Risk of inflammatory bowel disease following a diagnosis of irritable bowel syndrome

Background: Irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD) symptoms often overlap. In some IBS cases there are subtle inflammatory changes similar to the immune-mediated pathophysiology of IBD, and the risk of both increases after infectious gastroenteritis (IGE). Methods: To evaluate the effect of IBS and IGE on IBD risk utilizing US Department of Defense medical encounter data, active duty personnel with IBS were matched to subjects without IBS. Medical encounter history was analyzed to assess for incident IBD. IGE was identified from documented medical encounters and by self-report. Relative risks were calculated using Poisson regression models. Results: We identified 9,341 incident IBS cases and 18,678 matched non-IBS subjects and found an 8.6-fold higher incidence (p < 0.0001) of IBD among those with IBS (238.1 per 100,000 person-years) compared to our referent population (27.8 per 100,000 person-years). In a subset (n = 2,205) of well-defined IBS cases, IBD risk was 15 times that of subjects without IBS. The median time between IBS and IBD diagnoses was 2.1 years. IGE also increased IBD risk approximately 2-fold (p < 0.05) after controlling for IBS. Conclusions: These data reflect a complex interaction between illness presentation and diagnosis of IBS and IBD and suggest intercurrent IGE may increase IBD risk in IBS patients. Additional studies are needed to determine whether IBS lies on the causal pathway for IBD or whether the two are on a pathophysiological spectrum of the same clinical illness. These data suggest consideration of risk reduction interventions for IGE among IBS patients at high disease risk.