substituted for the treatment of susceptible S. aureus. The duration of therapy is empiric and is determined partly by the nature of concomitant infection. Generally after a pathogen is isolated and the antimicrobial susceptibilities are known, the most specific antimicrobial agent is continued intravenously for 3 to 4 weeks. Monitoring the C-reactive protein levels may help in determining the length of treatment.49 Using antimicrobial agents to treat tuberculous pericarditis has had a major impact on mortality. Before their use, the mortality rate in the acute phase was 80% to 90%. The other 10% to 20% of patients died of constrictive pericarditis or miliary tuberculosis.75 The use of three or four drugs, including isoniazid, pyrazinamide, rifampin, and possibly streptomycin, for 9 to 12 months is recommended. The role of corticosteroids in preventing progression to constriction or decreasing mortality is unclear.23,66,75 In selected cases, pericardiectomy may be indicated to prevent constrictive pericarditis. The reader is referred to Chapter 204 on histoplasmosis for details regarding treatment of pericarditis due to this organism. As with bacterial pericarditis, open pericardiectomy is crucial for the successful treatment of Candida pericarditis.71,81 General supportive therapy in the acute stage of infection may include the administration of oxygen, volume expansion to increase ventricular filling pressure, and cardiovascular agents to facilitate systolic emptying. The input of pediatric cardiologists is critical for the optimal management of these patients. Serial electrocardiograms may indicate the presence of occult arrhythmias and alert the physician to the degree of myocardial involvement. The patient must be monitored carefully for signs of reaccumulation of pericardial fluid and for the development of acute constrictive pericarditis. Strauss and colleagues89 reported this complication in two of 12 children with purulent pericarditis. Acute constriction may develop within weeks of the initial pericardial infection4,9 and has been reported at 8 days.80 Constrictive pericarditis may be suspected by increasing jugular and central venous pressure, weight gain, enlarging liver, worsening dyspnea, and decreased urinary output. The persistence of heart failure when the cardiac silhouette is becoming smaller also suggests the development of constrictive pericarditis. Complete pericardiectomy should be performed promptly when constriction is suspected.

Prognosis Accurate mortality rates are difficult to compute from the literature because of the relative rarity of this infection as well as the nature and severity of any underlying disease. Factors that contribute to mortality are delay in recognition, absence of early surgical drainage, presence of cardiac tamponade, degree of myocardial involvement, etiologic agent (particularly S. aureus), and age of the patient. Long-term follow-up of children with purulent pericarditis is recommended. They should be observed carefully for the presence of a constrictive component as a sequela to the acute infection. Most children recover fully, however, and return to normal activity.

VIRAL PERICARDITIS In 1951, Christian16 suggested that viral infections were responsible for cases of idiopathic or benign pericarditis. A viral cause has not been substantiated in many patients, however.

Etiology The principal viruses implicated in pericarditis are the coxsackieviruses.71,74 Adenoviruses have been recovered less frequently.51 Associations with varicella,92,96 cytomegalovirus,13 smallpox vaccinations, influenza43 (including H1N1),57 influenza vaccinations,90 parvovirus B19,38 and infectious mononucleosis46,96 have been reported.

FIG. 27.6  In this case of viral pericarditis there is a layer of fibrin and fibroblasts along the pericardial surface. The mononuclear cell infiltrate in the epicardium extends into the outer myocardium (H&E, ×400). (Courtesy Edith P. Hawkins, MD, Texas Children’s Hospital, Houston.)

Clinical Manifestations In 40% to 75% of cases, the patient has a history of upper respiratory tract infection for 10 days to 2 weeks preceding the onset of symptoms. Fever and chest and abdominal pain are the most common symptoms.16 A friction rub may be heard in 50% to 80% of cases.94 Children with viral pericarditis generally are less toxic and experience smaller elevations in body temperature than do children with purulent pericarditis. Some appear acutely ill, however. Large amounts of pericardial fluid accumulation and tamponade are rare findings.

Investigative Techniques The electrocardiographic, radiographic, echocardiographic, and nuclear scanning findings described for patients with purulent pericarditis also are observed in patients with viral pericarditis. Mononuclear cell infiltrates in the pericardium with extension into the myocardium may be seen (Fig. 27.6). If obtained, pericardial fluid should be sent for cell count and viral culture. Nasopharyngeal and rectal samples also should be obtained and cultured for viruses. Molecular methods may detect evidence of a specific virus. Acute and convalescent sera should be obtained so that appropriate titers can be measured if a virus is isolated.

Course and Prognosis Viral pericarditis generally resolves spontaneously over the course of 3 to 4 weeks.71 Large pericardial effusions and tamponade are rare occurrences. Generally bed rest for approximately 1 week and analgesics for pain are the only therapy that is required. Constrictive pericarditis is a rare occurrence, but pericarditis may recur. In adults with recurrent pericarditis, colchicine appears to be of more benefit than corticosteroids in terms of treatment effect and decreased recurrences in adults, but the use of colchicine for this indication in children is limited.48,63,82 NEW REFERENCES SINCE THE SEVENTH EDITION 38. Gouriet F, Levy PY, Casalta JP, et al. Etiology of pericarditis in a prospective cohort of 1162 cases. Am J Med. 2015;128(7):784.e1-784.e8.

49. Imazio M, Gaita F. Diagnosis and treatment of pericarditis. Heart. 2015;101(14): 1159-1168. 48. Imazio M, Brucato A, Cemin R, et al. A randomized trial of colchicine for acute pericarditis. N Engl J Med. 2013;369(16):1522-1528. 55. Kaplan SL, Schutze GE, Leake JA, et al. Multicenter surveillance of invasive meningococcal infections in children. Pediatrics. 2006;118(4):e979-e984. 64. Lutmer JE, Yates AR, Bannerman TL, et al. Purulent pericarditis secondary to community-acquired, methicillin-resistant Staphylococcus aureus in previously healthy children. A sign of the times? Ann Am Thorac Soc. 2013;10(3):235-238.

67. McCarty JM, Demetral LC, Dabrowski L, et al. Pediatric coccidioidomycosis in central California: a retrospective case series. Clin Infect Dis. 2013;56(11):1579-1585. 82. Shakti D, Hehn R, Gauvreau K, et al. Idiopathic pericarditis and pericardial effusion in children: contemporary epidemiology and management. J Am Heart Assoc. 2014;3(6):e001483. 96. Zakhour R, Burkholder H, Wanger A, et al. Epstein-Barr virus-associated pericarditis and pleural effusions in a 4-year-old girl. Pediatr Infect Dis J. 2015;34(4):458-459.

The full reference list for this chapter is available at ExpertConsult.com.

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Cardiac involvement with parasitic infections. Clin Microbiol Rev. 2010;23(2):324-349. 43. Hildebrandt HM, Maassab HF, Willis PW 3rd. Influenza virus pericarditis. Report of a case with isolation of Asian influenza virus from the pericardial fluid. Am J Dis Child. 1962;104:579-582. 44. Horan JM. Acute staphylococcal pericarditis. Pediatrics. 1957;19(1):36-43. 45. Horowitz MS, Schultz CS, Stinson EB, et al. Sensitivity and specificity of echocardiographic diagnosis of pericardial effusion. Circulation. 1974;50(2): 239-247. 46. Hudgins JM. Infectious mononucleosis complicated by myocarditis and pericarditis. JAMA. 1976;235(24):262. 47. Hussam MA, Ragai MF, Iman MF, et al. Community-acquired methicillin-resistant Staphylococcus aureus pericarditis presenting as cardiac tamponade. South Med J. 2010;103(8):834-836. 48. Imazio M, Brucato A, Cemin R, et al. A randomized trial of colchicine for acute pericarditis. N Engl J Med. 2013;369(16):1522-1528. 49. Imazio M, Gaita F. Diagnosis and treatment of pericarditis. Heart. 2015;101(14):1159-1168. 50. Jaiyesimi F, Abioye AA, Antia AU. Infective pericarditis in Nigerian children. Arch Dis Child. 1979;54(5):384-390. 51. Johnson RT, Portnoy B, Rogers NG, et al. Acute benign pericarditis. Virologic study of 34 patients. Arch Intern Med. 1961;108:823-832. 52. Juneja R, Kothari SS, Saxena A, et al. Intrapericardial streptokinase in purulent pericarditis. Arch Dis Child. 1999;80(3):275-277. 53. Kanarek KS, de Brigard T, Coleman J, et al. Purulent pericarditis in a neonate. Pediatr Infect Dis J. 1991;10(7):549-550. 54. Kaplan SL, Mason EO Jr, Wald E, et al. Six year multicenter surveillance of invasive pneumococcal infections in children. Pediatr Infect Dis J. 2002;21(2): 141-147. 55. Kaplan SL, Schutze GE, Leake JA, et al. Multicenter surveillance of invasive meningococcal infections in children. Pediatrics. 2006;118(4):e979-e984. 56. Kauffman CA, Watanakunakorn C, Phair JP. Purulent pneumococcal pericarditis. A continuing problem in the antibiotic era. Am J Med. 1973;54(6):743-750. 57. Koranyi K, Yontz D, Rohrer Z, et al. Pericardial effusion complicating novel influenza A (H1N1) infection in an infant. Pediatr Infect Dis J. 2010;29(8):782-783. 58. Kussmaul A. Ueber schwieglige mediastino-perikarditis und der paradoxen puls. Klin Wochenschr. 1873;10:443. 59. Lane EJ Jr, Carsky EW. Epicardial fat: lateral plain film analysis in normals and in pericardial effusion. Radiology. 1968;91(1):1-5. 60. Ledbetter MK. Aortic aneurysm complicating staphylococcal pericarditis. J Okla State Med Assoc. 1981;74(8):222-225. 61. Levy PY, Fournier PE, Charrel R, et al. Molecular analysis of pericardial fluid: a 7-year experience. Eur Heart J. 2006;27(16):1942-1946. 62. Lincoln EM, Savell EM. Tuberculosis in Children. New York: McGraw-Hill; 1963. 63. Lotrionte M, Biondi-Zoccai G, Imazio M, et al. International collaborative systematic review of controlled clinical trials on pharmacologic treatments for acute pericarditis and its recurrences. Am Heart J. 2010;160(4):662-670. 64. Lutmer JE, Yates AR, Bannerman TL, et al. Purulent pericarditis secondary to community-acquired, methicillin-resistant Staphylococcus aureus in previously healthy children. A sign of the times? Ann Am Thorac Soc. 2013;10(3):235-238. 65. Mack M, Acuff T, Hazelrigg S, et al. Thoracoscopic approach for the pericardium. Endosc Surg Allied Technol. 1993;1(5-6):271-274. 66. Mayosi BM, Burgess LJ, Doubell AF. Tuberculous pericarditis. Circulation. 2005;112(23):3608-3616. 67. McCarty JM, Demetral LC, Dabrowski L, et al. Pediatric coccidioidomycosis in central California: a retrospective case series. Clin Infect Dis. 2013;56(11): 1579-1585. 68. Mok GC, Menahem S. Large pericardial effusions of inflammatory origin in childhood. Cardiol Young. 2003;13(2):131-136. 69. Morgan RJ, Stephenson LW, Woolf PK, et al. Surgical treatment of purulent pericarditis in children. J Thorac Cardiovasc Surg. 1983;85(4):527-531. 70. Nadas AS, Levy JM. Pericarditis in children. Am J Cardiol. 1961;7:109-117. 71. Neill CA, Harouturuan LM. Diseases of the pericardium. In: Watson H, ed. Paediatric Cardiology. London: Lloyd-Luke; 1968:703.

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72. Nelson CT, Taber LH. Diagnosis of tuberculous pericarditis with a fluorochrome stain. Pediatr Infect Dis J. 1995;14(11):1004-1007. 73. O’Connell B. Pericarditis following meningococcic meningitis. Am J Dis Child. 1973;126(2):265-267. 74. Okoroma EO, Perry LW, Scott LP 3rd. Acute bacterial percarditis in children: report of 25 cases. Am Heart J. 1975;90(6):709-713. 75. Ortbals DW, Avioli LV. Tuberculous pericarditis. Arch Intern Med. 1979;139(2):231-234. 76. Phillips JH Jr, Burch GE. Selected clues in cardiac auscultation. Am Heart J. 1962;63:1-8. 77. Picardi JL, Kauffman CA, Schwarz J, et al. Pericarditis caused by Histoplasma capsulatum. Am J Cardiol. 1976;37(1):82-88. 78. Ratnapalan S, Brown K, Benson L. Children presenting with acute pericarditis to the emergency department. Pediatr Emerg Care. 2011;27(7):581-585. 79. Roodpeyma S, Sadeghian N. Acute pericarditis in childhood: a 10-year experience. Pediatr Cardiol. 2000;21(4):363-367. 80. Rubenstein JJ, Goldblatt A, Daggett WM. Acute constriction complicating purulent pericarditis in infancy. Am J Dis Child. 1972;124(4):591-594. 81. Schrank JH Jr, Dooley DP. Purulent pericarditis caused by Candida species: case report and review. Clin Infect Dis. 1995;21(1):182-187. 82. Shakti D, Hehn R, Gauvreau K, et al. Idiopathic pericarditis and pericardial effusion in children: contemporary epidemiology and management. J Am Heart Assoc. 2014;3(6):e001483. 83. Shreiner DP, Krishnaswami V, Murphy JH. Unsuspected purulent pericarditis detected by gallium-67 scanning: a case report. Clin Nucl Med. 1981;6(9): 411-412.

84. Simon HB, Tarr PI, Hutter AM Jr, et al. Primary meningococcal pericarditis. Diagnosis by counter-current immunoelectrophoresis. JAMA. 1976;235(3):278-280. 85. Spiegel R, Miron D, Fink D, et al. Eosinophilic pericarditis: a rare complication of idiopathic hypereosinophilic syndrome in a child. Pediatr Cardiol. 2004; 25(6):690-692. 86. Spodick DH. Acute Pericarditis. New York: Grune & Stratton; 1959:17. 87. Spodick DH. Pericardial rub. Prospective, Multiple observer investigation of pericardial friction in 100 patients. Am J Cardiol. 1975;35(3):357-362. 88. Spodick DH. Frequency of arrhythmias in acute pericarditis determined by Holter monitoring. Am J Cardiol. 1984;53(6):842-845. 89. Strauss AW, Santa-Maria M, Goldring D. Constrictive pericarditis in children. Am J Dis Child. 1975;129(7):822-826. 90. Streifler JJ, Dux S, Garty M, et al. Recurrent pericarditis: a rare complication of influenza vaccination. Br Med J (Clin Res Ed). 1981;283(6290):526-527. 91. Tan EC, Rieu PN, Nijveld A, et al. Pericarditis as complication of appendicitis. Ann Thorac Surg. 2004;78(3):1086-1088. 92. Tatter D, Gerard PW, Silverman AH, et al. Fatal Varicella pancarditis in a child. Am J Dis Child. 1964;108:88-93. 93. Thebaud B, Sidi D, Kachaner J. [Purulent pericarditis in children: a 15 yearexperience]. Arch Pediatr. 1996;3(11):1084-1090. 94. Weir EK, Joffe HS. Purulent pericarditis in children: an analysis of 28 cases. Thorax. 1977;32(4):438-443. 95. Wyler F, Knusli D, Rutishauser M, et al. Pericarditis purulenta in children. Helv Paediatr Acta. 1977;32(2):135-140. 96. Zakhour R, Burkholder H, Wanger A, et al. Epstein-Barr virus-associated pericarditis and pleural effusions in a 4-year-old girl. Pediatr Infect Dis J. 2015;34(4):458-459.

CHAPTER 28  Myocarditis

Myocarditis

277

28 

Jesus G. Vallejo Myocarditis is defined clinically and pathologically as inflammation of the myocardium. The clinical presentation and cause may be quite varied. This entity may go unrecognized in numerous patients whose illness may resolve spontaneously, or it may lead to significant morbidity and mortality. In the early part of the 20th century, most cases of myocarditis were classified as idiopathic, and a diffuse or focal interstitial inflammation was identified on histologic examination. Rheumatic fever, diphtheria, and other bacterial infections were the only diseases recognized as associated with myocarditis, although some experts suspected that viruses might play a significant etiologic role in many cases.163 After the discovery in 1947 of the coxsackievirus group and the subsequent isolation and identification of other viruses, the number of cases of myocarditis classified as idiopathic diminished rapidly.36

EPIDEMIOLOGY The diverse clinical manifestations have made the true incidence of myocarditis difficult to determine. The clinical course of acute myocarditis can be insidious, with limited inflammation and cardiac dysfunction, or it can be overwhelming, leading to severe cardiac injury and cardiac failure. As a clinical entity, myocarditis is an uncommon occurrence in children. At Texas Children’s Hospital, Houston, between 1954 and 1977, myocarditis represented 0.3% of the 14,322 patients seen by the Cardiology Service. Because not all cases of myocarditis are recognized clinically, a much higher incidence is recorded in autopsy series. An autopsy incidence of 1.15% was found from 4343 studies performed between 1954 and 1977 at Texas Children’s Hospital. This rate is considerably lower than the incidence of 6.83% reported by Saphir and Simon163 in 1944 for 1420 autopsies performed on children. In Saphir’s series, 32 of 97 cases had or probably had rheumatic carditis,162 whereas only two cases occurred in the Texas Children’s Hospital series. The discrepancy is even more pronounced when these observations are compared with those of Burch and colleagues,27 who demonstrated evidence of interstitial myocarditis in the hearts of 29 of 50 infants and who showed evidence of interstitial myocarditis in the hearts of 29 of 50 infants and young children undergoing routine postmortem studies. Recently Freedman et al.53 reported an estimated prevalence of myocarditis of 0.5 cases per 10,000 emergency center visits to a single pediatric Canadian center. Some of the discrepancies between the clinical and autopsy series may be explained by the fact that the manifestations of myocarditis are subclinical in many cases and may be recognized only by changes on electrocardiogram (ECG) or perhaps not at all. In many instances, myocarditis is only one component of a generalized illness, and the cardiac dysfunction, if mild, may be overlooked.

ETIOLOGIES Myocarditis may occur with many common infectious illnesses that affect infants and children (Box 28.1). In most cases of myocarditis, the etiologic agent is never identified, however. In the United States and Western Europe, viruses are the most common causes of acute myocarditis. Myocarditis generally is a sporadic disease, but epidemics have been reported. Most epidemics have been caused by coxsackievirus group B and have affected infants in the newborn period.44,49 Gear and Measroch62 were the first to identify coxsackievirus B in association with myocarditis after an epidemic occurred in a nursery in a maternity home in southern Rhodesia. The association between virus infection and the development of myocardial disease also was made by Grist and Bell72 who presented comprehensive serologic data correlating enterovirus infection with acute viral myocarditis. In the World Health Organization report during the 10-year period from 1975–85, the coxsackieviruses B represented the most frequent inflammatory agents in cardiovascular disease (34.6/1000), followed by influenza B virus (17.4/1000), influenza A virus (11.7/1000), coxsackievirus A (9.1 per 1000), and cytomegalovirus (CMV) (8/1000). Karjalainen and colleagues91 prospectively examined 104 conscripts during the 1978 influenza A virus (H1N1) epidemic in Sweden. The incidence of myocarditis was 9% of the 67 verified cases of influenza virus infection. Randolph and colleagues149 reported that of 838 children with pandemic H1N1 admitted to a pediatric intensive care unit, 1.4% were diagnosed with myocarditis. Although H1N1-related acute myocarditis was uncommon, it was found to be an independent risk factor for death. The development of molecular techniques such as polymerase chain reaction (PCR) has improved the testing of endomyocardial biopsy specimens for potential viral pathogens. A study using PCR identified viral genome in 38% of endomyocardial biopsy specimens from patients diagnosed with acute myocarditis.22 Of the positive PCR samples, 23% were positive for adenovirus, 14% for enterovirus, and 3% for CMV. Parvovirus B19, influenza A virus, Epstein-Barr virus, herpes simplex virus (HSV), and respiratory syncytial virus were detected in less than 1% of cases. In a recent retrospective study of pediatric myocarditis, viral studies (PCR of blood, myocardium, or serology) were performed in 30 of 58 patients.159 A viral cause was identified in 17 of 30 patients (56%) and included six parvovirus B19 with influenza coinfection, seven enterovirus, one EBV, and one CMV. In a recent study of children with the diagnosis of clinical myocarditis, Simpson et al.169 reported that blood PCR was positive at the time of presentation in 43% (9 of 21) for one of four known cardiotropic viruses (four enterovirus, two parvovirus B19, one adenovirus, and two HHV-6). The majority (89%) of the patients with clinical myocarditis and positive blood PCR were

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SECTION 3  Infections of the Heart

BOX 28.1  Causes of Myocarditis Viruses Coxsackieviruses A and B Echoviruses Polioviruses Rubella Measles Adenoviruses Vaccinia Mumps Herpes simplex Epstein-Barr Cytomegalovirus Rhinoviruses Hepatitis viruses Arboviruses Influenza viruses Varicella Rickettsia Rickettsia rickettsii Rickettsia tsutsugamushi Bacteria Meningococcus Klebsiella Leptospira Staphylococcus Treponema pallidum Haemophilus influenzae Hemolytic streptococci Mycobacterium tuberculosis Salmonella enterica subsp. enterica serovar Typhi (typhoid) Mycoplasma Mycoplasma pneumoniae Chlamydia psittaci

Other Parasites Toxocara canis Trichinella spiralis Fungi and Yeasts Actinomyces Coccidioides Histoplasma Candida Toxin Diphtheria Scorpion Drugs Sulfonamides Phenylbutazone Cyclophosphamide Neo-mercazole Hypersensitivity/ Autoimmunity Rheumatoid arthritis Rheumatic fever Ulcerative colitis Systemic lupus erythematosus Other Sarcoidosis Scleroderma Idiopathic Cornstarch

Protozoa Trypanosoma cruzi African trypanosomiasis Toxoplasma Amebiasis

younger than 12 months old. In contrast, only 3.5% of healthy control children (four of 114) had a positive blood PCR for any of these four viruses. In one pediatric case series of pediatric cardiac transplant patients, parvovirus B19 genome was detected in 100 of 700 (82.6%) biopsies from 99 patients.24 The presence of the parvovirus B19 genome did not correlate with rejection score. However, transplant coronary artery disease occurred in 20 patients, with persistent detection (>6 months) of parvovirus B19. In two retrospective studies, parvovirus B19 has been identified as a common cause of viral myocarditis in healthy children.126,127,188 Patients with parvovirus B19 myocarditis often demonstrate persistent myocardial dysfunction requiring medical therapy and transplantation. Given the high prevalence of parvovirus B19 infection in the pediatric population, its pathogenic role in pediatric myocarditis and dilated cardiomyopathy (DCM) is still being investigated. Investigators also have speculated for decades on the possibility that acute myocarditis is a common forerunner of idiopathic DCM. Evidence supporting this hypothesis was presented first by Orinius and Pernow142 who found cardiac disease in humans years after an apparent uncomplicated coxsackievirus infection. Subsequently, Bowles and colleagues23

using a slot-blot hybridization technique provided conclusive evidence for the presence of enterovirus in endomyocardial biopsy samples from patients with DCM. In another study, Bowles and associates22 detected viral genomes in 20% of 149 patients with the diagnosis of DCM. In these patients, adenovirus was identified in 12% and enterovirus in 8% of DCM cases. In all age groups, adenovirus and enterovirus were the viruses most commonly detected in acute myocarditis and DCM. In December 2002, the U.S. Department of Defense began mandatory smallpox vaccination for select service members and employees without contraindications to vaccination, and in January 2003, the U.S. Department of Health and Human Services implemented a voluntary civilian smallpox vaccination program. As of June 15, 2003, the Department of Defense identified more than 50 cases of suspected, probable, or confirmed myopericarditis occurring within 30 days of vaccination in these individuals, based on clinical evaluation of symptoms, electrocardiography, cardiac enzyme assays, echocardiography, and the exclusion of ischemic coronary artery disease. Myocarditis occurred in 7.8 per 100,000 primary vaccinees in the U.S. Army, an incidence that was 3.6-fold more than that in unvaccinated individuals.74

PATHOLOGY Isolated or idiopathic myocarditis is a rare pathologic entity. The pathologic cardiac findings usually are nonspecific; similar gross and microscopic changes occur regardless of the causative agent.68,138,146,156 Grossly all four chambers of the heart are enlarged, and the cardiac weight is increased. The heart usually is flabby and pale. In some instances, especially with coxsackievirus B infections, petechial hemorrhages may be seen on the epicardial surfaces; pericardial fluid may be tinged with blood. On cut section, the ventricular muscle walls may be thinned. Occasionally the ventricles are hypertrophied or increased in thickness because of edema. The valves are spared. The endocardial surface usually is unaffected but occasionally may be thickened and appear glistening white. This important observation suggested to some investigators that endocardial fibroelastosis, which manifests as congestive cardiomyopathy, represented a progression from acute viral myocarditis.77,86 In a study of 64 hearts of children who had myocarditis or endocardial fibroelastosis, Hutchins and Vie86 found 18 with endocardial fibroelastosis only, five with myocarditis only, and 41 with features of both diseases. When time from onset of illness to death was 2 weeks or less, only myocarditis was evident. When the time interval was 2 weeks to 4 months, a combined picture was seen, whereas only endocardial fibroelastosis with trivial myocarditis was evident when the time from onset of disease to death was more than 4 months. These findings were supported further by Hastreiter and Miller77 who found microscopic evidence of myocarditis after transthoracic needle biopsy of the myocardium in a child who had the classic clinical picture of endocardial fibroelastosis, including left ventricular hypertrophy on ECG. Fruhling and associates57 extended these observations by showing coxsackievirus B3 in the myocardium of 13 of 28 infants with endocardial fibroelastosis. Ni and associates137 analyzed 29 myocardial samples from patients with autopsy-proven endocardial fibroelastosis using specific PCR for enterovirus, adenovirus, mumps, CMV, parvovirus, influenza, and HSV. In 90% of samples, viral genome was amplified; more than 70% of the samples were positive for mumps viral RNA, whereas 28% were positive for amplified adenovirus. These data suggest that endocardial fibroelastosis also is a sequela of mumps virus infection. The microscopic picture of acute myocarditis typically shows a focal or diffuse interstitial collection composed predominantly of mononuclear cells, lymphocytes, plasma cells, and eosinophils (Figs. 28.1 and 28.2). Polymorphonuclear leukocytes rarely are seen unless the cause of the carditis is bacterial. Virus particles and inclusion bodies rarely are recognized.150,156 In severe infections caused by any agent, but especially coxsackieviruses and diphtheria, a loss of cross-striation in the muscle fibers, edema, and sometimes extensive necrosis of the myocardium occur. Giant cells with or without granulomata are markers for the diagnosis of giant-cell myocarditis.85 Granulomata have been observed in the myocardium of patients with tuberculosis, syphilis, rheumatoid arthritis,

CHAPTER 28  Myocarditis

FIG. 28.1  Right ventricular biopsy specimen. The presumed viral myocarditis is characterized by focal mononuclear cell infiltrates (H&E staining, ×160). (Courtesy Edith Hawkins, MD, Houston, TX.)

FIG. 28.2  Picornavirus myocarditis characterized by interstitial edema, mononuclear cell infiltrates, and focal myofiber disruption (H&E staining, ×400). (Courtesy Edith Hawkins, MD, Houston, TX.)

rheumatic heart disease, sarcoidosis, and certain fungal and parasitic infections. Occasionally giant cells have been seen in interstitial myocarditis (idiopathic or Fiedler). In many cases, giant-cell myocarditis occurs, but no cause is found.

PATHOGENESIS The pathogenesis of myocarditis in humans was derived largely from experimental models of coxsackievirus infection. Liu and Mason110 have suggested that myocarditis should be viewed as a continuum that comprises three separate phases: acute viral infection (phase I), autoimmunity (phase II), and DCM (phase III). Phase I of the disease is triggered by the entry and proliferation in the myocardium of the causative virus. Impairment of left ventricular

279

function in mice with histopathologically graded moderate cellular infiltration after coxsackievirus B3 infection supports the importance of direct viral damage of the myocardium.180 Phase I concludes with activation of the cellular immune response, which attenuates viral proliferation but also may enhance cardiac injury. Ideally the immune response should downregulate to a resting state when viral proliferation is controlled. If immune activation continues unabated despite elimination of the virus, autoimmune disease may result, initiating phase II of the disease. The continuous activation of T cells long after viral clearance occurs is detrimental to the host because cytokine-mediated and direct T-cell–mediated myocyte injury leads to impairment of contractile function (Fig. 28.3). Long-term remodeling and progression to DCM characterize phase III of the disease.82 Numerous effector cells and molecules work in concert to restrict this initial spread of an infectious focus. The responding cells include natural killer cells, natural killer/T cells, and γδ T cells. Several lines of evidence suggest that mediators of the innate immune system, such as tumor necrosis factor (TNF) and nitric oxide, play an important role in the pathogenesis of viral myocarditis.120,203 Elevated levels of TNF have been reported in patients with viral myocarditis, and TNF mRNA and protein are consistently upregulated in the hearts of these patients.122,164 In mice, the exogenous administration of TNF aggravates myocarditis, and the neutralization of TNF by antibodies or soluble receptors attenuates the disease.100,200 More recent studies also have shown that TNF and nitric oxide are beneficial to the host by virtue of their antiviral effects. Mice with defective TNF or nitric oxide expression have increased myocardial injury, a significant increase in viral titers in the heart, and significantly higher mortality rates after infection with encephalomyocarditis virus or coxsackievirus B3.189,203 Although the prevailing notion has been that production of cytokine in the heart during viral infection is detrimental, the host-pathogen relationship is changed fundamentally when the host is unable to produce molecules such as TNF or nitric oxide.189,203 An important component of the innate immune system uses pattern recognition receptors, such as the Toll-like receptors (TLRs), to recognize pathogen-associated molecular patterns present in microbes.4 The role of TLRs in the pathogenesis of viral myocarditis is still evolving. However, recent studies suggest that cardiac inflammation during viral infection depends on TLRs. The viral genome replicates using the positive-strand RNA as its template, resulting in the formation of dsRNA intermediates. Accordingly both single-strand RNA and dsRNA are present in virally infected cells. TLR3 and TLR7/8 signaling are activated by doublestranded RNA (dsRNA) and single-stranded RNA, respectively. Thus viral infection can activate innate immune signaling in the heart through myeloid differentiation factor 88 (MyD88)-dependent (TLR 7/8) and MyD88-independent pathways (TLR3). Fairweather and colleagues50 reported that mice with defective TLR4 signaling had decreased coxsackievirus B3 replication and less severe myocarditis 12 days after infection compared with wild-type mice. The presence of TLR4 also was associated with increased production of interleukin-1β (IL-1β) and IL-18 and increased viral replication in the heart. In a similar study, Fuse and associates59 reported that mice deficient in MyD88, an adapter protein involved in TLR signaling (except TLR3), also had less myocarditis and attenuated viral replication in the heart after infection with coxsackievirus B3. Coxsackievirus B3–infected, MyD88-deficient mice had significantly higher levels of interferon-β (IFN-β) but reduced expression of the coxsackievirus-adenovirus receptor in the heart. The enhanced IFN expression and lower expression of the coxsackie-adenovirus receptor in the heart could explain the attenuation of disease in the MyD88-deficient mice. Infection of TLR3-deficient mice with encephalomyocarditis virus (EMCV), a positive single-strand RNA virus, resulted in earlier mortality in TLR3-deficient mice that was associated with increased viral replication and myocardial injury when compared with wild-type mice.75 Similar observations have been reported for coxsackievirus group B serotype 3 in TLR3-deficient mice.136 Gorbea et al.67 screened TLR3 in patients diagnosed with enteroviral myocarditis or DCM and identified a rare variant in one patient as well as a significantly increased occurrence of a common polymorphism compared with controls. Expression of either variant resulted in significantly reduced TLR3-mediated signaling after stimulation with

280

SECTION 3  Infections of the Heart Direct viral-mediated cell lysis

FACTORS Host age Viral tropicity Viral strain Viral agents

Inoculation

MACROPHAGES MONOCYTES MYOCYTE

CYTOTOXIC T CELLS (nonspecific)

Surface receptor Viral replication

STIMULATES PRODUCTION OF CYTOTOXIC T CELLS (Viral-specific)

Delayed immunologic response ALTERED MYOCYTE ? incorporation of viral antigens; membrane altered from normal state (i.e., neoantigen)

CELL LYSIS

ANTIBODY-BINDING COMPLEMENT-MEDIATED DESTRUCTION NK CELLS (ADCC)

FIG. 28.3  Schema for pathogenesis of myocarditis. Viral agents attach to cells by means of surface receptors. After a cell is infected, the cell cycle is changed. Direct virus-mediated cytolysis occurs. Cellular effectors of injury (i.e., macrophages, monocytes, and nonspecific cytotoxic T cells) are involved in the primary reaction. Myocytes that survive are altered in their structure. Cytotoxic T cells specifically targeted against the altered myocyte, natural killer (NK) cells, and complement-activated, antibodymediated cardiocytolysis or antibody-dependent cellular cytotoxicity (ADCC) participate in the secondary reaction. (From Maisch B, Trostel-Soeder R, Stechemesser E, et al. Diagnostic relevance of humoral and cell-mediated immune reactions in patients with acute viral myocarditis. Clin Exp Immunol. 48:533;1982.)

synthetic double-stranded RNA. Furthermore coxsackievirus B3 infection of cell lines expressing mutated TLR3 abrogated activation of the type I IFN pathway, leading to increased viral replication. Woodruff and Woodruff,197 using a murine model, were the first to show a role for T lymphocytes in the pathogenesis of viral myocarditis. In this study, depletion of T lymphocytes using antithymocyte serum or thymectomy and irradiation led to a decrease in mortality rates and in the inflammatory infiltrate after coxsackievirus B3 infection. Huber and associates,84 using BALB/c mice infected with coxsackievirus B3, showed that cytolytic T cells were the agents responsible for the major part of myocardial cell injury. In addition, proinflammatory mediators, such as TNF, released by infiltration cells also adversely affect cardiac function. Opavsky and colleagues141 defined the specific contributions of T-cell subsets (CD4 and CD8) and the T-cell receptor β chain to the pathogenesis of viral myocarditis. When CD4−/− or CD8−/− mice were exposed to CVB3, loss of CD8+/+ immune cells did not affect survival significantly, but viral proliferation was attenuated. In contrast, CD4−/− mice showed a trend toward an improvement in survival and a small but significant decrease in the inflammatory infiltrate at 14 days after infection. Mice deficient in CD4/CD8 immune cells and T-cell receptor β had the best outcome in terms of decreased mortality. A marked decrease in inflammatory infiltrate was noted in CD4/CD8 double-knockout mice. Although no significant change occurred in viral titers, a marked decrease in myocardial TNF mRNA 4 days after infection was seen in CD4/CD8 double-knockout mice. These same investigators have shown that the T-cell receptor–associated tyrosine kinase p56lck is crucial for coxsack­ ievirus B3 proliferation in the heart and activation of T cells to target the heart.109 Mice deficient in p56lck were protected against the development of myocarditis, providing further support for the hypothesis that T-cell activation during viral myocarditis contributes to increased inflammation and myocyte destruction in the host.

