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Geographic and Gender Variability in the Prevalence of Bronchial Responsiveness in Canada^*

^* From the Department of Medicine (Drs. Manfreda and Anthonisen), University of Manitoba, Winnipeg, MB; Firestone Institute for Respiratory Health (Drs. Sears and Siersted), St. Joseph’s Healthcare and McMaster University, Hamilton, ON; Respiratory Epidemiology Unit (Drs. Becklake and Ernst), Joint Departments of Epidemiology and Biostatistics and of Occupational Health, McGill University, Montreal, QC; Respiratory Division (Drs. Chan-Yeung and Dimich-Ward), Department of Medicine, University of British Columbia, Vancouver, BC; Department of Health and Social Services (Drs. Sweet and Van Til), Charlottetown, PE; and Department of Medicine (Dr. Bowie), Dalhousie University, Halifax, NS, Canada.

Correspondence to: Jure Manfreda, MD, University of Manitoba, Department of Medicine, RS-115, 810 Sherbrook St, Winnipeg, MB, Canada R3A 1R8; e-mail: manfred{at}ms.umanitoba.ca

Objectives: Geographic variability in reported prevalences of asthma worldwide could in part relate to interpretation of symptoms and diagnostic biases. Bronchial responsiveness measurements provide objective evidence of a common physiologic characteristic of asthma. We measured bronchial responsiveness using the standardized protocol of the European Community Respiratory Health Survey (ECRHS) in six sites in Canada, and compared prevalences across Canada with international sites.

Design: Samples of 3,000 to 4,000 adults aged 20 to 44 years were randomly selected in Vancouver, Winnipeg, Hamilton, Montreal, Halifax, and Prince Edward Island, and a mail questionnaire was completed by 18,616 individuals (86.5%). Preselected random subsamples (n = 2,962) attended a research laboratory for examination including more detailed questionnaires, lung function testing including methacholine challenge, and skin testing with 14 allergens.

Results: Prevalences of bronchial hyperresponsiveness, measured as cumulative dose of methacholine required to produce a 20% fall from the post-saline solution FEV₁ 1 mg, ranged from 4.9% (95% confidence interval [CI], 1.6 to 8.5) in Halifax to 22.0% (95% CI, 18.1 to 26.0) in Hamilton (median, 10.7%). In all Canadian sites, bronchial hyperresponsiveness was more prevalent in women than in men. Neither the geographic nor gender differences were accounted for by differences in age, smoking, skin test reactivity, or baseline FEV_1. Geographic- and gender-related variability changed little when only bronchial hyperresponsiveness associated with asthma-like symptoms was considered.

Conclusions: A wide variability in bronchial responsiveness can occur within one country, almost as wide as the range found across all international sites participating in the ECRHS study and not explained by differences in gender, smoking, skin test reactivity, and FEV₁. While gender variability in the prevalence of bronchial responsiveness is likely due to hormonal and immunologic factors, geographic variability is likely to result from environmental factors.

Key Words: bronchial responsiveness • gender • geography • prevalence • variability

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