A 10-year serogroup B meningococcal disease epidemic in New Zealand: descriptive epidemiology, 1991-2000

Abstract

Objective: New Zealand has experienced an epidemic of meningococcal disease since 1991. This paper describes the characteristics of this epidemic during its first 10 years (1991-2000), current control measures, and potential future interventions.

Methodology: Meningococcal disease surveillance in New Zealand uses combined notification and laboratory data. Population census data from 1991 and 1996 were used to calculate disease rates.

Results: The annual incidence of meningococcal disease increased from 53 cases (1.6 per 100 000 population) in the pre-epidemic year of 1990 to a peak of 613 (16.9 per 100000) in 1997, followed by consistently raised rates. Over the 1996-2000 period, there was an average of 502 cases per year (13.9 per 100 000). The epidemic has resulted in 3547 cases since 1991 approximately 3000 in excess of the number expected based on pre-epidemic disease incidence. Of the total cases, 158 (4.5%) were fatal. A disproportionately large number of cases have been in Maori and Pacific Islands children in the northern part of the North Island of New Zealand. Since 1991, the epidemic has increasingly been dominated by serogroup B meningococci with subtype P1.7b,4, which by 2000 accounted for 84.6% of all cases for whom this testing was carried out. The majority of these organisms were characterised as B:4:P1.7b,4.

Conclusion: Meningococcal disease rates are likely to remain elevated in New Zealand for at least several more years. A vaccine which could induce immunity to the P1.7b,4 PorA subtype may have a role in controlling this epidemic. Efforts are underway to obtain and trial such a vaccine. Measures are also underway to reduce overcrowded living conditions which are contributing to the epidemic. Early recognition and antibiotic treatment of cases improves outcomes and should continue to be promoted. Integrated notification and laboratory-based surveillance of meningococcal disease provides relatively complete surveillance of this disease in New Zealand and has supported the development of public health interventions.