Aim: To estimate how risk of acute respiratory infection (ARI) hospitalization in children attending childcare facilities with a recently (within 1 month) hospitalized child is affected by gender, age and other characteristics.
Methods: Population-based prospective cohort study of 436 434 Danish 0-5-year-old children attending childcare during 1989-2004. Information was collected from Danish registers. Main outcome measure was incidence rate ratios (IRRs) of in-patient hospitalization for ARI.
Results: During 1 777 999 person-years of follow-up 42 681 hospitalizations for ARI occurred, of which 362 (1%) occurred within 1 month after another child was hospitalized for ARI in the facility. Children attending a facility with a recent ARI hospitalization had an increased risk of 42% (95% CI 27%;60%) compared with other children. The increased risk was higher in 0-2-year-old children than in 3-5-year-old children (55% vs 17%, p = 0.02) and if the latest hospitalized child was 0-2 years rather than 3-5 years (52% vs 19%, p = 0.04). The increased risk was similar in boys and girls, but was higher if the latest hospitalized child was a boy rather than a girl (52% vs 13%, p = 0.02).
Conclusion: Although occurring infrequently, clustering of ARI hospitalizations involve 0-2-year-olds and boys as first hospitalized child relatively more often than would be expected.