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

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. Multilocus enzyme electrophoresis (MEE) has demon-strated for meningococci a high degree of genetic variation, which permits differentiation among strains of different serotypes and subtypes of the organism (6, 8, 16). Conse-quently, MEE has been used to delineate the intercontinen-tal spread of group B disease due to a very closely related set of clones designated the ET 5 complex (5) and the intercon-tinental spread of group A disease due to a clone designated III-1 (14). During the winter of 1988 and 1989, a focal outbreak of nine cases of disease due to serogroup C, serotype 2