Air pollution and emergency department visits for respiratory diseases: A multi-city case crossover study.

Increasing evidence suggests that ambient air pollution is a major risk factor for both acute and chronic respiratory disease exacerbations and emergencies. The objective of this study was to determine the association between ambient air pollutants and emergency department (ED) visits for respiratory conditions in nine districts across the province of Ontario in Canada. Health, air pollutant (PM, NO, O, and SO), and meteorological data were retrieved from April 2004 to December 2011. Respiratory diseases were categorized as: chronic obstructive pulmonary disease (COPD, including bronchiectasis) and acute upper respiratory diseases. A case-crossover design was used to test the associations between ED visits and ambient air pollutants, stratified by sex and season. For COPD among males, positive results were observed for NO with lags of 3-6 days, for PM with lags 1-8, and for SO with lags of 4-8 days. For COPD among females, positive results were observed for O with lags 2-4 days, and for SO among lags of 3-6 days. For upper respiratory disease emergencies among males, positive results were observed for NO (lags 5-8 days), for O, (lags 0-6 days), PM (all lags), and SO (lag 8), and among females, positive results were observed for NO for lag 8 days, for O, PM among all lags. Our study provides evidence of the associations between short-term exposure to air pollution and increased risk of ED visits for upper and lower respiratory diseases in an environment where air pollutant concentrations are relatively low.