Worldwide, community-acquired pneumonia (CAP) is a leading cause of infectious morbidity and mortality in children. A major clinical challenge persists—determining the role of viral and bacterial pathogens in pediatric pneumonia. Studies that employ blood and respiratory cultures, serology, and molecular detection suggest a small role for bacterial pathogens, while those that rely on pneumococcal conjugate vaccines (PCVs) as a probe to determine the proportion of disease due to Streptococcus pneumoniae suggest that pneumococcus is the major pathogen. Evolving insight from epidemiologic, molecular detection, and vaccine probe studies suggests that viral-bacterial interactions have a substantial role in the pathogenesis of pediatric pneumonia. In addition, the importance of comorbid illness as a risk factor for both increased incidence and poorer outcomes of pneumonia has emerged from recent studies.
CAP is most frequent in infants and toddlers and remains the most common cause of hospitalization in children. During the period from 2010 to 2012, following the introduction of the 13-valent PCV (PCV13) in the United States, the incidence of CAP requiring hospitalization was 15.7 per 100,000 in those < 18 years of age, with the highest rate among those less than 2 years of age (62 per 100,000). Mortality due to CAP in high-income countries is low, at < 1 per 1000 patient-years in children less than 5 years of age. Males are affected almost twice as commonly as females. Differences in incidence are also reported by socioeconomic status and ethnicity. Rates of pneumococcal pneumonia are higher in native Alaskan children than in nonnatives, as well as in children of African American, Hispanic, and Asian ethnicity compared to Caucasian children. These differences have narrowed, but have not been completely eliminated, in the era of universal immunization with PCVs. The incidence of CAP also varies by season; studies in the United States and Israel report greater frequency in the winter and spring months and in association with annual peaks of respiratory syncytial virus (RSV), influenza A, and, in older children, Mycoplasma pneumoniae. Comorbid illness has been recognized as both predisposing to pneumonia and as being associated with increased severity and morbidity. Children with congenital and acquired immune deficiencies represent a well-known high-risk group, but excess risk and morbidity are also found in children with chronic cardiac and pulmonary disease (including severe asthma), diabetes mellitus, neuromuscular disorders, prematurity, and specific genetic disorders (ie, trisomy 21).
Lower respiratory tract infections (RTIs) are both more frequent and associated with increased mortality in low-income countries. The incidence among children less than 5 years old in 10 low-income countries is estimated to range from 0.2 to 8.1 new episodes per 100 child-weeks. Mortality from pneumonia has become uncommon in high-income countries as noted, yet it remains a major cause of death in low-income countries. The countries with the highest incidence of pneumonia in children are located in Africa and Southeast Asia; case fatality rates for pneumococcal pneumonia are estimated to be 5% globally, with 10 countries accounting for most of the deaths (India, China, Nigeria, Pakistan, Bangladesh, Indonesia, Ethiopia, Democratic Republic of the Congo, Kenya, and the Philippines).
A large spectrum of pathogens have the capacity to cause CAP in children. In recent studies using routine and molecular methods, potential pathogens are detected in 65% to 80% of cases. Figure 235-1 details the distribution of viral pathogens, bacterial pathogens, neither, and both isolated from hospitalized, radiograph-confirmed cases of pneumonia, and Figure 235-2 details the frequency of various pathogens recovered from these cases. However, in studies comparing pediatric pneumonia cases with asymptomatic controls, only RSV, influenza viruses, and human metapneumovirus (HMPV) were found more frequently and with greater density in the nasopharynx of pneumonia cases, whereas coronavirus and parainfluenza viruses were found more frequently, and rhinoviruses and ...