Course of occupational asthma depending on the duration of workplace exposure to allergens - a retrospective cohort study in bakers and farmers.

The management of occupational asthma requires valid information about prognostic factors. The present study therefore investigates the importance of exposure duration, work cessation, and confounding factors on allergic obstructive airway disease in bakers and farmers. Patients with confirmed allergic occupational airway disease registered in a German Occupational Health Inspectorate received a mailed questionnaire on their respiratory health and employment status. Relations between duration of exposure and course of disease were analysed by multifactorial logistic regression under consideration of confounding variables. 178 patients (65 [36.5%] farmers and 113 [63.5%] bakers) aged between 24 and 74 (mean 42.0 +/- standard deviation 12.7) years of age were included in the analysis. Farmers had much more severe respiratory complaints than bakers, and a significantly larger proportion of them (77.5%) had been employed for over 10 years (bakers: 36.6%). Unlike in bakers (Odds-Ratio for a sum score of more than 4 points 6.48 [95%CI 2.04-20.56]), among farmers (OR 1.47 [95%CI 0.30-7.29]) the duration of work under exposure did not independently explain the severity of respiratory complaints. The multivariate statistical analysis confirms the prognostic value of the cessation of work in occupational asthma; this remedy, however, is often not available for farmers.