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.
- occupational asthma
- health screening
- lung function
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Contributors MA, MRS, LF, NHdK and AW(B)M were involved in the development of the healthwise inception cohort study protocol and are responsible for the overall accuracy and integrity of the work. ADM, SMG, CD, MD and MM coordinated and conducted the acquisition and analysis of data. All authors were involved in the conception and design of the work and drafting and revising the manuscript and provided final approval for publication.
Funding The Healthwise study was funded by Alcoa of Australia (PO Box 252, Applecross, WA 6953). Martine Dennekamp, Lin Fritschi and William Musk were supported by the National Health & Medical Research Council of Australia.
Disclaimer The sponsor had no direct involvement in study design, the collection, analysis, and interpretation of data, the writing of the report or in the decision to submit the paper for publication.
Competing interests MJA holds investigator initiated grants from Pfizer and Boehringer-Ingelheim for unrelated research. He has undertaken an unrelated consultancy for and received assistance with conference attendance from Sanofi. He has received a speaker's fee from GSK. The other authors have no competing interests to declare.
Patient consent for publication Not required.
Ethics approval Healthwise was approved by the Monash University Human Research Ethics Committee and the Human Ethics Committee at the University of Western Australia. All participants provided written informed consent.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data are available upon reasonable request. Procedures for accessing study data are available through contacting the study team. Any proposals for collaborative analyses will be given due consideration.