Risk factors for invasive pneumococcal disease in a community with a high proportion of non vaccine serotypes.

The aim of this study was to investigate factors associated with vaccination with 7-pneumococcal conjugate vaccine (PCV7) and risk factors for invasive pneumococcal disease (IPD) and for penicillin-nonsusceptible strains in a community with intermediate vaccination coverage. We conducted a prospective, matched case-control study in children aged 3-59 months with IPD admitted to two hospitals in Catalonia. Three controls matched by hospital, age, sex, date of hospitalization and risk medical conditions were selected for each case. We calculated odds ratios for potential risk factors using logistic regression. Of the 1075 children included, 46.6% were considered fully vaccinated by age. 91.1% of cases were caused by non-PCV7 serotypes. Vaccination with PCV7 was positively associated with attending day care or school and negatively associated with age 24-59 months, >4 cohabitants and low social class. Attending day care or school and >4 cohabitants were risk factors for IPD. Previous antibiotic treatment in children aged 24-59 months was a protective factor for IPD; however, antibiotic use in the previous month and age <24 months were associated with penicillin-nonsusceptible IPD. In a community where IPD in children aged <5 years is caused mainly by non-PCV7 Streptococcus pneumoniae serotypes and where vaccine coverage is only intermediate, attending day care or school, age <24 months, >4 cohabitants and social class were associated with vaccination. Attending day care or school was a strong risk factor for IPD, while vaccination was protective in children aged <24 months. Age and antibiotic use in the previous month were associated with penicillin-nonsusceptible IPD.