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.

中文翻译：

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OP07：丹麦移民中炎症性肠病的流行病学：一项基于人群的队列研究

背景

IBD风险较低的移民和国家中，炎症性肠病（IBD）的发病率正在上升，这与IBD发病机制中的环境危险因素有关。我们研究的目的是根据移民的出生国和年龄，确定在IBD发病率高的国家丹麦的克罗恩病（CD）和溃疡性结肠炎（UC）的发病率。丹麦东道国人口的相应发病率。

方法

使用丹麦民事登记系统，我们确定了1977年1月至2018年12月间丹麦所有已知出生国的居民。第一代移民是指与父母一起在丹麦以外出生的人。第二代移民是丹麦出生的人，其父母在丹麦境外出生。我们记录了移民（或父母）的出生国家，移民年龄和在丹麦的停留时间。在丹麦国家患者注册中心对研究参与者进行CD和UC诊断。使用对数线性Poisson回归分析估算根据移民状况的发生率比（IRR），并根据出生国（低，中，高），第一代移民中IBD的流行程度，在移民年龄和在丹麦停留的时间。

结果

在这90,030,025名受试者中，有1,295,518名第一代移民和208,826名第二代移民符合入选条件，其中4,805名第一代和898名第二代移民被诊断患有CD或UC。第一代移民中IBD的风险反映出出生国的风险（低，中或高，表1），并在丹麦居住超过20年而增加（表2）。在第二代移民中，CD和UC的风险与丹麦原住民的风险相当（表1）。移民年龄较小并不影响IBD风险。

结论

在这项基于人群的研究中，第一代移民中IBD的风险反映出其出生国的情况，并随着在丹麦停留超过20年而增加。在第二代移民中，这种风险与当地的丹麦人相当。这些发现强调了环境危险因素在IBD病因中的作用。正在进行进一步的研究以确定丹麦移民中IBD的危险因素。