Occupational asthma due to cobalt in metal working fluid; a report of an outbreak

Introduction Occupational asthma (OA) due to cobalt exposure is reported in diamond polishers and cobalt production workers, but rarely in metalworkers. We describe a case series of cobalt OA in a valve manufacturing company, where exposure was from metal-working fluid (MWF) aerosols containing dissolved cobalt. Methods Cases of cobalt OA from a manufacturer of stellite (cobalt alloy) engine valves were identified from the West Midlands SHIELD database. Case note data on demographics and symptoms at diagnosis were gathered, along with details of diagnostic tests, including serial peak flow, skin prick tests (SPT), non-specific bronchial reactivity (NSBR) and specific inhalational challenge (SIC) tests to 1-10mg/ml cobalt chloride (CoCl2). Results 14 workers were diagnosed with OA 1996-2005. Workers were predominantly white, British males (86%), with a mean symptom latency of 30 months (24-48) to diagnosis. 70% had urinary cobalt concentrations suggestive of occupational exposure. Skin sensitization was demonstrated to ≥1 aeroallergen in 64% of workers, and to 1-10mg/ml CoCl2 in 75%. 86% had definite OA on peak-flow analysis (OASYS score 3.3-4.0); 43% of exposed workers demonstrated NSBR at diagnosis. Sensitization to cobalt was confirmed in 7 workers by SIC to 1-10mg/ml CoCl2, including 3 immediate, 1 late and 3 dual asthmatic reactions. Discussion Strong evidence for sensitization was demonstrated in most workers by positive SPT and SIC to CoCl2. This is the first case-series of cobalt asthma from the automotive industry, where hard-metal tipped tools and stellite alloys are in common usage. Awareness and vigilance is therefore required in this industry.