Seasonal variation in the prevalence of persistent otitis media with effusion in one-year-old infants

The objective of this population-based cohort study was to evaluate the pre valence of persistent otitis media with effusion (OMB) and its seasonal var iation in 12-month-old infants. All 30 099 infants born in the eastern part of The Netherlands between 1 January 1996 and 1 April 1997 were invited fo r hearing screening, comprising a protocol of three possible tests. Those w ho failed all three screening tests were referred to an ENT clinic for exam ination. Prevalences (i.e. the probability that a child would fail all the screening tests) were calculated by searching for the best logistic model f or the first, second and third screening test as well as for the visit to a n ENT department. By multiplying the prevalences found by the different mod els with each other, a prevalence was calculated that accounted for increas ing age and the timing of the successive hearing tests. Furthermore, 95% co nfidence intervals were calculated for this age-season-corrected prevalence . When all the children attended the hearing tests at 9, 10, 11 and 12 mont hs of age and when the number of births was the same in all months, the ove rall prevalence was 4.8% [95% CI 4.3, 5.2]. The highest prevalence (8.0%) w as found in April, and the lowest (1.5%) in October. Rates of bilateral OME during the late winter months were twice as high as those during the late summer.