Early acute otitis media and siblings' attendance at nursery.
To assess the relation between early acute otitis media and exposure to respiratory pathogens mediated by siblings and other children, a prospective cohort of 3754 Norwegian children born in 1992-3 was followed up from birth to 12 months. Of these, 25% had one or more episodes of acute otitis media during the first year. Results from multiple logistic regression analysis adjusted for confounding showed that siblings' attendance at daycare is the most important risk factor for early acute otitis media (adjusted odds ratio, ORadj = 1.9). The total number of children in the daycare setting is another determinant for early acute otitis media (ORadj = 2.0 in groups of four or more other children and ORadj = 1.3 in groups of one to three other children, as compared to those who are cared for alone). Having siblings in daycare outside the home and the number of children in the daycare setting are the most important determinants for early acute otitis media.