OP07 The epidemiology of inflammatory bowel diseases among immigrants to Denmark: A population-based cohort study
M. Agrawal1, S. Shrestha2, G. Corn3, N.M. Nielsen3, M. Frisch3, J.F. Colombel1, T. Jess3
1The Dr Henry D. Janowitz Division of Gastroenterology, Icahn School of Medicine at Mount Sinai, New York, USA, 2School of Medical Sciences, Orebro University, Orebro, Sweden, 3Department of Epidemiology Research, Statens Serum Institute, Copenhagen, Denmark
Background
The incidence of inflammatory bowel diseases (IBDs) among immigrants and in countries with historically low IBD risk is rising, implicating environmental risk factors in IBD pathogenesis. The purpose of our study was to determine the incidence rates of Crohn’s disease (CD) and ulcerative colitis (UC), among immigrants to Denmark, a high IBD incidence country, according to the country of birth and age at immigration, in comparison with the corresponding incidence rates in the Danish host population.
Methods
Using the Danish Civil Registration System, we identified all residents in Denmark with a known country of birth between January 1977 and December 2018. First-generation immigrants were persons who, along with parents, were born outside Denmark; second-generation immigrants were Danish-born persons whose parents were born outside Denmark. We recorded immigrants’ (or parents’) country of birth, age at immigration and duration of stay in Denmark. Study participants were followed for CD and UC diagnosis in the Danish National Patient Registry. Incidence rate ratios (IRRs) according to immigration status were estimated using log-linear Poisson regression analysis, and stratified by IBD prevalence in the country of birth (low, intermediate and high), and among first-generation immigrants, by age at immigration and duration of stay in Denmark.
Results
In this cohort of 9,038,025 subjects, among 1,295,518 first-generation and 208,826 second-generation immigrants eligible for inclusion, 4,805 first-generation and 898 second-generation immigrants were diagnosed with CD or UC. The risk of IBD among first-generation immigrants reflected risk in the country of birth (low, intermediate or high, Table 1), and increased with >20 years stay in Denmark (Table 2). Among second-generation immigrants, the risk of CD and UC was comparable to that in Danish natives (Table 1). Younger age at immigration did not impact IBD risk.
Conclusion
In this population-based study, the risk of IBD among first-generation immigrants reflected that in their country of birth, and increased with >20 years stay in Denmark. Among second-generation immigrants, the risk was comparable to native Danes. These findings underscore the role of environmental risk factors in the aetiology of IBD. Further studies to determine risk factors for IBD among immigrants to Denmark are ongoing.