The changing epidemiology of invasive meningococcal disease in Canada, 1985 through 1992. Emergence of a virulent clone of Neisseria meningitidis.

To describe the occurrence of invasive meningococcal disease (IMD) in Canada with respect to demographic variables and characteristics of the isolated strains of Neisseria meningitidis. National surveillance case series. Canada, 1985 through 1992. Morbidity and mortality. The incidence of IMD averaged 1.38 per 100,000 person-years, with considerable regional variation. In 1988, serogroup C organisms became more common, with one strain of the electrophoretic type 37 (ET-37) complex of N meningitidis, termed ET-15, the predominant group C strain identified. With the increase in group C disease, a greater proportion of cases were older than 5 years. By 1991, ET-15 was the most common strain identified in most parts of the country. Electrophoretic type 15 had a case fatality of 17.8% vs 8.1% for all other IMD (P < .001). Among cases 20 years and older the case fatality for ET-15 was 22.4%. The group C, ET-15 strain of N meningitidis, first identified in Canada, was more virulent than other prevalent strains during this period. Active surveillance, rapid identification, and typing of N meningitidis will assist public health decision making in the control of emerging strains.