THE LOW-PREVALENCE OF OCCUPATIONAL ASTHMA AND ANTIBODY-DEPENDENT SENSITIZATION TO DIPHENYLMETHANE DIISOCYANATE IN A PLANT ENGINEERED FOR MINIMAL EXPOSURE TO DIISOCYANATES

Background: Diisocyanate chemicals are leading causes of occupational asthma (OA). Methods: We conducted a cross-sectional study of 243 work ers exposed to diphenylmethane diisocyanate (MDI) in a urethane mold p lant that had been designed to minimize MDI exposure (levels were main tained below 0.005 ppm and were continuously monitored). All participa nts were screened by questionnaire and tests for serum antibodies to M DI-human serum albumin (HSA). On the basis of questionnaire responses, diagnoses were derived that included OA; non-OA; work-related and non -work-related rhinitis; and lower respiratory irritant responses. Seri al peak expiratory flow rate studies were performed for 2 weeks in 43 workers with and in 23 workers without lower respiratory symptoms. Res ults: Results of serial peak expiratory flow rate studies were abnorma l in 3 (33%) of 9 workers with OA, in 2 (50%) of 4 with non-OA, and in 2 (9%) of 23 case control subjects. A significant association was fou nd between peak flow rate variability and a questionnaire asthma diagn osis (chi2 p < 0.002). Physicians confirmed three cases of OA, one of which occurred in a control worker who was free of symptoms. In all th ree cases asthma symptoms remitted after the worker left the workplace . Serum specific IgE and IgG levels were elevated in 2 of 243 workers, one of whom was prick test positive to MDI-HSA and had had cutaneous anaphylaxis after MDI exposure. Conclusions: On the basis of these cas es, specific work activities associated with exposure to MDI were iden tified and corrective measures were instituted. Strict control and mon itoring of ambient MDI exposure was associated with a low prevalence o f specific sensitization to MDI and a lower than expected prevalence o f OA.