Respirable coal dust exposure and respiratory symptoms in South-African coal miners: a comparison of current and ex-miners

Abstract

Objectives: 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.

Methods: Work histories, interviews, and spirometry and cumulative exposure were assessed among 684 current and 212 ex-miners.

Results: 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.

Conclusions: 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.