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, aureus, which might explain the increase in S aureus-related otitis media after vaccination.