DEFINITIONS AND EPIDEMIOLOGY
There is no single universally accepted definition for pneumonia; definitions range from sensitive to specific, depending on intended use. For example, the World Health Organization defines pneumonia as the presence of cough and fast or difficult breathing (above 50 breaths per minute for children aged 2–12 months; above 40 breaths per minute for children aged 12 months–5 years).1 This sensitive definition may encompass other causes of lower respiratory tract infection, including bronchiolitis as well as noninfectious causes of respiratory distress such as asthma but was designed to identify all cases of pneumonia given the high pneumonia-associated mortality in the developing world. More specific definitions for pneumonia usually combine clinical signs and symptoms with radiograph findings or microbiologic confirmation. A commonly used definition is “the presence of fever, acute respiratory symptoms, or both, plus evidence of parenchymal infiltrates on chest radiography.”2 This definition allows for the possibility of bacterial as well as viral causes of pneumonia. Varied definitions have led to substantial variation in the management of children with CAP.3–5 In 2011, the Infectious Diseases Society of America (IDSA) and Pediatric Infectious Diseases Society (PIDS) published evidence-based guidelines for the management of children with community-acquired pneumonia (CAP) to address unwarranted variation and provide guidance for pediatric CAP diagnosis and management.6
Pneumonia is the leading worldwide cause of mortality in children younger than 5 years of age, accounting for >2 million deaths annually.7,8 Over 4 million children are diagnosed with pneumonia each year in the United States.9 The annual incidence of pneumonia of 34–56 per 1000 in children <5 years of age is higher than at any other time of life except perhaps in adults >75 years of age.9–12 This annual incidence decreases to approximately 16 cases per 1000 children aged ≥5 years.13 In 2015, the incidence of death from CAP in US children was 0.4 per 100,000 overall, with the highest mortality in infants <1 year of age (4 per 100,000).14 Although mortality rates attributable to CAP have decreased by 97% over the past 50 years,15 more than 150,000 children annually require hospitalization for the management of CAP and its complications.16 CAP is the second costliest and fifth most prevalent cause of hospitalization to children’s hospitals in the United States.17
A predisposition for respiratory tract infections seems to be a risk factor for developing pneumonia as evidenced by a study of 201 children with community-acquired pneumonia between 3 months and 15 years of age.18 Compared with a cohort of healthy controls, children with CAP were more likely to have a history of recurrent respiratory infections during the past year, wheezing episodes, otitis media, and tympanocentesis before the age of 2 years.
Relatively common causes of childhood pneumonia are summarized in Table 36-1. Viruses are the most frequently identified organisms in children <5 years of age with CAP.19–23 Respiratory viruses may be the primary cause of pneumonia, or viral infection may predispose to bacterial superinfection by causing extensive tracheobronchial inflammation. Respiratory syncytial virus (RSV) is the ...