Methods: A cohort of patients aged 20-74 years with an episode of acute infectious gastroenteritis (n 43,013) was identified. From the same source population, an age-, sex-, and calendar timematched control group free of gastroenteritis was sampled (n 50,000). Both cohorts were followed up for a mean duration of 3.5 years.

Results: The estimated incidence rate of IBD was 68.4 per 100,000 personyears after an episode of gastroenteritis and 29.7 per 100,000 person-years in the control cohort. The hazard ratio of IBD was 2.4 (95% confidence interval [CI], 1.7- 3.3) in the gastroenteritis cohort compared with the control cohort, and the excess risk was greater during the first year after the infective episode (hazard ratio, 4.1; 95% CI, 2.2-7.4). The relative risk of developing Crohn's disease in the gastroenteritis cohort was greater than that of ulcerative colitis, especially during the first year after the infective episode (hazard ratio, 6.6; 95% CI, 1.9-22.4).

Conclusions: Our results are compatible with the hypothesis that infectious agents causing an episode of infectious gastroenteritis could play a role in the initiation and/or exacerbation of IBD.