The World Health Organization defines pneumonia as the presence of cough and fast or difficult breathing (above 50 breaths per minute for children 2 to 12 months of age; above 40 breaths per minutes for children 12 months to 5 years of age).1 This broad definition may encompass other causes of lower respiratory tract infection including bronchiolitis as well as noninfectious causes of respiratory distress such as asthma. A more specific definition for pneumonia 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.
Over 4 million children are diagnosed with pneumonia each year in the United States.3 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.3–6 This incidence decreases to approximately 16 cases per 1000 children 5 years of age or older.7 In 1996, the incidence of death from community-acquired pneumonia (CAP) in US children was <5 per 100,000; this figure represents a mortality rate of <1% per episode of pneumonia that requires hospitalization. Though mortality rates attributable to CAP have decreased by 97% over the past 50 years,8 more than 600,000 children annually require hospitalization for the management of CAP and its complications.3,9
A predisposition for respiratory tract infections seems to be a risk factor for developing pneumonia as evidenced by a study of 201 children with CAP between 3 months and 15 years of age.10 Compared to 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 33–1. Viruses are an important cause of childhood pneumonia.11–14 Respiratory viruses may be the primary cause of pneumonia or viral infection may predispose to bacterial superinfection by causing extensive tracheobronchial inflammation. Streptococcus pneumoniae remains the most common bacterial cause of lobar pneumonia outside of the perinatal period though its frequency may be decreasing as a result of the seven valent pneumococcal protein–polysaccharide conjugate vaccine (PCV7) licensed in 2000.15 Three randomized, double-blind controlled trials, one in the United States and two in developing countries, have demonstrated that vaccination with a pneumococcal conjugate vaccine decreased the incidence of CAP.16–18 The Kaiser Permanente trial in Northern California enrolled 37,868 children; 11% of control patients developed CAP during the study period.16 The decrease in pneumonia among PCV7 vaccinated patients was 20.5% when pneumonia was defined by the presence of clinical symptoms plus an abnormal chest radiograph.16 A subsequent observational study revealed that pneumonia-associated hospitalizations decreased by 39% in the ...