The Incidence of Inflammatory Bowel Disease Across Time and Geography: A Systematic Review

Purpose: The incidence of inflammatory bowel disease (IBD) varies greatly around the world with a wide range of estimates both within and between geographic regions. Currently there is no comprehensive review of international incidence of IBD. The objectives of our study were to conduct a systematic review of the incidence of adult ulcerative colitis (UC) and Crohn's disease (CD) worldwide and to evaluate the change in incidence across different geographic regions. Methods: A systematic literature search of MEDLINE (1950 to Oct. 2009) and EMBASE (1980 to Oct. 2009) databases was conducted to identify studies investigating the incidence of IBD. The search was not limited by language to ensure capture of all appropriate papers. Two reviewers identified eligible articles based on the following pre-determined criteria: (1) reported the methods used to obtain the diagnosis of IBD; (2) identified a population-based cohort of IBD cases; (3) reported or provided enough information to calculate population-based incidence rates (IRs); (4) UC and/or CD were reported separately; and (5) published in full manuscript form. Studies not based on original data (e.g. review papers) were excluded. Geographic maps were created to evaluate worldwide differences in incidence of IBD. Time trend analyses were conducted to explore differences in incidence across time periods. Results: The search strategy retrieved 6940 unique citations and 180 studies were selected for inclusion. Of these, 120 described the incidence of UC and 137 described the incidence of CD. The studies were conducted in different geographic regions with 76% of studies from Europe, 11% from Asia, and 8.5% from North America. The remainder of the countries made up less than 5% of the included studies. The annual IRs varied by geographic region with UC estimates ranging from 0.4 to 20.3 per 100,000 in Europe; 0.27 to 5.8 in Asia; and 0.6 to 19.2 in North America, and CD estimates ranging from 0.17 to 9.8 per 100,000 in Europe; 0.13 to 4.2 in Asia; and 0.8 to 20.2 in North America. These included IRs ranged from 1950 to 2006 for Europeans studies, 1974 to 2004 for Asian studies, and 1940 to 2001 for North American studies. Time trend analyses were conducted in 61% of CD and 56% of UC studies, of which 70% of CD studies and 64% of UC studies showed increased incidence trends over time. Conclusion: The incidence of both UC and CD varies across geographic regions and time period. Overall, there has been an increased trend in the incidence of IBD over time. The incidence is greatest in European and North American countries.