Coarse particulate matter and hospitalization for respiratory infections in children younger than 15 years in Toronto: A case-crossover analysis

Objectives. The purpose of this study was to examine the association between ambient air pollution and hospitalization for respiratory infections among children who were younger than 15 years in Toronto during a 4-year period (1998-2001). Methods. Exposures averaged during periods that varied from 1 to 7 days were used to assess the effects of air pollutants, including thoracic particulate matter (PM10), fine (PM2.5) and coarse (PM10-2.5) particulate matter, carbon monoxide (CO), sulfur dioxide (SO2), nitrogen dioxide (NO2), and ozone (O-3), on hospitalization for respiratory infections. A case-crossover design was used to calculate odds ratios for the hospitalization adjusted for daily weather conditions with an incremented exposure corresponding to the interquartile range in air pollution exposures. Results. When particulate matter and gaseous pollutants were mutually taken into account, the effect remained pronounced for PM10-2.5 in both boys and girls. The adjusted odds ratio for 6-day average exposure to PM10-2.5 with an increment of 6.5 mu g/m(3) was 1.15 (95% confidence interval: 1.02-1.30) for boys and 1.18 (95% confidence interval: 1.01-1.36) for girls. The effect also remained for PM10 in boys and for NO2 in girls. PM2.5, CO, SO2, and O-3 showed no significant effects on hospitalization for respiratory infection in both genders when other pollutants were taken into consideration. Conclusion. Our study suggested a detrimental effect of relatively low levels of ambient particulate matter and gaseous pollutants, especially coarse particulate matter and NO2, on hospitalization for respiratory infections in children.