The panmictic nature of Neisseria meningitidis serogroup B during a periodof endemic disease in Canada

Three hundred and one (301) strains of Neisseria meningitidis serogroup B, isolated from patients with meningococcal disease during the years 1994-199 6, were subjected to multilocus enzyme electrophoresis, serotyping, and ser osubtyping. Based on the analyses of 14 enzyme loci, 177 electrophoretic ty pes (ETs) were identified. Of these, 136 were represented by single isolate s and 41 were represented by multiple isolates (range 2-31). The mean genet ic diversity for isolates was 0.444 and for ETs was 0.440. The index of ass ociation (I-A) between loci was 0.530 +/- 0.08 for isolates and 0.256 +/- 0 .10 for ETs. Cluster analysis revealed the presence of 39 lineages each rep resented by a single ET or clusters of ETs. The most common serotypes were 4, 15, and 14 and accounted for 84 (28.0%), 53 (17.6%), and 32 (10.6%) of t he isolates, respectively, and were dispersed amongst 46 ETs (1-122), 35 ET s (3-165), and 26 ETs (18-76), respectively. The 109 (36.6%) nontypable (NT ) isolates were amongst 74 ETs (6-177). The mean genetic diversity for sero types 4, 15, and 14 and NT isolates was 0.368, 0.371, 0.343, and 0.442, res pectively, and for ETs was 0.363, 0.354, 0.397, and 0.440, respectively. Co mbinations of serotypes and serosubtypes (number of isolates) that occurred most frequently were 4:P1.14 (17), 14:P1.16 (16), NT:P1.16 (16), 15:P1.16 (13), and NT:P1.13 (13). The majority of group B disease in Canada during 1 994-1996 was caused by meningococci of considerable genetic diversity, and reflects a situation of endemic disease. However, the results also indicate that organisms belonging to the ET-5 complex, which has been responsible f or outbreaks of group B disease globally for several decades, have been int roduced into the country.