Propensity of pneumococcal serotypes for invasive disease (meningitis) given carriage, relative to other serotypes or -groups.

The invasiveness index was calculated using all cases of pneumococcal meningitis with serotype or -group information identified during the dry season months of 2007–2009 (N = 113) and pneumococcal carriage (N = 166) identified in Bobo-Dioulasso, Burkina Faso, March 2007– February 2009. Serotyping was based on cerebrospinal fluid polymerase chain reaction testing [8] or Quellung reaction on invasive isolates; and on Quellung reaction for carriage isolates. The table reports serotypes that were found in at least one meningitis case, found in at least three carriers, or included in 10- or 13-valent pneumococcal conjugate vaccines.*Discrimination within the serogroup or between serotypes not possible for some meningitis cases due to PCR algorithm.†PCR serotyping on invasive isolates or CSF cannot discriminate between 12A/B/F, while Quellung typing of carriage isolates identified 12F only.‡Cornfield estimation of the confidence interval possible only under certain conditions.