Does air pollution increase the effect of aeroallergens on hospitalization for asthma?

Background: Clinical experiments demonstrate that the asthmatic response to an aeroallergen can be enhanced by prior exposure to an air pollutant. Objective: We sought to compare the effects of ambient aeroallergens on hospitalization for asthma between high and low air pollution days in 11 large Canadian cities. Methods: Daily time-series analysis was used, and results were adjusted for day of the week, temperature, barometric pressure, and relative humidity. Results: The relative risk of admission for an interquartile increase in tree pollen levels was 1.124 (95% CI, 1.101-1.147) on days of lower values of fine particulate matter with a median aerodynamic diameter less than or equal to 2.5 mu m (PM2.5) compared with 1.179 (95% CI, 1.149-1.21) on days of higher PM2.5 values. Significant (P <= .05) differences in the relative risks of admission between lower versus higher values of particulate matter with a median aerodynamic diameter less than or equal to 10 mu m in diameter were 1.149 (95% CI, 1.118-1.181) versus 1.210 (95% CI, 1.161-1.261) for ascomycetes, 1.112 (95% CI, 1.085-1.14) versus 1.302 (95% CI, 1.242-1.364) for basidiomycetes, 1.159 (95% CI, 1.125-1.195) versus 1.149 (95% CI, 1.129-1.169) for deuteromycetes, and 1.061 (95% CI, 1.016-1.107) versus 1.117 (95% CI, 1.092-1.143) for weeds. Conclusion: We identified an association between aeroallergens and hospitalizations for asthma, which was enhanced on days of higher air pollution. Minimizing exposure to air pollution might reduce allergic exacerbations of asthma. (J Allergy Clin Immunol 2012;129:228-31.)