The epidemic wave of meningococcal disease in Spain in 1996-1997: probably a consequence of strain displacement.

ABSTRACT

During 1996 and 1997 an epidemic wave of meningococcal disease took place in Spain. Initial studies described the antigenic expression of the epidemic strain as C2bP1.2,5 and proposed that it was a variant of the previously identified Spanish C2bnon-subtypable epidemic strain. To clarify this hypothesis, 1036 C2bP1.2(5) and 76 C2bNST isolates obtained during 1992-1999 were analysed by pulsed-field gel electrophoresis. The majority of the C2bP1.2,5 and C2bP1.2 isolates showed one of two very closely related profiles. During the epidemic period, 80% of the C2bNST strains showed these two pulsotypes. However, before the epidemic wave, most of these C2bNST strains (60%) showed a profile that was found infrequently among C2bP1.2,5 and C2bP1.2 isolates. A similar evolution was observed in C2bP1.5 isolates. Thirty-four C2bP1.2(5) and 10 C2bNST isolates, exhibiting representative pulsotypes, were subjected to multi-locus sequence typing. Isolates belonging to both A4 and ET-37 lineages were identified. These data point to the possibility that the A4 cluster has displaced the ET-37 complex among serogroup C meningococci in Spain.