Annual report of the Australian Meningococcal Surveillance Programme, 2005

In 2005 there were 345 laboratory-confirmed cases of invasive meningococcal disease (IMD) analysed by the National Neisseria Network, a nationwide network of reference laboratories. The phenotypes (serogroup, serotype and serosubtype) and antibiotic susceptibility of 214 isolates of Neisseria meningitidis from invasive cases of meningococcal disease were determined and an additional 131 cases were confirmed by non-culture-based methods. Nationally, 251 (73%) confirmed cases were infected with serogroup B and 50 (14.5%) with serogroup C meningococci. The total number of confirmed cases was 16 fewer than the 361 cases identified in 2004. The number of cases decreased in Queensland, Tasmania, New South Wales and the Australian Capital Territory and increased slightly in Victoria, South Australia, Western Australia and the Northern Territory. The age distribution of IMD showed a typical primary peak in those aged four years or less with a lower secondary peak in adolescents and young adults. Serogroup B cases were 90 per cent of all cases in those aged four years or less and 75 per cent in those aged 15-24 years. The proportion of all invasive disease represented by serogroup C disease was highest in the 20-24 years and older age groups. The common phenotypes circulating in Australia were B:15:P1.7 and C:2a:P1.5. However significant jurisdictional differences in the serogroup and phenotypic distribution of meningococci were again evident and considerable heterogeneity of subtypes was noted. No evidence of meningococcal capsular 'switching' or genetic recombination was detected. About two thirds of all isolates showed decreased susceptibility to the penicillin group of antibiotics (MIC 0.06-0.5 mg/L). A single isolate was penicillin resistant at 1 mg/L and another was rifampicin resistant.