Absence of increasing incidence of meningitis caused by Haemophilus influenza type b.

An epidemiologic survey of meningitis caused by Haemophilus influenzae type b in children aged zero to four years during an 11-year period (January 1965-December 1975) was conducted in the Baltimore, Maryland, metropolitan area to examine recent trends in the incidence of this disease. Cases of H. influenzae meningitis were identified at all 19 hospitals in the city and county of Baltimore and all 41 hospitals in the surrounding area. The population at risk (age, zero to four years) was estimated using yearly birth rates provided by the state of Maryland and U.S. Census information for 1960 and 1970. Yearly age-adjusted incidence was calculated; in contrast to previous studies, there was no significant increase in the annual incidence (range, 12-27; mean, 19.3/100,000 population at risk). Previous reports of recent increases in the incidence of meningitis caused by H. influenzae type b may be due to differences in study techniques.