Dose–response associations between respirable dust exposure and respiratory symptoms and between symptoms and spirometry outcomes among currently employed and formerly employed South-African coal miners were investigated.
Work histories, interviews, and spirometry and cumulative exposure were assessed among 684 current and 212 ex-miners.
Lower prevalences of symptoms were found among employed compared with ex-miners. Associations with increasing exposure for symptoms of phlegm and past history of tuberculosis were observed, whereas other symptom prevalences were higher in the higher exposure categories. Symptomatic ex-miners exhibited lower lung function compared to the nonsymptomatic.
Compared with published data, symptoms rates were low in current miners but high in ex-miners. Although explanations could include the low prevalence of smoking and/or reporting/selection bias, a “survivor” and/or a “hire” effect is more likely, resulting in an underestimation of the dust-related effect.
From the Centre for Occupational and Environmental Health, University of KwaZulu-Natal, Congella, South Africa (Dr Naidoo); Department of Environmental Health Sciences, University of Michigan (Dr Robins); Department of Environmental Health, University of Washington, Seattle (Dr Seixas); Department of Medicine, University of KwaZulu-Natal, Congella, South Africa (Dr Lalloo); Respiratory Epidemiology and Clinical Research Unit, Montréal Chest Institute, Montréal, Canada (Dr Becklake); and Departments of Medicine and of Epidemiology, Biostatistics and Occuptional Health, McGill University; Montréal, Canada (Dr Becklake).
Address correspondence to Rajen N. Naidoo, Centre for Occupational and Environmental Health/ Department of Community Health, Nelson R. Mandela School of Medicine, University of KwaZulu-Natal, Private Bag x7, Congella, 4013, South Africa; E-mail: email@example.com.