Epidemiology of central nervous system infections in Olmsted County, Minnesota, 1950-1981.

We identified all diagnosed cases of infections of the central nervous system (CNS), excluding poliomyelitis, in the population of Olmsted County, Minnesota, from 1950 to 1981 and described incidence, time trends, etiologic agents, and mortality for these infections. The adjusted incidence rate for bacterial meningitis was 8.6/100,000 person-years (with a case fatality ratio of 10%) and was highest in children less than five years of age; in this age-group, rates more than doubled from 1950 to 1981. The adjusted incidence rate of brain abscess was 1.1, with a case fatality ratio of 37%. The adjusted incidence rate of aseptic meningitis was 10.9/100,000 person-years. Age-specific rates were highest in children less than one year of age and in men, and increased during the study period. The adjusted incidence rate of viral encephalitis was 7.4, with a case fatality ratio of 3.8%. Rates were highest in children less than 10 years of age and in men. By 10 years of age, 0.9% of the men and 0.7% of the women were affected by a CNS infection. Cumulative incidence (risk) through age 80 was 2.3% for men and 1.5% for women.