Interpreting the rising incidence of meningococcal disease in Belgium: thecontribution of molecular typing

During a period of increasing meningococcal disease incidence in Belgium, a ll 538 serogroup B and all 87 serogroup C strains isolated between 1996 and 1998 were investigated by PCR with the arbitrary primer D8635, which is ab le to identify lineage III strains. In all, 399 strains (64%) were attribut ed to lineage III on the basis of PCR-based typing. Since their introductio n in the Belgian population in the early 1990s, lineage III strains have be come increasingly variable in phenotype. Currently, they are represented by strains belonging to 38 different phenotypes, of which 25 were not found i n the period 1990-1995. The 87 serogroup C strains were further investigate d by pulsed-field gel electrophoresis (PFGE), and a subset of 30 strains wa s also investigated by multilocus sequence typing (MLST). Strains of phenot ype C:2b:P1.5,2, which currently constitute the majority of the serogroup C strains, were demonstrated to belong to cluster A4. Comparison of the disc riminatory ability of D8635-primed PCR, PFGE and MLST revealed that D8635-p rimed PCR was the least discriminatory method and PFGE the most discriminat ory method. However, the MLST data were more readily interpreted than the P FGE fingerprint patterns and can be compared easily with data obtained in o ther studies. In conclusion, the ongoing increase of meningococcal disease in Belgium could be attributed not only to the further expansion of lineage III, but also to the introduction of C:2b:P1.5,2 strains of cluster A4 in to the Belgian population.