T-regulatory (T-reg) cells also are important in modulating the inflammatory response and preventing the development of autoimmunity through the production cytokines like IL-10 and tumor growth factor-β (TGF-β).195 T-regs express CD4, but they also express the α-subunit of the IL-2 receptor, CD25. They also are high expressors of the transcription factor FoxP3. Li and associates106 have shown that the allograft of M2 (antiinflammatory) macrophages led to improvement of virus-induced myocarditis, which was associated with enhanced levels of T-regs. Similarly, Huber and colleagues83 have reported decreased viral titers and inflammation after adoptive transfer of a CD4+ CD25+ regulatory–like T-cell population into a mouse model of coxsackievirus B3 infection. Thus modulating the immune response may be critical for the prevention of chronic virus replication. The ongoing injury that persists may be considered an autoimmune process.84,196 At least in murine models, it is clear that both cellular and humoral autoimmunity are involved in the progression to chronic heart disease. The recently identified T helper 17 (TH17) subset has been implicated in the onset of chronic myocarditis.76 These cells secrete high levels of IL-17 and have been implicated in the production of autoantibodies.76,201 In a mouse model of coxsackievirus B3 myocarditis these TH17 cells contribute to chronic myocarditis through persistent inflammatory signaling involving the secretion of IL-17. Consistent with this, there is significant TH17 expansion approximately 2 weeks after coxsackievirus B3 infection in mice.202 IL-17 and its various isotypes can induce expression of TNF and TH2 responses, which in turn leads to a prolonged inflammatory milieu that might foster the production of autoantibodies. More recent studies also have shed light on the mechanisms by which coxsackievirus B3 may contribute directly to the development of myocarditis and DCM. Badorff and colleagues9–11 reported that the 2A protease encoded by coxsackievirus B3 cleaves dystrophin in cultured myocytes and in infected mouse hearts, leading to disruption of

CHAPTER 28  Myocarditis dystrophin and the dystrophin-associated glycoprotein α-sarcoglycan and β-sarcoglycan complex. Dystrophin provides a structural link between the muscle cytoskeleton and extracellular matrix to maintain muscle integrity. Xiong and associates199 compared the effects of coxsackievirus B3 infection in dystrophin-deficient (mdx) and wild-type mice. Coxsackievirus B3 infection significantly enhanced sarcolemmal disruption in the mdx mice compared with wild-type mice; the disruption was detectable 2 days postinfection and continued to increase after initial infection. Viral titers were higher in the hearts of mdx mice than in the hearts of wild-type mice, indicating greater viral replication in the absence of dystrophin. The observed differences seemed to be a result of more efficient release of coxsackievirus B3 from dystrophin-deficient myocytes. The expression of wild-type dystrophin in cultured cells decreased the cytopathic effect induced by coxsackievirus B3 and the release of virus from the cell. The expression of a cleavage-resistant mutant of the dystrophin protein inhibited coxsackievirus B3–mediated cytopathic effect and viral release further.

PATHOPHYSIOLOGY Given the extensive interstitial inflammation, muscle cell injury, or both, myocardial contractility is reduced. Consequently the heart enlarges

and the end-diastolic volume of the ventricle increases. In the normal heart, an increase in filling volume leads, by the Starling mechanism, to an increased force of contraction, ejection fraction, and cardiac output. In patients with myocarditis, the myocardium is unable to respond in this manner, and cardiac output is reduced. Systemic blood flow may be maintained, however, by use of the cardiac reserve, mediated by the sympathetic nervous system and leading to vasoconstriction of the skin vessels and an increase in heart rate. With progressive disease, the heart may be unable to meet the oxygen demands of the tissues, and the clinical picture of congestive cardiac failure may become evident. In some infants and young children, the presentation is predominantly that of right-sided heart failure.155 An appreciation of the disturbance of myocardial function may be gained from the angiographic frames shown in Fig. 28.4. The left ventricle is dilated considerably, and the outline is irregular in diastole and systole. The ejection fraction is reduced significantly at 35% instead of the normal 60% to 75%. Another means of evaluating left ventricular function is the noninvasive technique of cardiac echocardiography. Gutgesell and colleagues73 established normal standards for children. An example is shown in Fig. 28.5A. The normal shortening fraction (i.e., percentage change in ventricular dimensions between end-diastole and end-systole) is 35% ± 4%, regardless

B

A

FIG. 28.4  The (A) end-diastolic and (B) end-systolic images from a left ventriculogram of a patient with idiopathic myocarditis show irregularity of the wall and poor contractility.

RV IVS

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B FIG. 28.5  (A) Normal echocardiogram of a 4-year-old child. (B) Echocardiogram of a 4-year-old child with idiopathic myocarditis shows left ventricular dilation and severely reduced shortening fraction. EDD, End-diastolic dimension; ESD, end-systolic dimension; IVS, interventricular septum; LVPW, left ventricular posterior wall; MA, mitral apparatus; MV, mitral valve, %ΔLVD, percent change in left ventricular dimension (shortening fraction).

282

SECTION 3  Infections of the Heart

of age (range, 28–44%). Fig. 28.5B illustrates the case of a 4-year-old child with idiopathic myocarditis and shows ventricular dilation with markedly reduced motion of the left ventricular posterior wall and septum, leading to a shortening fraction of only 12%. Further assessment of ventricular function can be achieved by measuring systolic time intervals obtained from simultaneous recording of the ECG and the semilunar valve opening and closing points on the echocardiogram.73

CLINICAL MANIFESTATIONS The clinical presentation of myocarditis varies with the age of the patient and the virulence of the organism. At one end of the spectrum is a fulminant, rapidly fatal illness and, at the other, no apparent clinical disturbance at all. A newborn especially is susceptible to the severe form of myocarditis usually caused by the coxsackieviruses B,38,93 but it also is recognized with rubella3 and HSV198 infections and with toxoplasmosis.85 In many of these infections, myocarditis is only one component of a generalized illness, often with severe hepatitis and encephalitis.17,93 In some instances, however, infections with these organisms may produce only a mild clinical disturbance.26,87 In the report by Brightman and colleagues,26 a nursery epidemic of coxsackievirus B5 infection in preterm infants was recognized only by chance because a virologic survey was in progress at the time in the institution. No cases of myocarditis were documented, and all the infants recovered. Findings included lethargy, failure to gain weight, and, in some infants, evidence of aseptic meningitis. As described in the review by Kibrick and Benirschke93 of 25 infants with coxsackievirus B myocarditis, vague symptoms such as lethargy and anorexia may herald the onset of the severe disease, emphasizing that close attention should be paid to all symptoms, especially in a newborn, no matter how nonspecific. Four infants had episodes of vomiting, and fever was documented for more than half of the cases; occasionally, the temperature was subnormal. Cyanosis, respiratory distress, and tachycardia, cardiomegaly, or ECG changes occurred in 19 of 23 infants. Tachypnea (respiratory rate >60/min in a newborn) is an early sign of heart failure in a young infant and should alert the clinician to this diagnosis. In older infants and children, the manifestations of myocarditis generally are less fulminant than are the manifestations in newborns.155,161,190,194 An acute and fatal illness has been associated, however, with idiopathic myocarditis108 and the myocarditis associated with enteroviruses,93 adenoviruses,78 mumps,102 chickenpox,143 diphtheria,15 cytomegalovirus,183 and many of the other causative agents listed in Box 28.1. Some older children have been reported with acute, substernal chest pain consistent with angina and have ECG changes of acute myocardial infarction.81,124 The usual clinical picture is that of an acute or a subacute illness, which often begins with a mild upper respiratory infection and a low-grade fever.8 Some infants have only vague, nonspecific suggestions of disease (e.g., irritability, periodic episodes of pallor) before the onset of cardiorespiratory symptoms, which begin a few days to 2 weeks after the onset of the initial symptoms. Abdominal pain may be a prominent complaint in some children.190 On examination, these infants and children often are anxious and apprehensive, but some appear apathetic and listless. Pallor may be striking, and mild cyanosis may be present. Respirations are rapid and labored, and grunting may be prominent. The pulse is thready, and blood pressure usually is normal or slightly reduced, unless the infant is in profound shock. The precordium is quiet, without a prominent cardiac impulse. Resting tachycardia invariably is present in children who are critically ill with myocarditis. The heart sounds are muffled, and a prominent gallop rhythm usually is heard. Fine and colleagues52 found the most sensitive clinical sign of myocarditis to be a soft S1 at the apex. A prolonged PR interval, which may be a nonspecific finding in many febrile illnesses, also can cause a soft S1, however, without any other evidence of myocarditis.168 Almost uniformly, the liver is enlarged; edema is a rare finding. Some infants are less distressed and have signs of only mild congestive cardiac failure, without the signs of peripheral circulatory failure. Other infants have no signs of cardiac compromise, and myocarditis is

recognized only as part of a generalized illness by a disturbance in the ECG pattern.

DIAGNOSIS Myocarditis often is difficult to diagnose, but it should be suspected in any infant or child who presents with congestive heart failure and who has or recently has had a febrile illness. The history should include information regarding travel, exposure to tuberculosis, recent drug ingestion, and illnesses in other family members or schoolmates. A quiet precordium in the presence of a gallop rhythm and decreased intensity or muffling of the heart sounds are findings that strongly suggest the diagnosis. A tachycardia out of proportion to the level of fever also should be viewed with suspicion. A physiologic S3 is a common finding in normal healthy children and in children with anemia and fever. An unusually prominent S3 suggests a disturbance of ventricular compliance without other evidence of compromised cardiac function and should be investigated further with an echocardiogram, a chest radiograph, and an ECG. The occurrence of an arrhythmia, especially after a febrile illness, should alert the clinician to look for other signs of myocarditis.34,172 Lind and Hulquist108 detected significant dysrhythmias in five infants with isolated myocarditis. Four of the five infants died, and three of these infants had paroxysmal atrial tachycardia. Paroxysmal atrial tachycardia has been reported in patients with viral myocarditis34,172 and has been described in patients with diphtheritic myocarditis.15 Atrial ectopic tachycardia may mimic sinus tachycardia and, if not carefully evaluated, may be the primary cause for significant myocardial dysfunction. Complete heart block has been described in children in association with acute idiopathic myocarditis89,107 and with rubella,111 coxsackievirus,165 and respiratory syncytial virus12,64 infections. In some instances, complete heart block is permanent; in others, it is temporary.12,65,89

Chest Radiography Chest radiographs of infants and children who have signs of congestive cardiac failure invariably show cardiomegaly, usually of a severe degree (Fig. 28.6). All four chambers may be enlarged, and evidence of pulmonary venous congestion often is found. Sometimes, especially in newborns, the first sign of illness is acute circulatory collapse, and, in this circumstance, the cardiac size may be normal. The same is true of children who have an arrhythmia rather than congestive heart failure. Other patients may present with Stokes-Adams attacks caused by complete heart block.107

Electrocardiogram The ECG is an essential diagnostic tool for all patients with suspected myocarditis. The classic ECG pattern in myocarditis is one of diffuse

FIG. 28.6  Marked cardiomegaly with a mild increase in the pulmonary venous pattern in the upper lobes.

283

CHAPTER 28  Myocarditis

I

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FIG. 28.7  Diffuse low-voltage or QRS complexes with T-wave flattening and 1-mm Q waves in the lateral precordial leads represents the classic pattern in myocarditis.

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FIG. 28.8  In addition to low voltage, there is evidence of acute myocardial ischemia with 4- to 5-mm ST-segment elevation dominantly in the middle and lateral precordial leads.

low-voltage QRS complexes (39°C [102.2°F]) suggest that perforation already has occurred or that another intraabdominal process is present. Rarely children present with erythema and tenderness of the scrotum or a scrotal or inguinal mass as the only manifestation of acute appendicitis.95,205 During the physical examination, tenderness in the right iliac fossa is the most sensitive sign of appendicitis. The psoas muscle may become irritated from the inflamed appendix, causing the child to feel increased pain when the right hip is flexed actively. Likewise if the obturator internus muscle is involved, pain is elicited when the flexed thigh is rotated internally. Guarding is found in most cases of appendicitis, compared with half of cases of mesenteric adenitis and 8% of cases of nonspecific abdominal pain.147 Similarly, rebound tenderness is found more commonly in children with appendicitis than with acute mesenteric adenitis or nonspecific abdominal pain; its presence triples the odds of the child having appendicitis.38,56 The development of diffuse abdominal tenderness and the absence of bowel sounds usually indicate perforation. Extremely hyperactive bowel sounds suggest that the patient may not have appendicitis. Occasionally a mass can be palpated in the right lower quadrant of the abdomen in children with appendicitis who are relaxed or well sedated. Rectal tenderness is present more commonly in children with appendicitis than with other causes of abdominal pain; however findings during the rectal examination seldom alter the clinical decision of the surgeon.147 In preschool-aged children, the diagnosis of appendicitis is more difficult to establish because of the inability of young children to express their symptoms and because they often do not cooperate during the physical examination.199 Young children with appendicitis are often seen early in the course of their symptoms and are prescribed antibiotics, antihistamines, or antipyretics. By the time one realizes that the child has appendicitis, the appendix usually is perforated (50% to 90%).20,199 In contrast to older children, vomiting is the initial symptom of appendicitis most frequently observed, and abdominal pain may be absent or may never localize in the right iliac fossa.147 Sleep disturbances, irritability, restlessness, and crying are common manifestations of appendicitis in this age group. The preschool-aged child is more likely to have a palpable inflammatory mass at presentation. During the newborn period, appendicitis is an extremely rare occurrence, although most cases are found when prematurity exists.87 Symptoms of neonatal appendicitis include abdominal distention; vomiting; irritability; diarrhea; erythema, edema, or cellulitis of the abdominal wall; gastrointestinal hemorrhage; abdominal rigidity; lethargy; and jaundice. Usually the symptoms of neonatal appendicitis are indistinguishable from those of necrotizing enterocolitis. Underlying conditions such as total colonic Hirschsprung disease, meconium plugs, esophageal atresia, or hernias may predispose the neonate to develop this condition. In children who are undergoing chemotherapy for leukemia, acute appendicitis may present as only vague abdominal pain, abdominal distention, lack of abdominal guarding, fever, dehydration, diarrhea, or unusual symptoms such as gastrointestinal bleeding.11 Symptoms of appendicitis in immunocompromised patients may be identical to those of typhlitis.

DIAGNOSIS A great emphasis has been placed on using various laboratory tests to help clinicians diagnose the appendicitis accurately.97 Patients who have received prior oral antibiotics may have milder symptoms and signs of classic appendicitis, necessitating further diagnostic studies.59

For decades, physicians have valued peripheral blood leukocyte counts, neutrophil counts, C-reactive protein concentrations, and erythrocyte sedimentation rates to help them distinguish appendicitis from other causes of abdominal pain. When properly evaluated, these tests have been found to be too insensitive to use as reliable tools for diagnosing appendicitis.23,137 Normal results do not rule out the possibility that the child has appendicitis, although these tests help to confirm a physician’s suspicions when results are positive. When the nonspecific tests are elevated, often perforation or abscess formation has occurred.8,135 Hyperbilirubinemia and increased serum procalcitonin levels also are signs of probable perforation.54,66,137 Certain groups of patients commonly have normal leukocyte counts despite having acute appendicitis. AfricanAmerican patients with acute appendicitis frequently do not develop leukocytosis.83 Patients with AIDS who develop appendicitis also frequently do not have elevated white blood cell counts.33 Routine radiographic studies for the diagnosis of appendicitis in children no longer are suggested. Radiographs of the abdomen are neither sensitive nor specific enough for diagnosing childhood appendicitis. Graded compression ultrasonography is increasingly becoming the diagnostic procedure of choice when evaluating a patient with possible appendicitis.18 A noncompressible, enlarged (>6 mm in diameter in adolescents) appendix or a fecalith is the major criterion used for diagnosing appendicitis by ultrasonography. Interruption in the continuity of the echogenic submucosa suggests necrosis of the appendiceal wall and impending perforation. An echogenic periappendiceal mass indicates inflammation of the mesenteric or omental fat. Loculated or generalized fluid collections suggest that perforation already has occurred. Because graded compression ultrasonography is highly operatordependent, a meta-analysis has demonstrated that the procedure is 88% sensitive and 94% specific in diagnosing acute appendicitis in children.52 False-positive ultrasound results occur in obese patients who have noncompressible appendices because of overlying fat and in children who have inflamed appendices caused by Crohn disease, ulcerative colitis, or adjacent salpingitis. False-negative results occur if retrocecally located appendices are not visualized properly; if the cecum is filled with gas or feces and is not compressed adequately; or if perforation has occurred, allowing the appendix to be compressible. In one study, a noncompressible appendix was identified in only 38% of pediatric patients with perforated appendicitis, thus rendering the other ultrasound findings of appendicitis important in diagnosing the disease.143 The examination should be directed to diagnose other causes of abdominal pain that can mimic appendicitis when a normal appendix is found during the evaluation. The advantages of using ultrasonography over computed tomography (CT) are that it is relatively inexpensive, is safe, does not require sedation, lacks radiation exposure, and is widely available. It is especially useful in adolescent girls with abdominal pain because gynecologic causes of the pain can be evaluated easily at the time of appendiceal examination. Bedside ultrasound in the emergency department is currently being used to identify children with appendicitis.113 High-resolution CT has higher sensitivity (94%) and similar specificity (95%) compared to ultrasonography in diagnosing appendicitis, and it is less operator dependent.52 Intravenous contrast agents and highresolution, thin-section scanning techniques must be used to visualize the appendix adequately. An enlarged appendix with a circumferentially and symmetrically thickened bowel wall is the most common CT finding in appendicitis. Periappendiceal inflammatory reaction or fluid collections may be identified. If the appendix is not well visualized, the presence of a fecalith, along with pericecal inflammatory changes, strongly suggests appendicitis. Fecaliths can be visualized in normal appendices by CT, however, and are of no clinical significance unless other inflammatory changes are present. Helical or multidetector CT techniques using rectal or no contrast have been shown to be very accurate in diagnosing appendicitis.53,111 By using a focused right lower quadrant approach, helical CT may be completed more rapidly. Waiting for a CT scan may delay a surgical consultation and increase the rate of perforation before surgery.105 Also CT is expensive and uses significant amounts of ionizing radiation in children who have greater radiosensitivity of organs and tissues compared with adults. Many medical centers have implemented protocols that initially use ultrasonography as the first diagnostic procedure for possible

CHAPTER 51  Appendicitis and Pelvic Abscess

499

BOX 51.1  Microorganisms Associated With Acute Appendicitis in Children Anaerobes Bacteroides spp. Bilophila wadsworthia Catabacter hongkongensis Clostridium spp., including C. difficile Fusobacterium spp. Peptostreptococcus spp. Pigmented bile-resistant, gram-negative rods Turicibacter sanguinis Enteric Aerobes and Facultative Anaerobes Aeromonas spp. Campylobacter spp. Citrobacter spp. Enterobacter spp. Enterococcus spp. Escherichia coli Klebsiella spp. Morganella morganii Proteus spp. Providencia rettgeri Salmonella spp. Shigella spp. Streptococcus anginosus (formerly milleri) group Yersinia spp. Other Bacteria Actinomyces spp. Atypical mycobacteria (in patients with AIDS) Chromobacterium violaceum Corynebacterium appendicis Eikenella corrodens Haemophilus spp.

appendicitis and only use CT when the ultrasound results are equivocal to reduce cost and radiation exposure. Whether the increasing use of ultrasonography and CT to diagnose appendicitis in children has decreased, the misdiagnosis of the disease and subsequent negative appendectomy rate in hospitals is unclear.45,116,207 Radiolabeled autologous leukocyte scans also have been used to diagnose appendicitis in children; however, this modality should be reserved for atypical presentations of disease when localizing signs are not present.78 Magnetic resonance imaging may be considered in patients with nondiagnostic ultrasound tests and concerns about radiation exposure.154

MICROBIOLOGY Numerous microorganisms have been implicated as a cause of acute appendicitis; however, considerable debate has ensued as to whether simply isolating an organism from the appendiceal lumen is sufficient proof to define causation (Box 51.1).

Bacteria In most cases of appendicitis, bacteria do not appear to be involved directly in the initial stages of the inflammatory process. Microorganisms that normally inhabit the appendix are liberated into the peritoneal cavity when appendiceal perforation occurs or when translocation through the inflamed tissues is present, and polymicrobial infections develop as a complication of the disease process. In a study of 30 adolescents and adults with nonperforated and perforated appendicitis, 223 different anaerobes and 82 aerobes were recovered from cultures of their appendiceal tissues, peritoneal fluid, and contents of abscesses.24

Ehrlichia chaffeensis Kluyvera ascorbata Pasteurella multocida Pseudomonas spp. Staphylococcus spp. Streptococcus pneumoniae Streptococcus pyogenes Parasites Angiostrongylus costaricensis Anisakis spp. Ascaris lumbricoides Balantidium coli Cryptosporidium parvum Entamoeba histolytica Enterobius vermicularis Schistosoma spp. Strongyloides stercoralis Taenia spp. Trichuris trichiura Viruses Adenoviruses Coxsackievirus B Cytomegalovirus Epstein-Barr virus Measles virus Fungi Candida albicans Coccidioides immitis Mucor spp. Histoplasma capsulatum

An average of 10 different organisms were isolated per specimen collected. In a recent microbiome study, 12 taxa were found to be increased from inflamed appendices compared to normal appendices.84 In most culture-based studies of appendiceal tissues and peritoneal fluid specimens from patients with appendicitis, B. fragilis is the strict anaerobe isolated most frequently, occurring in more than 70% of patients.24,149 Other anaerobes that are isolated frequently include Bacteroides spp., Bilophila wadsworthia, Peptostreptococcus spp., Fusobacterium spp., and Clostridium spp.188,202,209 A gram-negative anaerobic rod that develops a pigment in culture and is bile resistant also has been identified frequently.148,149 Anaerobes such as Turicibacter sanguinis and Catabacter hongkongensis continue to be newly described from patients with appendicitis.31,101 Rarely acute appendicitis has been seen in the setting of Clostridium difficile colitis, although the role of the anaerobe’s toxins in causing the appendiceal inflammation is unknown.35 E. coli is the aerobic or facultative anaerobic bacteria isolated most frequently from children with appendicitis. E. coli is found in more than 75% of patients.24,149 Certain E. coli strains with type 1C fimbriae may contribute to the development of appendiceal inflammation.164 Enterohemorrhagic E. coli O157:H7 and O111:H have been isolated infrequently from the stools and peritoneal fluid of children with appendicitis.186,193 Viridans streptococci of the S. anginosus group, especially S. milleri, can be found in more than 60% of cultures from children with appendicitis.85,106,149 Group D streptococci are isolated in 20% to 30% of patients with appendicitis. Pseudomonas spp. are isolated slightly less frequently, although they may be found more frequently in young children.62,149 Other aerobes or facultative anaerobes that can be isolated from appendiceal tissues, abscesses, or blood include Citrobacter spp., Klebsiella

500

SECTION 8  Other Intraabdominal Infections

spp., Enterobacter spp., Proteus spp., Morganella morganii, Providencia rettgeri, Eikenella corrodens, non–group A β-hemolytic streptococci, and staphylococci.42,76,86,145,149 Rarely encapsulated organisms, such as Streptococcus pneumoniae, Haemophilus influenzae, Haemophilus segnis, and Aggregatibacter aphrophilus have been isolated from appendiceal tissues or peritoneal fluid of children with appendicitis, and often these organisms have been isolated in pure culture.14,15,123,128 Very rarely organisms such as Pasteurella multocida, Streptococcus pyogenes, and Actinomyces spp. have been cultured from patients with appendicitis.55,109,146 Shigella, Salmonella, Campylobacter, Yersinia, and Aeromonas spp. also have been isolated occasionally from appendiceal tissues or peritoneal fluid of patients with nonperforated and perforated appendicitis, but, again, whether they played a role in the pathogenesis of disease is unknown.22,25,39,91,102,108,124 Much more commonly, these organisms cause enterocolitis or mesenteric adenitis, with symptoms mimicking appendicitis.190 Appendicitis has occurred during systemic infections caused by Brucella melitensis and Ehrlichia chaffeensis.10,167 Rarely Kluyvera ascorbata, Arcobacter butzleri, and Chromobacterium violaceum have been isolated from individuals with appendicitis, as well as newly described aerobes and facultative anaerobes, such as Corynebacterium appendicis.40,43,103,204 Rarely isolated primary tuberculosis can occur in children.26,144 The progression of disease is usually rapid; thus one should be suspicious when caseating granulomas are observed in histopathologic sections of the appendix. Adults and children with appendicitis usually are not bacteremic at the time they are diagnosed, especially if the appendix is not perforated. Occasionally Klebsiella pneumoniae, E. coli, B. fragilis, and B. wadsworthia are isolated from the blood of patients with nonperforated appendicitis.27,156,158 In a review of 1000 children and adults with appendicitis, 10% of patients with perforation had positive blood cultures, whereas none of the patients without perforation had bacteremia.107 A higher rate of bacteremia may occur when laparoscopic surgery is performed because of the air that is forced into the peritoneum, although the clinical significance of the induced bacteremia is unknown.133 In immunocompromised patients who develop appendicitis, the microorganisms that are isolated from appendiceal tissues or peritoneal cultures usually are identical to those found in immunocompetent patients. Patients with AIDS who have gastrointestinal Mycobacterium avium complex or Mycobacterium tuberculosis infections may develop symptoms that mimic appendicitis.49,192 Atypical mycobacteria have been isolated from an appendiceal abscess from a child with AIDS.58

Parasites In Turkey, parasites were found to be the cause of appendicitis in 1.4% of cases.203 Roundworms, such as Ascaris lumbricoides, may obstruct the appendiceal lumen occasionally and initiate the cascade of inflammatory events leading to perforated appendicitis.112,134 Parasites such as Enterobius vermicularis can be identified in the lumen of 1% to 12% of surgically removed appendices obtained from patients living in highly endemic areas.2,12,77 Pinworms have been found more frequently, however, in appendices with no evidence of appendiceal inflammation in some studies, suggesting that pinworms probably are a part of the normal appendiceal flora and do not play a role in the pathogenesis of appendicitis.157,206 Whether some parasites may cause abdominal pain that mimics the symptoms of appendicitis necessitating surgical intervention remains unclear. Scattered reports from mostly developing nations describe other worms, including Taenia spp., Anisakis spp., Trichuris trichiura, Strongyloides stercoralis, Schistosoma spp., and Angiostrongylus costaricensis, that have been identified in the lumen of appendices from patients with appendicitis.3,13,32,129 Similarly, protozoa such as Balantidium coli, Entamoeba histolytica, and Cryptosporidium parvum have been found in inflamed appendices of immunocompromised and immunocompetent patients, but whether they play a role in the pathogenesis of disease is unknown.36,51,136

Viruses The role that viruses play in causing appendicitis also has been debated. One suggestion is that a systemic viral infection may induce

hypertrophied lymphoid aggregates that obstruct the appendiceal lumen. In the 1960s, elevated levels of antibodies against group B coxsackieviruses and adenoviruses were found in the sera of some children with appendicitis.183 A later study, however, could not confirm this finding.125 Six adolescents with infectious mononucleosis have developed appendicitis; cytomegalovirus has occasionally been observed in immunodeficient and otherwise healthy patients’ inflamed appendices; and a child with acute varicella had virus demonstrated in the appendix following surgery for appendicitis.89,110,130,142,182 Other children have had histologic evidence of measles virus or adenovirus infection in the appendix.70,172 Because of the rarity of documented simultaneous viral infections and appendicitis, whether these viruses play a major role in the pathogenesis of acute appendicitis is doubtful.

