Invasive pneumococcal disease in Danish children, 1996-2007, prior to the introduction of heptavalent pneumococcal conjugate vaccine

Aim: The aim of this study was to document the epidemiology, microbiology and outcome of invasive pneumococcal disease (IPD) among children < 16 years with quality surveillance data, just prior to the introduction of the heptavalent pneumococcal conjugate vaccine (PCV7) into the Danish routine immunization programme October 2007. Methods: Clinical and microbiological records on cases of IPD in children < 16 years admitted to Hvidovre Hospital, Denmark 1996-2007, were retrospectively reviewed. Results: We identified 106 cases of IPD. The annual incidence of IPD was 11 per 100 000 in children < 16 years, but considerably higher, 62 per 100 000, in children < 2 years. Additionally, of the children with pneumococcal meningitis 86% were < 2 years. We observed no fatalities. A total of 10% developed sequelae, but of the patients with pneumococcal meningitis 27% developed sequelae. Nine patients had known risk factors. The Streptococcus pneumoniae serotype was available for 81 cases. Seventy-five percent of the IPD cases in children aged < 2 years were caused by one of the serotypes contained within PCV7, compared to only 24% in children >= 2 years. Conclusion: Our data indicate that an estimated 75% of all IPD cases among children < 2 years are caused by PCV7 serotypes and might therefore be prevented by PCV7 vaccination.