Investigating the hygiene hypothesis as a risk factor in pediatric onset Crohn's disease: a case-control study.

BACKGROUND AND OBJECTIVES: Evidence for the hygiene hypothesis in the etiology of Crohn's disease (CD) is unclear. We investigated the relationship between infection-related exposures and risk for CD in children. METHODS: A hospital-based case-control was carried out. Newly-diagnosed cases of CD (n = 194), less than 20 yr of age were recruited from the gastroenterology clinic of a large-pediatric inflammatory bowel disease (IBD) center in Montreal, Canada. Orthopedic patients pair-matched (n = 194) for timing of diagnosis and area of residence were recruited as controls. Information on infection-related exposures between birth and disease diagnosis was ascertained by administering a structured questionnaire to the mother and the index subject. The relationship between the frequency and timing of infection-related exposures with CD was studied. RESULTS: The mean age (SD) at diagnosis was 12.3 (5.1). CD was more common after 10 yr of age. Gender distribution was similar between comparison groups. In multivariate conditional logistic regression, family history of IBD (odds ratio (OR) = 4.6; 95% confidence interval (CI) = 1.6-13.3), age (OR = 1.2; 95% CI = 1.1-1.3), and owning a pet (OR = 2.0; 95% CI = 0.9-4.5) were associated with risk for CD, whereas regular use of a personal towel (OR = 0.5; 95% CI = 0.2-0.9) and lesser crowding in homes (OR = 0.3; 95% CI = 0.1-0.8) were protective. Day-care attendance during the first 6 months of life and "physician-diagnosed infections" between 5 and 10 yr of age were associated with increased risks for CD. CONCLUSIONS: Infection-related exposures seem to enhance risk for CD in children. The timing of these exposures during early childhood may be relevant to the etiology of pediatric CD.