Fungi Rarely Candida albicans is isolated from inflamed appendices or abscess cultures, but its role in pathogenesis of disease is unknown.100 Perforation of the appendix from intestinal mucormycosis has occurred in granulocytopenic patients and premature newborns.131,181 Also, appendicitis has been described in individuals with histoplasmosis, coccidioidomycosis, and aspergillosis.98,100,171

TREATMENT Nonperforated Appendicitis In previously healthy children with signs of acute appendicitis, nasogastric suctioning should be established and imbalances in fluid and electrolyte concentrations should be corrected quickly. In the United States, most children are taken to the operating room. However, many hospitals now perform appendectomies only during day and evening hours because of limitations on resident work hours and decreased services available at night. No differences have been noted in perforation rates, lengths of stay, or complication rates in children who are diagnosed with appendicitis at night and given analgesics until a scheduled morning surgery if the delay time is less than 12 hours.1,9 Morphine is often used to reduce the severity of abdominal pain in children with appendicitis, although there is no evidence that morphine reduces appendiceal pain compared with placebo.5,19 Prophylactic antibiotics given perioperatively decrease the rate of postoperative wound infection even in noncomplicated cases of childhood appendicitis.6,168 No consensus exists concerning the appropriate antimicrobial agent or agents that should be used to reduce the complication rate. Prospective, randomized studies demonstrate that a single perioperative dose of proper antibiotic(s) with antimicrobial activity against E. coli and enteric anaerobes is as effective as continuing the antibiotic(s) for 1 to 5 days after surgery.126,185 Few data support the routine intraoperative collection of peritoneal fluid or appendiceal cultures in children with nonperforated appendicitis, although immunocompromised patients should undergo intraoperative cultures, including cultures for mycobacteria and cytomegalovirus.67 Most surgeons are now performing laparoscopic appendectomies in children with nonperforated and perforated appendicitis. Advantages of the procedure are a reduction in wound infection, reduction in scarring, less postoperative pain at 24 hours, shorter hospital stay, and earlier return to normal activity, although the procedure must be performed by a surgeon experienced in laparoscopic technique.162,197 The mean total cost of a laparoscopic appendectomy is higher than that of open appendectomy, and meta-analyses have determined that there is increased operative time and a small increase in the risk for developing a postoperative abscess using the laparoscopic technique.121,162,197 Newer single-incision laparoscopic techniques reduce the length of hospital stay in children with appendicitis.115,208 There are now some centers that discharge children with uncomplicated appendicitis on the same day as surgery.61 Outside the United States and in a few places within the United States, children with nonperforated appendicitis are treated initially with intravenous fluids and antibiotics. In France, a trial of oral amoxicillin-clavulanic acid versus appendectomy in adults was not inferior in outcome.194 Proponents of initial conservative management consider that the complication rate is significantly lower than when a

CHAPTER 51  Appendicitis and Pelvic Abscess procedure is done during the acute stage of disease. More than 70% of patients are treated successfully without surgery.159,191,194 When the child does not clinically improve or a walled-off abscess develops, drainage of the area and appendectomy are performed. The presence of intraluminal appendiceal fluid appears to predict recurrent appendicitis after initial nonoperative management, although many surgeons do an interval appendectomy 6 to 8 weeks after resolution of the symptoms to prevent future complications even though most children do well.72,93

Perforated Appendicitis Most surgeons advocate early intervention when perforation has occurred to prevent severe complications such as fistula formation, abscess rupture, and death, despite the high chance of developing postoperative complications.104 Surgeons are increasingly performing primary closures without drains in children.57,65,119 A randomized prospective trial of appendiceal drains in children with perforated appendicitis showed no benefit compared with primary wound closure.178 Appendectomy wounds can be closed with continuous, absorbable sutures even in complicated cases.139 If incisions are not primarily closed, simple daily wound probing may decrease the incidence of wound infection.184 Recent studies demonstrate that extensive irrigation of the peritoneum with saline or antibiotics does not reduce the rate of postoperative complications in children with perforated appendicitis who are receiving systemic antibiotics.4,174 Ranitidine or diphenhydramine given to children with perforated appendicitis may increase the risk for developing a postoperative abscess.176 Antimicrobial agents should be administered routinely to children when perforation or appendiceal abscess is suggested or discovered during surgery. Antibiotics active against aerobes and anaerobes that normally inhabit the intestinal tract have been effective in treating children with perforated appendicitis. Treatment failures occur most commonly when B. fragilis or Pseudomonas spp. are isolated from intraoperative cultures and antimicrobial agents without activity against these organisms are used.79 Controversy continues regarding the value of obtaining routine intraoperative peritoneal cultures in cases of perforated appendicitis, although most studies demonstrate that culture results seldom change the clinical management of patients.47,67 The antimicrobial combination of ampicillin, gentamicin, and clindamycin has been the gold standard of therapy since the 1970s. The importance of including ampicillin in the regimen for adequate enterococcal coverage continues to be controversial. Animal studies and clinical trials using antibiotics with poor enterococcal activity have shown that ampicillin probably is not required in the treatment of perforated appendicitis.69 Because of the increasing problem of ampicillin resistance in enterococci, ampicillin probably should be reserved for the rare child with enterococcal bacteremia or with persistent intraabdominal infection in which enterococci have been isolated. Some medical centers use metronidazole instead of clindamycin because of its broader activity against enteric anaerobes, whereas other institutions substitute cefotaxime or ceftriaxone for gentamicin.165,175 In a small study, once-daily dosing of ceftriaxone and metronidazole was comparable in efficacy to standard three-drug therapy in children with perforated appendicitis.177 Single-agent antibiotic therapy for perforated appendicitis may offer improvement in terms of pharmacy and hospital costs.68 Agents that have been shown to be effective in treating children with perforated appendicitis include cefoxitin, imipenem-cilastatin, ticarcillin-clavulanate, piperacillin-tazobactam, ampicillin-sulbactam, meropenem, and ertapenem.46,114,127,169,170,187,200 In a few medical centers, nearly 50% of B. fragilis isolates are resistant to cefoxitin, raising the question as to whether cefoxitin should be used routinely as a single agent in these institutions.64 Generally, the convenience of monotherapy does not outweigh the potential development of resistance to these broad-spectrum agents. They may be useful in the treatment of appendicitis in children with renal disease or hearing loss when avoiding the use of gentamicin is prudent. Limiting the duration of antibiotic use to 3 days after surgery does not lead to higher rates of wound infections or intraabdominal abscesses in children who are afebrile and eating.169 Efforts have been made to shorten the hospital stay of children with perforated appendicitis. Some

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institutions have set criteria for hospital discharge and discontinuation of antibiotics, such as absence of fever for 24 hours, ability to eat well, and less than 3% band forms on the white blood cell differential.80 Many surgeons will switch to oral antibiotics at home after 3 to 5 days of intravenous antibiotics in the hospital, although the benefit of adding prolonged oral antibiotics has not been shown.63,180 Providing home single-intravenous antimicrobial therapy also can reduce costs and hasten hospital discharge in selected children with perforated appendicitis.173 Similar to nonperforated appendicitis, some controversy exists regarding whether immediate appendectomy should be performed on children in whom a palpable mass is associated with their appendicitis or who show evidence of appendiceal rupture with or without abscess formation at the time of presentation.29,120 Similarly there is a lack of prospective studies to determine if interval appendectomy is required after successful nonoperative treatment of an appendiceal mass in children.72 Families do experience more stress when nonoperative management of perforated appendicitis is implemented.166

PROGNOSIS AND COMPLICATIONS Currently in the United States, the risk of dying of appendicitis is very low. The mortality rate is higher in the rare newborn or premature infant who develops appendicitis. Also, factors contributing to the death of children rarely may include delay in establishing diagnosis, inadequate fluid replacement, immunodeficiency, and postoperative vascular or infectious complications. The most predictive factor of postoperative morbidity occurring from appendicitis is perforation.150 Age, obesity, duration of the surgical procedure, and nutritional status also are risk factors for the development of complications. Wound infection rates in children who receive perioperative antibiotics should be less than 7%; infections generally are caused by the same organisms that are isolated in cultures obtained during the appendectomy.168,185 Occasionally children develop peritonitis, intraabdominal abscesses, psoas abscesses, fistulas, pyelophlebitis of the portal vein, scrotal abscesses, empyema, or pneumoperitoneum during the course of treatment of appendicitis.17,71,81,153,201,205 CT can be successfully used to detect postoperative abscesses even in the first week after surgery. If complications occur, another surgical procedure often is performed and antibiotic treatment is prolonged. Abscesses may be treated successfully with antibiotics alone and without surgical drainage in stable patients after appendectomy.50

PELVIC ABSCESS The pelvic area is a common site for development of abscesses because it is the most dependent portion of the peritoneal cavity. Pelvic abscesses most commonly occur in children who have had intestinal perforations after appendicitis, have suffered penetrating abdominal or retroperitoneal injury, or have undergone an abdominal surgical procedure. Occasionally adolescents with pelvic inflammatory disease or Crohn disease develop a pelvic abscess. In children with perforated appendicitis, a coexisting pelvic abscess often is diagnosed at the time of surgery. In patients who recently have had penetrating trauma to the abdomen, have had pelvic inflammatory disease, or have undergone gastrointestinal surgery, a pelvic abscess should be suspected when they have continued fever or complain of abdominal pain despite receiving adequate treatment of the initial disease process. Symptoms may not develop until days to months after therapy is ended. No characteristic physical findings are associated with a pelvic abscess, although abdominal palpation or rectal examination may elicit tenderness or signs of intestinal obstruction may be present. If a pelvic abscess is suspected, contrast CT evaluation of the pelvis should be completed. Walled-off fluid collections in the pelvis can be identified and sometimes the rectum, sigmoid colon, or bladder is compressed because of mass effect from the abscess cavity. Because most pelvic abscesses develop as complications of intestinal or pelvic infections, enteric aerobes and anaerobes are the organisms most commonly isolated from the abscess cavity. Yeasts rarely cause pelvic abscesses.189,198 Actinomyces-related pelvic abscesses uncommonly are

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SECTION 8  Other Intraabdominal Infections

observed.140 Tuberculous abscesses can develop as a complication of genital tuberculosis.196 When a pelvic abscess is identified, antibiotics covering intestinal aerobes and anaerobes, such as clindamycin and gentamicin, should be started, and the abscess contents should be drained. In most situations, reaching the abscess cavity by an anterior approach is difficult. Considerable interest has developed in using CT or ultrasonography to guide percutaneous drainage of pelvic abscesses by transgluteal, transrectal, transsacrococcygeal, transiliopsoas, or transvaginal approaches.30,118,132,152,160 Although placement of a transgluteal catheter is easiest, the sciatic nerve and gluteal vessels must be avoided. Also an increased risk for development of a wound infection may occur because microorganisms may track along the outside of the catheter to the skin. Many surgeons prefer the transrectal approach because it often is the most direct route to the abscess. Transvaginal drainage has been used with good results in young women. Most often, drainage catheters can be removed after 7 to 10 days of treatment. Abscesses also may develop within the muscles of the pelvic girdle, including the psoas and internal obturator muscles. Similar to true pelvic abscesses, they usually cause fever and occasionally abdominal complaints in children. Most children begin to limp, refuse to walk, or complain of pain in the buttocks, thigh, or groin. Often a suppurative hip infection is suspected initially. A pelvic muscle abscess is usually diagnosed by CT or magnetic resonance imaging. Labeled leukocyte scans sometimes are useful in localizing the infection to within the pelvis, especially when the child has no symptoms other than fever or refusing to walk. Pelvic muscle abscesses can develop as a complication of Crohn disease or appendicitis; however, they often develop after an episode of bacteremia.28,161 Staphylococcus aureus is the most common cause of a primary pelvic muscle abscess, with methicillin-resistant strains being increasingly identified.138 S. pneumoniae, H. influenzae type B, E. coli, Enterococcus faecalis, S. anginosus, Yersinia enterocolitica, Salmonella spp., Proteus mirabilis, Capnocytophaga sputigena, and Actinomyces spp. also have been reported to cause hematogenously acquired abscesses.34,41,44,48,82,88,92,96 Bacteremia secondary to intravenous drug abuse or the presence of central lines occasionally predisposes patients to developing this type of infection.94,195 Rarely tuberculous psoas abscesses have been reported, often as a complication of vertebral osteomyelitis.179 Pelvic muscle abscesses usually are drained by a percutaneous or surgical approach, and antibiotic therapy is based on Gram stain and culture results. Successful therapy with antibiotics alone has been reported.122 Duration of treatment is individualized and depends on the child’s response and the drainage techniques that were used. NEW REFERENCES SINCE THE SEVENTH EDITION 2. Ahmed MU, Bilal M, Anis K, et al. The frequency of Enterobius vermicularis infections in patients diagnosed with acute appendicitis in Pakistan. Glob J Health Sci. 2015;7:196-201. 4. Akkoyun I, Tuna AT. Advantages of abandoning abdominal cavity irrigation and drainage in operations performed on children with perforated appendicitis. J Pediatr Surg. 2012;47:1886-1890. 7. Anderson JE, Bickler SW, Chang DC, et al. Examining a common disease with unknown etiology: trends in epidemiology and surgical management of appendicitis in California, 1995–2009. World J Surg. 2012;36:2787-2794. 18. Bachur RG, Levy JA, Callahan MJ, et al. Effect of reduction in the use of computed tomography on clinical outcomes of appendicitis. JAMA Pediatr. 2015;169:755-760. 20. Bansal S, Banever GT, Katter FM, et al. Appendicitis in children less than 5 years old: influence of age on presentation and outcome. Am J Surg. 2012;204:1031-1035. 30. Borofsky SE, Obi C, Cahill AM, et al. Transiliopsoas approach: an alternative route to drain pelvic abscesses in children. Pediatr Radiol. 2015;45:94-98. 32. Botes SN, Ibirogba SB, McCallum AD, et al. Schistosoma prevalence in appendicitis. World J Surg. 2015;39:1080-1083. 37. Buckius MT, McGrath B, Monk J, et al. Changing epidemiology of acute appendicitis in the United States: study period 1993–2008. J Surg Res. 2012;175:185-190. 43. Chen CY, Chen YC, Pun HN, et al. Bacteriology of acute appendicitis and its implication for the use of prophylactic antibiotics. Surg Infect (Larchmt). 2012;13:383-390.

46. Dalgic N, Karadag CA, Bayraktar B, et al. Ertapenem versus standard triple antibiotic therapy for the treatment of perforated appendicitis in pediatric patients: a prospective randomized trial. Eur J Pediatr Surg. 2014;24:410-418. 54. D’Souza N, Karim D, Sunthareswaran R. Bilirubin: a diagnostic marker for appendicitis. Int J Surg. 2013;11:1114-1117. 61. Farach SM, Danielson PD, Walford NE, et al. Same-day discharge after appendectomy results in cost savings and improved efficiency. Am Surg. 2014;80: 787-791. 62. Fernandez Ibieta M, Martinez Castano I, Reyes Rios P, et al. Study of bacteriology and resistances in pediatric appendicitis. Cir Pediatr. 2014;27:16-20. 65. Gasior AC, Marty Knott E, Ostlie DJ, et al. To drain or not to drain: an analysis of abscess drains in the treatment of appendicitis with abscess. Pediatr Surg Int. 2013;29:455-458. 66. Gavela T, Cabeza B, Serrano A, et al. C-reactive protein and procalcitonin are predictors of the severity of acute appendicitis in children. Pediatr Emerg Care. 2012;28:416-419. 85. Jackson HT, Mongodin EF, Davenport KP, et al. Culture-independent evaluation of the appendix and rectum microbiomes in children with and without appendicitis. PLoS ONE. 2014;9:e95414. 93. Koike Y, Uchida K, Matsushita K, et al. Intraluminal appendiceal fluid is a predictive factor for recurrent appendicitis after initial successful non-operative management of uncomplicated appendicitis in pediatric patients. J Pediatr Surg. 2014;49:1116-1121. 95. Kynes JM, Rauth TP, McMorrow SP. Ruptured appendicitis presenting as acute scrotal swelling in a 23-month-old toddler. J Emerg Med. 2012;43:47-49. 100. Larbcharoensub N, Boonsakan P, Kanoksil W, et al. Fungal appendicitis: a case series and review of the literature. Southeast Asian J Trop Med Public Health. 2013;44:681-689. 106. Leeuwenburgh MM, Monpellier V, Vlaminckx BJ, et al. Streptococcus milleri in intraabdominal abscesses in children after appendectomy: incidence and course. J Pediatr Surg. 2012;47:535-539. 113. Mallin M, Craven P, Ockerse P, et al. Diagnosis of appendicitis by bedside ultrasound in the ED. Am J Emerg Med. 2015;33:430-432. 115. Markar SR, Karthikesalingam A, Di Franco F, et al. Systematic review and metaanalysis of single-incision versus conventional multiport appendicectomy. Br J Surg. 2013;100:1709-1718. 118. McDaniel JD, Warren MT, Pence JC, et al. Ultrasound-guided transrectal drainage of deep pelvic abscesses in children: a modified and simplified technique. Pediatr Radiol. 2015;45:435-438. 121. Michailidou M, Goldstein SD, Sacco Casamassima MG, et al. Laparoscopic versus open appendectomy in children: the effect of surgical technique on healthcare costs. Am J Surg. 2015;210:270-275. 136. Otan E, Akbulut S, Kayaalp C. Amebic acute appendicitis: systematic review of 174 cases. World J Surg. 2013;37:2061-2073. 137. Panagiotopoulou IG, Parashar D, Lin R, et al. The diagnostic value of white cell count, C-reactive protein and bilirubin in acute appendicitis and its complications. Ann R Coll Surg Engl. 2013;95:215-221. 142. Pogorelic Z, Biocic M, Juric I, et al. Acute appendicitis as a complication of varicella. Acta Medica (Hradec Kralove). 2012;55:150-152. 152. Robert B, Chivot C, Fuks D, et al. Percutaneous, computed tomography-guided drainage of deep pelvic abscesses via a transgluteal approach: a report on 30 cases and a review of the literature. Abdom Imaging. 2013;38:285-289. 154. Rosines LA, Chow DS, Lampl BS, et al. Value of gadolinium-enhanced MRI in detection of acute appendicitis in children and adolescents. AJR Am J Roentgenol. 2014;203:w543-w548. 159. Salminen P, Paajanen H, Rautio T, et al. Antibiotic therapy vs appendectomy for treatment of uncomplicated acute appendicitis: the APPAC randomized clinical trial. JAMA. 2015;313:2340-2348. 163. Sawyer RG, Claridge JA, Nathens AB, et al. Trial of short-course antimicrobial therapy for intraabdominal infection. N Engl J Med. 2015;372:1996-2005. 174. St Peter SD, Adibe OO, Iqbal W, et al. Irrigation versus suction alone during laparoscopic appendectomy for perforated appendicitis: a prospective randomized trial. Ann Surg. 2012;256:581-585. 203. Yabanoglu H, Aytac HO, Turk E, et al. Parasitic infections of the appendix as a cause of appendectomy in adult patients. Turkiye Parazitol Derg. 2014;38: 12-16. 208. Zhao L, Liao Z, Feng S, et al. Single-incision versus conventional laparoscopic appendicectomy in children: a systemic review and meta-analysis. Pediatr Surg Int. 2015;31:347-353. 209. Zhong D, Brower-Sinning R, Firek B, et al. Acute appendicitis in children is associated with an abundance of bacteria from the phylum Fusobacteria. J Pediatr Surg. 2014;49:441-446.

The full reference list for this chapter is available at ExpertConsult.com.

CHAPTER 51  Appendicitis and Pelvic Abscess REFERENCES 1. Abou-Nukta F, Bakhos C, Arroyo K, et al. Effects of delaying appendectomy for acute appendicitis for 12 to 24 hours. Arch Surg. 2006;141:504-507. 2. Ahmed MU, Bilal M, Anis K, et al. The frequency of Enterobius vermicularis infections in patients diagnosed with acute appendicitis in Pakistan. Glob J Health Sci. 2015;7:196-201. 3. Ajmera RK, Simon GL. Appendicitis associated with Taenia species: cause or coincidental? Vector Borne Zoonotic Dis. 2010;10:321-322. 4. Akkoyun I, Tuna AT. Advantages of abandoning abdominal cavity irrigation and drainage in operations performed on children with perforated appendicitis. J Pediatr Surg. 2012;47:1886-1890. 5. Amoli HA, Golozar A, Keshavarzi H, et al. Morphine analgesia in patients with acute appendicitis: a randomized double-blind clinical trial. Emerg Med J. 2007;25:586-589. 6. Andersen BR, Kallehave FL, Andersen HK. Antibiotics versus placebo for prevention of postoperative infection after appendicectomy. Cochrane Database Syst Rev. 2005;(3):CD001439. 7. Anderson JE, Bickler SW, Chang DC, et al. Examining a common disease with unknown etiology: trends in epidemiology and surgical management of appendicitis in California, 1995–2009. World J Surg. 2012;36:2787-2794. 8. Andersson RE. Meta-analysis of the clinical and laboratory diagnosis of appendicitis. Br J Surg. 2004;91:28-37. 9. Andersson RE. Is appendicitis an emergency? World J Surg. 2011;35:1634-1635. 10. Andriopoulos P, Tsironi M, Simakopoulos G. Acute abdomen due to Brucella melitensis. Scand J Infect Dis. 2003;35:204-205. 11. Angel CA, Rao BN, Wrenn E, et al. Acute appendicitis in children with leukemia and other malignancies: still a diagnostic dilemma. J Pediatr Surg. 1992;27:476-479. 12. Arca MJ, Gates RL, Groner JI, et al. Clinical manifestations of appendiceal pinworms in children: an institutional experience and a review of the literature. Pediatr Surg Int. 2004;20:372-375. 13. Arenal Vera JJ, Marcos Rodriquez JL, Borrego Pintado MH, et al. Anisakiasis as a cause of acute appendicitis and rheumatologic picture: the first case in medical literature. Rev Esp Enferm Dig. 1991;79:355-358. 14. Astagneau P, Goldstein FW, Francoual S, et al. Appendicitis due to both Streptococcus pneumoniae and Haemophilus influenzae. Eur J Clin Microbiol Infect Dis. 1992;11:559-560. 15. Aye AM, Law CW, Sabet NS, et al. Isolation of Aggregatibacter aphrophilus from a patient with acute appendicitis. Eur Rev Med Pharmacol Sci. 2011;15:845-847. 16. Azodi OS, Lindstrom D, Adami J, et al. Impact of body mass index and tobacco smoking on outcome after open appendicectomy. Br J Surg. 2008;95:751-757. 17. Babcock DS. Ultrasound diagnosis of portal vein thrombosis as a complication of appendicitis. AJR Am J Roentgenol. 1979;133:317-319. 18. Bachur RG, Levy JA, Callahan MJ, et al. Effect of reduction in the use of computed tomography on clinical outcomes of appendicitis. JAMA Pediatr. 2015;169:755-760. 19. Bailey B, Bergeron S, Gravel J, et al. Efficacy and impact of intravenous morphine before surgical consultation in children with right lower quadrant pain suggestive of appendicitis: a randomized controlled trial. Ann Emerg Med. 2007;50:371-378. 20. Bansal S, Banever GT, Katter FM, et al. Appendicitis in children less than 5 years old: influence of age on presentation and outcome. Am J Surg. 2012;204:1031-1035. 21. Baron EJ, Bennion R, Thompson J, et al. Microbiological comparison between acute and complicated appendicitis. Clin Infect Dis. 1992;14:227-231. 22. Bartoli F, Guerra A, Dolina M, et al. Salmonella enterica serovar Israel causing perforating appendicitis. Int J Infect Dis. 2010;14:e538. 23. Beltran MA, Almonacid J, Vicencio A, et al. Predictive value of white blood cell count and C-reactive protein in children with appendicitis. J Pediatr Surg. 2007;42:1208-1214. 24. Bennion RS, Baron EJ, Thompson JE, et al. The bacteriology of gangrenous and perforated appendicitis revisited. Ann Surg. 1990;211:165-171. 25. Bennion RS, Thompson JE, Gil J, et al. The role of Yersinia enterocolitica in appendicitis in the southwestern United States. Am Surg. 1991;57:766-768. 26. Bercu TE, Rubin ZA, Agopian VG. Tuberculous appendicitis. Am J Med. 2011;124:e9-e10. 27. Bernard D, Verschraegen G, Claeys G, et al. Bilophila wadsworthii bacteremia in a patient with gangrenous appendicitis. Clin Infect Dis. 1994;18:1023-1024. 28. Bertrand SL, Lincoln ED, Prohaska MG. Primary pyomyositis of the pelvis in children: a retrospective review of 8 cases. Orthopedics. 2011;34:e832-e840. 29. Blakely ML, Williams R, Dassinger MS, et al. Early vs interval appendectomy for children with perforated appendicitis. Arch Surg. 2011;146:660-665. 30. Borofsky SE, Obi C, Cahill AM, et al. Transiliopsoas approach: an alternative route to drain pelvic abscesses in children. Pediatr Radiol. 2015;45:94-98. 31. Bosshard PP, Zbinden R, Altwegg M. Turicibacter sanguinis gen. nov., sp. nov., a novel anaerobic, Gram-positive bacterium. Int J Syst Evol Microbiol. 2002;52:1263-1266. 32. Botes SN, Ibirogba SB, McCallum AD, et al. Schistosoma prevalence in appendicitis. World J Surg. 2015;39:1080-1083. 33. Bova R, Meagher A. Appendicitis in HIV-positive patients. Aust N Z J Surg. 1998;68:337-339.

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34. Brooks DJ, Cant AJ, Lambert HP, et al. Recurrent Salmonella septicaemia with aortitis, osteomyelitis and psoas abscess. J Infect. 1983;7:156-158. 35. Brown TA, Rajappannair L, Dalton AB, et al. Acute appendicitis in the setting of Clostridium difficile colitis: case report and review of the literature. Clin Gastroenterol Hepatol. 2007;5:969-971. 36. Buch K, Nguyen S, Divino CM, et al. Cryptosporidiosis presenting as acute appendicitis: a case report. Am Surg. 2005;71:537-538. 37. Buckius MT, McGrath B, Monk J, et al. Changing epidemiology of acute appendicitis in the United States: study period 1993–2008. J Surg Res. 2012;175:185-190. 38. Bundy DG, Byerley JS, Liles EAI, et al. Does this child have appendicitis? JAMA. 2007;298:438-451. 39. Campbell LK, Havens JM, Scott MA, et al. Molecular detection of Campylobacter jejuni in archival cases of acute appendicitis. Mod Pathol. 2006;19:1042-1046. 40. Carter JE, Evans TN. Clinically significant Kluyvera infections—a report of seven cases. Am J Clin Pathol. 2005;123:334-338. 41. Chan JF, Wong SS, Leung SS, et al. Capnocytophaga sputigena primary iliopsoas abscess. J Med Microbiol. 2010;59:1368-1370. 42. Chen CY, Chen YC, Pun HN, et al. Bacteriology of acute appendicitis and its implication for the use of prophylactic antibiotics. Surg Infect (Larchmt). 2012;13:383-390. 43. Chen C-H, Lin L-C, Liu C-E, et al. Chromobacterium violaceum bacteremia: a case report. J Microbiol Immunol Infect. 2003;36:141-144. 44. Coakham HB, Ashby EC. Actinomycosis in recurrent psoas abscess. Proc R Soc Med. 1972;65:880. 45. Cosper GH, Hamann MS, Stiles A, et al. Hospital characteristics affect outcomes for common pediatric surgical conditions. Am Surg. 2006;72:739-745. 46. Dalgic N, Karadag CA, Bayraktar B, et al. Ertapenem versus standard triple antibiotic therapy for the treatment of perforated appendicitis in pediatric patients: a prospective randomized trial. Eur J Pediatr Surg. 2014;24:410-418. 47. Davies HOB, Alkhamesi NA, Dawson PM. Peritoneal fluid culture in appendicitis: review in changing times. Int J Surg. 2010;8:426-429. 48. Davies D, King SM, Parekh RS, et al. Psoas abscess caused by Haemophilus influenzae, type b. Pediatr Infect Dis J. 1991;10:411-412. 49. Dezfuli MG, Oo MM, Jones BE, et al. Tuberculosis mimicking acute appendicitis in patients with human immunodeficiency virus infection. Clin Infect Dis. 1994;18:650-651. 50. Dobremez E, Lavrand F, Lefevre Y, et al. Treatment of post-appendectomy intra-abdominal deep abscesses. Eur J Pediatr Surg. 2003;13:393-397. 51. Dodd LG. Balantidium coli infestation as a cause of acute appendicitis. J Infect Dis. 1991;163:1392. 52. Doria AS, Moineddin R, Kellenberger CJ, et al. US or CT for diagnosis of appendicitis in children and adults? A meta-analysis. Radiology. 2006;241: 83-94. 53. Doumit G, Abouhassan W, Reimer MW, et al. The role of multidetector computed tomography for diagnosing acute appendicitis. Ann Intern Med. 2011;154:136. 54. D’Souza N, Karim D, Sunthareswaran R. Bilirubin; a diagnostic marker for appendicitis. Int J Surg. 2013;11:1114-1117. 55. Dumas F, Kierzek G, Coignard S, et al. Acute appendicitis, an unusual presentation of Streptococcus pyogenes infection. Am J Emerg Med. 2009;27:254.e1-254.e2. 56. Ebell MK. Diagnosis of appendicitis, part 1: history and physical examination. Am Fam Physician. 2008;77:828-830. 57. Emil S, Laberge J-M, Mikhail P, et al. Appendicitis in children: a ten-year update of therapeutic recommendations. J Pediatr Surg. 2003;38:236-242. 58. Enami MA, Frayha HH, Halim MA. An appendiceal abscess due to Mycobacterium kansasii in a child with AIDS. Clin Infect Dis. 1998;27:891-892. 59. England RJ, Crabbe DCG. Delayed diagnosis of appendicitis in children treated with antibiotics. Pediatr Surg Int. 2006;22:541-545. 60. Ergul E. Heredity and familial tendency of acute appendicitis. Scand J Surg. 2007;96:290-292. 61. Farach SM, Danielson PD, Walford NE, et al. Same-day discharge after appendectomy results in cost savings and improved efficiency. Am Surg. 2014;80:787-791. 62. Fernandez Ibieta M, Martinez Castano I, Reyes Rios P, et al. Study of bacteriology and resistances in pediatric appendicitis. Cir Pediatr. 2014;27:16-20. 63. Fraser JD, Aguayo P, Leys CM, et al. A complete course of intravenous antibiotics vs a combination of intravenous and oral antibiotics for perforated appendicitis in children: a prospective, randomized trial. J Pediatr Surg. 2010;45:1198-1202. 64. Fraulin FOG, Thurston OG. Value of cultures of tissue samples taken at operation for lower intestinal perforation. Can J Surg. 1993;36:261-265. 65. Gasior AC, Marty Knott E, Ostlie DJ, et al. To drain or not to drain: an analysis of abscess drains in the treatment of appendicitis with abscess. Pediatr Surg Int. 2013;29:455-458. 66. Gavela T, Cabeza B, Serrano A, et al. C-reactive protein and procalcitonin are predictors of the severity of acute appendicitis in children. Pediatr Emerg Care. 2012;28:416-419. 67. Gladman MA, Knowles CH, Gladman LJ, et al. Intra-operative culture in appendicitis: traditional practice challenged. Ann R Coll Surg Engl. 2004;86: 196-201.

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SECTION 8  Other Intraabdominal Infections

68. Goldin AB, Sawin RS, Garrison MM, et al. Aminoglycoside-based triple-antibiotic therapy versus monotherapy for children with ruptured appendicitis. Pediatrics. 2007;119:905-911. 69. Gorbach SL. Intra-abdominal infections. Clin Infect Dis. 1993;17:961-967. 70. Grynspan D, Rabah R. Adenoviral appendicitis presenting clinically as acute appendicitis. Pediatr Dev Pathol. 2008;11:138-141. 71. Haas GP, Shumaker BP, Haas PA. Appendicovesical fistula. Urology. 1984;24:604-609. 72. Hall NJ, Jones CE, Eaton S, et al. Is interval appendicectomy justified after successful nonoperative treatment of an appendix mass in children? A systematic review. J Pediatr Surg. 2011;46:767-771. 73. Hardwick RH, Taylor A, Thompson MH, et al. Association between Streptococcus milleri and abscess formation after appendicitis. Ann R Coll Surg Engl. 2000;82:24-26. 74. Harlak A, Gulee M, Mentes O, et al. Atopy is a risk factor for acute appendicitis? A prospective clinical study. J Gastrointest Surg. 2008;12:1251-1256. 75. Deleted in review. 76. Hasan RA, Abuhammour W. Beta-hemolytic group F streptococcal bacteremia in children. Pediatr Infect Dis J. 2004;23:468-470. 77. HCUPnet. Healthcare Cost and Utilization Project. Rockville, MD: Agency for Healthcare Research and Quality; 2002. Available at: http://www.ahrq.gov/research/ data/hcup/index.html. 78. Henneman PL, Marcus CS, Inkelis SH, et al. Evaluation of children with possible appendicitis using technetium 99m leukocyte scan. Pediatrics. 1990;85: 838-843. 79. Heseltine PNR, Yellin AE, Appleman MD, et al. Perforated and gangrenous appendicitis: an analysis of antibiotic failures. J Infect Dis. 1983;148: 322-329. 80. Hoelzer DJ, Zabel DD, Zern JT. Determining duration of antibiotic use in children with complicated appendicitis. Pediatr Infect Dis J. 1999;18:979-982. 81. Hoffer FA, Ablow RC, Gryboski JD, et al. Primary appendicitis with an appendicotuboovarian fistula. AJR Am J Roentgenol. 1982;138:742-743. 82. Humphreys H, Keane CT, Marron P, et al. Infective sacroiliac arthritis and psoas abscess caused by Streptococcus milleri. J Infect. 1989;19:77-78. 83. Hyman P, Westring DW. Leukocytosis in acute appendicitis: observed racial difference. JAMA. 1974;229:1630-1632. 84. Jackson HT, Mongodin EF, Davenport KP, et al. Culture-independent evaluation of the appendix and rectum microbiomes in children with and without appendicitis. PLoS ONE. 2014;9:e95414. 85. Jackson DS, Welch DF, Pickett DA, et al. Suppurative infections in children caused by non-beta-hemolytic members of the Streptococcus milleri group. Pediatr Infect Dis J. 1995;14:80-82. 86. Jakobsen J, Andersen JC, Klausen IC. Beta-haemolytic streptococci in acute appendicitis. Acta Chir Scand. 1988;154:301-303. 87. Jancelewicz T, Kim G, Miniati D. Neonatal appendicitis: a new look at an old zebra. J Pediatr Surg. 2008;43:e1-e5. 88. Kahn FW, Glasser JE, Agger WA. Psoas muscle abscess due to Yersinia enterocolitica. Am J Med. 1984;76:947-949. 89. Kanafani ZA, Sharara AI, Shabb NS, et al. Cytomegalovirus appendicitis following acute Epstein-Barr virus infection in an immunocompetent patient. Scand J Infect Dis. 2004;36:505-507. 90. Kang JY, Hoare J, Majeed A, et al. Decline in admission rates for acute appendicitis in England. Br J Surg. 2003;90:1586-1592. 91. Kazlow PG, Freed J, Rosh JR, et al. Salmonella typhimurium appendicitis. J Pediatr Gastroenterol Nutr. 1991;13:101-103. 92. Knobel B, Sommer I, Schwartz G. Primary psoas abscess three years after ipsilateral nephrectomy. Infection. 1985;13:27-28. 93. Koike Y, Uchida K, Matsushita K, et al. Intraluminal appendiceal fluid is a predictive factor for recurrent appendicitis after initial successful non-operative management of uncomplicated appendicitis in pediatric patients. J Pediatr Surg. 2014;49:1116-1121. 94. Kwok T, Coles J. Psoas abscess as a complication of subclavian venous catheterization. Postgrad Med J. 1990;66:771-772. 95. Kynes JM, Rauth TP, McMorrow SP. Ruptured appendicitis presenting as acute scrotal swelling in a 23-month-old toddler. J Emerg Med. 2012;43:47-49. 96. Lachenal F, Meeus P, Thiesse P, et al. Streptococcus pneumoniae retroperitoneal and pelvic abscess. Lancet Infect Dis. 2011;11:720. 97. Lameris W, van Randen A, Go MNYH, et al. Single and combined diagnostic value of clinical features and laboratory tests in acute appendicitis. Acad Emerg Med. 2009;16:835-842. 98. Lamps LW, Molina CP, Haggitt RC, et al. The pathologic spectrum of gastrointestinal and hepatic histoplasmosis. Am J Clin Pathol. 2000;113: 64-72. 99. LaRaja RD, Rothenberg RE, Odom JW, et al. The incidence of intra-abdominal surgery in acquired immunodeficiency syndrome: a statistical review of 904 patients. Surgery. 1989;105:175-179. 100. Larbcharoensub N, Boonsakan P, Kanoksil W, et al. Fungal appendicitis: a case series and review of the literature. Southeast Asian J Trop Med Public Health. 2013;44:681-689.

