Received: December 4, 2011; Accepted: October 10, 2012; Published: October 10, 2012
Methods: Daily air pollutant measures were obtained from 14 regional monitoring stations in Ontario. Daily counts of asthma-attributed hospitalizations, emergency department (ED) visits, and outpatient visits were obtained from a provincial registry of 1.5 million individuals with asthma. Poisson regression was used to estimate health services rate ratios (RR) as a measure of association between the AQHI or individual pollutants and health services use. We adjusted for age, sex, season, year, and region of residence.