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