Increase in meningococcal disease associated with the emergence of a novel ST-11 variant of serogroup C Neisseria meningitidis in Victoria, Australia, 1999-2000.

In the years 1999-2000, there was an increase in the incidence of meningococcal disease in Victoria, largely caused by Neisseria meningitidis serogroup C. This change was associated with a shift in age distribution of cases, with relatively more disease appearing in the 15-29 year age group, and with 40/58 serogroup C isolates in 2000 exhibiting a new macrorestriction pattern (pattern A). Thirty-four of 52 pattern A isolates tested displayed the novel phenotype C:2a:P1.4, and were consistently porA VR type P1.7-2,4 by DNA sequencing. Nine of 10 representative pattern A isolates analysed displayed a housekeeping gene allele profile (ST-11) that is characteristic of the electrophoretic type (ET)-15 variant that has caused outbreaks in Canada, the Czech Republic and Greece. Meningococci belonging to the ST-11 complex that were isolated in Victoria prior to 1999 did not display either restriction pattern A or PorA VR type P1.7-2,4.