Geographical Variation and Factors Associated With Inflammatory Bowel Disease in a Central Canadian Province

Background: We investigated temporal trends, geographical variation, and geographical risk factors for incidence of inflammatory bowel disease (IBD). Methods: We used the University of Manitoba IBD Epidemiology Database to identify incident IBD cases diagnosed between 1990 and 2012, which were then geocoded to 296 small geographic areas (SGAs). Sociodemographic characteristics of the SGAs (proportions of immigrants, visible minorities, Indigenous people, and average household income) were obtained from the 2006 Canadian Census. The geographical variation of IBD incidence was modeled using a Bayesian spatial Poisson model. Time trends of IBD incidence were plotted using Joinpoint regression. Results: The incidence of IBD decreased over the study years from 23.6 (per 100,000 population) in 1990 to 16.3 (per 100,000 population) in 2012. For both Crohn's disease (CD) and ulcerative colitis (UC), the highest incidence was in Winnipeg and the southern and central regions of Manitoba, whereas most of northern Manitoba had lower incidence. There was no effect of sociodemographic characteristics of SGAs, other than the proportion of Indigenous people, which was associated with lower IBD incidence. Conclusions: Although the incidence of IBD in Manitoba is decreasing over time, we have identified geographic areas with persistently higher IBD incidence that warrant further study for etiologic clues.