PREVALENCE OF OCCUPATIONAL ASTHMA AMONG WORKERS EXPOSED TO EASTERN WHITE CEDAR

We assessed the prevalence of occupational asthma among current (n = 2 9/31, 94%) and former (n = 13/49, 27%) employees of a sawmill in which eastern white cedar has been made into shingles during the past 3 yr. All participants answered a respiratory questionnaire, and all except one underwent spirometry and methacholine inhalation tests. All those with bronchial hyperresponsiveness (PC20 methacholine less than or eq ual to 16 mg/ml) were invited to undergo specific inhalation challenge s. Mean duration of exposure was 13 mo (19 workers > 12 mo). Twenty-ei ght workers (65%) reported a history compatible with asthma, and 25 (5 8%) had symptoms that were suggestive of occupational asthma. Only two subjects had significant airway obstruction (FEV(1) < 80% pred) (mean value = 98% pred). Eighteen subjects (42%) had a PC20 less than or eq ual to 16 mg/ml. Specific inhalation tests with plicatic acid and/or w estern red cedar (which contains twice as much plicatic acid as easter n white cedar), were done on 12 subjects who had a PC20 less than or e qual to 16 mg/ml when they were assessed. Three subjects were consider ed to have positive tests (one had an isolated immediate reaction, one had a]ate reaction, and one had significant changes in PC20 each time he was exposed but no changes in FEV(1)). Environmental monitoring sh owed concentrations of total dusts above 2 mg/m(3) in half of the samp les. The prevalence of occupational asthma in this workplace was three of 42 participants (7%) or at least three of 80 (3.8%) of all current or ex-workers. This is comparable to the prevalence of occupational a sthma in subjects exposed to western red cedar.