Published online Jan 21, 2018. doi: 10.3748/wjg.v24.i3.424
Peer-review started: August 28, 2017
First decision: October 10, 2017
Revised: November 15, 2017
Accepted: November 21, 2017
Article in press: November 21, 2017
Published online: January 21, 2018
Epidemiologic studies suggest an increasing incidence and prevalence of inflammatory bowel disease (IBD) in developed countries. Some studies have reported a change in migrants moving from developing low incidence countries to developed high incidence countries, whereby they exhibit the incidence of the adopted country. This implies there may be an environmental trigger for the disease, as the onset is too rapid to be accounted for by genetic changes.
Disease presentation following migration offers a unique opportunity to examine how environmental factors might influence disease expression in migrants. Describing epidemiological changes in migrant groups may identify susceptible ethnic groups and help target further studies.
The authors sought to summarise the current literature on IBD manifestation after migration to developed countries. As there may be an overlap between race, ethnicity and migration, we aimed to study epidemiology of IBD in ethnic migrant and racial groups compared with the indigenous population.
A systematic review using PRISMA guidelines was undertaken. Studies on incidence, prevalence and disease phenotype of migrants and race compared with indigenous groups were eligible for inclusion. A statistical meta-analysis comparing the incidence between migrants and Caucasian groups was performed.
Thirty-three studies met the inclusion criteria. South Asians showed consistently higher incidence than indigenous groups for ulcerative colitis (UC). Pooled analysis could only be undertaken for incidence studies on South Asians compared to Caucasians. There was significant heterogeneity between the studies [95% for UC, 83% for Crohn’s disease (CD)]. The difference between incidence rates was not significant, with a rate ratio for South Asian:Caucasian of 0.78 (95%CI: 0.22-2.78) for CD and 1.39 (95%CI: 0.84-2.32) for UC. In six studies, there were more South Asians with pan-colonic disease than Caucasians, and this was a significant finding in four studies. A similar pattern was observed for Hispanics in the United States. Bangladeshis and African-Americans showed an increased risk of CD with perianal disease.
This the first study to show consistent differences in disease incidence, prevalence and phenotypes between migrants and non-migrants. The South Asian migrant population are particularly susceptible to developing UC. This review has demonstrated the absence of high-quality, prospective, population-based epidemiological studies on this topic. Investigation of migrant populations may provide insight into the role of environmental change and diet in the aetiology of IBD.
A prospective inception cohort to describe real-time epidemiological features of IBD will address the limitations observed in this systematic review. The potential role of environmental factors on microbial colonisation is an area of increasing interest. Studying second generation migrants bought up in a ‘western’ environment, for example South Asians, may help to decipher the impact of genetic and environmental factors. Parallel in-depth analysis of microbial factors may show a specific microbial profile related to migration and explain differing disease phenotype, whilst addressing confounding factors.