Pneumococcal isolations from patients with pneumonia and control subjects in a prepaid medical care group.

The incidence of pneumococcal infections and pneumonia among the 150,000 members of a prepaid medical care group in Seattle was assessed by an intensive study of outpatients for one year from June 1971 through May 1972. Respiratory specimens (sputum, pharyngeal, and nasal) from patients with pneumonia or febrile respiratory disease and from age- and sex-matched control subjects were cultured for pneumococci on media and in mice. Total rate of pneumonia was 11 per 1,000. Twenty-four per cent of patients with pneumonia and 12 per cent of control subjects carried pneumococci. The patients with pneumonia from whom the pneumococcus was isolated did not differ clinically on average from those without such isolates. Lobar and bacteremic pneumonia were extremely rare. The rate of pneumococcal infections and carriers was highest in the spring. Although young children had the highest rate of pneumonia from all causes there was no difference in the isolation rate between ill children and control children. The highest rate attributable to pneumococci was in those larger than 40 years of age. Pneumococcal carrier rates were much lower than those reported in the 1930s. Thirty-nine per cent of patients with pneumonia had evidence of viral or mycoplasmal infection, as determined primarily by serologic methods. Pneumococcal pneumonia was not a serious problem in this average, employed population in Seattle.