Childhood farm environment and asthma and sensitization in young adulthood

Background: Farm environment in childhood may protect against sensitization, allergic rhinitis, and asthma. Methods: Subjects were obtained from 10 667 Finnish first-year university students who responded to a questionnaire survey on IgE-mediated diseases. Two random samples were selected from 1631 respondents in Turku: subjects with asthma or wheezing, and subjects without asthmatic symptoms. A total of 296 subjects (72%) participated. Skin prick tests (SPT), measurements of IgE-antibodies, methacholine challenge, and bronchodilation tests were performed. Weighted occurrence of current asthma and sensitization among students from "childhood" farm and childhood nonfarm environments were analyzed. Results: Current asthma was found in 3.1% of subjects with childhood farm environment, and in 12.4% with nonfarm environment (odds ratio (OR) 0.22; 95% confidence interval (CI) 0.07-0.70). There were fewer positive SPT to birch (8.3 vs. 24.2%, OR 0.28, 95% CI 0.07-1.15) and timothy pollen (12.6 vs. 30.3%, OR 0.33, 95% CI 0.09-1.20) among subjects with childhood farm environment, but more sensitization to house-dust mite (22.0 vs. 4.9%, OR 5.43, 95% CI 1.60-18.46). Sensitization to cat (RAST class 3) was less common in subjects with farm compared to nonfarm environments in childhood (1.5 vs. 13.1%; OR 0.10, 95% CI 0.02-0.47). Conclusions: Farm environment in childhood protects against adult asthma and sensitization especially to cat the most important asthma related allergen. In contrast, sensitization to house-dust mite was more common in farming subjects.