Abstract

Objective
To assess the predictive value of bronchial hyper-responsiveness (BHR) for the subsequent development of respiratory symptoms, airflow limitation and decline in lung function among aluminium smelter workers.

Methods
An inception cohort study of new employees at two Australian aluminium smelters was conducted. Participants completed a modified British Medical Research Council respiratory questionnaire, spirometry and a methacholine bronchial challenge test at baseline and at annual follow-up reviews. BHR was defined as PD20 =4000?µg. Poisson and mixed effects models were fitted to respiratory symptoms and lung function (forced expiratory volume in 1?s (FEV1) and FEV1/forced vital capacity (FVC)).

Results
Baseline interview and lung function testing were completed by 278 workers, who were followed for a median of 4 years. BHR at baseline, present in 82 workers, was not associated with incident wheeze risk ratio (RR)=1.07 (95% CI 0.74 to 1.55) and cough RR=0.78 (95% CI 0.45, 1.35), but there was some increased risk of chest tightness RR=1.40 (95% CI 0.99, 1.98) after adjustment for age, sex, smoking and atopy. BHR at baseline was associated with lower FEV1 and FVC, although the rate of annual decline in FEV1 or FVC was similar between those with or without BHR. The specificity of BHR was 77% for wheeze, 70% for cough and 77% for chest tightness, but the sensitivity was poor, at 33%, 24% and 39%, respectively.

Conclusion
Methacholine challenge testing at entry to employment was not sufficiently predictive of later adverse respiratory outcomes, and notwithstanding the study limitations is unlikely to be a useful pre-employment or preplacement screening test in the aluminium smelting industry.

Full Text

Comments

This is a well preformed difficult study to achieve which investigated the predictive value of measuring pre-employment methacholine reactivity (NSBR) in a cohort of aluminium smelter workers, where there is a high risk of development of occupational asthma. It found that pre-employment NSBR did not predict asthma which developed in 28/278, or respiratory symptoms over the next 5 years. The rate of decline in FEV1 was non-significantly higher tin the NSBR group (-47.1 vs -42.4 ml/year), both greater than often found in unexposed younger populations. There is debate as to whether potroom asthma is due to the respiratory irritants present in potroom (predominately sulphur dioxide and hydrogen fluoride)), or to sensitisation to the aluminium fluoride. Whichever is the mechanism, this paper shows that lower exposures are needed to prevent new-onset asthma in exposed workers and that pre-employment measurement of NSBR does not contribute to worker selection.

1/26/2021