Opposing trends in the prevalence of health professional-diagnosed asthma by sex: a Canadian National Population Health Survey study.

BACKGROUND: The prevalence of asthma is on the rise worldwide, with large variations in prevalence existing between and within countries. Little is known regarding the variation in asthma prevalence in adults living in rural and urban settings. OBJECTIVES: Using questionnaire data from the Canadian National Population Health Survey, the prevalence of asthma at four time periods (1994/1995 [cycle 1], 1996/1997 [cycle 2], 1998/1999 [cycle 3] and 2000/2001 [cycle 4]) was compared between rural and urban populations stratified by sex, smoking status and age group. Asthma was defined as a positive response to the question: "Do you have asthma diagnosed by a health professional?" METHODS: To account for the complexity of the survey design, the bootstrap method was used to calculate prevalences and 95% CIs. RESULTS: Overall, the prevalence of asthma increased from 7.3% (cycle 1) to 7.5% (cycle 4). After stratifying by sex, the asthma prevalence decreased among men, but in women, there was a steady increase. Asthma prevalence increased for both the rural population and the urban population. After stratifying each cycle by sex and location (rural or urban), both rural and urban men showed a decrease in asthma prevalence. On dividing according to age groups (0 to 14 years, 15 to 34 years, 35 to 64 years, and 65 years and older), the prevalence of asthma was greatest in the 15- to 34-year age group of urban and rural women. CONCLUSIONS: Asthma prevalence increased among rural and urban women. The prevalence of asthma was highest among female smokers and male nonsmokers when stratified by smoking status. Based on these findings, the rate of increase in asthma prevalence is different for men and women.