Epidemiology of meningococcal disease in England and Wales 1993/94 to 2003/04: contribution and experiences of the Meningococcal Reference Unit.

The laboratory confirmation of meningococcal disease and characterization of Neisseria meningitidis isolates was improved considerably in England and Wales by the Meningococcal Reference Unit between epidemiological years 1993/94 and 2003/04 to meet the challenge of increasing numbers of cases of clinical disease and the requirement for enhanced surveillance. Improved case ascertainment was made possible by the rapid introduction of an innovative centralized reference service for non-culture PCR-based DNA detection of meningococci utilizing the ctrA and siaD PCR assays, complemented by consistent phenotypic characterization of submitted isolates from culture-proven cases. This allowed the increased prevalence of serogroup C disease in specific age groups and the apparent associated increase in mortality from 1995/96 to 1999/00 to be defined, thereby prompting accelerated intervention with the newly licensed meningococcal serogroup C conjugate (MCC) vaccines into the under-25-year UK population (in November 1999). The continued increase in and predominance of serogroup B cases (1993/94 to 2000/01) were observed in conjunction with their diverse and changing phenotypic characteristics. Trends observed to be associated with the predominant phenotypic combinations of serogroup, serotype and sero-subtype were: a decline of both C : 2b and B : 2b meningococci, and a decline of B : 15 : P1.7,16 with a concomitant increase of B : 4 : P1.4 over the 11-year period. Detailed routine surveillance rapidly confirmed the introduction of W135 : 2a : P1.5,2 meningococci into the UK during 2000 and 2001. The importance of continued detailed surveillance of this important pathogen cannot be overestimated, both to monitor the effectiveness of the MCC vaccine and to identify changes within the meningococcal population that can inform the design of anti-serogroup B vaccines.