Regional variation of multiple sclerosis prevalence in Canada Cynthia A Beck* ,1 , Luanne M Metz 2 , Lawrence W Svenson 3 and Scott B Patten 4 1 Departments of Psychiatry and Community Health Sciences, University of Calgary, Calgary, Canada; 2 Department of Clinical Neurosciences, University of Calgary, Calgary, Canada; 3 Health Surveillance Branch, Alberta Health and Wellness, Edmonton, Canada Department of Public Health Sciences, University of Alberta, Edmonton, Canada; 4 Departments of Psychiatry and Community Health Sciences, University of Calgary, Calgary, Canada Objective: To describe the regional distribution of multiple sclerosis (MS) prevalence in Canada, controlling for age and sex. Methods: This study used data from the Canadian Community Health Survey, a large general health survey (n  /131,535) conducted in 2000/2001. Subjects aged 18 and over were included in the current analysis (n  /116,109). The presence of MS was determined by self-report. Prevalence was computed in five regions (Atlantic, Quebec, Ontario, Prairies and British Columbia). Logistic regression was used to compare regions and examine for confounding/interaction by age and sex. Results: The overall Canadian MS prevalence was 240 per 100 000 (95%CI: 210  /280). Prevalence ranged from 180 (95%CI: 90 /260) in Quebec to 350 (95%CI: 230  /470) in Atlantic Canada. Logistic regression revealed no statistical difference between the odds of MS in Quebec, Ontario and British Columbia adjusted for age and sex. The adjusted odds of MS in the Prairies and Atlantic regions were significantly higher than in the other regions combined, with odds ratios of 1.7 (95%CI: 1.1  /2.4, P B /0.01) and 1.6 (95%CI: 1.1  /2.4, P B /0.05) respectively. Sensitivity analysis demonstrated similar prevalence in the nonaboriginal/nonimmigrant group (n  /96 219). Conclusion: Results suggest that Canadian MS prevalence differs by region. If validated, these regional differences may facilitate investigation of environmental influences. Multiple Sclerosis (2005) 11, 516  /519 Key words: adult; Canada; epidemiologic studies; multiple sclerosis; prevalence Introduction The causes of multiple sclerosis (MS) are unknown, but evidence points to a multifactorial aetiology involving both genetic and environmental components. 1,2 Identifi- cation of regional MS distribution could facilitate the generation of hypotheses regarding environmental factors. In Canada, MS prevalence is known to be high, with recent estimates ranging between 55 and 240 per 100 000. 3  5 It has, however, been unclear whether there are provincial or regional differences in prevalence, as there has been no systematic process in place to evaluate this. Comparison of prevalence between published regio- nal studies has limited validity, due to differences in age distribution, ethnic composition and case ascertainment, as well as possible changes in prevalence over time. 4,6 The prevalence of MS has been shown to be lower in Canadian native peoples, and to differ in certain immigrant groups. 6 A population-based general health survey, the Canadian Community Health Survey Cycle 1.1 (CCHS), provided data on MS as well as age, sex, immigration status and ethnicity in a large sample representing all regions of Canada (n  /131 535). 7 This allowed comparison of MS prevalence across regions at a single time point, taking demographics into account. Methods The CCHS was a cross-sectional nationally representative survey conducted between September 2000 and October 2001. 8 Participants aged 12 and older were selected from households in all ten provinces and three territories of Canada, using a sampling design developed by the Canadian national statistics agency (www.statcan.ca). Institutions, reserves (almost exclusively populated by aboriginal Canadians), crown lands, Canadian Forces bases and certain remote areas were excluded. The sample was constructed in two stages: first, households were selected, mostly by a multistage stratified cluster design (83%), but partially by random digit dialling (7%) and random sampling from telephone lists (10%). Secondly, one or two respondents were chosen within each house- hold according to a defined strategy. Verbal informed consent was obtained from each participant. Analyses were performed in a secure Statistics Canada Data Centre designed to protect the confidentiality of participants. In these Centres, results must be vetted by a Statistics Canada analyst prior to leaving the Centre. The overall response *Correspondence: Cynthia Beck MD FRCPC, Department of Psychiatry, Foothills Medical Centre, 1403 29 Street NW, Calgary, AB, Canada T2N 2T9. E-mail: cabeck@ucalgary.ca Received 18 November 2004; accepted 17 December 2004 These results have been presented at the Canadian Congress of Neurological Sciences, Calgary, Canada, June 2004. Disclaimer: This research and analysis were based on data from Statistics Canada, but the opinions expressed do not represent the views of Statistics Canada. Multiple Sclerosis 2005; 11: 516  /519 www.multiplesclerosisjournal.com # 2005 Edward Arnold (Publishers) Ltd 10.1191/1352458505ms1192oa