S4 Occupational asthma; is this the cause of excess respiratory symptoms and COPD described in bitumen exposed workers?
Introduction Epidemiological studies suggest increased risk of asthma and COPD in asphalt exposed workers.1 Bitumen is used in this industry. In this case we describe occupational asthma caused by bitumen exposure in a lab environment. This is the first such report to our knowledge.
Case History A 49-year old male with no history of asthma or atopy and <5 pack years smoking history presented with airflow obstruction on surveillance spirometry, cough and wheeze. He analysed hot bitumen samples (1900 C) in a lab environment without using respiratory protective equipment. Spirometry FEV1 57%, FVC 85% ratio 55%. Respiratory symptoms improved after 3 weeks off work, returning soon after he rejoined the lab. Peak flow rates were variable and lower at work. Analysis with OASYS scored 3.08 (Abstract S4 figure 1). Histamine challenge test was positive (PC20 2.216 mg/ml). Skin prick test to paraldehyde was positive. After 8 weeks away from the exposed environment the subject was asymptomatic, continued to have obstructive spirometry but improved bronchial reactivity (PC20 7.489 mg/ml) without medication and improved peak flows with little diurnal variation. One week after restarting work the respiratory symptoms returned. Repeat OASYS charts scored 3.14 with histamine reactivity similar to baseline (PC20 2.81 mg/ml) after 4 weeks. A specific challenge test was not possible due to the problems with heating bitumen to 1900°C in the hospital lab.
Conclusion The progression of symptoms and lung function in relation to work history supports the diagnosis of occupational asthma induced by bitumen fume exposure. This has not been reported previously. The possible mechanisms include sensitisation to short chain aldehydes, produced by partial combustion of bitumen which oxidises at these temperatures. Other potential sensitisers contained in bitumen are nickel and vanadium. Further studies are needed to investigate the by-products of heated bitumen and whether the previously described excess of COPD and respiratory disease in these workers is due to unidentified occupational asthma from bitumen fume exposure.