Assessing individual employee risk factors for occupational asthma in primary aluminium smelting

Aims: To assess the significance of individual risk factors in the development of occupational asthma of aluminium smelting (OAAS). Methods: A matched case-control study nested in a cohort of 545 workers employed in areas with moderate to high levels of smelting dust and fume. The cohort comprised those who had their first preemployment medical examination between 1 July 1982 and 1 July 1995; follow up was until 31 December 2000. Forty five cases diagnosed with OAAS and four controls per case were matched for the same year of pre-employment and age within 5 years. The pre-employment medical questionnaires were examined, blinded as to case-control status, and information obtained on demographics and details of allergic symptoms, respiratory risk factors, respiratory symptoms, and spirometry. Data from the subsequent medical notes yielded subsequent history of hay fever, family history of asthma, full work history, date of termination or diagnosis, and tobacco smoking history at the end-point. Results: There was a significant positive association between hay fever diagnosed either at or during employment and OAAS ( adjusted OR 3.58, 95% CI 1.57 to 8.21). A higher forced expiratory ratio (FEV1/FVC%) at employment reduced the risk of developing OAAS ( adjusted OR 0.93, 95% CI 0.88 to 0.99). The risk of OAAS was more than three times higher in individuals with an FER of 70.0 - 74.9% than in individuals with an FER greater than or equal to 80.0% ( adjusted OR 3.46, 95% CI 1.01 to 11.89). Conclusions: Individuals with hay fever may be more susceptible to occupational asthma when exposed to airborne irritants in aluminium smelting. The pathological basis may be reduced nasal filtration and increased bronchial hyperresponsiveness.