The risk of asthma among Finnish patients with farmer's lung

OBJECTIVES: To assess the incidence and risk of asthma in patients with farmer's lung in comparison with farm workers without farmer's lung. METHODS: The details of farmers and animal-husbandry workers notified in 1988-1999 for farmer's lung ( n=1,272) or other occupational disease ( n=5,045) to the Finnish Register of Occupational Diseases were followed until 31 December 2000 through two national registries of individuals eligible for reimbursement of the cost of asthma medication and the Population Register Center. Incidence rates of asthma were calculated, and a log-linear model adjusted for age, gender and occupation was used to estimate relative risks of asthma among those with farmer's lung compared to those with other occupational disease. RESULTS: Of the patients with farmer's lung, 109 (8.6%) were diagnosed with asthma during the follow-up compared with 202 (4.0%) incident cases of asthma among those in the reference population. The crude relative risk of asthma was 2.1 (95% CI 1.6-2.6) among those with farmer's lung compared with the reference population. The age- and occupation-adjusted relative risk of asthma among patients with farmer's lung was 2.5 (1.8-3.5) in men and 1.4 (1.0-1.9) in women. The rate of asthma was especially high during the first 2 years after notification of farmer's lung. CONCLUSIONS: Patients with farmer's lung have an increased risk of developing asthma in comparison to farm workers in general. Most of the cases of asthma occur relatively shortly after the diagnosis of farmer's lung, which should be taken into account in medical follow-up of patients with farmer's lung.