Changing patterns of case ascertainment and trends in meningococcal disease in England and Wales.

We have reviewed data on meningococcal disease routinely collected in England and Wales from 1989 to 1995 to illustrate and explain changing patterns and guide future surveillance. Statutory notifications of meningococcal meningitis and septicaemia, laboratory confirmed infections, and death registrations coded as meningococcal disease were analysed in terms of their numbers, the age of cases, season of the report, and (if available) site of isolation, serogroup, and serotype. Case fatality rates were estimated for clinically diagnosed and culture confirmed cases. The number of cases notified each year, in particular those notified as septicaemia, rose significantly over the period (p < 0.0001) but there was no net change in the number of culture confirmed cases. Case fatality rates estimated from routine data fell, most markedly for cases notified as septicaemia, but the true case fatality rate of culture confirmed cases did not change between 1993 and 1995. These data suggest that reporting practice changed between 1989 and 1995 and that the ascertainment of clinically diagnosed disease improved, particularly for meningococcal septicaemia. Late in 1995, reports from all data sources increased and the age distribution of both notified and laboratory confirmed cases changed. These changes were accompanied by an increase in the proportion of infections due to Neisseria meningitidis of serogroup C and a significant increase in serotype C2a infections (p < 0.0001). Continuing efforts to reconcile data from several sources will be needed to ensure that routine data can be interpreted accurately to provide evidence for the development of future vaccination policy and to monitor vaccination programmes. In addition, the role of non-culture diagnosis will be crucial in enhancing surveillance based on clinical diagnoses.