Incidence of clinically confirmed farmer's lung in Finland and its relation to meteorological factors.

In Finland, data about the incidence of clinically confirmed (according to predefined criteria) farmer's lung have been collected in successive years since 1980. All special hospitals for pulmonary diseases and departments of pulmonary diseases in other hospitals (23 clinical units throughout Finland) took part in the study. This report deals with the results collected from 1980 to 1982 (inclusive), during which 512 new cases of farmer's lung were recorded, 186 in 1980, 153 in 1981, and 173 in 1982. The mean age of the patients was 47 years (range 14-75), 45 years for men and 48 years for women. About two-thirds of the patients were women. The mean annual incidence of farmer's lung among the entire farming population (standardized for age and sex to the total population in Finland in 1975) was 44 per 100,000 persons in farming. Both the standardized mean annual incidence (range 8-60 per 100,000 persons in farming) and the female/male ratio of the standardized incidence showed distinct regional differences. Most cases of farmer's lung occurred during the indoor feeding season for cattle. The highest frequency of new cases was observed in April and the lowest in October. The incidence of farmer's lung was positively correlated with measures of daily rainfall and negatively correlated with days without rainfall and with sunshine during the haymaking period preceding the diagnosis. A rainy haymaking period calls for artificial drying of hay in order to reduce the incidence of farmer's lung.