Occupational asthma from cobalt sensitivity in workers exposed to hard metal dust.

Eight asthmatic patients who had no history of asthma before starting work in a hard-metal plant and eight control subjects (three atopic, three nonatopic asthmatic, and two normal volunteers) without a history of exposure to hard metal dust were subjected to provocation tests, skin tests, radioallergosorbent tests (RAST) and Farr test with cobalt. Four of the eight patients were atopic, and seven showed bronchial hyperresponsiveness to methacholine (BHR). Patch and intradermal skin tests with cobalt chloride (CoCl2) could not discriminate the patients from control subjects. All patients had positive reactions to CoCl2 in the provocation tests; two developed immediate asthmatic reaction (IAR), four late asthmatic reaction (LAR), and two dual asthmatic reaction (DAR), while the control subjects showed no reaction. Evidence of specific IgE antibodies to cobalt-conjugated human serum albumin (Co-HSA) was presented by four patients (RAST score greater than 2) based on comparison of serum samples from 60 asthmatic patients and 25 asymptomatic workers in the same plant. Positive serum samples selectively bound 57Co, and the test was blocked by nonlabled cobalt sulfate (CoSO4). These findings suggest the development of hard metal-induced asthma from cobalt sensitivity.