Prevalence and incidence of chronic bronchitis and farmer's lung with respect to socioeconomic factors.

This study was based on data provided by 9,483 farmers from a larger sample of 12,056 Finnish farmers. The data were gathered in two postal surveys (with a 3-year interval between surveys) conducted by the Social Insurance Institution of Finland. When age, sex, atopy, and smoking habits were controlled, neither the family structure nor the level of vocational education significantly affected the occurrence of either chronic bronchitis or farmer's lung. The prevalence of farmer's lung was smallest on farms with the largest area under cultivation; the difference in prevalence between the area categories was statistically significant. An opposite trend, although not statistically significant, was present in the incidence rate of but not in the prevalence of chronic bronchitis. The incidence of farmer's lung was largest (p less than 0.05) on the farms with the most intensive cattle raising. Other chronic diseases occurred more often among farmers with chronic bronchitis or farmer's lung than among farmers without respiratory symptoms. Our results imply that factors associated with farm work may be more involved in the occurrence of chronic bronchitis or farmer's lung among farmers, than the socioeconomic background per se.