Association of Streptococcus pneumoniae nasopharyngeal colonization and other risk factors with acute otitis media in an unvaccinated Indian birth cohort

In order to study the epidemiology of acute otitis media (AOM) and Streptococcus pneumoniae nasopharyngeal colonization in the first 2 years of life, we followed up an unvaccinated birth cohort monthly and at visits when sick, with otoscopy to detect AOM and performed nasopharyngeal swabbing to detect S. pneumoniae. Serotyping of positive cultures was also performed. Of 210 babies who were enrolled at birth, 61 (29.05%) experienced 128 episodes of AOM [relative risk 2.63, 95% confidence interval (CI) 1.21-5.75] with maximum incidence in the second half of the first year of life. Episodes ranged from 1 to 7 (mean 2.1 episodes). Most (86.9%) babies with AOM had a positive culture swab giving an odds ratio (OR) of 1.93 (95% CI 1.03-3.62, P = 0.041) for this association. Other risk factors identified for AOM were winter season (OR 3.46, 95% CI 1.56-7.30, P = 0.001), upper respiratory infection (OR 2.43, 95% CI 1.43-4.51, P = 0.005); residents of small households were less likely to develop AOM (OR 0.32, 95% CI 0.17-0.57, P < 0.01). Common S. pneumoniae serotypes isolated during episodes were 19, 6, 15, 35, 7, 23, 9 and 10 which indicated a theoretical coverage for pneumococcal vaccines PCV10 and PCV13 constituent serotypes of 62.8%. We conclude that AOM in Indian infants is often associated with S. pneumoniae colonization of the nasopharynx as well as other risk factors.