The evolving epidemiology of inflammatory bowel disease

Purpose of review Epidemiologic studies in inflammatory bowel disease (IBD) include assessments of disease burden and evolving patterns of disease presentation. Although it is hoped that sound epidemiologic studies provide aetiological clues, traditional risk factor-based epidemiology has provided limited insights into either Crohn's disease or ulcerative colitis etiopathogenesis. In this update, we will summarize how the changing epidemiology of IBD associated with modernization can be reconciled with current concepts of disease mechanisms and will discuss studies of clinically significant comorbidity in IBD. Recent findings The increased frequency of IBD, which has been consistently observed as society becomes developed or modernized, may be linked with changes in the gastrointestinal microbiota which, in turn, may affect the development of the immune system and influence the risk of inflammatory diseases. Although extra-intestinal disease associations have long been recognized to be linked to IBD, there is a disturbing increase in comorbidity with Clostridium difficile-associated disease, arterial and venous thromboembolism and abnormalities of cervical cytology. These have important implications in an era of increased use of immunomodulatory drugs. Summary Advances in understanding the basic biology of IBD with rapidly emerging therapeutic strategies have prompted a shift in traditional epidemiologic approaches away from risk factor anthologies toward rapprochement with disease mechanisms and pursuit of changing patterns of comorbidity of clinical relevance.