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

OBJECTIVE: 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.
DESIGN: National surveillance case series.
SETTING: Canada, 1985 through 1992. OUTCOME MEASURES: Morbidity and mortality. MAIN
RESULTS: 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%.
CONCLUSIONS: 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.