Pneumococcal acute otitis media in relation to pneumococcal nasopharyngeal carriage

Background: Acute otitis media (AOM) is closely associated with viral upper respiratory tract infections, but the most common microbial agent found in the middle ear fluid during AOM is Streptococcus pneumoniae (Pnc). Pnc is also a common colonizer of the nasopharynx, and its prevalence is further increased during the viral infection. The aim of this study was to investigate the interplay between viral infection, pneumococcal acquisition and carriage in the development of Pnc AOM. Methods: Pnc carriage was assessed in a longitudinal study of 329 infants at scheduled visits at 3, 6, 9, 12, 15 and 18 months of age (N = 1715). The clinical outcome of the first episode of respiratory infection (sick visit, N = 774) in the following 3-month period was recorded. The occurrence and timing of Pnc AOM in relation to serotype specific carriage at the start of the observation period were assessed. Results: The occurrence, timing and duration of symptoms of the sick visits or the frequency of overall AOM were not associated with preceding pneumococcal carriage. Pnc AOM was in each case associated with concurrent carriage and 3.8 times (95% confidence interval, 1.4-10.0) more often with carriage acquired after the start of the observation period than with carriage already present at the scheduled visit. In all, 79% (55 of 70) of Pnc AOM events were caused by a serotype acquired after the start of the period. Conclusion: The majority of Pnc AOM events develop in association with newly acquired carriage of pneumococcus.