Continuing diversification of Neisseria meningitidis W135 as a primary cause of meningococcal disease after emergence of the serogroup in 2000

Abstract

The occurrence of a clonal outbreak of serogroup W135 (of the electrophoretic type 37 [ET-37] clonal complex) meningococcal disease among Hajj pilgrims in 2000 has led to enhanced surveillance of the evolution of this particular serogroup, formerly considered rare, in invasive infections. Since the first case of meningococcal disease due to a serogroup W135 strain was detected in France in 1994, all isolates were characterized phenotypically. We further used phenotypic and genotypic approaches to type the 101 serogroup W135 strains isolated from patients with invasive meningococcal diseases in France in 2001 and 2002. Overall, 55% of these isolates had Hajj strain-related phenotypes (60 and 52% in 2001 and 2002, respectively), although only 45% belonged to the ET-37 clonal complex. Moreover, pulsed-field gel electrophoresis of the ET-37 clonal complex isolates showed that only 32% of the serogroup W135 isolates were indistinguishable from the 2000 Hajj-related strain. Our results suggest the continuous emergence of new genetic lineages of serogroup W135 independently of the 2000 global outbreak.

FIG. 1.

Distribution of meningococcal isolates with Hajj strain-related or non-Hajj strain-related phenotypes among invasive W135 strains isolated in France between 1994 and 2002. The percentage of meningococcal invasive strains of serogroup W135 is given for each year with respect to the total number of invasive strains.

FIG. 2.

MLDF-based dendrogram obtained by the unweighted pair-group method of averages algorithm showing the genetic distances among invasive W135 strains isolated in 2001 (A) and 2002 (B) in France. Genetic distances were calculated on the basis of the amplified fragment length restriction polymorphisms of the pilA, pilD, crgA, regF, and iga genes. Each MLDF group was assigned an arbitrary number. The number of strains in each group as well as the phenotypes observed in each group is indicated. The corresponding sequence type was determined for the major MLDF group. Hajj strain-related phenotypes are underlined. ND, not determined.

FIG. 3.

PFGE profiles observed among strains belonging to the ET-37 clonal complex. The dendrogram on the left was obtained by using the Taxotron package and the unweighted pair-group method of averages algorithm. Each PFGE group was assigned an arbitrary letter. All 45 strains were typed by MLST. The number of strains in each group and their sequence types are indicated. Profile A corresponds to the strain from the Hajj 2000 outbreak.