Pneumococcal phenotype and interaction with nontypeableHaemophilus influenzaeas determinants of otitis media progression

ABSTRACT Background All-cause otitis media (OM) incidence has declined in numerous settings following introduction of pneumococcal conjugate vaccines (PCVs) despite increases in carriage of non-vaccine pneumococcal serotypes escaping immune pressure. To understand the basis for declining incidence, we assessed the intrinsic capacity of pneumococcal serotypes to cause OM independently and in polymicrobial infections involving nontypeable Haemophilus influenzae (NTHi) using samples obtained from middle ear fluid and nasopharyngeal cultures before PCV7/13 rollout. Methods Data included OM episodes (11,811) submitted for cultures during a 10-year prospective study in southern Israel and nasopharyngeal samples (1588) from unvaccinated asymptomatic children in the same population. We compared pneumococcal serotype diversity across carriage and disease isolates with and without NTHi co-isolation. We also measured associations between pneumococcal phenotype and rate of progression from colonization to OM in the presence and absence of NTHi. Results Whereas pneumococcal serotype diversity in single-species OM is lower than in single-species colonization, serotype diversity does not differ significantly between colonization and OM in mixed-species episodes. Serotypes differed roughly 100-fold in progression rates, and these differences were attenuated in polymicrobial episodes. Vaccine-serotype pneumococci had higher rates of progression than non-vaccine serotypes. While serotype invasiveness was a weak predictor of OM progression rate, efficient capsular metabolic properties—traditionally thought to serve as an advantage in colonization—predicted an enhanced rate of progression to complex OM. Conclusions The lower capacity of non-vaccine serotypes to cause OM may partially account for reductions in all-cause OM incidence despite serotype replacement in carriage following rollout of PCVs.