Incidence of inflammatory bowel disease in South Asian and Chinese people: a population-based cohort study from Ontario, Canada

Background — Inflammatory bowel disease (IBD) is now a global disease with incidence increasing throughout Asia.

Aim — To determine the incidence of IBD among South Asians and Chinese people residing in Ontario, Canada’s most populous province.

Methods — All incident cases of IBD in children (1994– 2015) and adults (1999– 2015) were identified from population-based health administrative data. We classified South Asian and Chinese ethnicity using immigration records and surnames. We determined standardized incidence of IBD and adjusted incidence rate ratio (aIRR) in South Asians and Chinese compared to the general population.

Results — Among 16,230,638 people living in Ontario, standardized incidence of IBD per 100,000 person-years was 24.7 (95% CI 24.4– 25.0), compared with 14.6 (95% CI 13.7– 15.5) in 982,472 South Asians and with 5.4 (95% CI 4.8– 5.9) in 764,397 Chinese. The risk of IBD in South Asians was comparable to the general population after adjusting for immigrant status and confounders (aIRR 1.03, 95% CI 0.96– 1.10). South Asians had a lower risk of Crohn’s disease (CD) (aIRR 0.66, 95% CI 0.60– 0.77), but a higher risk of ulcerative colitis (UC) (aIRR 1.47, 95% CI 1.34– 1.61). Chinese people had much lower rates of IBD (aIRR 0.24, 95% CI 0.20– 0.28), CD (aIRR 0.21, 95% CI 0.17– 0.26), and UC (aIRR 0.28, 95% CI 0.23– 0.25).

Conclusion — Canadians of South Asian ethnicity had a similarly high risk of developing IBD compared to other Canadians, and a higher risk of developing UC, a finding distinct from the Chinese population. Our findings indicate the importance of genetic and environmental risk factors in people of Asian origin who live in the Western world.