Colonisation by Streptococcus pneumoniae and Staphylococcus aureus in healthy children

A trial with a 7-valent pneumococcal-conjugate vaccine in children with recurrent acute otitis media showed a shift in pneumococcal colonisation towards non-vaccine serotypes and an increase in Staphylococcus aureus-related acute otitis media after vaccination. We investigated prevalence and determinants of nasopharyngeal carriage of Streptococcus pneumoniae and S aureus in 3198 healthy children aged 1–19 years. Nasopharyngeal carriage of S pneumoniae was detected in 598 (19%) children, and was affected by age (peak incidence at 3 years) and day-care attendance (odds ratio [OR] 2·14, 95% CI 1·44–3·18). S aureus carriage was affected by age (peak incidence at 10 years) and male sex (OR 1·46, 1·25–1·70). Serotyping showed 42% vaccine type pneumococci. We noted a negative correlation for co-colonisation of S aureus and vaccine-type pneumococci (OR 0·68, 0·48–0·94), but not for S aureus and non-vaccine serotypes. These findings suggest a natural competition between colonisation with vaccine-type pneumococci and S aureus, which might explain the increase in S aureus-related otitis media after vaccination.