Microbial etiology of community-acquired pneumonia in the adult populationof 4 municipalities in eastern Finland

To determine the etiology of community-acquired pneumonia in the adult popu lation of a defined area, specific antibody responses in paired serum sampl es. levels of circulating pneumococcal immune complexes in serum samples, a nd pneumococcal antigen in urine were measured. Samples (304 paired serum s amples and 300 acute urine samples) were obtained from 345 patients greater than or equal to 15 years old with community-acquired, radiologically conf irmed pneumonia, which comprised all cases in the population of 4 municipal ities in eastern Finland during 1 year. Specific infecting organisms were i dentified in 183 patients (including 49 with mixed infection), as follows: Streptococcus pneumoniae, 125 patients; Haemophilus influenzae, 12; Moraxel la catarrhalis, 8; chlamydiae, 37 (of which, Chlamydia pneumoniae, 30); Myc oplasma pneumoniae, 30; and virus species, 27. The proportion of patients w ith pneumococcal infections increased and of those with Mycoplasma infectio ns decreased with age, but for each age group, the etiologic profile was si milar among inpatients and among outpatients. S. pneumoniae was the most im portant etiologic agent. The annual incidence of pneumococcal pneumonia per 1000 inhabitants aged greater than or equal to 60 years was 8.0.