Otitis media in children: seasonal changes and socioeconomic level.

OBJECTIVE: Our objective was to determine the frequency of otitis media (OM) in relation to socioeconomic and seasonal factors in a city in southern Brazil.
METHODS: A prospective, longitudinal study was carried out with a 3-4-year-old cohort of children randomly selected in schools serving populations of higher socioeconomic status (AB; monthly family income >10 minimum wages, US$ 1000) or lower socioeconomic status (CD; monthly family income < or = 3 minimum wages, US$ 300). The children were assessed in the fall, winter, and spring of 1997 using otoscopy and tympanometry.
RESULTS: Among 156 children who finished the study, 53.8% belonged to socioeconomic group CD. Otoscopy suggested chronic suppurative otitis media (OM) (tympanic membrane perforation or otorrhea) in <6% of children in the CD group, with no seasonal variation. Alterations suggesting secretory otitis media (SOM) were significantly more frequent in the CD group (P< or = 0.001), with a peak in the winter. The prevalence of SOM on otoscopy was: fall (20.9% AB; 38.1% CD); winter (28.6% AB; 81% CD), and spring (23% AB; 49.3% CD). The incidence of SOM in the winter according to tympanometry was 18.4% (group AB) and 72.9% (group CD). Among children with a normal tympanogram in the fall, 44.7% presented a type B tympanogram (presence of middle ear effusion) in the winter. Only 17.6% still presented a type B tympanogram in the spring. From the ears with type B tympanogram in the fall, 80% had the same result in the winter, and 60.9%, in the spring. A sharp seasonal SOM peak was observed in the CD group in the winter.
CONCLUSION: Children in the lower socioeconomic group have a peak incidence of serous otitis media (OM) in the winter. Presence of type B tympanogram in the fall and belonging to socioeconomic group CD are indicators of poor prognosis in terms of the spontaneous resolution of SOM.