Abstract
BACKGROUND: Pneumonia is recognized as a leading cause of morbidity in seniors. However, the overall burden of this disease--and, in particular, the contribution of ambulatory cases to that burden--is not well defined. To estimate rates of community-acquired pneumonia and to identify risk factors for this disease, we conducted a large, population-based cohort study of persons aged >or=65 years that included both hospitalizations and outpatient visits for pneumonia. METHODS: The study population consisted of 46,237 seniors enrolled at Group Health Cooperative who were observed over a 3-year period. Pneumonia episodes presumptively identified by International Classification of Diseases, Ninth Revision, Clinical Modification codes assigned to medical encounters were validated by medical record review. Characteristics of participants were defined by administrative data sources. RESULTS: The overall rate of community-acquired pneumonia ranged from 18.2 cases per 1000 person-years among persons aged 65-69 years to 52.3 cases per 1000 person-years among those aged >or=85 years. In this population, 59.3% of all pneumonia episodes were treated on an outpatient basis. In multivariate analysis, risk factors for community-acquired pneumonia included age, male sex, chronic obstructive pulmonary disease, asthma, diabetes mellitus, congestive heart failure, and smoking. CONCLUSIONS: On the basis of these data, we estimate that roughly 915,900 cases of community-acquired pneumonia occur annually among seniors in the United States and that approximately 1 of every 20 persons aged >or=85 years will have a new episode of community-acquired pneumonia each year.