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 diseas e (IMD) in Canada with respect to demographic variables and characteri stics of the isolated strains of Neisseria meningitidis. Design.-Natio nal surveillance case series. Setting.-Canada, 1985 through 1992. Outc ome 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 on e strain of the electrophoretic type 37 (ET-37) complex of N meningiti dis,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 surv eillance, rapid identification, and typing of N meningitidis will assi st public health decision making in the control of emerging strains.