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Community-Acquired Pneumonia Requiring Hospitalization.

To the Editor: With regard to the results of the Centers for Disease Control and Prevention (CDC) Etiology of Pneumonia in the Community (EPIC) study reported by Jain et al. (July 30 issue),1 two related points warrant emphasis. First, although the authors found an increased incidence of pneumonia with increasing age, this study shows that “old” is not so old. The results showed that half of all hospitalizations for communityacquired pneumonia in adults involved patients who were 57 years of age or younger. Second, as noted by the authors, concerted efforts to define a microbial cause did not reveal a pathogen of especially great concern. Responsible microbes were not detected in nearly two thirds of the patients, and no single microbe was associated with more than a small fraction of cases (<9% for every microbe). Thus, pneumonia in adults is less about the microbe and more about the host. The combination of immunemediating antimicrobial activities with homeostatic pathways limiting physiological disruption provides an integrated host defense2 that increases during childhood, in part because of adaptive immunity to respiratory infections,3 but it then becomes compromised by diverse factors during aging, with the result that the risk of pneumonia is increased.4 A person’s susceptibility to pneumonia cannot be measured. New tools are needed to diagnose, track, and counter susceptibility to pneumonia, a chronic disease of aging that has not been effectively addressed.