DETERMINANTS OF ASTHMA IN A FARMING POPULATION

Objectives This study examined the determinants of asthma in a populat ion of farmers, including as a crude indicator of genetic predispositi on ''history of asthma in next-of-kin'' (family history), and exposure factors such as animal production and smoking. Methods In a cross-sec tional study of 8482 farmers or farmers' spouses in Norway a questionn aire with information on asthma among the subjects and their next-of-k in, production type and farming activities, exposures outside farming, and smoking was applied. Spirometry was performed. Results The lifeti me prevalence of self-reported asthma in the population was 6.3%. Sign ificant risk factors for current asthma were asthma among next-of-kin, asthma as child or adolescent, animal production, and age. Ln a compa rison with subjects with no family history of asthma and no animal pro duction the adjusted odds ratio for current asthma in never smokers wa s 1.9 [95% confidence interval (95% CI) 0.4-8.9] for subjects with fam ily history only, 2.2 (95% CI 1.1-4.2) for subjects with animal produc tion only, and 6.3 (95% CI 3.1-13.1) for subjects with both factors. A combination of animal production, smoking, and a positive family hist ory gave an odds ratio of 8.1 (95% CI 4.0-16.2) for current asthma. Co nclusions The study can be interpreted as support for the hypothesis o f an interaction between genetic factors and exposure factors in the c ausation of asthma. Since familial associations may be exposure-relate d, the necessity of considering indicators of both inheritance and exp osure in epidemiologic studies of asthma is emphasized.