101. Lau SKP, McNabb A, Woo GKS, et al. Catabacter hongkongensis gen. nov., isolated from blood cultures of patients from Hong Kong and Canada. J Clin Microbiol. 2007;45:395-401. 102. Lau SKP, Woo PCY, Chan CYF, et al. Typhoid fever associated with acute appendicitis caused by an H1-j strain of Salmonella enterica serotype Typhi. J Clin Microbiol. 2005;43:1470-1472. 103. Lau SKP, Woo PCY, Teng JLL, et al. Identification by 16S ribosomal RNA gene sequencing of Arcobacter butzleri bacteraemia in a patient with acute gangrenous appendicitis. Mol Pathol. 2002;55:182-185. 104. Lee SL, Islam S, Cassidy LD, et al. Antibiotics and appendicitis in the pediatric population: an American Pediatric Surgical Association outcomes and clinical trials committee systematic review. J Pediatr Surg. 2010;45:2181-2185. 105. Lee SL, Walsh AJ, Ho HS. Computed tomography and ultrasonography do not improve and may delay the diagnosis and treatment of acute appendicitis. Arch Surg. 2001;136:556-562. 106. Leeuwenburgh MM, Monpellier V, Vlaminckx BJ, et al. Streptococcus milleri in intraabdominal abscesses in children after appendectomy: incidence and course. J Pediatr Surg. 2012;47:535-539. 107. Lewis F, Holcroft J, Boey J, et al. Appendicitis in critical review of diagnosis and treatment in 1000 cases. Arch Surg. 1975;110:677-684. 108. Lim PL. Appendicitis associated with travelers’ diarrhea caused by Aeromonas sobria. J Travel Med. 2009;16:132-133. 109. Liu V, Val S, Kang K, et al. Case report: actinomycosis of the appendix—an unusual cause of acute appendicitis in children. J Pediatr Surg. 2010;45:20502052. 110. Lopez-Navidad A, Domingo P, Cada Falch G. Acute appendicitis complicating infectious mononucleosis: case report and review. Rev Infect Dis. 1990;12:297-302. 111. Lowe LH, Penney MW, Stein SM, et al. Unenhanced limited CT of the abdomen in the diagnosis of appendicitis in children: comparison with sonography. AJR Am J Roentgenol. 2001;176:31-35. 112. Malde HM, Chadha D. Roundworm obstruction: sonographic diagnosis. Abdom Imaging. 1993;18:274-276. 113. Mallin M, Craven P, Ockerse P, et al. Diagnosis of appendicitis by bedside ultrasound in the ED. Am J Emerg Med. 2015;33:430-432. 114. Maltezou HC, Nikolaidis P, Lebesii E, et al. Piperacillin/tazobactam versus cefotaxime plus metronidazole for treatment of children with intra-abdominal infections requiring surgery. Eur J Clin Microbiol Infect Dis. 2001;20:643-646. 115. Markar SR, Karthikesalingam A, Di Franco F, et al. Systematic review and metaanalysis of single-incision versus conventional multiport appendicectomy. Br J Surg. 2013;100:1709-1718. 116. Martin AE, Vollman D, Adler B, et al. CT scans may not reduce the negative appendectomy rate in children. J Pediatr Surg. 2004;39:886-890. 117. McCahy P. Continuing fall in the incidence of acute appendicitis. Ann R Coll Surg Engl. 1994;76:282-283. 118. McDaniel JD, Warren MT, Pence JC, et al. 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CHAPTER 51  Appendicitis and Pelvic Abscess 132. Nielsen MB, Torp-Pedersen S. Sonographically guided transrectal or transvaginal one-step catheter placement in deep pelvic and perirectal abscesses. AJR Am J Roentgenol. 2004;183:1035-1036. 133. Nordentoft T, Bringstrup FA, Bremmelgaard A, et al. Effect of laparoscopy on bacteremia in acute appendicitis: a randomized controlled study. Surg Laparosc Endosc Percutan Tech. 2000;10:302-304. 134. Ochoa B. Surgical complications of ascariasis. World J Surg. 1991;15:222-227. 135. Okamoto T, Sano K, Ogasahara K. Receiver-operating characteristic analysis of leukocyte counts and serum C-reactive protein levels in children with advanced appendicitis. Surg Today. 2006;36:515-518. 136. Otan E, Akbulut S, Kayaalp C. Amebic acute appendicitis: systematic review of 174 cases. World J Surg. 2013;37:2061-2073. 137. Panagiotopoulou IG, Parashar D, Lin R, et al. 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Ann Emerg Med. 1991;20:45-50. 156. Ruff ME, Friedland IR, Hickey SM. Escherichia coli septicemia in nonperforated appendicitis. Arch Pediatr Adolesc Med. 1994;148:853-855. 157. Sah SP, Bhadani PP. Enterobius vermicularis causing symptoms of appendicitis in Nepal. Trop Doct. 2006;36:160-162. 158. Salemis NS. Acute appendicitis presenting with Klebsiella pneumoniae septicemia due to bacterial translocation. Am J Emerg Med. 2009;27:1023.e3-1023.e4. 159. Salminen P, Paajanen H, Rautio T, et al. Antibiotic therapy vs appendectomy for treatment of uncomplicated acute appendicitis: the APPAC randomized clinical trial. JAMA. 2015;313:2340-2348. 160. Saokar A, Arellano RS, Gervais DA, et al. Transvaginal drainage of pelvic fluid collections: results, expectations, and experience. AJR Am J Roentgenol. 2008;191:1352-1358. 161. Sauer C, Gutgesell M. Ballet dancer with hip and groin pain: Crohn disease and psoas abscess. Clin Pediatr (Phila). 2005;44:731-733. 162. 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165. Schropp KP, Kaplan S, Golladay ES, et al. A randomized clinical trial of ampicillin, gentamicin and clindamycin versus cefotaxime and clindamycin in children with ruptured appendicitis. Surgery. 1991;172:351-356. 166. Schurman JV, Cushing CC, Garey CL, et al. Quality of life assessment between laparoscopic appendectomy at presentation and interval appendectomy for perforated appendicitis with abscess: analysis of a prospective randomized trial. J Pediatr Surg. 2011;46:1121-1125. 167. Sehdev AES, Sehdev PS, Jacobs R, et al. Human monocytic ehrlichiosis presenting as acute appendicitis during pregnancy. Clin Infect Dis. 2002;35:e99-e102. 168. Simpson J, Speake W. Appendicitis. Clin Evid. 2005;14:529-535. 169. Sirinek KR, Levine BA. Antimicrobial management of surgically treated gangrenous or perforated appendicitis: comparison of cefoxitin and clindamycin-gentamicin. Clin Ther. 1987;9:420-428. 170. Sirinek KR, Levine BA. 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196. Wehner JH, De Bruyne K, Kagawa FT, et al. Pulmonary tuberculosis, amenorrhea, and a pelvic mass. West J Med. 1994;161:515-518. 197. Wei B, Qi C-L, Chen T-F, et al. Laparoscopic versus open appendectomy for acute appendicitis: a metaanalysis. Surg Endosc. 2011;25:1199-1208. 198. Wiesenfeld HC, Berg SR, Sweet RL. Torulopsis glabrata pelvic abscess and fungemia. Obstet Gynecol. 1994;83:887-889. 199. Williams N, Kapila L. Acute appendicitis in the under 5-year-old. J R Coll Surg Edinb. 1994;39:168-170. 200. Wilson SE. Results of a randomized, multicenter trial of meropenem versus clindamycin/tobramycin for the treatment of intra-abdominal infections. Clin Infect Dis. 1997;24(suppl 2):S197-S206. 201. Wong K, Kumar R. Fever following appendicectomy: think about thoracic empyema. N Z Med J. 2007;120:U2561. 202. Woo PCY, Lau SKP, Woo GKS, et al. Bacteremia due to Clostridium hathewayi in a patient with acute appendicitis. J Clin Microbiol. 2004;42: 5947-5949.

203. Yabanoglu H, Aytac HO, Turk E, et al. Parasitic infections of the appendix as a cause of appendectomy in adult patients. Turkiye Parazitol Derg. 2014;38:12-16. 204. Yassin AF, Steiner U, Ludwig W. Corynebacterium appendicis sp. nov. Int J Syst Evol Microbiol. 2002;52:1165-1169. 205. Yasumoto R, Kawano M, Kawanishi H, et al. Left acute scrotum associated with appendicitis. Int J Urol. 1998;5:108-110. 206. Yildirim S, Nursal TZ, Tarim A, et al. A rare cause of acute appendicitis: parasitic infection. Scand J Infect Dis. 2005;37:757-759. 207. York D, Smith A, Phillips JD, et al. The influence of advanced radiographic imaging on the treatment of pediatric appendicitis. J Pediatr Surg. 2005;40:1908-1911. 208. Zhao L, Liao Z, Feng S, et al. Single-incision versus conventional laparoscopic appendicectomy in children: a systemic review and meta-analysis. Pediatr Surg Int. 2015;31:347-353. 209. Zhong D, Brower-Sinning R, Firek B, et al. Acute appendicitis in children is associated with an abundance of bacteria from the phylum Fusobacteria. J Pediatr Surg. 2014;49:441-446.

Pancreatitis

52 

Thomas L. Kuhls Pancreatitis was thought to be an uncommon cause of abdominal pain in children and a disease primarily of adults. Because of better recognition of symptoms in children and the more frequent use of medications that cause pancreatic inflammation, acute pancreatitis currently is being diagnosed more frequently in institutions specializing in pediatric care.114 Compared with causes of acute pancreatitis in adults—primarily alcoholism, cholelithiasis, and trauma—causes of childhood pancreatitis are more diverse. Microorganisms account for a significant proportion of cases of pancreatitis in children. In addition, antimicrobial agents have been associated with severe and occasionally fatal episodes of pancreatitis, and bacterial infections may complicate the natural history of acute and chronic pancreatitis. Pediatricians who care for children with pancreatitis must have expertise in the diagnosis and treatment of infectious diseases.

CLINICAL MANIFESTATIONS More than 80% of children with acute pancreatitis complain of abdominal pain.94 However, only 30% of pediatric patients have epigastric pain, as usually described by adults.167 In children, other sites of focal tenderness or diffuse pain include the right upper quadrant of the abdomen, the periumbilical area, the entire abdomen, and, less commonly, the right lower quadrant of the abdomen. The onset of pain usually is rapid and increases to a maximal intensity in a few hours, but occasionally the onset may be slow and gradual. Most often the pain is sharp and excruciating. Only one-third of children complain of pain that radiates to other areas, including the back, lower part of the abdomen, upper abdominal quadrants, and anterior chest wall. In school-aged children, the pain often intensifies after meals. Two-thirds of children with acute pancreatitis have vomiting.16 Children younger than 5 years occasionally experience vomiting without abdominal tenderness. Fever is present in only 30% of children with pancreatitis, but temperatures greater than 38.5°C (101.3°F) are observed occasionally. Children may present with only the symptom of cough, and pleural effusions are found on radiography.92 On physical examination, children are classically found lying quietly on their sides with their knees flexed. They usually have epigastric tenderness to palpation and decreased or absent bowel sounds. Abdominal distention is found in 30% of children with pancreatitis and occurs more commonly in preschool-aged children.167 Rebound tenderness, guarding of the epigastrium, jaundice, an abdominal mass, or ascites occasionally is detected. Rarely ecchymoses of the flanks (Grey Turner sign) or the umbilical area (Cullen sign) can be identified but usually only when life-threatening hemorrhagic pancreatitis is present. In severe pancreatitis, children may present with evidence of shock and multipleorgan failure. Chronic pancreatitis occurs when irreversible damage in the pancreatic architecture causes abnormalities in the function of the pancreas.85 Children with chronic pancreatitis often have lengthy or recurrent bouts of abdominal pain and vomiting.

LABORATORY DIAGNOSIS The single most common useful laboratory test for the clinical diagnosis of pancreatitis in children is measurement of the serum amylase concentration, but the level correlates poorly with the severity of the disease. In most studies of childhood pancreatitis, the diagnosis is confirmed when the serum amylase level is greater than three times the normal level for the particular laboratory completing the test. The serum concentration rises quickly within hours after symptoms develop.

High serum amylase concentrations can be observed, however, in numerous other illnesses, including acute cholecystitis, intestinal obstruction, perforations of abdominal organs, appendicitis, salpingitis, ruptured ectopic pregnancy, and salivary gland disease. The serum amylase concentration can return to normal in 24 to 72 hours after the onset of symptoms; thus the diagnosis of pancreatitis can be missed. In this situation, the urine amylase concentration can remain elevated for at least 1 week. Serum amylase concentrations occasionally are not elevated during the course of pancreatitis in children.34 Marked hyperlipidemia may interfere with the laboratory measurement of amylase.17 Serum lipase is useful in these situations; however, high serum concentrations often are not detected until 24 hours after the beginning of the illness. Because lipase is produced only in the pancreas and intestinal cells, measurement of its serum concentration helps distinguish children with high serum amylase concentrations of pancreatic as opposed to salivary origin. Some children with pancreatitis have high amylase levels without an elevation of serum lipase.86 Laboratory findings in children with severe and/or necrotizing pancreatitis may include leukocytosis with increased immature polymorphonuclear leukocytes, an elevated erythrocyte sedimentation rate, and elevated C-reactive protein level. In children with fulminant hemorrhagic pancreatitis, anemia develops quickly. Other associated findings include hyperglycemia, hypertriglyceridemia, hypoalbuminemia, and hypocalcemia. Scoring systems for children have been devised to predict severe pancreatitis, but these are extrapolated from adult studies or are difficult to use in clinical practice.43,82 Procalcitonin or D-dimer plasma levels may be useful in predicting severe pancreatitis and later complications.20,96 Elevated aminotransferase and alkaline phosphatase levels generally are observed only when the episode of pancreatitis is caused by biliary obstruction, such as in gallstone-related disease. The radiographic features of childhood pancreatitis also are nonspecific. Radiographs of the abdomen may show localized ileus of the jejunum in the midepigastric or left upper quadrant region adjacent to the pancreas (sentinel loop), a distended transverse colon without visualization of the descending colon because of adjacent pancreatic inflammation (colon cutoff sign), duodenal distention with air-fluid levels, or loss of the left psoas shadow. Occasionally chest radiography reveals an elevated left hemidiaphragm or pleural effusion. The ability to diagnose pancreatitis in children has been improved greatly by ultrasonography. The echodensity of the pancreas is normally equal to or greater than that of the left lobe of the liver. During acute pancreatitis, edema causes the gland to enlarge and become less dense than the liver. These two findings can aid in establishing the diagnosis of pancreatitis, and complications such as abscesses and pseudocysts can be identified. Also, ultrasonography may delineate dilations of the pancreatic ducts due to obstruction or ductal stones. Visualization of the pancreas by ultrasonography may be obscured because of overlying bowel gas. In such cases, computed tomography (CT) is useful in detecting pancreatic size and density. CT of the pancreas should be performed in complicated cases of pancreatitis after a few days of treatment to determine the severity of disease and extent of pancreatic necrosis.30,120 It is especially useful when surgery is being considered for drainage of abscesses and pseudocysts. Endoscopic retrograde cholangiopancreatography (ERCP) is used in children with pancreatitis to treat gallstones, strictures, or Ascaris infection.123 Because of ongoing improvement in image quality, magnetic resonance cholangiopancreatography (MRCP) is being increasingly used as a noninvasive technique for evaluating children with chronic or recurrent pancreatitis, with results similar to those from ERCP.31,148 503

504

SECTION 8  Other Intraabdominal Infections

CAUSES A cause for childhood pancreatitis can be determined in more than 90% of cases if diagnostic evaluation is thorough, especially in children younger than 6 years. The frequency of each specific cause depends on the patient population of the particular medical center. The most common noninfectious causes of pancreatitis in children include trauma, medications, obstructive diseases, vasculitis, autoimmune diseases, and genetic and metabolic diseases. Physicians with expertise in the management of infectious diseases are becoming more aware of drug-induced pancreatitis because many antimicrobial agents can cause pancreatic inflammation. Pentamidine isethionate has been used in the treatment of Pneumocystis jejuni pneumonia, African trypanosomiasis, and leishmaniasis. It may cause hypoglycemia because of toxicity to pancreatic islet cells and is associated with severe and occasionally fatal episodes of pancreatitis.95,172 In children, aerosolized pentamidine prophylaxis for P. jejuni pneumonia also has been associated with severe cases of pancreatitis in patients with acquired immunodeficiency syndrome (AIDS).61,95 Similarly, pentavalent antimonial agents such as sodium stibogluconate and meglumine antimonite, used for the treatment of visceral leishmaniasis, can induce pancreatic inflammation.11,133 Sulfonamides, including trimethoprim-sulfamethoxazole, have been implicated occasionally as a cause of acute pancreatitis in adults.7,161 Symptoms have recurred when patients have been reexposed to the medication. The abdominal pain often is accompanied by a hypersensitivity-type rash. Tetracycline- and doxycycline-induced pancreatitis have been described in children with and without overt liver disease.152,163 In addition, clarithromycin,52,130 erythromycin,146 rifampin,118 roxithromycin,121 linezolid,124 dapsone,36 nitrofurantoin,103 isoniazid,127 tigecycline,119 and metronidazole108 have been added to the list of agents that can cause pancreatitis in previously healthy individuals when given in routine doses or when high amounts are consumed. Although uncommonly used in children, quinolone antibiotics, such as gatifloxacin and ciprofloxacin, have been associated with hepatotoxicity and acute pancreatitis.33,143 An adolescent who was receiving ceftriaxone also developed pancreatitis secondary to obstruction of the biliary tract from gallstones.91 Pancreatitis has been a major dose-limiting toxic effect of the human immunodeficiency virus (HIV)-inhibiting nucleoside analogue reverse transcriptase inhibitor (NRTI) class of medications because of mitochondrial toxicity, especially dideoxyinosine andstavudine.23,47,113 Most episodes of pancreatitis associated with dideoxyinosine occur when the dose is 360 mg/m2 per day or greater, and usually the pancreatic inflammation resolves when the medication is discontinued. Concomitant administration of pentamidine or another NRTI, such as ribavirin, used in the treatment of hepatitis C infection may increase the risk for developing pancreatitis.98 In pediatric patients with AIDS, serum amylase concentrations often are elevated in patients without pancreatic symptoms, whereas children with pancreatitis can have normal serum amylase concentrations. The serum lipase concentration is useful in evaluating HIV-infected children for possible pancreatic inflammation.23,95 Increased liver aminotransferase or lipase concentrations before the administration of an NRTI may be helpful in predicting those children in whom pancreatitis will develop. In all children with symptoms consistent with pancreatitis, NRTIs should be withheld pending the results of a lipase assay, and they should be discontinued if the concentration is elevated. Similarly, they should be discontinued for 1 week after treatment with pentamidine.46 Because of increased awareness of NRTI toxicity, the incidence rate of pancreatitis in HIV-infected children in the highly active antiretroviral therapy (HAART) era appears to be decreasing.99 Interferon-α, which is used in the treatment of chronic hepatitis, has been associated with the development of pancreatitis.29 The antifungal agents liposomal amphotericin B, micafungin, and itraconazole rarely cause pancreatic toxicity.117,128,142

INFECTIOUS CAUSES Infections caused by various microorganisms have been shown by culture, histologic examination, or antibody titer rise during the course of acute

BOX 52.1  Microorganisms Associated With Episodes of Acute Pancreatitis Viruses Adenoviruses Cytomegalovirus Epstein-Barr virus Group B coxsackieviruses Hepatitis A virus Hepatitis B virus Hepatitis E virus Herpes simplex viruses Human immunodeficiency virus H1N1 influenza A virus Measles virus Mumps virus Parainfluenza viruses Rotavirus Rubella virus Varicella zoster virus West Nile virus

Fasciola hepatica Plasmodium falciparum Taenia saginata Toxoplasma gondii Wuchereria bancrofti

Parasites Ascaris lumbricoides Clonorchis sinensis Cryptosporidium parvum Echinococcus granulosus

Fungi Aspergillus spp. Candida spp. Cryptococcus neoformans

Mycoplasmas and Bacteria Brucella melitensis Campylobacter jejuni Escherichia coli Legionella spp. Leptospira spp. Moraxella catarrhalis Mycobacterium tuberculosis Mycoplasma pneumoniae Salmonella spp. Streptococcus pyogenes Yersinia spp.

pancreatitis (Box 52.1). A true causal relationship usually is not shown. Although not all of the following infectious agents have been shown to be associated with childhood pancreatitis, they must be considered as possible etiologic agents because adult patients with infectious pancreatitis have been described. Compared with previous decades, infectious agents are being encountered less as a cause of acute pancreatitis, most likely because of mumps vaccination.

Viral Infections Group B coxsackieviruses and mumps virus are the best documented causes of pancreatitis in children. Group B coxsackieviruses usually cause pancreatitis along with other clinical manifestations, including aseptic meningitis, mild diarrhea, rash, and myocarditis.25,67 They rarely cause death in young infants with myocarditis and pancreatitis.38 How commonly these enteroviruses cause pancreatic inflammation is unknown. Thirty-one percent of patients with aseptic meningitis during an epidemic of group B coxsackievirus infection had increased serum amylase concentrations.102 Numerous studies have shown coxsackievirus B–induced damage to pancreatic acinar cells in mouse models of infection, and it is believed that the pancreas is the primary replication site for these viruses.66,154 Coxsackievirus B strains have caused worsening bouts of pancreatic disease in children with chronic pancreatitis and the primary episode of pancreatitis in children later found to have the hereditary form of disease.53,139 Group A coxsackieviruses have only rarely been associated with pancreatitis in humans.5 Usually mumps pancreatitis occurs in the presence of parotitis; however, abdominal pain and vomiting may occur for days before the development of salivary swelling.166 Rarely mumps virus can cause pancreatitis without other common clinical manifestations.100,159 Because more than 80% of children with mumps parotitis have elevated serum amylase concentrations, ultrasonography and serum lipase concentrations should be obtained to aid in establishing the diagnosis.58 An estimated 15% of children with mumps virus infection have abdominal tenderness and vomiting suggestive of the diagnosis of pancreatitis. In only a single report has the pancreatitis been hemorrhagic and severe.44 Occasionally chronic or recurring pancreatitis develops after mumps infection.170 Researchers previously thought that acute pancreatitis occurred in cases of viral hepatitis only when fulminant liver disease developed.

CHAPTER 52  Pancreatitis Increasingly children with mild hepatitis A infection and pancreatitis are being described.42 In addition, a 16-year-old with acute hepatitis A infection died of severe pancreatitis with multiple-organ failure.75 Individuals with acute hepatitis and pancreatitis have also been found to have hepatitis E viral infection.149 Hepatitis B viral antigens have been detected in the pancreatic glandular cells of patients with severe acute hemorrhagic pancreatitis.137 The role of hepatitis B virus in the pathogenesis of pancreatic inflammation in these patients is unknown; however, a young adult has developed three episodes of acute pancreatitis during acute exacerbations of chronic hepatitis B infection that resolved after lamivudine therapy.32 It has been suggested that edema of the ampulla of Vater caused by biliary sludge formed during hepatitis viral infection leads to outflow obstruction of pancreatic fluid and the development of pancreatitis.68 Human herpesviruses are uncommon causes of childhood pancreatitis in immunocompetent patients. Occasionally pancreatitis develops in children and adolescents with infectious mononucleosis.76 Acute pancreatitis and occasionally pseudocyst formation also have been reported in previously healthy individuals with varicella infection.48,80,153 In addition, previously healthy adults have developed pancreatitis during primary cytomegalovirus and herpes simplex virus infections.74,81,111 Interstitial pancreatitis occurs relatively commonly in children with congenital rubella syndrome.97 In addition, severe pancreatitis has been identified in immunocompetent patients with mild and fatal measles virus infection.50,160 An adolescent has been described with measles encephalitis and pancreatitis that responded to corticosteroids.145 Influenza A viruses have been shown to be capable of infecting human pancreatic cells, and H1N1 influenza A has caused pancreatitis in a previously healthy adult.18,26 Rarely other viruses including adenovirus, West Nile virus, rotavirus, and dengue virus have been associated with the development of pancreatitis in previously healthy adults and children.21,51,78,87,136 Viral pancreatitis also occurs in immunocompromised patients. Cytomegalovirus has been identified in pancreatic specimens obtained during autopsies of patients who had AIDS, transplant recipients, individuals taking corticosteroids for autoimmune diseases, and cancer chemotherapy patients.70,147 The symptoms of pancreatitis have resolved in a few patients with AIDS treated with ganciclovir or foscarnet.35 Varicella zoster and herpes simplex viruses have also caused pancreatitis and death in patients with various immunodeficient conditions.45,138 Adenovirus has caused hemorrhagic pancreatitis and death in children with bone marrow transplants, whereas an infant with disseminated adenoviral infection and pancreatitis survived with cidofovir therapy.15,28,107 Researchers have suggested that stool cultures for adenoviruses should be obtained when posttransplant patients develop pancreatitis. A disseminated parainfluenza virus infection in an infant with severe combined immunodeficiency was associated temporally with the development of pancreatitis; however, no attempt was made to culture the virus from postmortem pancreatic tissue.49 Whether HIV directly causes pancreatitis is unclear. Laboratorydiagnosed episodes of pancreatitis in adults and children with AIDS do occur, but whether the pancreatic inflammation is caused by HIV or an unrecognized opportunistic pathogen is unknown.171 HIV-infected children frequently have elevated amylase and lipase levels with no correlation to antiviral therapy.27 Increasing numbers of adults with primary manifestations of HIV infection have presented with acute pancreatitis, suggesting a role of HIV in the pathogenesis of the disease.157

Parasite Infestations and Infections Ascaris lumbricoides can migrate in the intestines to the ampulla of Vater and subsequently to the pancreatic duct or common bile duct. Obstruction of the biliary or pancreatic duct can cause acute pancreatitis.2,12 Ascariasis is diagnosed when adult roundworms are identified in the duodenum by radiographs of the upper gastrointestinal tract (Fig. 52.1) or more commonly by ultrasonography or ERCP. Often a history of seeing worms in the feces can be elicited. Other roundworms including hookworms and Strongyloides stercoralis can cause obstruction and acute pancreatitis.89,156 The flukes Clonorchis sinensis and Fasciola hepatica and the cestode Taenia saginata similarly can migrate to the pancreatic and biliary drainage systems and cause pancreatitis.73,84,140

505

FIG. 52.1  An ascaris close to the ampulla of Vater, with the body and tail lying in the second and third parts of the duodenum. The patient was a 9-year-old girl with acute pancreatitis.

Rarely hepatic hydatid cysts caused by Echinococcus can obstruct biliary drainage and cause pancreatic inflammation.71 Wuchereria bancrofti occasionally has been found to cause chronic pancreatitis.69 Parasitic infestations should be considered as a cause of pancreatitis, particularly in immigrant children and patients who have traveled to developing nations. The protozoan Cryptosporidium parvum has been identified in the bile of an AIDS patient with elevated serum amylase levels and right upper quadrant abdominal pain.54 ERCP demonstrated biliary and pancreatic ductal disease, and no other opportunistic pathogens were isolated. Cryptosporidia also have been observed in the interlobular pancreatic ducts of experimentally infected immunocompromised mice.158 Whether cryptosporidial infection causes pancreatitis in immunocompetent patients is unknown; however, a previously healthy adolescent developed pancreatitis after having cryptosporidial diarrhea.62 Toxoplasma gondii cysts have been found in the postmortem pancreatic tissue of patients with AIDS.4,65 Rarely pancreatitis occurs during acute episodes of malaria.150 Other systemic manifestations of malaria that often are present include high fever, hepatitis, intestinal malabsorption, encephalitis, and pulmonary insufficiency.

Mycoplasmal and Bacterial Infections In older children and adults, moderately severe symptoms of pancreatitis have occurred just before or during the course of atypical pneumonia.6,64 Most patients have had cold agglutinins in their sera, and all have had significant changes in Mycoplasma pneumoniae antibody titer. Some controversy has ensued over whether M. pneumoniae can cause acute pancreatitis without evidence of pneumonia. Although complementfixing IgM antibodies against M. pneumoniae often increase significantly during the course of acute pancreatitis, researchers have argued that pancreatic cellular antigenic components similar to Mycoplasma lipid antigens are exposed during the disease process and that the antibodies elicited cross-react in Mycoplasma serologic assays.83 Rarely Mycoplasma has caused severe necrotizing pancreatitis.101 Along with M. pneumoniae infection, legionellosis must be considered when acute pancreatitis develops along with pneumonia.94,168 Miliary tuberculosis also can cause symptoms of pancreatitis.125 Pancreatitis

506

SECTION 8  Other Intraabdominal Infections

may occasionally be the only manifestation of tuberculosis and is usually diagnosed by fine-needle aspiration of the pancreas.60,104 Common pyogenic bacteria usually do not cause acute pancreatitis. Secondary invasion of inflamed pancreatic tissue does occur. Some evidence exists that circulating endotoxin from Escherichia coli can cause extrahepatic cholestasis and pancreatitis.39 Acute pancreatitis also has been seen in children with hemolytic-uremic syndrome.122,129 Pancreatitis can occur during acute episodes of enteritis. Salmonella typhimurium, Salmonella typhosa, Campylobacter jejuni, Yersinia enterocolitica, and Yersinia pseudotuberculosis all have been reported to cause clinically evident and laboratory-confirmed cases of pancreatitis.10,37,93,131 There have been single reports of Moraxella catarrhalis and Streptococcus pyogenes causing severe pancreatitis in young children.1,110 Pancreatitis has been reported in children with leptospirosis.109,141 Brucella melitensis also has been added to the list of uncommon causes of acute pancreatitis.115 Helicobacter pylori has been suggested to influence the clinical course of pancreatitis in humans, but data are still lacking to imply a role in pancreatic pathology.90

Fungal Infections Fungal infections have not been reported to cause acute pancreatitis in immunocompetent patients. Aspergillus has caused fatal hemorrhagic pancreatitis, however, in an adult patient with cancer who was undergoing chemotherapy.56 Candida spp. and Cryptococcus neoformans have been isolated from the pancreatic tissue of patients with AIDS, but whether they cause clinical symptoms of pancreatitis is unknown.171

PATHOGENESIS When trypsinogen is activated prematurely to trypsin within the pancreatic acinar cells, autodigestion occurs within the pancreas, causing edema. The microcirculation may be compromised, leading to ischemia, hemorrhage, or necrosis. An inflammatory response develops, which may be mild, as occurs in episodes of infectious pancreatitis, or may be more severe with hemorrhagic necrosis. Major mediators of an intense immune response include chemoattractant chemokines and their upregulated receptors; cytokines including tumor necrosis factor, interleukin (IL)-1, IL-6, IL-8, IL-10, and IL-33; and platelet-activating factor.55,88,116,132,134 Mast cells may also play an active role in the proinflammatory process.112 If an imbalance of the proinflammatory response occurs within the pancreas, a systemic inflammatory response including shock may occur, leading to high morbidity and mortality. Also sepsis may occur because of extensive necrotic tissue within the pancreas and translocation of microorganisms from the intestines.

TREATMENT Despite increasing recognition of cases of childhood pancreatitis, no major pharmacologic advances have been made in the treatment of the disease since the mid-1970s. Animal data have shown that medications such as glucagon, aprotinin, 5-fluorouracil, somatostatin, probiotics, and vitamin-based antioxidants may be useful in the treatment of pancreatitis, but human benefit is lacking.13,40,135 Clinical trials in adults and children using high-dose octreotide or gabexate mesilate have shown no or only modest benefit.77,164 The continuing main objectives of treatment are to relieve abdominal pain and treat aggressively systemic manifestations, such as shock, electrolyte abnormalities, and anemia. Meperidine continues to be the medication most commonly used for controlling pain. Meta-analyses in adults and series of pediatric patients have shown that feeding with a low-fat elemental diet decreases the complication rate of patients with acute pancreatitis and now is considered the treatment of choice over total parenteral nutrition.8,24,144 Intravenous fluids and colloids are used during the acute episode to maintain intravascular volume. During the entire course of acute pancreatitis, the hematologic and biochemical parameters of the child must be monitored closely. If the episode of pancreatitis is drug induced, use of the medication should be curtailed immediately. Often the symptoms recur if the medication is restarted. Pancreatitis caused by M. pneumoniae or that involve bacteria should be treated with proper antimicrobial agents.

