Emergence of a virulent clone of Neisseria meningitidis serotype 2a that is associated with meningococcal group C disease in Canada.

Multilocus enzyme electrophoresis was used to characterize 378 isolates of Neisseria meningitidis serogroup C recovered during a period of an increase in group C meningococcal disease in Canada. Thirty-four enzyme electrophoretic types were found among the isolates, which were predominantly (96.0%) serotype 2a. One clone (ET 15), characterized by a rarely occurring allele for the enzyme fumarase, was responsible for a focal outbreak in Ontario followed by the spread of group C disease across the province. This clone, which occurred infrequently among strains isolated in 1986, accounted for over 65% of group C strains associated with meningococcal disease in Canada in 1990.