Background: Migrants from eastern low incidence countries are reported to develop the incidence of their adopted country. The South Asian (SA) community has a wide diaspora and presents an ideal group to study migration. We aimed to summarise the epidemiology of IBD in SA migrants through a systematic literature review and meta-analysis.
Methods: Studies reporting the incidence of IBD in SA migrants compared with Caucasian groups were eligible for inclusion. Quality assessment of the studies was performed by examining the number of studies which fulfilled the following criteria: use of recognised diagnostic criteria, self-reporting of ethnic background and whether the study was population based. The p-value from the test of heterogeneity is given, with the I2 value. Size of difference between both groups is reported as a rate ratio, along with corresponding confidence intervals. This is quantified as the incidence in SA relative to the incidence in Caucasians.
Results: Eight studies met the inclusion criteria for Crohn's disease (CD) and Ulcerative Colitis (UC), seven in the UK and one study in Canada (Table 1). The total population was 2,569,074. The UC incidence was higher in SA in 3/4 studies with a rate ratio of UC 1.39 (0.84, 2.32) whereas CD incidence was lower in 5/6 CD studies with a rate ratio of 0.78 (0.22, 2.78) compared with Caucasians (Table 2). There was significant heterogeneity between both UC and CD studies. (I2 – 83%, p<0.001 and I2 – 95%, p<0.001).
Conclusions: There is a lack of good quality recent data in the literature. One UC study reported a lower incidence rate (Jayanthi) but only studied the Bangladeshi subgroup of the SA population whereas the others reported on a predominantly North Indian population. This finding suggests a difference in the presentation of IBD within the SA population. One study showed a higher incidence of CD in SA group than Caucasians which included a paediatric population. Early environmental influences may be more important for the pathogenesis of CD than UC. We conclude that SA migrants have increased risk of developing UC potentially due to exposure to new environmental factors in the adopted country. Larger prospective population based studies are needed to support these findings including differences between first and second generation migrants to implicate the environmental exposure.