Environmental Risk Factors for Inflammatory Bowel Disease: A Case-Control Study in a Middle Eastern Migrant Population

Abstract

Crohn’s disease (CD) and ulcerative colitis (UC) are inflammatory bowel diseases (IBD) of multifactorial etiology. Environmental risk factors may explain the recent striking rise in IBD incidence, especially in developing areas. As yet there are few migration population studies assessing the influence of genes and the environment, and no studies focusing on the Middle Eastern (ME) population and their IBD risk upon migration to Western countries. This prospective case-control study focused on an ME migrant population in Australia and investigated known and speculative IBD environmental factors. Cases were recruited from central-South Western Sydney to maximize ME case recruitment. Comparisons with Australian Caucasian IBD factors for ethnic differences, with matched controls from Lebanon to identify environmental changes upon migration, and between first- and second-generation migrants, were done. Matched population controls were randomly selected from similar locations. Adjusted and unadjusted odds ratios (OR) with 95% confidence intervals (CI) were calculated. Multivariate logistic regression analysis and Mann-Whitney U test for continuous variables were used. The study recruited 673 subjects: 84 migrant ME IBD cases (CD, 51; UC, 33), 136 Australian Caucasian IBD cases (CD, 81; UC, 55), 150 migrant ME controls, 153 Caucasian controls and 150 controls from Lebanon. In the migrant ME group, adjusted ORs for significant factors were: IBD family history (CD, 11.23; 95% CI, 2.38-35.00; UC, 20.40; 95% CI, 4.95-84.12), smoking (CD, 2.63; 95% CI, 1.18-5.86), breastfeeding at 6–12 months and >12 months for CD and UC (P < .05), rural dwelling, owning pets, farm animal contact, bedroom sharing for CD and UC (P < .01), and appendectomy (CD, 6.32; 95% CI, 1.85-21.62; UC, 7.01, 95% CI, 1.79-27.54). Novel risk factors are pet feeding (CD, 0.27; 95% CI, 0.11-0.70) and owning dogs (CD, 0.42; 95% CI, 0.15-0.72). Caucasians share some speculative factors: breastfeeding, rural dwelling and owning pets. Migration exposes Middle Easterners to increased risks such as appendectomy (CD, 4.58; 95% CI, 1.42-14.79; UC, 4.76; 95% CI, 1.24-18.24). Earlier age of diagnosis for second-generation ME CD cases was found (mean age, 22 vs 31 years; P = .02). Great influences on second- compared to first-generation migrants are rural dwelling (CD, 0.29 [95% CI, 0.09-0.96] vs 0.49 [95% CI, 0.16-0.98]) and pet ownership (CD, 0.21 [95% CI, 0.06-0.75] vs 0.45 [95% CI, 0.17-0.88]). The hygiene hypothesis, breastfeeding’s protective effect and known environmental factors are supported in a migrant group. Contact with childhood pets is a novel protective factor. Upon migration, Middle Easterners are greatly exposed to risk factors of appendectomies with loss of protective effects. Hygiene hypothesis factors are more frequently detected in migrant Middle Easterners than Caucasians and in second- than first-generation migrants.