O-004 Inflammatory Bowel Disease in Immigrants to Canada and their Children

Inflammatory bowel disease (IBD) is more common in developed nations, and Canada has amongst the highest incidence in the world. Determining risk in migrants from low prevalence countries can illuminate the risk contributed by the Canadian environment. Using population-based data, we assessed the risk of IBD in immigrants to Canada and their Ontario-born children, compared to non-immigrants. The Ontario Crohn’s and Colitis Cohort (OCCC) is derived from health administrative data using validated algorithms and comprises all IBD patients in Ontario, Canada’s most populous province. The OCCC was linked to the Citizenship and Immigration Canada database to determine the adjusted risk of IBD in immigrants who arrived to Ontario after 1985, compared with non-immigrant residents of Ontario. Nations were grouped into regions based on World Bank classification. Age- and sex-standardized incidence in immigrants compared with non-immigrants, and Ontario-born children of immigrant mothers (born 1991–2009) compared to the children of non-immigrants. Standardized incidence and incidence rate ratios (IRR) were calculated. Hazard ratios (HR) from a multivariable Cox proportionate hazard model were used to determine whether younger age at immigration was associated with increased risk of IBD. We included 2,144,660 immigrants, 12,036,921 non-immigrants, 277,008 children of immigrants, and 1,024,049 children of non-immigrants. Standardized incidence of IBD in immigrants was 7.3 per 100,000 person-years compared to 23.9 per 100,000 in non-immigrants (IRR 0.34, 95% CI, 0.26–0.44). Incidence was lower in immigrants from all world regions, with the lowest risk in East Asians (IRR 0.14, 95% CI, 0.11–0.18) and highest risk in those from Western Europe/North America (IRR 0.59, 95% CI, 0.46–0.75) (see Figure). The attenuation of risk was greater for Crohn’s (IRR 0.25, 95% CI, 0.19–0.32) than ulcerative colitis (IRR 0.42, 95% CI, 0.33–0.53). The risk of IBD was lower in immigrants for adult-onset IBD (IRR 0.30, 95% CI, 0.21–0.41) and elderly-onset IBD (IRR 0.25, 95% CI, 0.14–0.45), compared to less attenuation of risk in children (IRR 0.48, 95% CI, 0.41–0.57). Each year of increased age at immigration was associated with decreased risk of IBD (HR 0.986, 95% CI, 0.982–0.990), corresponding to 14% increased risk per younger decade of life on arrival to Canada. Children of immigrants also had lower incidence of IBD compared to the children of non-immigrants (4.6 versus 7.2 per 100,000, IRR 0.63, 95% CI, 0.53–0.75), but this was region-specific. Children of immigrants from the Middle East/North Africa, South Asia, Sub-Saharan Africa, and North America/Western Europe had similar risk of IBD as children of non-immigrants. Risk of IBD in the children of immigrants from East Asia, Eastern Europe/Central Asia, and Latin America/Caribbean remained lower than children of non-immigrants (see Figure). The risk of IBD in immigrants to Canada is low, however younger age at arrival to Canada increased the risk. Ontario-born children of immigrants from some (but not all) regions assumed the same risk of IBD as the children of non-immigrants. These results indicate that underlying risk is activated with earlier life exposure to the Canadian environment in immigrants from certain regions.

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