Risk factors associated with inflammatory bowel disease: A multicenter case-control study in Brazil

BACKGROUND: The etiology of inflammatory bowel disease (IBD) is unknown, but it is believed to be multifactorial. The hygiene hypothesis proposes that better hygiene conditions would lead to less infectious disease during childhood and favor the development of immune-mediated diseases. AIM: To test the hygiene hypothesis in IBD by assessing the environmental risk factors associated with IBD development in different regions of Brazil with diverse socioeconomic development indices. METHODS: A multicenter case-control study was carried out with 548 Crohn’s disease (CD) and 492 ulcerative colitis (UC) outpatients and 416 healthy controls, from six IBD centers within different Brazilian states at diverse socioeconomic development stages. A semi-structured questionnaire with 87 socioeconomic and environmental questions was applied. Logistic regression model was created to assess the odds ratio (OR) with P value and 95% confidence intervals (CI). RESULTS: Predictive variables for both diseases (CD and UC) were women [odd ratios (OR) = 1.31; OR = 1.69], low monthly family income (OR = 1.78; OR = 1.57), lower number of cohabitants (OR = 1.70; OR = 1.60), absence of vaccination (OR = 3.11; OR = 2.51), previous history of bowel infections (OR = 1.78; OR = 1.49), and family history of IBD (OR = 5.26; OR = 3.33). Associated risk factors for CD were age (18-39 years) (OR = 1.73), higher educational level (OR = 2.22), absence of infectious childhood diseases (OR = 1.99). The UC predictive variables were living in an urban area (OR = 1.62), inadequate living conditions (OR = 1.48) and former smokers (OR = 3.36). Appendectomy was a risk factor for CD (OR = 1.58) with inverse association with UC (OR = 4.79). Consumption of treated and untreated water was associated with risk of CD (OR = 1.38) and UC (OR = 1.53), respectively. CONCLUSION: This is the first examining environmental exposures as risk factors for inflammatory bowel disease in Brazil. Most of the variables associated with disease risk support the role of the hygiene hypothesis in IBD development.