Environmental and Occupational Disorders
Influence of outdoor aeroallergens on hospitalization for asthma in Canada

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Abstract

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.

Section snippets

Description of the study data

All Canadian cities with current and past daily information available for hospitalizations and aeroallergens and air pollutants were included. The study population consisted of all emergency hospitalizations for asthma between April 1, 1993 and March 31, 2000 in the cities of Saint John, Halifax, Ottawa, Toronto, London, Windsor, Winnipeg, Calgary, Edmonton, and Vancouver. The hospitalization data were provided by the Canadian Institute for Health Information, which collects information on

Results

The results are based on 60,066 asthma admissions to 108 hospitals from 10 cities with an estimated population of 7.83 million people (Table I). Across cities, O3, NO2, and CO varied 2-fold, SO2 3-fold, and temperature and humidity by 50%. Descriptive statistics for pollen grains and fungal spores are presented in Table II. There was significant variation in aeroallergen concentrations and climate across cities, with the greatest difference seen in weeds. Ragweed is infrequent on both the

Discussion

In major cities from the Atlantic to Pacific coasts, daily increases in outdoor aeroallergens were associated with daily increases in hospital admissions for asthma. For a given proportionate increase, fungal spores tended to have a greater influence than pollens. Differences in effect sizes between cities were relatively small, given the relatively larger differences in geography and climate. The results cannot necessarily be extrapolated to more southern climates, but many of these

Acknowledgments

We thank Lee Coates, Medical Laboratory Technologist, Aerobiology Research Laboratories, Ottawa, Ontario, Canada, and the data managers and supervisors at the Canadian Institute of Health Information.

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