Obstructions to pancreatic flow (e.g., gallstones, roundworms, congenital abnormalities) may have to be excised or altered either by surgery or endoscopy.3,19,72 Overall the mortality rate of acute pancreatitis in children today is 5%, with a mean duration of hospital stay at 13 days.57

COMPLICATIONS During the acute episode of pancreatitis, the systemic inflammatory response syndrome may develop, leading to renal, hematologic, central nervous system, pulmonary, and cardiovascular complications. In 12% of children with pancreatitis, an inflammatory mass develops in the first weeks after the onset of illness; however, these masses more commonly occur after trauma.165 Continued or increasing abdominal pain, nausea, or vomiting often accompanies the development of a phlegmon, abscess, or pseudocyst. An inflammatory phlegmon usually develops into a thin-walled pseudocyst of the lesser sac but may become secondarily infected and induce the formation of an abscess. Patients in whom an inflammatory mass develops must be monitored closely with frequent physical examinations and serial CT studies. In children with pseudocysts, acute abdominal pain accompanied by hypotension often signifies bleeding into the pseudocyst or rupture of the pseudocyst into the peritoneum. Slowly leaking pseudocysts may cause pancreatic ascites. Pseudocysts should be treated conservatively but have to be resected surgically, drained externally, or drained by endoscopy when complications occur.9 Approximately 77% of pseudocysts in children resolve spontaneously and require no surgical intervention.126 The development of fever and leukocytosis during the course of pancreatitis should suggest an infected pseudocyst, pancreatic abscess, or sepsis. In adults, infectious complications account for 80% of deaths associated with acute pancreatitis.22 Isolates from pancreatic abscesses and necrotic pancreatic tissue have yielded intestinal flora, including anaerobes, in more than 90% of cases, but Candida spp. are being isolated more frequently in many medical centers.41,79,155 Candida skin colonization appears to best predict subsequent pancreatic tissue infection in critically ill patients.59 Rarely Streptococcus pneumoniae can be isolated from infected pancreatic tissues of adults with chronic pancreatitis.151 Carbapenems, such as imipenem and meropenem, are used commonly to treat adult patients with suppurative complications of pancreatitis because these antibiotics penetrate well into pancreatic tissues and have activity against intestinal flora. Performing percutaneous catheter drainage under CT guidance may reduce the mortality rate associated with treating pancreatic abscesses.14 Rarely fistulas from pseudocysts or abscesses to other abdominal organs may develop.63 The role of prophylactic antibiotics in preventing the suppurative complications of acute pancreatitis remains controversial despite three decades of debate. Most recent meta-analyses on the subject conclude that prophylactic antibiotics do not prevent pancreatic necrotic tissue from being infected and do not prevent death, although a poorly powered 2010 Cochrane review suggests that imipenem may reduce the number of pancreatic infections.106,162,169 Infections, when they do occur after the administration of prophylactic antimicrobial agents, often are caused by multiresistant bacteria or by fungi. Osteolytic lesions resembling osteomyelitis may develop weeks to months after an acute episode of pancreatitis.105 Elevated systemic levels of lipase activity possibly may cause intramedullary fat necrosis in the bone. Usually the lesions are asymptomatic and resolve spontaneously without therapy. NEW REFERENCES SINCE THE SEVENTH EDITION 3. Agarwal J, Nageshwar RD, Talukdar R, et al. ERCP in the management of pancreatic diseases in children. Gastrointest Endosc. 2014;79:271-278. 5. Akuzawa N, Harada N, Hatori T, et al. Myocarditis, hepatitis, and pancreatitis in a patient with coxsackievirus A4 infection: a case report. Virol J. 2014;11:3. 20. Boskovic A, Pasic S, Soldatovic I, et al. The role of D-dimer in prediction of the course and outcome in pediatric acute pancreatitis. Pancreatology. 2014;14:330-334. 26. Capua I, Mercalli A, Pizzuto MS, et al. Influenza A viruses grow in human pancreatic cells and cause pancreatitis and diabetes in an animal model. J Virol. 2013;87:597-610. 30. Chang YJ, Chao HC, Kong MS, et al. Acute pancreatitis in children. Acta Paediatr. 2011;100:740-744.

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The full reference list for this chapter is available at ExpertConsult.com.

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Influenza A viruses grow in human pancreatic cells and cause pancreatitis and diabetes in an animal model. J Virol. 2013;87:597-610. 27. Carroccio A, Fontana M, Spagnuolo MI, et al. Serum pancreatic enzymes in human immunodeficiency virus–infected children. Scand J Gastroenterol. 1998;33:998-1001. 28. Carter BA, Karpen SJ, Quiros-Tejeira RE, et al. Intravenous cidofovir therapy for disseminated adenovirus in a pediatric liver transplant recipient. Pediatr Infect Dis J. 2002;74:1050-1052. 29. Cecchi E, Forte P, Cini E, et al. Pancreatitis induced by pegylated interferon alfa-2b in a patient affected by chronic hepatitis C. Emerg Med Australas. 2004;16:473-475. 30. Chang YJ, Chao HC, Kong MS, et al. Acute pancreatitis in children. Acta Paediatr. 2011;100:740-744. 31. Chavhan GB, Babyn PS, Manson D, et al. Pediatric MR cholangiopancreatography: principles, technique, and clinical applications. Radio Graphics. 2008;28:1951-1962. 32. Chen C, Changchien C, Lu S, et al. Lamivudine treatment for recurrent pancreatitis associated with reactivation of chronic B hepatitis. Dig Dis Sci. 2002;47:564-567. 33. Cheung O, Chopra K, Yu T, et al. Gatifloxacin-induced hepatotoxicity and acute pancreatitis. Ann Intern Med. 2004;140:73-74. 34. Coffey MJ, Nightingale S, Ooi CY. Diagnosing acute pancreatitis in children: what is the diagnostic yield and concordance for serum pancreatic enzymes and imaging within 96 h of presentation? Pancreatology. 2014;14:251-256.

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35. Colebunders R, Van den Abbeele K, Fleerackers Y, et al. Two AIDS patients with life-threatening pancreatitis successfully treated, one with ganciclovir, the other with foscarnet. Acta Clin Belg. 1994;49:229-232. 36. Corp CC, Ghishan FK. The sulfone syndrome complicated by pancreatitis and pleural effusion in an adolescent receiving dapsone for treatment of acne vulgaris. J Pediatr Gastroenterol Nutr. 1998;26:103-105. 37. de Bois MH, Schoemaker MC, van der Werf SD, et al. Pancreatitis associated with Campylobacter jejuni infections: diagnosis by ultrasonography. BMJ. 1989;298:1004. 38. Dettmeyer RB, Padosch SA, Madea B. Lethal enterovirus-induced myocarditis and pancreatitis in a 4-month-old boy. Forensic Sci Int. 2006;156:51-54. 39. Dev G, Sikka M, Sehgal S, et al. Escherichia coli infection producing pancreatitis and extrahepatic cholestasis. Indian Pediatr. 1987;24:249-253. 40. De Waele JJ, Hoste E. Current pharmacotherapeutic recommendations for acute pancreatitis. Expert Opin Pharmacother. 2006;7:1017-1025. 41. De Waele JJ, Vogelaers D, Colardyn F. Fungal infections in patients with severe acute pancreatitis and the use of prophylactic therapy. Clin Infect Dis. 2003;37:208-213. 42. El-Sayed R, El-Karaksy H. Acute pancreatitis complicating acute hepatitis A virus infection. Arab J Gastroenterol. 2012;13:184-185. 43. Fabre A, Petit P, Gaudart J, et al. Severity scores in children with acute pancreatitis. J Pediatr Gastroenterol Nutr. 2012;55:266-267. 44. Feldstein JD, Johnson FR, Kallick CA, et al. Acute hemorrhagic pancreatitis and pseudocyst due to mumps. Ann Surg. 1974;180:85-88. 45. Fernández RA, Varona TL, Jaquotot JMK, et al. Pancreatitis aguda asociada a infección por virus de la varicela-zoster en un paciente con sindrome de immunodeficiencia adquirida. Med Clin (Barc). 1992;98:339-341. 46. Foisy MM, Slayter KL, Hewitt RG, et al. Pancreatitis during intravenous pentamidine therapy in an AIDS patient with prior exposure to didanosine. Ann Pharmacother. 1994;28:1025-1028. 47. Foster C, Lyall H. HIV and mitochondrial toxicity in children. J Antimicrobial Chemother. 2008;61:8-12. 48. Franco J, Fernandes R, Oliveira M, et al. Acute pancreatitis associated with varicella infection in an immunocompetent child. J Paediatr Child Health. 2009;45:547-548. 49. Frank JA, Warren RW, Tucker JA, et al. Disseminated parainfluenza infection in a child with severe combined immunodeficiency. Am J Dis Child. 1983;137:1172-1174. 50. Fusilli G, De Mitri B. Acute pancreatitis associated with the measles virus case report and review of literature data. Pancreas. 2009;38:478-480. 51. Giordano S, Serra G, Dones P, et al. Acute pancreatitis in children and rotavirus infection. Description of a case and minireview. New Microbiol. 2013;36:97-101. 52. Gonzalez Carro P, Perez Roldan F, Legaz Huidobro ML, et al. Acute pancreatitis and modified-release clarithromycin. Ann Pharmacother. 2004;38:508-509. 53. Groeneweg M, Poley JW, Dansen M, et al. 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Prediction of invasive candida infection in critically ill patients with severe acute pancreatitis. Crit Care. 2013;17:R49. 60. Hari S, Seith A, Srivastava DN, et al. Isolated tuberculosis of the pancreas diagnosed with needle aspiration: a case report and review of the literature. Trop Gastroenterol. 2005;26:141-143. 61. Hart CC. Aerosolized pentamidine and pancreatitis. Ann Intern Med. 1989;111:691. 62. Hawkins SP, Thomas RP, Teasdale C. Acute pancreatitis: a new finding in Cryptosporidium enteritis. BMJ. 1987;294:483-484. 63. Henderson JM, MacDonald JAE. Fistula formation complicating pancreatic abscess. Br J Surg. 1976;63:233-234. 64. Herbaut C, Tielemans C, Burette A, et al. Mycoplasma pneumoniae infection and acute pancreatitis. Acta Clin Belg. 1983;38:186-188. 65. Hofman P, Michiels J-F, Mondain V, et al. Pancréatite aiguë toxoplasmique. Gastroenterol Clin Biol. 1994;18:895-897. 66. Huber S, Ramsingh AI. Coxsackievirus-induced pancreatitis. Viral Immunol. 2004;17:358-369. 67. 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SECTION 8  Other Intraabdominal Infections

70. Joe L, Ansher AF, Gordin FM. Severe pancreatitis in an AIDS patient in association with cytomegalovirus infection. South Med J. 1989;82:1444-1445. 71. Karakas E, Tuna Y, Basar O, et al. Primary pancreatic hydatid disease associated with acute pancreatitis. Hepatobiliary Pancreat Dis Int. 2010;9: 441-442. 72. Kawahara H, Takahashi T, Okada A. Characteristics of duodenal duplications causing pancreatitis in children and adolescents: a case report and review of the literature. J Pediatr Gastroenterol Nutr. 2002;35:372-376. 73. Kaya M, Bestas R, Cetin S. Clinical presentation and management of Fasciola hepatica infection: single-center experience. World J Gastroenterol. 2011;17:4899-4904. 74. Keidar S, Porath EB, Naftali V, et al. Acute pancreatitis associated with rising cytomegalovirus titer. Isr J Med Sci. 1987;23:296-297. 75. Khanna S, Vij JC. Severe acute pancreatitis due to hepatitis A virus infection in a patient of acute viral hepatitis. Trop Gastroenterol. 2003;24:25-26. 76. Khawcharoenporn T, Lau WKK, Chokrungvaranon N. Epstein-Barr virus infection with acute pancreatitis. Int J Infect Dis. 2008;12:227-229. 77. Kim SC, Yang HR. Clinical efficacy of gabexate mesilate for acute pancreatitis in children. Eur J Pediatr. 2013;172:1483-1490. 78. Kir S, Aydin Y, Kocaman O, et al. Acute pancreatitis after severe ophthalmic adenoviral infection. Acta Gastroenterol Belg. 2011;74:361-362. 79. Kochhar R, Noor MT, Wig J. Fungal infections in severe acute pancreatitis. J Gastroenterol Hepatol. 2011;26:952-959. 80. Kole AK, Roy R, Kole DC. An observational study of complications in chickenpox with special reference to unusual complications in an apex infectious disease hospital, Kolkata, India. J Postgrad Med. 2013;59:93-97. 81. Konstantinou GN, Liatsos CN, Patelaros EG, et al. Acute pancreatitis associated with herpes simplex virus infection: report of a case and review of the literature. Eur J Gastroenterol Hepatol. 2009;21:114-116. 82. Lautz TB, Chin AC, Radhakrishnan J. Acute pancreatitis in children: spectrum of disease and predictors of severity. J Pediatr Surg. 2011;46:1144-1149. 83. Leinikki PO, Panzar P, Tykka H. Immunoglobulin M antibody response against Mycoplasma pneumoniae lipid antigen in patients with acute pancreatitis. J Clin Microbiol. 1978;8:113-118. 84. Liu Y-M, Bair M-J, Chang W-H, et al. Acute pancreatitis caused by tapeworm in the biliary tract. Am J Trop Med Hyg. 2005;73:377-380. 85. Lowe ME. Pancreatitis in children. Curr Gastroenterol Rep. 2004;6:240-246. 86. Lowe ME, Greer JB. Pancreatitis in children and adolescents. Curr Gastroenterol Rep. 2008;10:128-135. 87. Majumdar R, Jana CK, Ghosh S, et al. Clinical spectrum of dengue fever in a tertiary care centre with particular reference to atypical presentation in the 2012 outbreak in Kolkata. J Indian Med Assoc. 2012;110:904-906. 88. Makhija R, Kingsnorth AN. Cytokine storm in acute pancreatitis. J Hepatobiliary Pancreat Surg. 2002;9:401-410. 89. Makker J, Balar B, Niazi M, et al. Strongyloidiasis: a case with acute pancreatitis and a literature review. World J Gastroenterol. 2015;21:3367-3375. 90. Manes G, Balzano A, Vaira D. Helicobacter pylori and pancreatic disease. J Pancreas. 2003;4:111-116. 91. Maranan MC, Gerber SI, Miller GG. Gallstone pancreatitis caused by ceftriaxone. Pediatr Infect Dis J. 1998;17:662-663. 92. Marchi A, Caimmi S, Caimmi D, et al. Recurrent pleural effusion as an unusual presentation of acute pancreatitis in children. Pancreas. 2011;40:321-323. 93. Martinez-Roig A, Bonet-Alcaina M, Casellas-Montagut M, et al. Pancreatitis in typhoid fever relapse. Pediatr Infect Dis J. 2008;28:74. 94. Michel O, Naeije N, Csoma M, et al. Acute pancreatitis in legionnaires’ disease. Eur J Respir Dis. 1985;66:62-64. 95. Miller TL, Winter HS, Luginbuhl LM, et al. Pancreatitis in pediatric human immunodeficiency virus infection. J Pediatr. 1992;120:223-227. 96. Mofidi R, Suttie SA, Patil PV, et al. The value of procalcitonin at predicting the severity of acute pancreatitis and development of infected pancreatic necrosis: systematic review. Surgery. 2009;146:72-81. 97. Monif GRG. Rubella virus and the pancreas. Med Chir Dig. 1974;3:195-197. 98. Moreno A, Quereda C, Moreno L, et al. High rate of didanosine-related mitochondrial toxicity in HIV/HCV-coinfected patients receiving ribavirin. Antiviral Ther. 2004;9:133-138. 99. Nachman SA, Chernoff M, Gona P, et al. Incidence of noninfectious conditions in perinatally HIV-infected children and adolescents in the HAART era. Arch Pediatr Adolesc Med. 2009;163:164-171. 100. Naficy K, Nategh R, Ghadimi H. Mumps pancreatitis without parotitis. BMJ. 1973;1:529-533. 101. Nakagawa M, Ogino H, Shimohira M, et al. Continuous regional arterial infusion therapy for acute necrotizing pancreatitis due to Mycoplasma pneumoniae infection in a child. Cardiovasc Intervent Radiol. 2009;32:581-584. 102. Nakao T, Nitta T, Miura R, et al. Clinical and epidemiological studies on an outbreak of aseptic meningitis caused by Coxsackie B5 and A9 viruses in Aomori in 1961. Tohoku J Exp Med. 1964;83:94-102. 103. Nelis GF. Nitrofurantoin-induced pancreatitis: report of a case. Gastroenterology. 1983;84:1032-1034.

104. Netherland NA, Chen VK, Eloubeidi MA. Intra-abdominal tuberculosis presenting with acute pancreatitis. Digest Dis Sci. 2006;51:247-251. 105. Neuer FS, Roberts FF, McCarthy V. Osteolytic lesions following traumatic pancreatitis. Am J Dis Child. 1977;131:738-740. 106. Nicholson LJ. Acute pancreatitis: should we use antibiotics? Curr Gastroenterol Rep. 2011;13:336-343. 107. Niemann TH, Trigg ME, Winick N, et al. Disseminated adenoviral infection presenting as acute pancreatitis. Hum Pathol. 1993;24:1145-1148. 108. Nigwekar SU, Casey KJ. Metronidazole-induced pancreatitis: a case report and review of literature. J Pancreas. 2004;5:516-519. 109. O’Brien MM, Vincent JM, Person DA, et al. Leptospirosis and pancreatitis: a report of ten cases. Pediatr Infect Dis J. 1998;17:436-438. 110. Ohkusu K, Nakamura A, Horie H, et al. Fatal sepsis associated with acute pancreatitis caused by Moraxella catarrhalis in a child. Pediatr Infect Dis J. 2001;20:914-915. 111. Oku T, Maeda M, Waga E, et al. Cytomegalovirus cholangitis and pancreatitis in an immunocompetent patient. J Gastroenterol. 2005;40:987-992. 112. Ouziel R, Gustot T, Moreno C, et al. The ST2 pathway is involved in acute pancreatitis: a translational study in humans and mice. Am J Pathol. 2012;180(6):2330-2339. 113. Palmer M, Chersich M, Moultrie H, et al. Frequency of stavudine substitution due to toxicity in children receiving antiretroviral treatment in sub-Saharan Africa. AIDS. 2013;27:781-785. 114. Pant C, Deshpande A, Olyaee M, et al. Epidemiology of acute pancreatitis in hospitalized children in the United States from 2000–2009. PLoS ONE. 2014;9:e95552. 115. Papaioannides D, Korantzopoulos P, Sinapidis D, et al. Acute pancreatitis associated with brucellosis. J Pancreas. 2006;7:62-65. 116. Park J, Chang JH, Park SH, et al. Interleukin-6 is associated with obesity, central fat distribution, and disease severity in patients with acute pancreatitis. Pancreatology. 2015;15:59-63. 117. Passier JL, van Puijenbroek EP, Jonkers GJ, et al. Pancreatitis associated with the use of itraconazole. Neth J Med. 2010;68:285-289. 118. Perry W, Jenkins MV, Stamp TCB. Lysosomal enzymes and pancreatitis during rifampicin therapy. Lancet. 1979;1:492. 119. Prot-Labarthe S, Youdaren R, Benkerrou M, et al. Pediatric acute pancreatitis related to tigecycline. Pediatr Infect Dis J. 2010;29:890-891. 120. Raizner A, Phatak UP, Baker K, et al. Acute necrotizing pancreatitis in children. J Pediatr. 2013;162:788-792. 121. Renkes P, Petitpain N, Cosserat F, et al. Can roxithromycin and betamethasone induce acute pancreatitis? A case report. J Pancreas. 2003;4:184-186. 122. Robitaille P, Gonthier M, Grignon A, et al. Pancreatic injury in the hemolyticuremic syndrome. Pediatr Nephrol. 1997;11:631-632. 123. Rocca R, Castellino F, Daperno M, et al. Therapeutic ERCP in paediatric patients. Dig Liver Dis. 2005;37:357-362. 124. Rose PC, Hallbauer UM, Seddon JA, et al. 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Association of pancreas infection and yersiniosis. Acta Med Scand. 1979;205:255-256. 132. Sesti-Costa R, Silva GK, Proenca-Modena JL, et al. The IL-33/ST2 pathway controls coxsackievirus B5-induced experimental pancreatitis. J Immunol. 2013;191:283-292. 133. Shahian M, Alborzi A. Effect of meglumine antimonials on the pancreas during treatment of visceral leishmaniasis in children. Med Sci Monit. 2009;15:CR290-CR293. 134. Shanmugam MK, Bhatia M. The role of pro-inflammatory molecules and pharmacological agents in acute pancreatitis and sepsis. Inflamm Allergy Drug Targets. 2010;9:20-31. 135. Sharma B, Srivastava S, Singh N, et al. Role of probiotics on gut permeability and endotoxemia in patients with acute pancreatitis. J Clin Gastroenterol. 2011;45:442-448. 136. Sharma V, Sharma A, Aggarwal A, et al. Acute pancreatitis in a patient with vivax malaria. JOP. 2012;10:215-216. 137. Shimoda T, Shikata T, Karasawa T, et al. Light microscopic localization of hepatitis B virus antigens in the human pancreas: possibility of multiplication of hepatitis B virus in the human pancreas. Gastroenterology. 1981;81:998-1005.

CHAPTER 52  Pancreatitis 138. Shintaku M, Umehara Y, Iwaisako K, et al. Herpes simplex pancreatitis. Arch Pathol Lab Med. 2003;127:231-234. 139. Shirobokov VP, Zhurba TB, Zemlyansky VV. Properties of the Coxsackie viruses isolated from pancreatic tissue of patients with chronic pancreatitis. Mikrobiol Z. 1988;50:78-81. 140. Shugar RA, Ryan JJ. Clonorchis sinensis and pancreatitis. Am J Gastroenterol. 1975;65:400-403. 141. Spichler A, Spichler E, Moock M, et al. Acute pancreatitis in fatal anicteric leptospirosis. Am J Med Hyg. 2007;76:886-887. 142. Stuecklin-Utsch A, Hasan C, Bode U, et al. Pancreatic toxicity after liposomal amphotericin B. Mycoses. 2002;45:170-173. 143. Sung HY, Kim JI, Lee HJ, et al. Acute pancreatitis secondary to ciprofloxacin therapy in patients with infectious colitis. Gut Liver. 2014;8:265-270. 144. Szabo FK, Fei L, Cruz LA, et al. Early enteral nutrition and aggressive fluid resuscitation are associated with improved clinical outcomes in acute pancreatitis. J Pediatr. 2015;167:397-402. 145. Takebayashi K, Aso Y, Wakabayashi S, et al. Measles encephalitis and acute pancreatitis in a young adult. Am J Med Sci. 2004;327:299-303. 146. Tenenbein MS, Tenenbein M. Acute pancreatitis due to erythromycin overdose. Pediatr Emerg Care. 2005;21:675-676. 147. Terada T. Cytomegalovirus-associated severe fatal necrotizing pancreatitis in a patient with interstitial pneumonitis treated with steroids. J Pancreas. 2011;12:158-161. 148. Thai TC, Riherd DM, Rust KR. MRI manifestations of pancreatic disease, especially pancreatitis, in the pediatric population. AJR Am J Roentgenol. 2013;201:W877-W892. 149. Thapa R, Biswas B, Mallick D, et al. Acute pancreatitis–complicating hepatitis E virus infection in a 7-year-old boy with glucose-6-phosphate dehydrogenase deficiency. Clin Pediatr. 2009;48:199-201. 150. Thapa R, Mallick D, Biswas B. Childhood Plasmodium falciparum malaria complicated by acute pancreatitis. Trop Doc. 2010;40:184-185. 151. Thege MK, Pulay I, Balla E, et al. Streptococcus pneumoniae as an etiologic agent in infectious complications of pancreatic disease. Microbial Drug Resistance. 2002;8:73-76. 152. Torosis J, Vender R. Tetracycline-induced pancreatitis. J Clin Gastroenterol. 1987;9:580-581. 153. Torre JAC, Martin JJD, Garcia CB, et al. Varicella infection as a cause of acute pancreatitis in an immunocompetent child. Pediatr Infect Dis J. 2000;19:1218-1219.

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154. Tracy S, Gauntt C. Group B coxsackievirus virulence. Curr Top Microbiol Immunol. 2008;323:49-63. 155. Trikudanathan G, Navaneethan U, Vege SS. Intra-abdominal fungal infections complicating acute pancreatitis: a review. Am J Gastroenterol. 2011;106:1188-1192. 156. Tseng LM, Sun CK, Wang TL, et al. Hookworm infestation as unexpected cause of recurrent pancreatitis. Am J Emerg Med. 2014;32:1435.e3-1435.e4. 157. Tyner R, Turett G. Primary human immunodeficiency virus infection presenting as acute pancreatitis. South Med J. 2004;97:393-394. 158. Ungar BLP, Burris JA, Quinn CA, et al. New mouse models for chronic Cryptosporidium infection in immunodeficient hosts. Infect Immun. 1990;58:961-969. 159. Vanlioglu B, Chua TC. Presentation of mumps infection as acute pancreatitis without parotitis. Pancreas. 2011;40:167-168. 160. Vargas PA, Bernardi FDC, Alves VAF, et al. Uncommon histopathological findings in fatal measles infection: pancreatitis, sialoadenitis and thyroiditis. Histopathology. 2000;37:141-146. 161. Versleijen MWJ, Naber AHJ, Riksen NP, et al. Recurrent pancreatitis after trimethoprim-sulfamethoxazole rechallenge. Neth J Med. 2005;63:275-277. 162. Villatoro E, Mulla M, Larvin M. Antibiotic therapy for prophylaxis against infection of pancreatic necrosis in acute pancreatitis (review). Cochrane Database Syst Rev. 2010;(5):CD002941. 163. Wachira JK, Jensen CH, Rhone K. Doxycycline-induced pancreatitis: a rare finding. S D Med. 2013;66:227-229. 164. Wang R, Yang F, Wu H, et al. High-dose versus low-dose octreotide in the treatment of acute pancreatitis: a randomized controlled trial. Peptides. 2013;40:57-64. 165. Warner RL, Othersen HB, Smith CD. Traumatic pancreatitis and pseudocyst in children: current management. J Trauma. 1989;29:597-601. 166. Warren WR. Serum amylase and lipase in mumps. Am J Med Sci. 1955;230:161-168. 167. Weizman Z, Durie PR. Acute pancreatitis in childhood. J Pediatr. 1988;113:24-29. 168. Westblom TU, Hamory BH. Acute pancreatitis caused by Legionella pneumophila. South Med J. 1988;81:1200-1201. 169. Wittau M, Mayer B, Scheele J, et al. Systematic review and meta-analysis of antibiotic prophylaxis in severe acute pancreatitis. Scand J Gastroenterol. 2011;46:261-270. 170. Wood CB, Bradbrook RA, Blumgart LH. Chronic pancreatitis in childhood associated with mumps virus infection. Br J Clin Pract. 1974;28:67-69. 171. Zazzo JF, Pichon F, Regnier B. HIV and the pancreas. Lancet. 1987;2:1212-1213. 172. Zuger A, Wolf BZ, El-Sadr W, et al. Pentamidine-associated fatal acute pancreatitis. JAMA. 1986;256:2383-2385.

CHAPTER 53  Peritonitis and Intraabdominal Abscess

Peritonitis and Intraabdominal Abscess

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53 

Judith R. Campbell Intraabdominal infection can be a life-threatening condition that occurs spontaneously or as a result of intraabdominal disease, injury, or surgery. Given the compartmental anatomy and physiology of the abdominal cavity, intraabdominal infection frequently is categorized as peritonitis, intraperitoneal abscess, retroperitoneal abscess, and visceral abscess.3 In this chapter peritonitis and intraabdominal abscess are reviewed; liver abscess, appendicitis and pelvic abscess, and retroperitoneal abscess, are reviewed in Chapters 49, 51, and 54, respectively.

PERITONITIS Anatomy Knowledge of the anatomic relationships within the abdomen is important for understanding the source and routes of spread of infection. The peritoneal cavity extends from the undersurface of the diaphragm to the pelvis. In males it is a closed space, whereas in females the ends of the fallopian tubes penetrate into the peritoneal cavity. The transverse mesocolon and greater omentum separate the upper and lower peritoneal cavity. Peritoneal reflections divide the intraperitoneal space further into several compartments: the lesser sac, the paracolic gutters, and the subhepatic and subphrenic spaces (Fig. 53.1). The most dependent area of the peritoneal cavity is the pelvis. Exudate can extend to any of the recesses within the peritoneal cavity distant from the original source, however, and cause diffuse inflammation.3 When inflamed, the anterior

parietal peritoneum, which is supplied by somatic afferent nerves, gives the sensation of localized pain. Stimulation of the visceral peritoneum causes dull, poorly localized pain.

Pathogenesis Peritonitis is defined as inflammation of the serosal lining of the abdominal cavity or the peritoneum and may be caused by any chemical or infectious agent that irritates the peritoneal surfaces. Noninfectious peritonitis is caused by extravasation of irritants, such as gastric juice, bile, urine, blood, pancreatic secretions, or the contents of a ruptured cyst, into the peritoneal cavity. Although chemical peritonitis generally is aseptic, it may be an important antecedent event to the development of infectious peritonitis. After peritoneal contamination by bacteria has occurred, the first mechanism of host defense is lymphatic clearance. In experimental peritonitis, this clearance is so efficient that peritonitis and abscess formation occur only if adjuvant substances, such as hemoglobin or necrotic tissue, are present.24,25,48 In the first hours after bacterial contamination occurs, local resident macrophages are the predominant phagocytic cells. The macrophages then are cleared by the lymphatic system. After bacterial proliferation occurs, polymorphonuclear leukocytes become more numerous in the peritoneal cavity, and inflammation ensues. These peritoneal defense mechanisms also have adverse effects. Fibrin is deposited, which potentially entraps bacteria into a sequestered

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SECTION 8  Other Intraabdominal Infections Left suprahepatic subphrenic

Anterior suprahepatic right subphrenic

Left infrahepatic subhepatic Pericholecystic subhepatic Left subphrenic Posterolateral right subphrenic

Lesser sac

Morrison pouch Left paracolic Right paracolic

Pelvic

Left lower quadrant

Right lower quadrant appendiceal

Hepatic

Anterior suprahepatic subphrenic

Subphrenic Subphrenic Subhepatic

Lesser sac Left subhepatic

Subhepatic

Lesser sac

Morrison pouch Right paracolic Interloop Right lower quadrant appendiceal

Pelvic

LEFT

RIGHT

FIG. 53.1  Anterior and sagittal views of the peritoneal cavity. (From Altemeier WA, Culbertson WR, Fullen WD. Intra-abdominal sepsis. Adv Surg. 1971;5:281–3.)

environment. An increase in splanchnic blood flow causes exudation of fluid into the peritoneal space, further impairing host defenses by diluting important peritoneal opsonins.24,25 These host responses serve as a means of containing infection, but they also may contribute to the formation of abscesses. Infectious peritonitis is subdivided into primary and secondary peritonitis based on the pathophysiology of the infection. Peritonitis that is associated with peritoneal dialysis or the presence of a ventriculoperitoneal shunt is a unique form of peritonitis that also is reviewed in this chapter. The microbial causes of peritonitis vary with the underlying cause and are summarized in Table 53.1.

Primary Peritonitis Primary, or spontaneous, bacterial peritonitis is a rare infection defined as bacterial peritonitis in the absence of intraabdominal findings, such as intestinal perforation. The incidence of spontaneous peritonitis in children is unknown; however, in the early 20th century, 8% to 10% of abdominal emergencies requiring surgical intervention were due to spontaneous peritonitis.17,73 Freij and colleagues30 conducted a 22-year review of children with primary peritonitis in Dallas, Texas. Primary peritonitis was diagnosed in seven previously healthy children compared

with 1840 cases of appendicitis during the same period. Currently, 1% to 2% of abdominal emergencies requiring surgical intervention are due to primary peritonitis.39,42 Now that this condition frequently is recognized clinically with the assistance of computed tomography (CT), the diagnosis often is made without exploratory laparotomy. The peak incidence of spontaneous peritonitis in children occurs when they are 5 to 9 years of age. In children, the most common predisposing factor is nephrotic syndrome, but this form of peritonitis also occurs in children with postnecrotic cirrhosis.3,17,33,39,43,47,73,74 Spontaneous peritonitis rarely develops in previously healthy individuals without underlying conditions.34,49 The exact pathophysiologic mechanism for primary peritonitis is unknown; however, hematogenous inoculation is thought to be the most likely mechanism because the same organism frequently is recovered from cultures of blood and peritoneal fluid.17,33,39 Alternative mechanisms include peritoneal seeding via the lymphatics, transmural migration through edematous bowel, and ascending infection from the female genitourinary tract.33,39 In certain cases, impaired host defenses allow proliferation of bacteria that invade the peritoneal cavity, but a few children with primary peritonitis have no apparent impaired defense. Ascitic fluid from patients with nephrotic syndrome or cirrhosis contains

CHAPTER 53  Peritonitis and Intraabdominal Abscess

TABLE 53.1  Most Commonly Identified Etiologic Agents Primary Peritonitis

Secondary Peritonitis

Escherichia coli (25–40%) Haemophilus influenzae type b Klebsiella Mycobacterium bovis Mycobacterium tuberculosis Neisseria meningitidis Other enteric gram-negative bacilli Other streptococci (α-hemolytic and β-hemolytic) Staphylococcus aureus (2–4%) Streptococcus pneumoniae (30–50%)

Aerobes Enterobacter Enterococcus E. coli Klebsiella Pseudomonas aeruginosa Proteus mirabilis Serratia Anaerobes Bacteroides fragilis group Peptostreptococcus Clostridium spp. Prevotella spp. Fusobacterium spp. Eubacterium spp.

