Epidemiology of invasive pneumococcal disease in the pre-conjugate vaccine era: England and Wales, 1996-2006

OBJECTIVE: To describe the epidemiology of invasive pneumococcal disease (IPD) in England & Wales in the pre-conjugate vaccine era. METHODS: We analysed reports of culture-confirmed IPD submitted to the national surveillance system between July 1996 and June 2006. RESULTS: The incidence of IPD was 10 per 100,000 overall, and increased over time. The typical pattern of IPD by age was observed, with the highest incidence in young children and older adults. There was little change in IPD incidence in the elderly, despite the widespread use of 23-valent pneumococcal polysaccharide vaccines since 2003. The distribution of serotypes changed over time; notably the proportion of cases caused by serotype 14 decreased, and the proportion due to serotype 1 increased. The incidence of meningitis was 0.6 per 100,000 overall, and as a proportion of all IPD cases was most common in children under 1 year of age (30%). Particular serotypes were significantly associated with a presentation of meningitis, after controlling for age and year, and the case:carrier ratio varied markedly by serotype. CONCLUSIONS: This paper provides a baseline for evaluating the impact of 7-valent pneumococcal conjugate vaccines, introduced in September 2006. Ongoing high-quality laboratory-based surveillance of IPD in all age groups is essential.