Occupational asthma in sawmills of eastern Canada and United States.

Eleven individuals with a history of work-related asthma are described. They were employed in 10 different sawmills of northwestern and southeastern Quebec and Maine where coniferous trees (spruces, firs, and pines) are cut into boards. Duration of exposure and symptomatology varied from 1.5 to 40 years and 0.5 to 10 years, respectively. Ten subjects were atopic and seven demonstrated immediate skin reactivity to mixed tree pollens. The diagnosis of occupational asthma was confirmed by significant and sustained changes in serial peak expiratory flow rates at work as compared with a period off work in every individual and significant changes in bronchial responsiveness to histamine at work as compared with a period off work in eight individuals or significant changes in FEV1 at work in the three other subjects. Specific inhalation tests by exposing four workers to sawdust in our laboratory were negative. We conclude that working in this specific type of sawmills of eastern Canada and northeastern United States can cause occupational asthma. Although the causative agent is unknown, the presence of atopy and/or immediate skin reactivity to tree pollens and/or bronchial hyperresponsiveness might be risk factors.