CAPD-Associated Peritonitis Candida Coagulase-negative staphylococci Enteric gram-negative bacilli Mycobacterium Other fungi Pseudomonas S. aureus Stenotrophomonas

VP Shunt–Associated Peritonitis Coagulase-negative staphylococci Enterobacter E. coli Klebsiella Pseudomonas S. aureus

CAPD, Continuous ambulatory peritoneal dialysis; VP, ventriculoperitoneal.

lower levels of complement and immunoglobulin than does peritoneal fluid from a healthy host.17,73,81 Deficiency of these important opsonins diminishes the natural clearance of organisms from the peritoneal cavity. Proliferation of organisms triggers the influx of phagocytes, release of inflammatory mediators, and localized or diffuse peritoneal irritation that gives rise to symptoms of abdominal pain and fever. Since the preantibiotic era, researchers have recognized that primary peritonitis frequently is caused by Streptococcus pneumoniae,33 Streptococcus pyogenes,34 and Staphylococcus aureus.17 Rarely primary peritonitis in prepubescent girls is caused by extension of upper genital tract S. pneumoniae infection.39,68 Since the 1960s, the bacteriology of primary peritonitis has shifted to include an increased proportion of infections caused by gram-negative enteric organisms, such as Escherichia coli and Klebsiella spp.17,39,43,74,81 In some instances, primary E. coli peritonitis may occur concurrently with bacteremic urinary tract infection. Tuberculous peritonitis may be caused by Mycobacterium tuberculosis or Mycobacterium bovis. It may occur as a complication of primary mycobacteremia or be caused by reactivation of latent intraabdominal infection within lymphoid tissue but only rarely does it seem to occur as a function of the ingestion of swallowed organisms from a pulmonary primary focus.36,37,67,78 Peritoneal infection with M. bovis, which is clinically similar to M. tuberculosis peritonitis, is acquired from unpasteurized dairy products and has been reported in children living along the border between the United States and Mexico. These organisms may cause peritonitis from either mycobacteremia or erosion of organisms through the mesenteric lymph nodes or bowel wall into the peritoneal cavity.20 Salmonella spp. rarely cause primary peritonitis and have been reported primarily in patients with underlying conditions.49

Secondary Peritonitis Secondary peritonitis, the most common form of peritonitis, arises as a complication of intraabdominal injury or disease when microorganisms, secretions, and the particulate material of an intraabdominal organ enter the peritoneal cavity. Congenital or acquired conditions that result in ischemia, inflammation, or perforation of abdominal viscera may

509

be complicated by secondary peritonitis.23,48,70 In premature infants, necrotizing enterocolitis is the most common cause of secondary peritonitis.53 In infants and children, appendicitis is the most common cause; however, it also may occur with volvulus, intussusception, incarcerated hernia, or rupture of a Meckel diverticulum.53 Although less common in children than in adults, peritonitis also occurs as a complication of mucosal diseases, such as peptic ulcer, ulcerative colitis, Crohn disease, and pseudomembranous colitis.53 Rupture of or injury to an intraabdominal viscus results in spillage of the luminal contents and contamination of the peritoneal cavity with bacteria, gastrointestinal secretions, and debris. Chemical and infectious sources of inflammation are introduced. The stomach and upper gastrointestinal tract contents contain only 103 to 104 or fewer organisms per gram because of the low pH of gastric secretions. Gramnegative aerobic organisms colonize the upper gastrointestinal tract. In contrast, the colonic contents have predominantly anaerobes, with 1011 anaerobes and 108 aerobes per gram.11,23,39,66,70 Secondary peritonitis usually is a polymicrobial infection, with 5 to 10 different bacterial species of anaerobes and facultative gram-negative bacilli. Synergy among the various bacterial species enhances bacterial proliferation.11,70 Members of the Bacteroides fragilis group and Peptostreptococcus spp. are the anaerobic organisms reported most commonly in secondary peritonitis. Of the aerobic organisms, E. coli, Klebsiella spp., Pseudomonas aeruginosa, and Enterococcus spp. are isolated most often. Several authors have noted P. aeruginosa was isolated from 20% to 30% of children with complicated ruptured appendicitis.8,23,40,70 When secondary peritonitis occurs in patients with a history of prolonged hospitalization, underlying chronic conditions, or recent antibiotic therapy, the etiology may include nosocomial pathogens that have colonized the gastrointestinal tract, such as P. aeruginosa, Enterobacter spp., Acinetobacter spp., or other antibiotic-resistant organisms. Focal suppurative infection may be present within an intraabdominal or retroperitoneal solid organ or within intraabdominal lymphoid tissue. Organisms spread from this purulent focus through the capsule of the organ or lymphoid tissue and enter the peritoneal cavity, with the subsequent development of peritonitis. The intraabdominal organ or lymphoid tissue may be inoculated either via bacteremia (e.g., S. aureus and renal infection) or as a complication of the normal function of the organ (e.g., E. coli and renal infection or Yersinia and mesenteric adenitis).13,38,44

Peritonitis and Implanted Devices Peritonitis is the most significant infectious complication of longterm peritoneal dialysis. Contamination of the dialysis tubing, migration of skin flora from the exit site, or contamination of the dialysate may lead to peritonitis in patients undergoing continuous ambulatory peritoneal dialysis (CAPD). In each instance, a single pathogen usually is isolated. Gram-positive organisms, coagulase-negative staphylococci, and S. aureus account for 30% to 45% of peritonitis episodes in children undergoing CAPD. Of CAPD-associated peritonitis episodes, 20% to 30% are caused by Enterobacteriaceae.27 In these instances, contamination of the catheter site with fecal material most often occurs in young children who wear diapers and children with incontinence, an open urogenital sinus, or nephrostomy tubes. The waterborne pathogens Pseudomonas and Acinetobacter account for 6% and 4%, respectively, of peritonitis episodes in children receiving CAPD. Pseudomonas peritonitis is especially difficult to treat with the dialysis catheter in situ and may recur despite administration of appropriate antimicrobial therapy.27 Fungal peritonitis is another complication of CAPD that is difficult to treat successfully without removal of the catheter. Although fungal pathogens have accounted for only 2% of peritonitis episodes in children undergoing CAPD, this problem is occurring more commonly.15,26,27,50,58,79 Most patients with fungal peritonitis have had previous episodes of bacterial peritonitis and antibiotic therapy. The most common fungal pathogens are Candida spp.26,27; however, rare fungi, such as Curvularia spp.,15 Fusarium spp.,27 Trichosporon asahii,50 and Aspergillus spp.,27 have been reported.58,79 Other rare causes of CAPD-associated peritonitis include Mycobacterium fortuitum and Mycobacterium chelonae.80

510

SECTION 8  Other Intraabdominal Infections

Intraabdominal infectious complications develop on average in less than 5% of infants and children who undergo ventriculoperitoneal shunt placement or revision for hydrocephalus.57,65,71 Peritonitis, peritoneal pseudocyst, or perforation of the bowel by the abdominal catheter rarely occurs in children with such shunts.5,31,35,62,63,65,69,75 Cerebrospinal fluid (CSF) in the peritoneal cavity may be seeded during transient bacteremia or a febrile illness or after abdominal trauma. In addition, peritonitis may develop as a complication of infection within the ventricles being drained71 as organisms descend into the peritoneal cavity via the distal tubing. A peritoneal pseudocyst containing CSF is the most common manifestation of peritoneal inflammation in patients with ventriculoperitoneal shunts. These patients often have a history of symptoms compatible with a shunt infection before the formation of a pseudocyst and may have signs of peritoneal inflammation and a palpable abdominal mass. The microbial etiology of ventriculoperitoneal shunt–associated peritonitis varies and reflects the pathogenesis of infection. Infections occurring within months of surgery often are caused by skin flora, Staphylococcus epidermidis, other coagulase-negative staphylococci, and S. aureus.31,62 The microbiology of late shunt-associated peritonitis is similar to that of spontaneous bacterial peritonitis and may include gram-negative enteric organisms and gram-positive cocci.62 Peritonitis caused by colonic flora also rarely has been associated with bowel perforation by the distal end of the ventriculoperitoneal shunt.35,62,69

Clinical Manifestations The initial signs and symptoms of primary bacterial peritonitis include nausea, vomiting, diarrhea, and diffuse abdominal pain.39,42,43 These signs and symptoms are similar to those of secondary peritonitis caused by a ruptured appendix. Rupture of the appendix is the most common cause of secondary peritonitis in children; the initial symptoms of anorexia, vomiting, and localized abdominal pain frequently precede the signs and symptoms of diffuse peritoneal inflammation. In primary and secondary peritonitis, patients typically lie very still because any movement exacerbates the abdominal pain. Physical findings include fever, tachycardia, abdominal distention, hypoactive bowel sounds, abdominal tenderness, rebound tenderness, abdominal wall rigidity, and tenderness on rectal or vaginal examination. Peritoneal inflammation is associated with an increase in splanchnic blood flow, capillary permeability, and a shift of fluid into the peritoneal space, which may lead to intravascular hypovolemia and shock, in addition to systemic absorption of endotoxin and bacteria.48 Fever and abdominal pain in any child undergoing peritoneal dialysis should be evaluated carefully. Turbid dialysate fluid raises the suspicion of CAPD-associated peritonitis. Similarly, symptomatic children with ventriculoperitoneal shunts should be evaluated for shunt-associated peritonitis.63,65,71,83 In a retrospective report of 19 children with ventriculoperitoneal shunts and peritonitis, Reynolds and associates63 noted that fever and abdominal pain were the most common symptoms in 14 of their patients. Stamos and colleagues71 found that fever, lethargy, nausea, and vomiting were the most frequently reported symptoms in a review of 23 children with gram-negative infection of ventriculoperitoneal shunts. Primary tuberculous peritonitis usually is gradual in onset and associated with weight loss, malaise, and night sweats.36,37,39,67 The degree of tenderness is less than that present with acute pyogenic peritonitis and may be nonexistent. Palpation of the abdomen may reveal an extensive, irregular collection of masses, often described as “doughy,” caused by widespread granulomatous inflammation.36,39

Diagnosis Laboratory findings in a child with peritonitis often are nonspecific. The peripheral white blood cell count usually is elevated (16,000 to ≥25,000 cells/mm3), with a predominance of polymorphonuclear leukocytes and an increase in immature forms.39 The hematocrit may be elevated because of dehydration and hemoconcentration. Mild pyuria is noted occasionally because of irritation of the urinary bladder or ureters. Diagnostic imaging studies can be useful in evaluating intraabdominal infections. Upright and lateral decubitus radiographs of the abdomen may show distended adynamic loops of bowel suggestive of ileus and

obliteration of the peritoneal fat lines and psoas shadows. Free intraperitoneal air below the diaphragm indicates a ruptured viscus. The presence of a fecalith or right lower quadrant mass may be consistent with appendicitis. Abdominal ultrasonography and CT may reveal an underlying cause of the peritonitis.49,53 Analysis of peritoneal fluid aspirate or lavage material may be helpful in differentiating primary from secondary peritonitis. Free air, blood, or bile indicates peritonitis secondary to intestinal perforation. In peritonitis, the leukocyte count in peritoneal fluid usually is greater than 250 to 300 white blood cells/mm3 and sometimes 3000 to 5000 white blood cells/mm3, with granulocytes predominating in 80% of cases.39,47,70,73 A total protein content greater than 1 g/dL, a glucose level less than 50 mg/dL, or an elevated lactate dehydrogenase concentration (>25 mg/dL) is consistent with secondary peritonitis.17,33,39,73 If a Gram stain of peritoneal fluid shows only gram-positive cocci, primary peritonitis is most likely. The presence of gram-negative bacilli is consistent with primary or secondary peritonitis, but the presence of many different organisms on Gram stain is diagnostic of secondary peritonitis. Bacteremia occurs in 75% of patients with primary peritonitis. Specimens of peritoneal fluid and blood should be sent for culture.39 Similarly secondary peritonitis also can be associated with bacteremia, suggesting the need for obtaining cultures of blood in addition to peritoneal fluid. Specimens of peritoneal fluid should be processed to optimize the recovery of aerobic and anaerobic organisms, and the use of specific transport tubes or an airless, capped syringe is required.11,39,70 The wide variety of pathogens isolated from intraabdominal infections along with the variable antibiotic susceptibility of these pathogens supports taking an aggressive approach to obtaining samples for microbiologic evaluation. A child undergoing CAPD who is suspected of having peritonitis should have dialysate sent for cell count, Gram stain, and culture for bacterial, mycobacterial, and fungal pathogens. If a child with a ventriculoperitoneal shunt is suspected of having peritonitis, CSF from the proximal portion of the shunt should be sent for culture, cell count, and determination of glucose and protein levels in addition to Gram stain and culture of peritoneal fluid.31 Abdominal imaging by ultrasonography or CT is useful in identifying a peritoneal pseudocyst and the location of distal tubing.

Differential Diagnosis Other infectious diseases that may mimic primary or secondary bacterial peritonitis include mesenteric adenitis, gastroenteritis, hepatitis, streptococcal pharyngitis, lower lobe pneumonia, pyelonephritis, and pelvic inflammatory disease. Noninfectious diseases to be considered in the differential diagnosis are pancreatitis, diabetic ketoacidosis, HenochSchönlein purpura, ovarian torsion, sickle-cell pain crisis, and lead poisoning.53

Treatment Optimal management of peritonitis involves prompt and aggressive physiologic support, surgical consultation, and antimicrobial therapy. Correction of fluid and electrolyte imbalances and hemodynamic stabilization should be initiated as soon as the diagnosis of peritonitis is suspected. Spontaneous bacterial peritonitis usually is managed medically unless the diagnosis is uncertain, in which case exploratory laparotomy or laparoscopy is performed. Before resistant strains of S. pneumoniae emerged, primary peritonitis in children was treated with aqueous penicillin G.17,33 Given the increased prevalence of S. pneumoniae with reduced susceptibility to penicillin, third-generation cephalosporins such as cefotaxime or ceftriaxone are recommended until susceptibility results are available.47,74 If primary peritonitis is caused by gram-negative organisms, appropriate empiric therapy includes cefotaxime or ceftriaxone, with or without an aminoglycoside, a carbapenem, ticarcillinclavulanate, or piperacillin-tazobactam, pending completion of culture and susceptibility testing. Patients with secondary peritonitis may require either immediate surgery to control the source of contamination and to remove necrotic tissue, blood, and intestinal contents from the peritoneal cavity or a drainage procedure if a limited number of large abscesses can be shown.45,49,54,70,82 In cases of phlegmon, or extensive inflammatory edema,

CHAPTER 53  Peritonitis and Intraabdominal Abscess surgery usually is not performed acutely because of the child’s unstable metabolic state and friable intraabdominal tissues. Surgery is delayed for several hours or weeks to allow the inflammation to resolve. Surgery also may be postponed indefinitely.6,14,59,77 Empiric antimicrobial therapy for secondary peritonitis should have activity against anaerobes, especially the B. fragilis group, and enteric gram-negative aerobes.7 Although controversial, some regimens also include an antibiotic effective against enterococci. The gold standard for antimicrobial therapy historically has been clindamycin or metronidazole, gentamicin, and ampicillin.7,11,28,45,48,54,64,70 Alternative efficacious regimens, as single or combination therapy, include aztreonam, cefotaxime, cefoxitin, imipenem-cilastatin, meropenem, piperacillintazobactam, and ticarcillin-clavulanate.7,9,32,45,48,51,54,76,82 Rates of resistance to cefoxitin and clindamycin among the B. fragilis group have increased and are reported to be 49%; therefore metronidazole is now recommended, and, in some institutions, alternative regimens are used routinely.2,48,70 Therapy for secondary peritonitis that is a health care–associated infection should be selected based on local antimicrobial susceptibility patterns at that institution.70 Other studies have examined the use of a single broad-spectrum antibiotic, which allows a portion of the therapy to be delivered less expensively on an outpatient basis. Fishman and coworkers28 prospectively evaluated the clinical outcomes of 150 children with perforated appendicitis treated postoperatively with a 10-day course of piperacillintazobactam. They compared the outcome with that of historical controls treated with a 10-day course of ampicillin, gentamicin, and clindamycin. Rates of postoperative infectious complications were similar in both groups. Bradley and colleagues8 prospectively identified 87 children with complicated appendicitis in five pediatric centers, also comparing costs and outcomes with historical controls. Although inpatient treatment courses were reduced by an average of 42% in meropenem-treated children, outcome measures were equivalent to those of historical controls. Table 53.2 summarizes randomized trials of monotherapy versus combination therapy for ruptured appendicitis in children. Although no differences in outcome were observed, the potential of emerging resistance to broad-spectrum agents versus the convenience of monotherapy must be considered and balanced against the possible decreased risk for developing nosocomial infection among children who can receive a substantial component of parenteral therapy in the home.40 Goldin and colleagues32 retrospectively compared the use of triple antibiotic therapy versus monotherapy in a cohort of children with perforated appendicitis and found that single-agent antibiotic therapy in the treatment of perforated appendicitis was at least equal in efficacy to the traditional aminoglycoside-based combination therapy. The potential benefits of a single-agent regimen are reduced length of stay and lower pharmacy and hospital charges. Empiric antibiotic treatment of CAPD-associated peritonitis should be effective against gram-positive and gram-negative organisms until culture results are available. Intraperitoneal antibiotics, with or without concomitant intravenous antibiotics, achieve adequate serum and

511

dialysate concentrations. Vancomycin is used for empiric therapy for gram-positive infections, but if staphylococcal organisms are susceptible to β-lactam agents, treatment with cefazolin is effective.27 Aminoglycosides (gentamicin or tobramycin) or cephalosporins are used for gram-negative infections; however, because most intraperitoneal antibiotics are absorbed into the systemic circulation, serum aminoglycoside or vancomycin concentrations should be monitored for possible toxicity. Therapy for fungal peritonitis usually is intravenous amphotericin B, although successful use of fluconazole or intraperitoneal amphotericin B has been reported.27,58 Indications for removal of a dialysis catheter include persistent infection with S. aureus or Pseudomonas, tunnel infection, or fungal peritonitis.27 Treatment of peritonitis associated with ventriculoperitoneal shunts usually requires externalization of the distal end of the catheter in addition to institution of antibiotic therapy.31 Empiric antibiotic therapy should include an antistaphylococcal agent active against coagulasepositive and coagulase-negative staphylococci. Coagulase-negative staphylococci are a common cause of ventriculoperitoneal shunt infection; vancomycin should be administered pending culture and susceptibility results. If Gram stain of ventricular CSF or peritoneal fluid reveals gram-negative organisms, cefotaxime, ceftriaxone, ceftazidime, or meropenem should be added.5,63 The duration of antibiotic therapy for peritonitis should be dictated by the clinical course of the patient because no single regimen or treatment course is accepted universally.39,70 Indicators of sufficient therapy include resolution of fever and abdominal pain and return of the leukocyte and differential counts to normal.39,54,70,72 Primary peritonitis caused by streptococci is treated successfully with a 10- to 14-day course of antibiotics.17,39 Primary peritonitis with gram-negative organisms may require 10 days to 3 weeks of antibiotic treatment.17 The duration of therapy for secondary peritonitis after adequate surgery usually is 5 to 10 days, but it depends on the clinical response to therapy.39,54,70,72 Short-course therapy for 5 days has been shown to be efficacious in some patients,39,54 but longer courses are required if fever persists or abdominal signs and symptoms are present. Standard therapy for tuberculous peritonitis consists of a minimum of two antituberculous drugs. As with other forms of extrapulmonary tuberculosis in children, empiric therapy with isoniazid, rifampin, and pyrazinamide is advised pending culture and susceptibility results. Although M. bovis is resistant to pyrazinamide, most strains are susceptible to isoniazid, rifampin, and ethambutol.

Complications Acute complications associated with peritonitis include septic shock, adult respiratory distress syndrome, septic thrombophlebitis of the portal vein, acute renal failure, and multiorgan system failure.48 Postoperative complications include wound infection, adhesions, bowel obstruction, formation of a fistula, and formation of an intraabdominal or retroperitoneal abscess. Recurrent peritonitis (tertiary peritonitis) is an entity described as occurring late in the course of therapy for secondary peritonitis.39,46,70,82

TABLE 53.2  Monotherapy vs. Combination Therapy for Ruptured Appendicitis in Children NO. PATIENTS

Study

Monotherapy (A)

Combination Therapy (B)

Meller et al.51 Dougherty et al.22 Uhari et al.76 Collins et al.19

Cefoxitin Ticarcillin-clavulanate Imipenem-cilastatin Ampicillin-sulbactam ± aminoglycoside Piperacillin-tazobactam

Clindamycin/gentamicin Clindamycin/gentamicin ± ampicillin Metronidazole/tobramycin Ampicillin/clindamycin ± aminoglycoside

Meropenem

Cefotaxime ± amikacin or tobramycin, clindamycin or metronidazole

Fishman et al.,28 Lund and Murphy45 Bradley et al.9 a

Ampicillin/gentamicin/clindamycin

Wound infections, intraabdominal abscess, or rehospitalization. Modified from Kaplan SL. Antibiotic usage in appendicitis in children. Pediatr Infect Dis J. 1998;17:1047–8.

A

B

COMPLICATIONSa

A (%)

B (%)

29 79 9 75

27 45 10 39

1 (3) 14 (18) 2 (22) 2 (1)

4 (15) 5 (11) 1 (10) 1 (3)

150

373

14 (9)

24 (6)

22

13

2 (9)

1 (8)

512

SECTION 8  Other Intraabdominal Infections

Patients with this condition continue to have symptoms despite receiving appropriate antimicrobial therapy, and peritoneal fluid reveals persistent inflammation. Bacterial cultures often are negative or may yield an organism of low virulence. Multiorgan system failure and a poor outcome frequently are associated with tertiary peritonitis. The mechanism of ongoing peritoneal inflammation is unknown; however, some investigators have proposed that immunoregulatory dysfunction and poor nutrition are contributing factors.

INTRAABDOMINAL ABSCESS Intraabdominal abscesses often are categorized as intraperitoneal, visceral, or retroperitoneal (see Chapter 54).4,10 In children, intraperitoneal abscesses are most common. The most common underlying conditions associated with an intraabdominal abscess in children are appendicitis and trauma.10,53 Reviews of gangrenous or perforated appendicitis in children indicate that 2% to 20% of cases are complicated by the formation of an abscess.54,64 Two basic mechanisms exist for the development of an intraperitoneal abscess. In the first mechanism, diffuse peritonitis may cause loculations of purulent material to form in the areas anatomically most dependent— typically the pelvic, subphrenic, and paracolic regions (see Fig. 53.1). The second mode of formation of an abscess involves a localized focus related to contiguous disease or injury in which host defenses and the inflammatory response prevent diffuse spread and peritonitis.4 The microbiology of intraperitoneal abscesses is polymicrobial and reflects that of the intestinal flora. In a review of intraabdominal abscess in 36 children, Brook10,11 noted that the predominant organisms were the B. fragilis group, Peptostreptococcus, E. coli, and other Enterobacteriaceae. The most common sites of visceral abscess in children are the liver (see Chapter 49), pancreas, and spleen. Underlying conditions that may lead to the development of a pancreatic abscess include pancreatic injury, pancreatitis, and biliary obstruction. Pancreatitis or surgical or accidental injury to the pancreas causes the release of pancreatic enzymes and focal necrosis.29 Reflux of contaminated bile into the pancreatic duct is hypothesized to be the mechanism by which enteric organisms gain access to the injured pancreas and proliferate. A pancreatic abscess usually is a polymicrobial infection caused by aerobic (E. coli, Klebsiella pneumoniae, group D streptococci) or anaerobic (peptostreptococci, B. fragilis group) organisms that inhabit the gastrointestinal tract. Rare instances of S. aureus pancreatic abscess occur as a result of bacteremia.12,13 Splenic abscesses are unusual findings in infants and children. Before the 1970s, most reports involved solitary pyogenic abscesses. Since then, the number of reports of multiple splenic abscesses has increased.16,41,60 Splenic abscess usually is associated with one of five underlying conditions: endocarditis, injury, hemoglobinopathy, immunodeficiency, or adjacent infection. Given the filtering function of the spleen, an abscess can form as a result of any metastatic hematogenous infection, such as endocarditis. Although rare, splenic abscess can be a delayed complication of the nonoperative management of splenic injuries. Splenic infarcts associated with hemoglobinopathies such as sickle-cell disease may become secondarily infected and form an abscess.16 Immunodeficiency, such as malignancy or acquired immunodeficiency syndrome, is another significant risk factor for the development of multiple splenic abscesses.41,55,60 Rarely infection or disease in a contiguous focus may extend to the spleen. In a review of 56 children with splenic abscesses, 7 (12.5%) were cryptogenic with no apparent cause.41 In most instances, a single pathogen is isolated, with S. aureus, streptococci, E. coli, and Salmonella spp. being the most common. Fungi, most often Candida spp., have been isolated from splenic abscesses primarily in immunocompromised hosts.41,55,60

Clinical Manifestations The typical clinical features of an intraabdominal abscess include fever, abdominal pain, and tenderness over the involved area. Subphrenic abscesses also may be manifested as referred pain or pulmonary or pleuritic symptoms. Pancreatic abscess may be associated with a palpable

epigastric mass and elevated serum lipase and amylase.12 Splenomegaly or a splenic mass may be noted in approximately half of patients with splenic abscesses.41 In postoperative patients, persistence of abdominal symptoms or fever warrants evaluation for an intraperitoneal abscess.3 Leukocytosis (20,000 to 50,000 cells/mm3) frequently is present in children with an intraabdominal abscess.3,39

Diagnosis Imaging studies are helpful in diagnosing an intraabdominal abscess. Plain radiographs are useful as an initial procedure and may show an extraintestinal air-fluid level, right lower quadrant mass, or localized ileus.1 Chest radiographs should be obtained because subphrenic abscesses often are associated with a pleural effusion. In a series of 27 children with splenic abscesses, chest radiographs were abnormal in 20 cases, with the most common findings being left pleural effusion and an elevated left hemidiaphragm.41 Ultrasonography is a useful noninvasive technique that can detect abdominal and pelvic abscesses. The quality of the images depends on the examiner, however. In addition, conditions such as ileus, postoperative drains, or dressings may hinder ultrasound detection of an abscess.1,49,52 CT is the most sensitive tool for detecting an intraabdominal abscess, and it provides good anatomic resolution. Disadvantages of CT are the radiation and, if used, exposure to intravenous, oral, or rectal contrast material.1,49,52 Although more recent experience with the use of magnetic resonance imaging for detecting an intraperitoneal abscess has been described in the literature,56 this modality should be considered in children only when an abscess may not be detected more easily by other methods or in patients who should not have exposure to radiation.56 Gallium scanning is a sensitive technique for diagnosing an abscess, but it is nonspecific, particularly in the abdomen.1

Treatment Management of an intraabdominal abscess includes physiologic and nutritional support, antimicrobial therapy, and drainage. After blood cultures have been obtained, empiric antibiotic therapy should be instituted with agents effective against anaerobes, Enterobacteriaceae, and other enteric flora as discussed earlier for peritonitis. Antibiotic therapy usually is begun before surgery is done to minimize any complications of bacteremia during the procedure. Abscess material should be obtained for culture of aerobic, anaerobic, fungal, and mycobacterial pathogens. Effective surgical management depends on accurate localization of the abscess, discrimination between single and multiple abscesses, and early and adequate drainage.3,4,48 Traditional therapy for intraperitoneal abscesses has relied on open surgical drainage, although drainage of intraperitoneal abscesses percutaneously under ultrasound or CT guidance now is used often.1,18,21,48,52,61 In instances of multiple intraperitoneal abscesses or if the source of peritoneal contamination has not been controlled, laparotomy is indicated.48 Pancreatic abscesses require intensive surgical and medical therapy. Antimicrobial therapy for mixed aerobic and anaerobic infection is suggested,12 but splenectomy remains the definitive treatment of bacterial splenic abscesses. In selected patients, percutaneous drainage or splenotomy has the advantage of preserving splenic function, however.41,55,60 Multiple small splenic abscesses and fungal lesions generally are treated medically.41 Antibiotic therapy for a pyogenic splenic abscess should be guided by the pathogens associated with the child’s underlying condition. Therapy should include antibiotics effective against S. aureus, streptococci, and gram-negative enteric bacilli. Specific therapy should be revised after culture and susceptibility results are available.

Complications Intraperitoneal and visceral abscesses, if not adequately drained, may be associated with significant complications, including ongoing spread of the infectious process and, for splenic or pancreatic abscesses, a high mortality rate. Fistula formation, adhesions, and bowel obstruction may be late complications of intraabdominal infection. The full reference list for this chapter is available at ExpertConsult.com.

CHAPTER 53  Peritonitis and Intraabdominal Abscess REFERENCES 1. Afshani E. Computed tomography of abdominal abscesses in children. Radiol Clin North Am. 1981;19:515-526. 2. Aldridge KE, Ashcraft D, Cambre K, et al. Multicenter survey of the changing in vitro antimicrobial susceptibilities of clinical isolates of Bacteroides fragilis group, Prevotella, Fusobacterium, Porphyromonas, and Peptostreptococcus species. Antimicrob Agents Chemother. 2001;45:1238-1243. 3. Altemeier WA, Culbertson WR, Fuller WD. Intra-abdominal sepsis. Adv Surg. 1971;5:281-333. 4. Altemeier WA, Culbertson WR, Fuller WD, et al. Intra-abdominal abscesses. Am J Surg. 1973;125:70-79. 5. Baird C, O’Connor D, Pittman T. Late shunt infections. Pediatr Neurosurg. 1999;31:269-273. 6. Blakely ML, Spurbeck WW, Lobe TE. Current status of laparoscopic appendectomy in children. Semin Pediatr Surg. 1998;7:225-227. 7. Bohnen JM, Solomkin JS, Dellinger EP, et al. Guidelines for clinical care: antiinfective agents for intra-abdominal infection. A Surgical Infection Society policy statement. Arch Surg. 1992;127:83-89. 8. Bradley JS, Behrendt CE, Arrieta AC, et al. Convalescent phase outpatient parenteral antiinfective therapy for children with complicated appendicitis. Pediatr Infect Dis J. 2001;20:19-24. 9. Bradley JS, Faulkner KL, Klugman KP. Efficacy, safety and tolerability of meropenem as empiric antibiotic therapy in hospitalized pediatric patients. Pediatr Infect Dis J. 1996;15:749-757. 10. Brook I. Intra-abdominal abscess in children: a 13 year experience. Hosp Pract. 1990;25:20-23. 11. Brook I. Intra-abdominal infections in children: pathogenesis, diagnosis and management. Drugs. 1993;46:53-62. 12. Brook I, Frazier EH. Microbiological analysis of pancreatic abscess. Clin Infect Dis. 1996;22:384-385. 13. Brook I, Frazier EH. Aerobic and anaerobic microbiology of retroperitoneal abscesses. Clin Infect Dis. 1998;26:938-941. 14. Bufo AJ, Shah RS, Li MH, et al. Interval appendectomy for perforated appendicitis in children. J Laparoendosc Adv Surg Tech A. 1998;8:209-214. 15. Canon HL, Buckingham SC, Wyatt RJ, et al. Fungal peritonitis caused by Curvularia species in a child undergoing peritoneal dialysis. Pediatr Nephrol. 2001;16:35-37. 16. Chun CH, Raff MJ, Contreras L, et al. Splenic abscess. Medicine (Baltimore). 1980;59:50-65. 17. Clark JH, Fitzgerald JF, Kleiman MB. Spontaneous bacterial peritonitis. J Pediatr. 1984;104:495-500. 18. Clark RA, Towbin R. Abscess drainage with CT and ultrasound guidance. Radiol Clin North Am. 1983;21:445-459. 19. Collins MD, Dajani AS, Kim KS, et al. Comparison of ampicillin/sulbactam plus aminoglycoside vs. ampicillin plus clindamycin plus aminoglycoside in the treatment of intraabdominal infections in children. Pediatr Infect Dis J. 1998;17(suppl):15-18. 20. Dankner WM, Davis CE. Mycobacterium bovis as a significant cause of tuberculosis in children residing along the United States–Mexico border in the Baja California region. Pediatrics. 2000;105:E79. 21. Diament MJ, Stanley P, Kangarloo H, et al. Percutaneous aspiration and catheter drainage of abscesses. J Pediatr. 1986;108:204-208. 22. Dougherty SH, Sirinek KR, Schauer PR, et al. Ticarcillin/clavulanate compared with clindamycin/gentamicin (with or without ampicillin) for the treatment of intra-abdominal infections in pediatric and adult patients. Am Surg. 1995;61: 297-303. 23. Dumont R, Cinotti R, Lejus C, et al. The microbiology of community-acquired peritonitis in children. Pediatr Infect Dis J. 2011;30:131-135. 24. Dunn DL, Barke RA, Ahrenholz DH, et al. The adjuvant effect of peritoneal fluid in experimental peritonitis: mechanism and clinical implications. Ann Surg. 1984;199:37-43. 25. Dunn DL, Barke RA, Knight NB, et al. Role of resident macrophages, peripheral neutrophils, and translymphatic absorption in bacterial clearance from the peritoneal cavity. Infect Immun. 1985;49:257-264. 26. Enriquez JL, Kalia A, Travis LB. Fungal peritonitis in children on peritoneal dialysis. J Pediatr. 1990;117:830-832. 27. Feinstein EI, Chesney RW, Zelikovic I. Peritonitis in childhood renal disease. Am J Nephrol. 1988;8:147-165. 28. Fishman SJ, Pelosi L, Klavon SL, et al. Perforated appendicitis: prospective outcome analysis for 150 children. J Pediatr Surg. 2000;35:923-926. 29. Ford EG, Hardin WD, Mahour GH, et al. Pseudocysts of the pancreas in children. Am Surg. 1990;56:384-387. 30. Freij BJ, Votteler TP, McCracken GH. Primary peritonitis in previously healthy children. Am J Dis Child. 1984;138:1058-1061. 31. Gaskill SJ, Marlin AE. Spontaneous bacterial peritonitis in patients with ventriculoperitoneal shunts. Pediatr Neurosurg. 1997;26:115-119. 32. Goldin AB, Sawin RS, Garrison MM, et al. Aminoglycoside-based triple-antibiotic therapy versus monotherapy for children with ruptured appendicitis. Pediatrics. 2007;119:905-911.

