ASSOCIATION BETWEEN OZONE AND ASTHMA EMERGENCY DEPARTMENT VISITS IN SAINT-JOHN, NEW-BRUNSWICK, CANADA

This study examines the relationship of asthma emergency department (E D) visits to daily concentrations of ozone and other air pollutants in Saint John, New Brunswick, Canada. Data on ED visits with a presentin g complaint of asthma (n = 1987) were abstracted for the period 1984-1 992 (May-September). Air pollution variables included ozone, sulfur di oxide, nitrogen dioxide, sulfate, and total suspended particulate (TSP ); weather variables included temperature, humidex, dewpoint, and rela tive humidity. Daily ED visit frequencies were filtered to remove day of the week and long wave trends, and filtered values were regressed o n air pollution and weather variables for the same day and the 3 previ ous days. The mean daily 1-hr maximum ozone concentration during the s tudy period was 41.6 ppb. A positive, statistically significant (p<0.0 5) association was observed between ozone and asthma ED visits 2 days later, and the strength of the association was greater in nonlinear mo dels. The frequency of asthma ED visits was 33% higher (95% CI, 10-56% ) when the daily 1-hr maximum ozone concentration exceeded 75 ppb (the 95(th) percentile). The ozone effect was not significantly influenced by the addition of weather or other pollutant variables into the mode l or by the exclusion of repeat ED visits. However, given the limited number of sampling days for sulfate and TSP, a particulate effect coul d not be ruled out. We detected a significant association between ozon e and asthma ED visits, despite the vast majority of sampling days bei ng below current U.S. and Canadian standards.