Air pollution and ED visits for asthma in Australian children: a case-crossover analysis

Objective We aimed to determine the effects of ambient air pollutants on emergency department (ED) visits for asthma in children. Methods We obtained routinely collected ED visit data for asthma (ICD9 493) and air pollution (PM10, PM2.5, O-3, NO2, CO and SO2) and meteorological data for metropolitan Sydney for 1997-2001. We used the time stratified case-crossover design and conditional logistic regression to model the association between air pollutants and ED visits for four age-groups (1-4, 5-9, 10-14 and 1-14 years). Estimated relative risks for asthma ED visits were calculated for an exposure corresponding to the inter-quartile range in pollutant level. We included same day average temperature, same day relative humidity, daily temperature range, school holidays and public holidays in all models. Results Associations between ambient air pollutants and ED visits for asthma in children were most consistent for all six air pollutants in the 1-4 years age-group, for particulates and CO in the 5-9 years age-group and for CO in the 10-14 years age-group. The greatest effects were most consistently observed for lag 0 and effects were greater in the warm months for particulates, O-3 and NO2. In two pollutant models, effect sizes were generally smaller compared to those derived from single pollutant models. Conclusion We observed the effects of ambient air pollutants on ED attendances for asthma in a city where the ambient concentrations of air pollutants are relatively low.