Effect of Rural Living on the Development of the Inflammatory Bowel Diseases: A Nested Case-control Study

Abstract

Purpose: Observational studies have demonstrated an increase in ulcerative colitis (UC) and Crohn's disease (CD) incidence in more densely populated areas; however, the risk of developing the inflammatory bowel diseases (IBD) in rural areas has been inadequately studied. The purpose of this study was to investigate the effect of two distinct levels of rural living on the risk of developing IBD. Methods: The health improvement network (THIN) database, which includes prospectively gathered health data in the United Kingdom (UK), was used to identify incident cases of CD (n=367) or UC (n=588), and age and sex-matched controls (5 controls per case). The urban-rural spectrum was divided into three distinctly defined levels based on settlement density profiles of 1 hectare (100 x 100 meters) squares in the UK: urban; town and fringe; village, hamlet, and isolated dwelling. Conditional logistic regression was used to assess whether CD and UC patients were more likely to live in rural areas after adjusting for smoking, socioeconomic status (SES), nonsteroidal anti-inflammatory drugs (NSAIDs), and appendectomy. Risk estimates were presented as odds ratios (OR) with 95% confidence intervals (CI). Joint age-sex modification were explored through likelihood ratio tests. Results: Significant associations were not observed between level of rural living and CD after adjusting for smoking (current versus never OR=1.55; 95% CI: 1.14-2.12), SES (OR= 0.75, 95% CI: 0.49-1.14), NSAIDs (OR=1.31, 95% CI: 0.82-2.09), and appendectomy (OR=1.96, 95% CI: 1.29-2.98). In contrast, living in the most rural area, defined as village, hamlet, or isolated dwelling, was significantly associated with a reduced risk of developing UC (OR 0.59; 95% CI 0.39-0.90) after adjusting for smoking (current versus never OR=0.58; 95% CI 0.42-0.79), SES (OR=0.91; 95% CI 0.64-1.29), NSAIDs (OR=1.05; 95% CI 0.74-1.50), and appendectomy. (OR=0.38; 95% CI 0.22-0.64). However, living in the less rural area, defined as town and fringe, was not associated with UC (OR 0.88; 95% CI = 0.67-1.15) after adjustment for confounders. Effect modification was not observed (p-value 0.8). Conclusion: Rurality was not associated with the risk of CD. In contrast, living in extreme rural areas as defined by settlement density was associated with decreased incidence of UC.