Influence of outdoor aeroallergens on hospitalization for asthma in Canada

J Allergy Clin Immunol. 2004 Feb;113(2):303-6. doi: 10.1016/j.jaci.2003.11.016.


Background: The risk of hospitalization for asthma caused by outdoor aeroallergens is largely unknown.

Objective: The objective of this study was to determine the association between changes in outdoor aeroallergens and hospitalizations for asthma from the Pacific coast to the Atlantic coast of Canada.

Methods: A daily time series analysis was done to test the association between daily changes in aeroallergens and daily changes in hospitalizations for asthma during a 7-year period between 1993 and 2000 in 10 of the largest cities in Canada. Results were adjusted for long-term trends, day of the week, climate, and air pollution.

Results: A daily increase, equivalent to the mean value of each allergen, was associated with the following percentage increase in asthma hospitalizations: 3.3% (95% CI, 2.3 to 4.1) for basidiomycetes, 3.1% (95% CI, 2.8 to 5.7) for ascomycetes, 3.2% (95% CI, 1.6 to 4.8) for deuteromycetes, 3.0% (95% CI, 1.1 to 4.9) for weeds, 2.9% (95% CI, 0.9 to 5.0) for trees, and 2.0% (95% CI, 1.1 to 2.8) for grasses. After accounting for the independent effects of trees and ozone, the combination of the 2 was associated with an additional 0.22% increase in admissions averaged across cities (P <.05).

Conclusion: These findings provide evidence for the hypothesis that aeroallergens are an important cause of severe asthma morbidity across Canada, and in some situations there might be a modest synergistic adverse effect of ozone and aeroallergens combined.

MeSH terms

  • Adolescent
  • Adult
  • Air Pollutants / analysis*
  • Allergens / adverse effects
  • Allergens / analysis*
  • Asthma / epidemiology*
  • Asthma / etiology
  • Canada / epidemiology
  • Child
  • Child, Preschool
  • Hospitalization / trends*
  • Humans
  • Poaceae / adverse effects
  • Pollen / adverse effects*
  • Seasons
  • Spores, Fungal / isolation & purification*
  • Trees / adverse effects


  • Air Pollutants
  • Allergens