Emergency department visits for asthma in relation to the Air Quality Health Index: a case-crossover study in Windsor, Canada.

OBJECTIVES In this study, associations of short-term changes in ambient air pollution with emergency department (ED) visits for asthma were examined in hospitals in the area of Windsor, Ontario. Ambient air pollution quality was represented by the Air Quality Health Index(AQHI), calculated using a formula that combines the concentrations and the relative health impacts of three ambient air pollutants: ozone , nitrogen dioxide and fine particulate matter. METHODS Data on ED visits were retrieved from the National Ambulatory Care Reporting System. Only patients two years of age and older were considered. A time-stratified case-crossover design was applied to 6,697 ED visits for asthma for the period of April 2004 to December 2010. Odds ratios (ORs) and their corresponding 95% confidence intervals (CIs) for ED visits associated with increased (by one unit) levels of AQHI were calculated by applying conditional logistic regression. RESULTS Positive and statistically significant results were observed between AQHI levels and ED visits for asthma. For all patients the largest value, OR=1.17 (CI: 1.09, 1.26), was obtained for exposures lagged by 9 days in the warm season (April-September). Effects among children 2 to 14 years of age were observed for same-day exposure (lag 0), with an OR=1.11(CI: 1.01, 1.21). CONCLUSION Exposure to ambient air pollution in Windsor increases the risk of ED visits for asthma. When the adverse effects of air pollutants are increased, patient visits to the ED depend on the patient's age.