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33. Gorensek MJ, Lebel MH, Nelson JD. Peritonitis in children with nephrotic syndrome. Pediatrics. 1988;81:849-856. 34. Graham JC, Moss PJ, McKendrick MW. Primary group A streptococcal peritonitis. Scand J Infect Dis. 1995;27:171-172. 35. Grosfeld JL, Cooney DR, Smith J, et al. Intra-abdominal complications following ventriculoperitoneal shunt procedures. Pediatrics. 1974;54:791-796. 36. Gurkan F, Ozates M, Bosnak M, et al. Tuberculous peritonitis in 11 children: clinical features and diagnostic approach. Pediatr Int. 1999;41:510-513. 37. Jakubowski A, Elwood RK, Enarson DA. Clinical features of abdominal tuberculosis. J Infect Dis. 1988;158:687-692. 38. Jelloul L, Fremond B, Dyon JF, et al. Mesenteric adenitis caused by Yersinia pseudotuberculosis presenting as an abdominal mass. Eur J Pediatr Surg. 1997;7:180-183. 39. Johnson CC, Baldessarre J, Levison ME. Peritonitis: update on pathophysiology, clinical manifestations, and management. Clin Infect Dis. 1997;24:1035-1047. 40. Kaplan SL. Antibiotic usage in appendicitis in children. Pediatr Infect Dis J. 1998;17:1047-1048. 41. Keidl CM, Chusid MJ. Splenic abscesses in childhood. Pediatr Infect Dis J. 1989;8:368-373. 42. Kimber CP, Hutson JM. Primary peritonitis in children. Aust N Z J Surg. 1996;66:169-170. 43. Krensky AM, Ingelfinger JR, Grupe WE. Peritonitis in childhood nephrotic syndrome. Am J Dis Child. 1982;136:732-736. 44. Lamps LW, Madhusukhan KT, Greenson JK, et al. The role of Yersinia enterocolitica and Yersinia pseudotuberculosis in granulomatous appendicitis: a histologic and molecular study. Am J Surg Pathol. 2001;25:508-515. 45. Lund DP, Murphy EU. Management of perforated appendicitis in children: a decade of aggressive treatment. J Pediatr Surg. 1994;29:1130-1134. 46. Malangoni MA. Evaluation and management of tertiary peritonitis. Am Surg. 2000;66:157-161. 47. Markenson DS, Levine D, Schacht R. Primary peritonitis as a presenting feature of nephrotic syndrome: a case report and review of the literature. Pediatr Emerg Care. 1999;15:407-409. 48. McClean KL, Sheehan GJ, Harding GKM. Intraabdominal infection: a review. Clin Infect Dis. 1994;19:100-116. 49. McConkey SJ, McCarthy ND, Keane CT. Primary peritonitis due to nonenteric salmonellae. Clin Infect Dis. 1999;29:211-212. 50. Melez KA, Cherry J, Sanchez C, et al. Successful outpatient treatment of Trichosporon beigelii peritonitis with oral fluconazole. Pediatr Infect Dis J. 1995;14:1110-1113. 51. Meller JL, Reyes HM, Loeff DS, et al. One drug versus two-drug antibiotic therapy in pediatric perforated appendicitis: a prospective randomized study. Surgery. 1991;110:764-768. 52. Montgomery RS, Wilson SE. Intraabdominal abscesses: image-guided diagnosis and therapy. Clin Infect Dis. 1996;23:28-36. 53. Neblett WW, Pietsch JB, Holcomb GW Jr. Acute abdominal conditions in children and adolescents. Surg Clin North Am. 1988;68:415-430. 54. Neilson IR, Laberge JM, Nguyen LT, et al. Appendicitis in children: current therapeutic recommendations. J Pediatr Surg. 1990;25:1113-1116. 55. Nelken N, Ignatius J, Skinner M, et al. Changing clinical spectrum of splenic abscess: a multicenter study and review of the literature. Am J Surg. 1987;154:27-34. 56. Noone TC, Semelka RC, Worawattanakul S, et al. Intraperitoneal abscesses: diagnostic accuracy of and appearances at MR imaging. Radiology. 1998;208:525-528. 57. Odio C, McCracken GH, Nelson JD. CSF shunt infections in pediatrics: a seven-year experience. Am J Dis Child. 1984;138:1103-1108. 58. Oh SH, Conley SB, Rose GM, et al. Fungal peritonitis in children undergoing peritoneal dialysis. Pediatr Infect Dis J. 1985;4:62-66. 59. Olika D, Yamini D, Udani VM, et al. Nonoperative management of perforated appendicitis without periappendiceal mass. Am J Surg. 2000;179:177-181. 60. Phillips GS, Radosevich MD, Lipsett PA. Splenic abscess: another look at an old disease. Arch Surg. 1997;132:1331-1336. 61. Ramakrishnan MR, Sarathy TKP. Percutaneous drainage of splenic abscess: case report and review of literature. Pediatrics. 1987;79:1029-1031. 62. Rekate HL, Yonas H, White RJ, et al. The acute abdomen in patients with ventriculoperitoneal shunts. Surg Neurol. 1979;11:442-445. 63. Reynolds M, Sherman JO, Mclone DG. Ventriculoperitoneal shunt infection masquerading as an acute surgical abdomen. J Pediatr Surg. 1983;18:951-955. 64. Schwartz MZ, Tapper D, Solenberger RI. Management of perforated appendicitis in children: the controversy continues. Ann Surg. 1983;197:407-411. 65. Sells CJ, Loeser JD. Peritonitis following perforation of the bowel: a rare complication of a ventriculoperitoneal shunt. J Pediatr. 1973;83:823-824. 66. Simon GL, Gorbach SL. Intestinal flora in health and disease. Gastroenterology. 1984;86:174-193. 67. Sioson PB, Stechenberg BW, Courtney R, et al. Tuberculous peritonitis in a three-year-old boy: case report and review of the literature. Pediatr Infect Dis J. 1992;11:409-411. 68. Sirotnak AP, Eppes SC, Klein JD. Tuboovarian abscess and peritonitis caused by Streptococcus pneumoniae serotype 1 in young girls. Clin Infect Dis. 1996;22:993-996. 69. Snow RB, Lavyne MH, Fraser RAR. Colonic perforation by ventriculoperitoneal shunts. Surg Neurol. 1986;25:173-177.

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SECTION 8  Other Intraabdominal Infections

70. Solomkin JS, Muzuski JE, Bradley JS, et al. Diagnosis and management of complicated intra-abdominal infection in adults and children: guidelines by the Surgical Infection Society and the Infectious Diseases Society of America. Surg Infect. 2010;11:79-109. 71. Stamos JK, Kaufman BA, Yogev R. Ventriculoperitoneal shunt infections with gram-negative bacteria. Neurosurgery. 1993;33:858-862. 72. Stone HH, Bourneuf AA, Stinson LD. Reliability of criteria for predicting persistent or recurrent sepsis. Arch Surg. 1985;120:17-20. 73. Such J, Runyon BA. Spontaneous bacterial peritonitis. Clin Infect Dis. 1998;27:669-676. 74. Tain YL, Lin GJ, Cher TW. Microbiological spectrum of septicemia and peritonitis in nephrotic children. Pediatr Nephrol. 1999;13:835-837. 75. Tchirkow G, Verhagen AD. Bacterial peritonitis in patients with ventriculoperitoneal shunt. J Pediatr Surg. 1979;14:182-184. 76. Uhari M, Seppanen J, Heikkinen E. Imipenem-cilastatin vs. tobramycin and metronidazole for appendicitis-related infections. Pediatr Infect Dis J. 1992;11:445-450.

77. Vargas HI, Averbook A, Stamos MJ. Appendiceal mass: conservative therapy followed by interval laparoscopic appendectomy. Am Surg. 1994;60:753-758. 78. Veeragandham RS, Lynch FP, Canty TG, et al. Abdominal tuberculosis in children: review of 26 cases. J Pediatr Surg. 1996;31:170-176. 79. Warady BA, Bashir M, Donaldson LA. Fungal peritonitis in children receiving peritoneal dialysis: a report of the NAPRTCS. Kidney Int. 2000;58: 384-389. 80. White R, Abreo K, Flanagan R, et al. Nontuberculous mycobacterial infections in continuous ambulatory peritoneal dialysis patients. Am J Kidney Dis. 1993;22:581-587. 81. Wilfert CM, Katz SL. Etiology of bacterial sepsis in nephrotic children 1963–1967. Pediatrics. 1968;42:840-843. 82. Wittmann DH, Schein M, Condon RE. Management of secondary peritonitis. Ann Surg. 1996;224:10-18. 83. Younger JJ, Simmons JCH, Barrett FF. Occult distal ventriculoperitoneal shunt infections. Pediatr Infect Dis J. 1985;4:557-558.

Retroperitoneal Infections

54 

Alice Pong • John S. Bradley Retroperitoneal infections consist primarily of suppurative bacterial infections that originate within the retroperitoneal structures. In children, these infections are much less common than intraabdominal infections; however, they can lead to significant morbidity if missed. Symptoms often are indolent and poorly localized. Consequently there can be a delay in diagnosis. The retroperitoneal structures are separated from the intraabdominal organs by the posterior peritoneal fascia (Fig. 54.1). Structures posterior to this fascia layer, in the anterior retroperitoneal space, include the duodenum, pancreas, and parts of the colon. The kidneys and ureters are encased by the renal fascia. The iliopsoas and psoas muscles lie at the posterior aspect of the retroperitoneal space and are separated from the other retroperitoneal structures by the transversalis fascia. Pelvic structures, including the bladder, uterus, and rectum, that lie inferior to the pelvic peritoneum constitute the pelvic portion of the retroperitoneal space. The fascial layers limit the spread of retroperitoneal infections; however, the deep location is difficult to assess by physical examination.

ETIOLOGY AND PATHOGENESIS Retroperitoneal infections in children arise in numerous anatomic structures. Brook8 reviewed cases of retroperitoneal infections from five US hospitals from 1974 to 1994. Forty-one children were identified. Twenty-one had infections in the anterior retroperitoneal space related to the pancreas (n = 4) and intestines (n = 13), 6 had perinephric abscesses, 7 had iliopsoas abscesses, and 7 had pelvic retroperitoneal abscesses. Retroperitoneal infections may occur from hematogenous seeding of bacteria from another site, ascending infection from the urinary tract, or as an extension of infection from the gastrointestinal tract. Infections of the perinephric retroperitoneal space include those involving the kidney and adrenal glands. Although renal or perinephric abscesses can result from bacteremic inoculation of renal tissue,54,63 more recent case series report ascending urinary tract infections being a more common source.13,16,41 Clinical presentation usually includes fever and flank or abdominal pain. Nephronia (i.e., focal renal cellulitis, focal bacterial nephritis) is thought to be an intermediate stage of renal infection between pyelonephritis and renal abscess, resulting from an ascending infection of the urinary tract.14 Adrenal abscesses are reported more frequently in neonates than in older children and are suspected to be related to adrenal hemorrhages that become secondarily infected.47 Within the anterior retroperitoneal space, secondary infections occur as a direct extension from gastrointestinal perforations such as ruptured appendices or those related to Crohn disease.8,26,28 Greenstein and associates reported retroperitoneal abscesses in 12 of 231 patients with Crohn disease.26 Retroperitoneal infections, particularly of the pelvic space, can also develop secondary to primary infections of the vertebral spine, pelvic bones, and sacroiliac joint.30,59 Suppurative iliac or retroperitoneal lymph nodes are another source of retroperitoneal infections. Prior surgery has been reported as a predisposing factor in perinephric abscesses7,22 and in vascular grafts in adults.10 Pancreatic abscesses are seen more commonly in adult patients and are associated with underlying biliary tract disease, alcoholism, surgery, and trauma.9 Acute pancreatitis occurs less frequently in children than in adults; however, when it occurs, infections are often implicated.32,62 Iliopsoas abscesses may be a consequence of hematogenous seeding of the muscle, with trauma as a predisposing factor.29,55 Although primary infection occurs most commonly,6 the iliopsoas muscle extends from the ribs and lumbar vertebrae to its insertion on the femur and is exposed to the risk of extension of infection from numerous adjacent

structures. Psoas abscesses have developed as a consequence of vertebral infections, intestinal perforations, and genitourinary sources.29,33,34 Neonatal iliopsoas abscesses have also been reported and present with symptoms similar to those of a septic hip.20,23,50 Complications of retroperitoneal abscesses include both rupture into the intraperitoneal space and extension of the infection along fascial planes to adjacent muscles that extend from origins in the pelvis and trunk to insertion sites on the femur. Rupture into the thoracic cavity also has been reported.1 Other reported complications include pneumonia, recurrent abscess, renal failure, and venous and arterial thrombosis.17

MICROBIOLOGY The microbiology of retroperitoneal infections is determined by the source of the infection and the retroperitoneal compartment involved. Most primary infections thought to result from bacteremia are caused by Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA).51 Secondary infection related to the gastrointestinal tract is caused by mixed bowel flora including Escherichia coli, other gramnegative enteric bacteria, Pseudomonas spp., and gastrointestinal anaerobes, particularly Bacteroides fragilis and Peptostreptococcus.8 Most infections in the anterior retroperitoneal space are associated with a gastrointestinal source and may be polymicrobial. Actinomyces infections can also present as retroperitoneal infections.4,39 Ascending infections from the urinary tract usually are caused by E. coli; however, perinephric abscesses also are reported as a complication of renal infection caused by S. aureus, group B Streptococcus, and Salmonella.22,63,64 S. aureus is the leading pathogen isolated in iliopsoas abscesses unless the infection is secondary to erosion of a primary gastrointestinal focus. In that situation, gram-negative enteric bacteria and anaerobes are more likely to be the causative agents.6,55 Retroperitoneal necrotizing fasciitis from group A Streptococcus has also been reported.19 Tuberculosis caused by Mycobacterium tuberculosis or M. bovis may involve the retroperitoneal space as an extension of vertebral tuberculous osteomyelitis.1,21,33,34 Abdominal tuberculosis usually manifests as an intraperitoneal infection but can produce retroperitoneal adenopathy. The most common infectious agents associated with acute pancreatitis are viral pathogens including adenovirus, coxsackie B, mumps, and hepatitis viruses (A, B, E).3,15,27,31,46,52,60 Varicella, herpes simplex virus (HSV), cytomegalovirus (CMV), Epstein-Barr virus (EBV), and rotavirus have also been reported as associated infections in patients with acute pancreatitis.18,24,36,52,53 Bacterial pathogens including Salmonella and mycoplasma45,48,52 are less frequently associated with pancreatitis. Ascaris lumbricoides can cause acute pancreatitis via obstruction of the common bile duct or other intrahepatic and pancreatic ducts.35,52

CLINICAL PRESENTATION Children with retroperitoneal infections present clinically in a variety of ways, ranging from nonspecific fever to overwhelming sepsis. The most common clinical symptoms associated with retroperitoneal infections include fever and pain in the hip, back, and abdomen.17,43 Psoas abscesses often manifest with the child limping or refusing to walk.6 Neonates with a retroperitoneal abscess may present with an abdominal mass.57 In children, acute pancreatitis presents most commonly with abdominal pain and vomiting, rather than back pain.27,45,62 Symptoms associated with retroperitoneal infections can be vague, and pain is not well localized. Patients often have been evaluated previously for fevers and have been treated with antibiotics before a diagnosis has been made.6,38,56 513

514

SECTION 8  Other Intraabdominal Infections

Pancreas Ascending colon

Duodenum

Kidney

Inferior vena cava

Transversalis fascia Descending colon Peritoneum

Aorta

Kidney

FIG. 54.1  Axial diagram of the abdomen at the level of the kidneys showing the anatomy of the retroperitoneum. (From Gore RM, Meyers MA, Rabin DN. Pathways of abdominal and pelvic disease spread. In: Gore RM, Levine MS, editors. Textbook of Gastrointestinal Radiology, 4th ed. Philadelphia: Saunders; 2015.)

FIG. 54.2  Percutaneous drainage of a perinephric abscess by computed tomography scan.

DIFFERENTIAL DIAGNOSIS

TREATMENT

Retroperitoneal infections can be confused with a variety of other infections. Limp and fever caused by pyogenic arthritis of the hip and infection of the sacroiliac joint and pelvic bones are more common than retroperitoneal infections. Abdominal pain and fever are more frequently seen in patients with intraabdominal infections, including appendicitis and intraabdominal abscesses. Trauma and malignant disease are more frequent causes of retroperitoneal masses compared with infectious causes and should also be considered.

Although small retroperitoneal abscesses may resolve with antibiotic therapy alone,13,16,41 percutaneous or open surgical drainage should be considered for all retroperitoneal infections for both diagnostic and treatment purposes. Culture of the aspirated fluid for aerobic and anaerobic bacteria, mycobacteria, and fungi is vital to selecting appropriate antimicrobial therapy. Treatment of patients with antibiotics alone without surgical drainage may not be effective, particularly in cases involving larger abscesses.1,12 Initial antimicrobial therapy of retroperitoneal infections should be directed by the presumed source of the infection, with definitive therapy guided by microbiologic culture results. Infections related to gastrointestinal perforation should include coverage directed primarily against enteric gram-negative bacteria and gastrointestinal anaerobes such as β-lactamase–producing B. fragilis. Coverage for Pseudomonas and Enterococcus spp. also should be considered, as these may be present in up to 25% to 30% of otherwise healthy children with complicated appendicitis. Historically antibiotic combinations such as ampicillin for enterococcus, metronidazole or clindamycin for anaerobes, and an aminoglycoside (e.g., gentamicin) or a third-generation cephalosporin for gram-negative bacteria have been used. The β-lactam and β-lactamase inhibitor combinations (e.g., ticarcillin-clavulanate, piperacillintazobactam), with or without an aminoglycoside, are also likely to be effective. Carbapenems such as meropenem, imipenem, or ertapenem as single agents may be more cost effective, particularly if any outpatient antibiotic therapy is being considered. Infections of renal origin, usually caused by E. coli or other gramnegative enteric organisms, can be treated with extended-spectrum (third-generation) cephalosporins such as ceftriaxone, or, if abscesses have been drained successfully, with aminoglycosides such as gentamicin or tobramycin. The activity of aminoglycosides may be compromised by the anaerobic and acidic environment of abscess cavities and may lead to clinical failures despite in vitro susceptibility of the organism.11 Resistance to ampicillin is often seen in E. coli,2,5 rendering it unreliable for empiric use in severe urinary tract infections requiring the use of second- or third-generation cephalosporins. However, extendedspectrum β-lactamase (ESBL)-producing E. coli, Klebsiella spp., and other Enterobacteriaceae with resistance to third- and fourth-generation cephalosporins, are increasing in prevalence, particularly with urinary tract infections.28,42 Carbapenems (and, in certain circumstances, fluoroquinolones) may be some of the very few options available for

SPECIFIC DIAGNOSIS Laboratory tests often are nonspecific and of minimal benefit. Sedimentation rates and leukocyte counts often are elevated.6,8,55,56 Pancreatic enzymes including amylase and lipase are usually elevated with acute pancreatitis. Pyuria often is absent in children with perinephric and renal abscesses, and the urine culture result may be negative.7,13,22,61,63 However, in patients with nephronia, pyuria and positive urine cultures are more likely.14,37 Blood cultures may be helpful in identifying a bacterial pathogen. Brook8 reported that 40% of blood cultures were positive for the same organism isolated from abscesses in children with retroperitoneal infections who had blood cultures collected. For children with psoas abscesses, Santaella55 reported that 71% of blood cultures were positive. Imaging studies are the most useful diagnostic tools. Ultrasonography can be used to diagnose perinephric infections7,61 and has been used to diagnose abscesses of the iliopsoas muscle.28 Computed tomography (CT) with contrast enhancement can be the most helpful12,17,55 because of superior delineation of organ involvement and the extent of infection. CT also can provide clues about the primary focus of the infection, thereby helping to guide empiric antibiotic therapy. Abscess fluid is seen on CT as areas of low attenuation, often with an enhancing rim.12,38,63 Percutaneous drainage and biopsy of the lesions may also be accomplished with ultrasound or CT (Fig. 54.2).13,29,41 Magnetic resonance imaging (MRI) offers the advantage over CT of superior visualization of inflamed bone and muscle tissue, although calcifications may not be as well identified.49 Although alternative diagnoses also can be evaluated with CT,58 hematomas and certain tumors may not be easily distinguished radiographically from infection. These noninfectious entities may be better identified by MRI. Decreased radiation exposure is an additional advantage of MRI.

CHAPTER 54  Retroperitoneal Infections treatment. Pseudomonas is not an uncommon pathogen in children with recurrent infections caused by anatomic genitourinary abnormalities.2 Pseudomonas spp. usually are resistant to ceftriaxone; extendedspectrum cephalosporins such as ceftazidime or cefepime or carbapenems may be needed. Urine or abscess culture and susceptibility results help to focus the antibiotic choice to the most narrow-spectrum agent available. Psoas abscesses and primary perinephric abscesses caused by methicillin-susceptible strains of S. aureus should be treated with an antistaphylococcal agent such as nafcillin (or oxacillin) or a firstgeneration cephalosporin such as cefazolin. The prevalence of community-acquired MRSA (CA-MRSA) has increased significantly as a soft tissue pathogen, particularly in children.25,44 Vancomycin or clindamycin should be considered as empiric therapy for serious infections in areas with high rates of CA-MRSA (>5% of all invasive S. aureus infections) until culture results are available. Recent data suggest that clindamycin resistance in S. aureus is also increasing in certain regions, prompting the clinician to access local susceptibility data in making empiric therapy decisions. These agents also may be effective in treating the patient who is unable to tolerate penicillin or cephalosporin antibiotics. For children unable to tolerate vancomycin due to renal compromise, newer agents including ceftaroline fosamil, daptomycin, and linezolid are also promising alternatives against MRSA infections. These agents may also be options against S. aureus with minimum inhibitory concentrations to vancomycin of 2 mg/dL or greater. Infections originating in the vertebrae are most often caused by S. aureus or may result from tuberculosis. Empiric antistaphylococcal therapy can be started, but culture and histologic examination of tissue are needed to direct appropriate therapy. For the child with risk factors for tuberculosis, a positive tuberculin skin test or interferon-γ release assays and a negative Gram stain result, empiric therapy with three or four antituberculous antibiotics should be considered. A chest radiograph should be obtained to look for evidence of pulmonary tuberculosis. After adequate drainage is achieved, the duration of antimicrobial therapy depends on several factors, including the organism, the site and extent of infection, and clinical improvement. Most small or drained retroperitoneal bacterial abscesses of renal or muscle origin are treated for 2 to 3 weeks with initial parenteral and follow-up oral antibiotics.

515

Infections involving bone may require 6 to 8 weeks or longer, depending on how quickly the infection responds to treatment. Radiographic studies, erythrocyte sedimentation rate, and C-reactive protein measurements can be helpful to monitor recovery. Tuberculous infections are treated for 6 to 12 months, depending on the presence of bone involvement. Actinomyces infection can be difficult to treat because of lack of susceptibility to many antibiotics and the need for prolonged courses of antibiotic therapy, preferentially with penicillin. Treatment of pancreatitis is primarily supportive with elimination of enteral feedings and pain control. There have been some reports of adenovirus treatment with cidofovir, particularly in the bone marrow transplant population.3,40,65

PROGNOSIS Historically, retroperitoneal infections are reported to have high morbidity and mortality rates. However, with modern imaging techniques enabling more timely diagnoses, the overall prognosis is good, and most children with no underlying disease recover without sequelae. NEW REFERENCES SINCE THE SEVENTH EDITION 13. Cheng CH, Tsai MH, Su LH, et al. Renal abscess in children: a 10-year clinical and radiologic experience in a tertiary medical center. Pediatr Infect Dis J. 2008;27:1025-1027. 16. Comploj E, Cassar W, Farina A, et al. Conservative management of paediatric renal abscess. J Pediatr Urol. 2013;9:1214-1217. 28. Hochreiter D, Lin J, Singh J, Shetty AK. Renal abscess due to community-acquired extended-spectrum β-lactamase-producing Escherichia coli in a 15-year-old girl. Urology. 2015;85:1480-1482. 34. Karli A, Belet N, Danaci M, et al. Iliopsoas abscess in children: report on five patients with a literature review. Turk J Pediatr. 2014;56:69-74. 41. Linder BJ, Granberg CF. Pediatric renal abscesses: a contemporary series. J Pediatr Urol. 2015;1:e1-e5. 42. Logan LK, Braykov NP, Weinstein RA, et al. Extended-spectrum β-lactamaseproducing and third-generation cephalosporin-resistant Enterobacteriaceae in children: trends in the United States, 1999–2011. J Pediatric Infect Dis Soc. 2014;3:320-328. 54. Rote AR, Bauer SB, Retik AB. Renal abscess in children. J Urol. 1978;119:254-258.

The full reference list for this chapter is available at ExpertConsult.com.

CHAPTER 54  Retroperitoneal Infections REFERENCES 1. Altemeier WA, Alexander JW. Retroperitoneal abscess. Arch Surg. 1961;83:512-524. 2. Ashkenazi S, Even-Tov S, Samra Z, et al. Uropathogens of various childhood populations and their antibiotic susceptibility. Pediatr Infect Dis J. 1991;10:742-746. 3. Bateman CM, Kesson AM, Shaw PJ. Pancreatitis and adenoviral infection in children after blood and marrow transplantation. Bone Marrow Transplant. 2006;38:807-811. 4. Benammar S, Helardot PF, Sapin E, et al. Childhood actinomycosis: report of two cases. Eur J Pediatr Surg. 1995;5:180-183. 5. Bonadio WA, Smith DS, Madagame E, et al. Escherichia coli bacteremia in children. Am J Dis Child. 1991;145:671-674. 6. Bresee JS, Edwards MS. Psoas abscess in children. Pediatr Infect Dis J. 1990;9:201-206. 7. Brook I. The role of anaerobic bacteria in perinephric and renal abscesses in children. Pediatrics. 1994;93:261-264. 8. Brook I. Microbiology of retroperitoneal abscesses in children. J Med Microbiol. 1999;48:697-700. 9. Brook I, Frazier EH. Microbiological analysis of pancreatic abscess. Clin Infect Dis. 1996;22:384-385. 10. Brook I, Frazier EH. Aerobic and anaerobic microbiology of retroperitoneal abscesses. Clin Infect Dis. 1998;26:938-941. 11. Bryant RE, Fox K, Oh G, et al. Beta-Lactam enhancement of aminoglycoside activity under conditions of reduced pH and oxygen tension that may exist in infected tissues. J Infect Dis. 1992;165:676-682. 12. Chen WC, Huang JK, Chen KK, et al. Retroperitoneal abscesses. Chin Med J. 1990;46:208-212. 13. Cheng CH, Tsai MH, Su LH, et al. Renal abscess in children: a 10-year clinical and radiologic experience in a tertiary medical center. Pediatr Infect Dis J. 2008;27:1025-1027. 14. Cheng CH, Tsau YK, Lin TY. Is acute lobar nephronia the midpoint in the spectrum of upper urinary tract infections between acute pyelonephritis and renal abscess? J Pediatr. 2010;156:82-86. 15. Chrysos G, Kokkoris S, Protopsaltis J, et al. Coxsackie infection associated with acute pancreatitis. J Pancreas. 2004;5:384-387. 16. Comploj E, Cassar W, Farina A, et al. Conservative management of paediatric renal abscess. J Pediatr Urol. 2013;9:1214-1217. 17. Crepps JT, Welch JP, Orlando R III. Management and outcome of retroperitoneal abscesses. Ann Surg. 1987;205:276-281. 18. De la Rubia L, Herrera MI, Cebrero M, et al. Acute pancreatitis associated with rotavirus infection. Pancreas. 1996;12:98-99. 19. Devin B, McCarthy A, Mehran R, et al. Necrotizing fasciitis of the retroperitoneum: an unusual presentation of group A Streptococcus infection. Can J Surg. 1998;41:156-160. 20. Dib M, Bedu A, Garel C, et al. Ilio-psoas abscess in neonates: treatment by ultrasound-guided percutaneous drainage. Pediatr Radiol. 2000;30:677-680. 21. Dinc H, Onder C, Turhan AU, et al. Percutaneous catheter drainage of tuberculous and nontuberculous psoas abscesses. Eur J Radiol. 1996;23:130-134. 22. Edelstein H, McCabe RE. Perinephric abscess in pediatric patients: report of six cases and review of the literature. Pediatr Infect Dis J. 1989;8:167-170. 23. Feo CF, Dessanti A, Franco B, et al. Retroperitoneal abscess and omphalitis in young infants. Acta Paediatr. 2003;92:122-125. 24. Franco J, Fernandes R, Oliveira M, et al. Acute pancreatitis associated with varicella infection in an immunocompetent child. J Paediatr Child Health. 2009;45: 547-548. 25. Frank AL, Marcinak JF, Mangat D, et al. Community-acquired and clindamycin susceptible methicillin-resistant Staphylococcus aureus in children. Pediatr Infect Dis J. 1999;18:993-1000. 26. Greenstein AJ, Dreiling DA, Aufses AH Jr. Crohn’s disease of the colon. Am J Gastroenterol. 1975;64:306-318. 27. Haddock G, Coupar G, Youngson GG, et al. Acute pancreatitis in children: a 15 year review. J Pediatr Surg. 1994;29:719-722. 28. Hochreiter D, Lin J, Singh J, et al. Renal abscess due to community-acquired extended-spectrum β-lactamase-producing Escherichia coli in a 15-year-old girl. Urology. 2015;85:1480-1482. 29. Hoffer FA, Shamberger RC, Teele RL. Ilio-psoas abscess: diagnosis and management. Pediatr Radiol. 1987;17:23-27. 30. Holliday PO 3rd, Davis CH Jr, Shaffner LS. Intervertebral disc space infection in a child presenting as a psoas abscess: case report. Neurosurgery. 1980;7:395-397. 31. Jain P, Nijhawan S, Rai RR, et al. Acute pancreatitis in acute viral hepatitis. World J Gastroenterol. 2007;13:5741-5744. 32. Kandula L, Lowe ME. Etiology and outcome of acute pancreatitis in infants and toddlers. J Pediatr. 2008;152:106-110. 33. Kang M, Gupta S, Gulati M, et al. Ilio-psoas abscess in the paediatric population: treatment by US-guided percutaneous drainage. Pediatr Radiol. 1998;28:478-481.

