Epidemiologic information frequently is useful in guiding differential diagnosis and management (see Chapter 21). 18 In most cases of acute pneumonia, extensive invasive testing is not warranted. 2, 16, 17 Etiologic agents causing pneumonia vary by age, underlying illnesses, maturity, and condition of the immune system. 15 Confirming etiology of bacterial pneumonia is challenging because of coexistence of bacteria as pathogens as well as normal upper respiratory tract flora, and because of occurrence of bacteremia in only 1% to 10% of hospitalized children with presumed bacterial pneumonia. 13, 14 Some cases have more than one pathogen identified, making assigning etiology difficult. 12 In two studies of immunocompetent children with pneumonia, specific etiologic agents were confirmed in only 43% to 66%. The true prevalence of the pathogens causing LRI is uncertain because microbial etiology is ascertained infrequently, owing to difficulty in differentiating infection from colonization and lack of dependable diagnostic laboratory tests. Multiple microbes, most predominantly viruses and bacteria, cause LRI in infants and children.
Risk factors for pneumonia in children >5 years of age include wheezing at any age and ≥3 episodes of URI within 12 months. 1, 8, 9, 10 Additional risk factors associated with pneumonia in children 3 episodes in 12 months), wheezing at any age, and history of otitis media requiring tympanocentesis before 2 years of age. 7 Multiple factors predispose to acquisition of LRI: daycare and school attendance, indoor crowding, passive exposure to smoke, lack of or underimmunization, alcohol abuse in adolescents causing aspiration pneumonia, and underlying medical conditions such as low birth weight, bronchopulmonary dysplasia, asthma, heart disease, seizures, neuromuscular illness, gastroesophageal reflux disease, malnutrition, immunocompromised state, sickle cell disease, and cystic fibrosis.
In the US, lower respiratory infections (LRIs) occur throughout the year but excessively during the fall and winter when children are confined indoors, resulting in more efficient spread of the infections by contact or droplet transmission.
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