Background: Our objective was to use a causal model for childhood asthma to determine whether the effect of day care attendance on asthma was mediated by recurrent respiratory tract infections.
Material and methods: The study is based on a cross-sectional survey among 1,447 children aged 6-16 years in Oslo. Their parents completed written questionnaires. A recursive logit model was used to estimate direct effects in terms of adjusted odds ratios (aOR).
Results: Year of birth, number of siblings and length of maternal education were significantly associated with after-school care attendance. Attendance increased the risk of early infections, aOR = 1.8 (1.3-2.5), and infections were associated with asthma, aOR = 4.9 (3.4-7.3). The crude association between after-school care and asthma was cOR = 1.5 (1.0-2.2), whereas the estimated direct effect was small and non-significant, aOR = 1.2 (0.8-1.9). The results may be influenced by over-reporting of infections among parents with children with asthma.
Interpretation: Our results suggest that children who attend day care have an increased risk of asthma, with early infections as a mediator of risk.