515.e1

34. Karli A, Belet N, Danaci M, et al. Iliopsoas abscess in children: report on five patients with a literature review. Turk J Pediatr. 2014;56:69-74. 35. Khuroo MS, Zargar SA, Mahajan R. Hepatobiliary and pancreatiac ascariasis in India. Lancet. 1990;335:1503-1506. 36. Konstantinou GN, Liatsos CN, Patelaros EG, et al. Acute pancreatitis associated with herpes simplex virus infection: report of a case and review of the literature. Eur J Gastroenterol Hepatol. 2009;21:114-116. 37. Kline MW, Kaplan SL, Baker CJ. Acute focal bacterial nephritis: diverse clinical presentations in pediatric patients. Pediatr Infect Dis J. 1988;7:346-349. 38. Kuhns LR. Computed tomography of the retroperitoneum in children. Radiol Clin North Am. 1981;19:495-501. 39. Latawiec-Mazurkiewicz I, Juszkiewicz P, Pacanowski J, et al. Tumour-like inflammatory abdominal conditions in children. Eur J Pediatr Surg. 2005;15:38-43. 40. Legrand F, Berrebi D, Houhou N, et al. Early diagnosis of adenovirus infection and treatment with cidofovir after bone marrow transplantation in children. Bone Marrow Transplant. 2001;27:621-626. 41. Linder BJ, Granberg CF. Pediatric renal abscesses: a contemporary series. Eur J Pediatr Urol. 2015;1:e1-e5. 42. Logan LK, Braykov NP, Weinstein RA, et al. Extended-spectrum β-lactamaseproducing and third-generation cephalosporin-resistatnt Enterobacteriaceae in children: trends in the United States, 1999–2011. J Pediatr Infect Dis Soc. 2014;3:320-328. 43. March AW, Riley LH, Robinson RA. Retroperitoneal abscess and septic arthritis of the hip in children. J Bone Joint Surg. 1972;54-A:67-74. 44. Martinez-Aguilar G, Avalos-Mishaan A, Hulten K, et al. Community-acquired, methicillin-resistant and methicillin-susceptible Staphylococcus aureus musculoskeletal infections in children. Pediatr Infect Dis J. 2004;23:701-706. 45. Martinez-Roig A, Bonet-Alcaina M, Casellas-Montagut M, et al. Pancreatitis in typhoid fever relapse. Pediatr Infect Dis J. 2009;28:74. 46. Mishra A, Saigal S, Gupta R, et al. Acute pancreatitis associated with viral hepatitis: a report of six cases with review of literature. Am J Gastroenterol. 1999;94:2292-2295. 47. Mondor C, Gauthier M, Garel L, et al. Nonsurgical management of neonatal adrenal abscess. J Pediatr Surg. 1988;23:1048-1050. 48. Nakagawa M, Ogino H, Shimohira M, et al. Continuous regional arterial infusion therapy for acute necrotizing pancreatitis due to Mycoplasma pneumoniae infection in a child. Cardiovasc Intervent Radiol. 2009;32:581-584. 49. Negus S, Sidhu PS. MRI of retroperitoneal collections: a comparison with CT. Br J Radiol. 2000;73:907-912. 50. Okada Y, Yamataka A, Ogasawara Y, et al. Ilio-psoas abscess caused by methicillinresistant Staphylococcus aureus (MRSA): a rare but potentially dangerous condition in neonates. Pediatr Surg Int. 2004;20:73-74. 51. Pannaraj P, Hulten JG, Gonzalez BE, et al. Infective pyomyositis and myositis in children in the era of community-acquired methicillin-resistant Staphylococcus aureus infection. Clin Infect Dis. 2006;43:953-960. 52. Parenti DM, Steinberg W, Kang P. Infectious causes of acute pancreatitis. Pancreas. 1996;13:356-371. 53. Parri N, Innocenti L, Collini S, et al. Acute pancreatitis due to rotavirus gastroenteritis. Pediatr Emer Care. 2010;26:592-593. 54. Rote AR, Bauer SB, Retik AB. Renal abscess in children. J Urol. 1978;119:254-258. 55. Santaella RO, Fishman EK, Lipsett PA. Primary vs secondary iliopsoas abscess. Arch Surg. 1995;130:1309-1313. 56. Schwaitzberg SD, Pokorny WJ, Thurston RS, et al. Psoas abscess in children. J Pediatr Surg. 1985;20:339-342. 57. Sedaghatian MR, Barkhordar J, Gerami S. Retroperitoneal abscess presenting as an abdominal mass in neonate. J Pediatr Surg. 1978;13:544-545. 58. Siegel MJ, Balfe DM, McClennan BL, et al. Clinical utility of CT in pediatric retroperitoneal disease: 5 years’ experience. Am J Roentgenol. 1982;138:1011-1017. 59. Simons GW, Sty JR, Starshak RJ. Retroperitoneal and retrofascial abscesses. J Bone Joint Surg Am. 1983;65:1041-1058. 60. Thapa R, Biswas B, Mallick D, et al. Acute pancreatitis – Complicating hepatitis E virus infection in a 7-year-old boy with glucose 6 phosphate dehydrogenase deficiency. Clin Pediatr. 2009;48:199-201. 61. Vachvanichsanong P, Dissaneewate P, Patrapinyokul S, et al. Renal abscess in healthy children: report of three cases. Pediatr Nephrol. 1992;6:273-275. 62. Werlin SL, Kugathasan S, Frautschy BC. Pancreatitis in children. J Pediatr Gastroenterol Nut. 2003;37:591-595. 63. Wippermann CF, Schofer O, Beetz R, et al. Renal abscess in childhood: diagnostic and therapeutic progress. Pediatr Infect Dis J. 1991;10:446-450. 64. Woods CR, Edwards MS. Renal abscess caused by group B Streptococcus. Clin Infect Dis. 1994;18:662-663. 65. Yusuf U, Hale GA, Carr J, et al. Cidofovir for the treatment of adenoviral infection in pediatric hematopoietic stem cell transplant patients. Transplantation. 2006;81:1398-1404.

SECTION 9  ■  Musculoskeletal Infections

55 

Osteomyelitis Paul Krogstad

INTRODUCTION The term osteomyelitis denotes inflammation of bone and marrow but generally implies the presence of infection. Osteomyelitis is considered acute if diagnosed within 2 weeks of the onset of symptoms or subacute if symptoms have been present for more than 2 weeks at the time of presentation. Although bacteria are the most common cause, fungi, parasites, and other microorganisms also may cause osteomyelitis. These microorganisms can be introduced into bone in three ways: (1) by direct inoculation, usually traumatic, but also during surgery or due to the presence of orthopedic fixation devices; by local invasion from a contiguous focus of infection; and (3) by hematogenous delivery. In children, osteomyelitis is generally of hematogenous origin. Regardless of the route of infection, the goal of treatment is to arrest the infection and limit the extent of the injury to bone. The incidence of osteomyelitis in normal children has been examined in several populations. Estimates have varied from 1 in 20,000 adolescent girls in New Zealand to 1 in 1000 Australian Aboriginals.37,64,65,106,175 Boys contract the disease 1.2 to 3.7 times more often than do girls.106,114,207,243 Osteomyelitis occurs most often in the first 2 decades of life. Approximately 25% of children with osteomyelitis are younger than 2 years old, and 50% are younger than 5 years.107,153,193,270 The incidence is increased in people with sickle-cell disease and in some other immunocompromised individuals (see the section on special populations). Although routine cultures fail to identify bacterial pathogens in approximately one-quarter to one-half of all cases of osteomyelitis in children, most microbiologically confirmed infections are caused by a single type of organism.10,33,193,211 When polymicrobial infections are encountered, they may reflect the spread of infection from contiguous infectious foci and most often occur in the skull, face, hands, or feet. Distal extremities compromised by vascular insufficiency or immobilized because of peripheral neuropathy also are sites of polymicrobial osteomyelitis.211 Gram-positive bacteria are most often identified, especially Staphylococcus aureus9,10,107,175,178,193,206,222,263 and Streptococcus pyogenes; together they account for 80% to 90% of cases in most series (Table 55.1). However, these data are largely derived from studies using traditional microbiological approaches. By contrast enhanced culture techniques and PCR studies285 have revealed that Kingella kingae, a fastidious gram-negative organism, is an important cause of osteoarticular infections in young children, including osteomyelitis, diskitis, and septic arthritis. Reports demonstrating the importance of Kingella infections as a cause of osteoarticular infections in young children have come from countries as diverse as Israel, the United States, Australia, Switzerland, and Iceland.66,76,112,166,175,271,286 K. kingae osteomyelitis has been identified at a frequency equal to S. pyogenes in some series,166,175 and in several reports Kingella infections exceeded those of gram-positive pathogens.50,51,54 Streptococcus pneumoniae has been a frequent cause of osteomyelitis in the past, but protein conjugate vaccines have markedly reduced the frequency of invasive pneumococcal infections, including pneumococcal osteomyelitis. Similarly Haemophilus influenzae used to cause approximately 5% to 8% of cases and was found primarily in infants and younger children.84,94,115,142,153,193,216,222,256,268 Cases of H. influenzae osteomyelitis are noticeably absent from case series published since 2000, likely reflecting the impact of widespread immunization against this organism.10,107,144,206,216,289 516

Even in affluent countries Salmonella spp. are occasionally a cause of osteomyelitis in immunocompetent patients, and Salmonella spp. appear to be the most common organism found in cases of osteomyelitis in patients with sickle-cell disease (see later discussion).9,43,178,193 Osteomyelitis caused by Escherichia coli and other aerobic enteric gram-negative organisms is also seen, generally in neonates and young infants.94,148 Osteomyelitis caused by Pseudomonas aeruginosa has been associated with injection drug use.129,159,279 Although rare in comparison to osteomyelitis caused by aerobic bacteria, four distinct clinical entities of osteomyelitis caused by anaerobic bacteria are recognized: (1) bacteremic seeding of previously normal bones in children and young adults161; superinfection of a fracture site already infected with S. aureus; (3) indolent (months to years after surgery) infection of a prosthetic device; and (4) contiguous chronic infection,257 which most often occurs in the skull and the extremities. Bacteroides spp. are found most commonly and are associated with paranasal, sinus, or mastoid infection. In most cases, a foul odor is noted when the bone is incised or the focus is opened; trauma often has been an inciting influence.161 Osteomyelitis caused by fungi and other rare bacterial pathogens is discussed in greater detail later.

HEMATOGENOUS OSTEOMYELITIS Pathogenesis In long tubular bones, hematogenous osteomyelitis generally begins in the metaphysis, the broad cancellous end of the bone shaft adjacent to the epiphyseal growth plate. The cartilaginous epiphyseal growth plate (the physis) is nourished by diffusion of nutrients from capillaries fed by the metaphyseal branches of a nutrient artery. In a long-standing model of disease, capillaries drain into a large sinusoidal plexus that ultimately joins the large sinusoidal veins in the bone marrow (Fig. 55.1).127 Trauma or emboli lead to occlusion of the slow-flowing sinusoidal vessels, establishing a nidus for infection. Blood-borne bacteria can seed the poorly perfused area and proliferate.58,138,265 Others have suggested that the capillaries adjacent to the physis are open ended, permitting deposition of bacteria into this critical location.245 The high frequency of S. aureus in osteomyelitis may reflect specific pathogenic properties of the organisms, including the ability to adhere to type I collagen of bone fibrils.44 When S. aureus binds to collagen, bacterial replication gives rise to microcolonies surrounded by a glycocalyx.120 Continued injury, elicited by S. aureus exoproducts and the host cellular inflammatory response to the injury, causes the accumulation of exudate under pressure. The pressure compresses blood vessels of bone and produces focal bone necrosis. The low ratio of surface area to mass, combined with the blood vessel anatomy described earlier, interferes with reabsorption of necrotic cortical bone58,138 and the effectiveness of host defense mechanisms. The very early stages of osteomyelitis may be aborted by administration of appropriate chemotherapy. In the absence of therapy, necrosis of cortical bone and marrow continues. The exudate under pressure is forced through the Haversian systems and Volkmann canals and into the cortex (see Fig. 55.1). Beginning in the late 1990s, community-acquired methicillin-resistant S. aureus (CA-MRSA) isolates became a common cause of musculoskeletal infections in the United States and other countries. Most of these CA-MRSA isolates from cases of osteomyelitis carry genes encoding

517

CHAPTER 55  Osteomyelitis

TABLE 55.1  Etiology of Acute Hematogenous Osteomyelitis in Children in Microbiologically Confirmed Cases (%) Organisms Gram-Positive Bacteria Staphylococcus aureus Coagulase-negative staphylococci Streptococcus pneumoniae Other streptococci Gram-Negative Bacteria Haemophilus influenzae Pseudomonas aeruginosa Salmonella spp. Escherichia coli Kingella kingae Mixed or unusual organisms

Nelson193 (n = 296)

LaMont et al.153 (n = 90)

Peltola et al.206 (n = 252)

Masson et al.175 (n = 95)

Goegens et al.107 (n = 45)

McNeil et al.178 (n = 190)

67 3

70 1

75

65 4

85

83

2 12

5 16

4 10

2 10

4 8

2 10

4 3 2 64 >64 >64 0.25 0.5–1 2 0.25 >32 8 0.12–0.5 ≤0.12 >4

Modified from Jacobs MR. Antimicrobial-resistant Streptococcus pneumoniae: trends and management. Expert Rev Anti Infect Ther. 2008;6(5):619–35. a Susceptible, ≤0.06 µg/mL; intermediate, 0.12–1 µg/mL; resistant, ≥2 µg/mL). Values are shown as MIC values or ranges in µg/mL that inhibit 90% or more of isolates (MIC90). b Amoxicillin component. c Trimethoprim component. MIC, Minimum inhibitory concentration; NA, not available.

is determined by how many and to what extent targets are modified.93 Restructuring of PBPs is mediated by stepwise alterations in PBPs. The high-molecular-weight PBPs—types 1A, 2X, and 2B—that usually are detected in S. pneumoniae are involved in transpeptidase activity and play an important role in resistance.222 Alterations in PBP-2B are associated with low-level resistance to penicillin, and alterations in PBP-2X mediate low-level resistance to cephalosporins. The additional alterations in PBP-1A raise penicillin MICs to 1 µg/mL or greater and cefotaxime MICs to 0.5 µg/mL or greater. Genomic comparison between S. pneumoniae and commensal S. mitis and S. oralis strains has documented the mosaic nature of PBPs among these species, with pneumococci acquiring their altered PBP genes from S. mitis and S. oralis.221 Many other mosaic gene clusters not associated with penicillin resistance also have been found.187 The capacity to produce branched cell wall stem peptides encoded by altered murM and murN genes, as well as altered

PBPs, is required for expression of penicillin resistance in S. pneumoniae.169 The fibA and fibB genes, which are homologous to the Staphylococcus aureus femA/B genes required for expression of methicillin resistance in this organism, encode proteins involved in the formation of interpeptide bridges and also are required for expression of PBPmediated penicillin resistance.588 Other mechanisms of β-lactam resistance have been described in laboratory mutants and in a clone of Hungarian pneumococcal strains with notably high levels of β-lactam resistance (penicillin MIC, 16 µg/mL; cefotaxime MIC, 4 µg/mL).222,519 Resistance to Non–Β-Lactam Drugs The molecular and genetic mechanisms of resistance to macrolides, chloramphenicol, tetracycline, fluoroquinolones, and trimethoprimsulfamethoxazole in S. pneumoniae also have been determined. Resistance genes for several agents are carried on a transposon, Tn1545.110 It confers

874

SECTION 16  Bacterial Infections

TABLE 85.4  In Vitro Activity of Selected Antimicrobial Agents Against 891 Pneumococci Collected in 2008 From 22 Centers in the United States for All Isolates and for the 11 Predominating Serotypes PERCENT SUSCEPTIBILITY OF ISOLATES BY SEROTYPE (NO. OF ISOLATES)

Agent (CLSI Breakpoint for Susceptibility [µg/mL])

All (891)

19A (189)

3 (82)

35B (59)

7F (52)

11A (49)

6C (43)

15A (38)

22F (35)

23A (33)

23B (33)

19F (29)

Penicillin G (≤2) Ceftriaxone (≤1) Imipenem (≤0.12) Penicillin V (≤0.06) Amoxicillin/clavulanate (≤2) Cefuroxime (≤1) Erythromycin (≤0.25) Clindamycin (≤0.25) Levofloxacin (≤2) Moxifloxacin (≤1) Vancomycin (≤1) SXT (≤0.5) Linezolid (≤2)

86.2 90.7 76.2 58.6 83.1 70.1 61.6 79.2 99.4 99.6 100 66.2 100

46.6 65.6 40.2 13.8 45.0 36.1 26.5 43.4 100 100 100 16.9 100

100 100 100 98.8 100 100 95.1 96.3 100 100 100 97.6 100

98.3 98.3 15.3 10.2 62.7 9.6 64.4 100 98.3 100 100 100 100

100 100 100 100 100 100 100 100 100 100 100 100 100

100 98.0 95.9 95.9 98.0 95.2 75.5 95.9 100 100 100 87.8 100

100 100 90.7 37.2 100 47.5 41.9 97.7 100 100 100 34.9 100

100 100 100 10.5 100 91.4 5.3 10.5 100 100 100 55.3 100

100 100 100 100 100 100 88.6 100 100 100 100 97.1 100

100 100 100 36.4 100 96.4 78.8 81.8 100 100 100 90.9 100

100 97.0 100 84.8 100 96.8 75.8 100 97.0 97.0 100 84.8 100

37.9 65.5 20.7 20.7 37.9 20.7 17.2 31.0 96.6 96.6 100 17.2 100

Modified from Jacobs MR, Good CE, Windau AR, et al. Activity of ceftaroline against recent emerging serotypes of Streptococcus pneumoniae in the United States. Antimicrob Agents Chemother. 2010;54(6):2716-9. CLSI, Clinical and Laboratory Standards Institute; SXT, trimethoprim-sulfamethoxazole.

resistance to three antimicrobial classes—kanamycin (aphA-3), macrolidelincosamide-streptogramin B–type antibiotics (ermB), and tetracycline (tetM). This transposon has been conjugated and transposed to the chromosome of Enterococcus faecalis, oral streptococci, and Listeria monocytogenes. The properties of this transposon account for the sudden emergence, rapid dissemination, and stabilization of resistance to multiple antibiotics in S. pneumoniae in the absence of plasmids. Resistance mechanisms include the production of chloramphenicol acetyltransferase, an enzyme capable of catalyzing the conversion of chloramphenicol to nonfunctional derivatives. Chloramphenicol acetyltransferase is encoded by a chloramphenicol acetyltransferase (cat) gene identical to the cat gene from the S. aureus plasmid pC194. Tetracycline resistance occurs through ribosomal protection encoded by the genes tetM and tetO. The tetM and tetO proteins are thought to cause tetracycline to be released from the ribosome. Resistance to fluoroquinolones primarily involves mutations in the DNA gyrase gene gyrA and in the topoisomerase IV genes parC and parE, as well as an efflux mechanism that affects some fluoroquinolones. Resistance to trimethoprim is mediated through a single amino acid substitution in the chromosomal dihydrofolate reductase gene of S. pneumoniae, which is thought to disrupt the bond with trimethoprim without affecting the action of dihydrofolate reductase. Sulfonamide resistance appears to result from repetitions of one or two amino acids in the chromosomal dihydropteroate synthase.597 Two major mechanisms have been described for resistance to erythromycin. Co-resistance to macrolides, clindamycin, and streptogramin B–type antibiotics is a result of modification of the ribosome through methylation of an adenine residue in domain V of the 23S rRNA. Methylation is encoded by a methylase gene, ermB (previously called ermAM). Resistance to 14- and 15-membered macrolides (erythromycin, azithromycin, and clarithromycin) but not to 16-membered macrolides (roxithromycin, josamycin, and spiramycin), ketolides, or clindamycin is a result of efflux of the antibiotic from the cell; such resistance is encoded by the gene mefE in S. pneumoniae and appears to be emerging rapidly as the predominant mechanism of resistance to erythromycin in many countries.187 Other macrolide resistance mechanisms that have been described include mutations in position 2059 of the 23S rRNA and in genes encoding ribosomal protein L4.537 Vancomycin Tolerance Although vancomycin resistance has not been described in pneumococci, antibiotic tolerance, or the ability of bacteria to survive but not grow in the presence of antibiotics, has been described. It has been shown

to be caused by loss of function of the VncS histidine kinase of a twocomponent gene expression sensor-regulator system in S. pneumoniae that produces tolerance to vancomycin and other classes of antibiotics.409 Evolution of Antibiotic Resistance Pneumococci initially were susceptible to many antimicrobial agents, but they became resistant with varying degrees of rapidity to many of these agents. The earliest example was the development of resistance to optochin (ethylhydrocupreine) when this agent was used experimentally in mice in the early part of the 20th century. With the introduction of sulfonamides in 1939, pneumococci similarly exhibited an ability to acquire resistance in experimental infections in mice, as well as in a human case of meningitis.310 Sulfonamide resistance was identified sporadically thereafter, and a trimethoprim-sulfamethoxazole–resistant strain was recognized first in 1972. Trimethoprim-sulfamethoxazole resistance subsequently has become widespread in virtually all serotypes throughout the world, including developing countries, and resistance to this agent is greater than that to any other antimicrobial class worldwide.245 Tetracycline resistance emerged in the 1960s and chloramphenicol resistance in 1970. However, little attention was paid to the development of resistance in this species until 1977, when isolates resistant to several antimicrobial classes—including penicillins, chloramphenicol, tetracyclines, macrolides, clindamycin, and trimethoprimsulfamethoxazole—were detected in South Africa.22,270 Subsequently, multiresistant clones of pneumococci have spread throughout many regions of the world. Noteworthy is that multiresistant clones are confined mostly to serotype 14 and serogroups 6, 9, 19, and 23.131 Whereas resistance to penicillins occurs in a stepwise fashion and in many cases can be overcome by using β-lactams with appropriate pharmacokinetics, resistance to other drug classes usually is absolute, and distinct populations of strains are found to be susceptible and resistant to agents such as macrolides, clindamycin, tetracyclines, trimethoprim-sulfamethoxazole, and chloramphenicol. Unlike enterococci, resistance to vancomycin has not developed in pneumococci yet, although vancomycin-tolerant strains have been detected.46,242 Cross-resistance among S. pneumoniae to macrolides and other classes of antibiotics usually increases with increasing MICs to penicillin268 (Fig. 85.12). Whereas only 6% of penicillin-susceptible pneumococci are resistant to macrolides and 14% to trimethoprim-sulfamethoxazole, approximately half of the penicillin-intermediate isolates were resistant to these agents. In the case of penicillin-resistant strains, three-quarters were resistant to macrolides, 90% to trimethoprim-sulfamethoxazole,

CHAPTER 85  Pneumococcal Infections

Percentage of isolates (µg/mL)

100 90 80 70

TMP-SMX–resistant Macrolide-resistant Clindamycin-resistant Doxycycline-resistant

60 50 40 30 20 10 0

Penicillinsusceptible

Penicillinintermediate

Penicillinresistant

FIG. 85.12  Pneumococci often are resistant to several drug classes, and cross-resistance to macrolides and other classes of antibiotics increases as minimal inhibitory concentrations of penicillin increase. TMP-SMX, trimethoprim-sulfamethoxazole. (From Jacobs MR. Antimicrobial-resistant Streptococcus pneumoniae: trends and management. Expert Rev Anti Infect Ther. 2008;6:619–35.)

and 28% to clindamycin. However, this pattern is not the case in all countries, and at least one multiresistant clone resistant to chloramphenicol, tetracycline, erythromycin, clindamycin, and trimethoprimsulfamethoxazole has remained susceptible to penicillin.135,536 Strains of S. pneumoniae were exquisitely susceptible to penicillin (MICs of 0.01 to 0.03 µg/mL) when this agent initially was used clinically in the 1940s and 1950s, and this MIC range is referred to as the baseline activity of penicillin against “wild-type” S. pneumoniae.264 Evolution of resistance to this class of agents was noted first when a few strains of S. pneumoniae were isolated in the 1960s in Australia and New Guinea. These strains had decreased susceptibility to penicillin, with MICs of 0.1 to 0.25 µg/mL, approximately 10-fold higher than the MICs of baseline strains. Strains with penicillin MICs of 2 to 4 µg/mL, approximately 100-fold higher than baseline strains, were isolated in South Africa in 1977; subsequently, strains with even higher MICs (16 µg/ mL, approximately 1000-fold higher than baseline strains) were described in Hungary.519 Pneumococci conventionally are classified as penicillinsusceptible if the MICs are 0.06 µg/mL or less, intermediate if the MICs are 0.12 to 1.0 µg/mL, and resistant if the MICs are 2.0 µg/mL or greater. This classification is useful mainly in characterizing strains as fully susceptible to β-lactams if susceptible or as having decreased susceptibility if intermediate or resistant. Strains with such decreased susceptibility are better referred to as β-lactam drug-challenged because the mechanism of resistance can be overcome if the pharmacokinetics of the β-lactam drug used in serum or at the site of infection exceeds the MIC for 40% to 50% of the dosing interval.112 Similar variations in MIC ranges are seen with all β-lactams, although MIC ranges for many β-lactams are much higher than that for penicillin itself. Agents such as ampicillin, amoxicillin, cefotaxime, and ceftriaxone have MIC ranges similar to that of penicillin, whereas agents such as cefazolin, cefaclor, cefprozil, ceftazidime, and cefixime have much higher MIC ranges. For example, the baseline activity of cefaclor against S. pneumoniae is 0.5 to 1 µg/ mL, which is a concentration approximately 20- to 30-fold higher than that required for penicillin to inhibit the most susceptible strains. Changes in susceptibility that occur over the course of time were illustrated in a study of recent versus archived otitis media strains. In this study, the MIC90 for cefaclor against archived isolates was 1 µg/mL, whereas the MIC90 against recent isolates was greater than 64 µg/mL.266 A few agents, such as imipenem and meropenem, have slightly lower MIC ranges than those of penicillin. The proportion of pneumococci that are penicillin susceptible, intermediate, and resistant vary considerably throughout the world. Resistance to macrolides in strains of S. pneumoniae was noted first in 1964 and was detected sporadically in the United States until it became widespread in the latter half of the 1990s.245,259,310 The baseline activity of macrolides (0.03 µg/mL) and MIC distributions (1000-fold

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concentration range, 0.03 to >32 µg/mL) against S. pneumoniae are somewhat similar to those of penicillin. The MIC distribution of macrolides is trimodal, with strains being exquisitely susceptible (erythromycin MIC ≤0.03 µg/mL) or highly resistant (erythromycin MIC ≥32 µg/mL) or demonstrating low-level resistance (MICs of 1–16 µg/mL).163 These distributions closely correlate with macrolide ribosomal methylase and efflux resistance mechanisms. The prevalence of macrolide resistance and reports of clinical failure resulting from strains with efflux and ribosomal methylase resistance mechanisms continue to increase. Some authors, however, have argued that isolates with efflux-mediated resistance could be susceptible to the high intracellular concentrations that these agents achieve in phagocytic cells and in epithelial lining fluid of the alveoli.14 However, no clinical or animal data support these arguments for extracellular pathogens such as S. pneumoniae, whereas considerable clinical and animal data support the use of current breakpoints.43,111,112,385 The rising incidence of macrolideresistant pneumococci was directly proportional to the increasing use of macrolides in various communities and age groups.184,259,440 Strains with multiple antibiotic resistance have greater selective advantages than do strains resistant to just one antibiotic because the opportunity for positive selection is increased as the number of drug classes to which isolates are resistant increases.311 Exposure to different classes of antibiotics allows more opportunity for selective advantage to a multiple antibiotic–resistant organism than to a monoresistant strain, which must wait to encounter the one antibiotic to which it is resistant and is likely to be killed by agents of other antibiotic classes. Thus, the increasing prevalence of antibiotic-resistant pneumococci is associated with the increasing prevalence of multidrug-resistant strains. Therefore, one is not surprised that the use of one class of antibiotics (mainly macrolides and trimethoprim-sulfamethoxazole) can be associated with an increase in resistance to other classes of antibiotics (mainly β-lactam drugs).3,23,202,440 Many authorities now think that antibiotic agents such as the newer macrolides (e.g., clarithromycin and azithromycin) and trimethoprim-sulfamethoxazole are stronger promoters of antibiotic resistance among S. pneumoniae strains than are the β-lactam drugs.23,202,440 Researchers also have suggested that among the β-lactam drugs, cephalosporins are stronger promoters of resistance in S. pneumoniae than are the aminopenicillins.184,488 Although many strains are resistant to tetracyclines and macrolides, they are susceptible to the new tetracycline derivatives, the glycylcyclines, as well as to streptogramins, ketolides, glycopeptides, oxazolidinones, and rifampin. Many strains are resistant to trimethoprim-sulfamethoxazole worldwide, with more than 40% being resistant in the United States. Fluoroquinolones with antipneumococcal activity (e.g., gatifloxacin, levofloxacin, moxifloxacin) are active against most strains of S. pneumoniae. However, in several countries where fluoroquinolones have been prescribed widely, clinically relevant levels of resistance have been described.95,245 No doubt, antibiotic resistance will continue to evolve and challenge us.

HOST DEFENSES Although anticapsular antibody is the most prominent protective mechanism against pneumococcal infection, many host responses to infection occur and many other factors are associated with protection against disease.399 Pneumococcal infection and disease have been modeled in several animal species. Most are models of sepsis arising from intravenous or intraperitoneal inoculation of bacteria, and only a few were designed to study disease arising from intranasal infection. Chinchillas provide the only animal model of middle ear pneumococcal infection in which the disease can be produced by very small inocula injected into the middle ear or intranasally. This model, developed at the University of Minnesota in 1975, has been used to study pneumococcal pathogenesis at a mucosal site, the immunogenicity and efficacy of pneumococcal capsular polysaccharide vaccine antigens, and the kinetics and efficacy of antimicrobial drugs.193

Anticapsular Serum IgG Antibody IgG to the capsular polysaccharide of S. pneumoniae is thought to provide the greatest degree of protection against systemic pneumococcal disease

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SECTION 16  Bacterial Infections

and limited protection against colonization. The reference method for measurement of antibody is the opsonophagocytosis assay, which involves serial dilutions of serum, viable pneumococci, complement, and viable PMNs incubated together for 1 hour.472 An infant mouse assay system for assessment of protective concentrations of human serum pneumococcal anticapsular antibodies correlated well with opsonophagocytic titer but not with naturally occurring IgG antibody concentrations or IgG produced in response to nonconjugated polysaccharide vaccines, as determined by ELISA.283,404 However, the ELISA method of serotypespecific antibody assay with absorption of cross-reacting antibody to cell wall polysaccharides does correlate well with protection after vaccination with conjugated vaccine, and it is the method used most commonly to predict serotype-specific immunity.21,561,562 The development of a phagocytosis assay based on flow cytometry has not overcome the limitations of the ELISA method and is inferior to the opsonophagocytosis method.276 Investigation of polymorphisms in the variable region of IgG that affect protective function has indicated that the capsular polysaccharide antibody repertoire in adults is derived from memory B-cell populations that have switched class and undergone extensive hypermutation.355 Functionally disparate anticapsular polysaccharide antibodies can arise within individuals both by activation of independent clones and by intraclonal somatic mutation, which illustrates the complexity of assaying and interpreting serum capsular polysaccharide antibody levels.

Anticapsular IgA Antibody The role of IgA in the control of invasive mucosal pathogens such as S. pneumoniae is understood poorly. Human pneumococcal capsular polysaccharide–specific IgA initiates dose-dependent killing of S. pneumoniae in the presence of complement and phagocytes. The majority of specific IgA in serum is of the polymeric form, and the efficiency of killing initiated by this polymeric form exceeds that of monomeric IgA–initiated killing. In the absence of complement, specific IgA induces minimal bacterial adherence, uptake, and killing. Killing of S. pneumoniae by resting phagocytes with immune IgA requires complement, predominantly via the C2-independent alternative pathway, which, in turn, requires factor B but not calcium. Pneumococcal capsule–specific IgA may have distinct roles in effecting the clearance of pneumococci in the presence or absence of inflammation, and the polymeric form may control pneumococcal infections locally and after the pathogen’s entry into the bloodstream by several mechanisms.274

Phagocytosis and Leukocyte IgG Receptors IgG-mediated phagocytosis by PMNs is the main defense against S. pneumoniae. Two leukocyte IgG receptors, FcγRIIa and FcγRIIIb, are expressed constitutively on PMNs. Blocking experiments have shown that FcγRIIa is crucial for opsonophagocytosis of serum-opsonized S. pneumoniae. In adults, serum-induced phagocytic activity depends mainly on antipneumococcal IgG2 antibodies.471 However, in infants and young children, the main response to pneumococcal conjugate vaccines occurs in the IgG1 subclass.21,571 Investigators have suggested that IgG1 subclass antibodies are at least as highly functional as IgG2.158 Recruitment and function of neutrophils also are important host defenses. In a pneumococcal infection model in immunocompetent and immunodeficient mice intranasally infected with S. pneumoniae type 2, immunocompetent BALB/c mice were resistant and immunodeficient CBA/Ca mice were susceptible to infection. BALB/c mice recruited significantly more neutrophils in the lungs, and inflammatory lesions were visible much earlier than in CBA/Ca mice.197

Antibodies to Surface Proteins and Pneumolysin PspA, PsaA, and pneumolysin are common to virtually all pneumococcal isolates. The development of antibodies to PspA, PsaA, and pneumolysin as a result of pneumococcal infection and carriage in young children was determined by measurement of serum antibodies to these proteins by ELISA in children at ages 6, 12, 18, and 24 months and in their mothers. All age groups were shown to produce antibodies to the three proteins, which increased with age and were associated strongly with pneumococcal exposure as a result of carriage or AOM.456 IgA to PspA, PsaA, and pneumolysin has been detected by ELISA in the saliva of

children aged 6 to 24 months.511 This finding was associated with pneumococcal carriage and otitis media. Serum antipneumolysin IgG at the time of hospital admission has been found to be higher in patients with nonbacteremic pneumococcal pneumonia than in those with bacteremic pneumococcal pneumonia or uninfected control subjects.403 Serum antipneumolysin IgG levels also rose significantly during convalescence in patients with bacteremic pneumonia, and the levels attained were equal to those observed in nonbacteremic patients. Children aged 6 to 24 months were shown to produce antibodies to pneumolysin, and antibody concentrations increased with age and were associated strongly with pneumococcal exposure, whether by carriage or infection such as AOM.456 Infants also have been shown to mount a specific antibody response to pneumolysin during AOM.457

Defense Mechanisms of the Spleen The spleen is the principal organ that clears pneumococci from the bloodstream.399,326 Opsonized particles are removed from the circulation by the liver, but with decreasing opsonization, the spleen increasingly assumes the role of clearance. The slow passage of blood through the spleen and the prolonged contact time with reticuloendothelial cells in the cords of Billroth and the splenic sinuses allow time for the removal of nonopsonized particles. Overwhelming pneumococcal infection occurs in children and adults whose spleens have been removed or do not function normally. Pneumococcal disease progresses so rapidly in such individuals that pneumonia is not detectable clinically or by chest radiographs, although it is seen at autopsy. The increase in the incidence of pneumococcal bacteremia and meningitis in children with sickle-cell disease is due largely to splenic dysfunction. Splenectomy also results in a marked, sustained elevation in risk of severe infection due to S. pneumoniae in HIV patients.445

Vitamin A The association of nasopharyngeal colonization with S. pneumoniae and vitamin A supplementation in infants in an area with endemic vitamin A deficiency in southern India showed that neonatal vitamin A supplementation delayed the age at which colonization occurs. Therefore, it may play a role in lowering morbidity rates associated with pneumococcal disease.107

C-Reactive Protein C-reactive protein (CRP) is a normal constituent of human serum that is synthesized by hepatocytes and induced by proinflammatory cytokines. The function of this acute-phase reactant includes activation of complement and enhancement of opsonophagocytosis. CRP binds to phosphorylcholine, a constituent of eukaryotic membranes that also is found on the cell surface of the major bacterial pathogens of the human respiratory tract, including S. pneumoniae and H. influenzae. CRP is present in inflamed (0.17–42 µg/mL) and uninflamed (