SILICOSIS, CHRONIC AIR-FLOW LIMITATION, AND CHRONIC-BRONCHITIS IN SOUTH-AFRICAN GOLD MINERS

In a cross-sectional study of a working population of black South African gold miners, 1,197 men were studied with respiratory and occupational questionnaires, lung function tests, and chest radiographs. The study was designed to examine the effects of silicosis on respiratory symptoms and lung function. A total of 857 men with chronic, simple silicosis and 340 men without silicosis were included in the sample. Other determinants of lung disease including the duration and intensity of underground dust exposure and tobacco smoking were also examined. Three distinct pulmonary disorders could be discerned: silicosis-associated pulmonary dysfunction with dyspnea on effort; chronic airflow limitation, which was related to the duration of underground exposure; and a chronic bronchitic symptom complex, which reflected the intensity of dust exposure in the workplace. Chronic, uncomplicated silicosis was found to be associated with significant loss of lung function, and all of the measured indices, FVC, FEV1, FEV1/FVC%, maximal midexpiratory flow rate (MMEF), and lung diffusion for carbon monoxide measured by the single-breath method (DL(CO)) were reduced. When comparing men with Category 3/3 nodule profusion with men without silicosis, reductions of FVC of 351 ml, FEV1 of 447 ml, MMEF of 1.04 L/s, and DL(CO) of 4.7 ml/min/mm Hg (p = 0.0001) were detected after controlling for age, height, the direct effects of the underground environment, and tobacco smoking. Dyspnea on effort was more common in the men with silicosis (p < 0.001). The duration of exposure to the underground environment was found to be associated with significant reductions of FEV1, FEV1/FVC%, and MMEF, to an extent equivalent to or slightly greater than that produced by tobacco smoking in the same population. Chronic sputum production was common and was most prevalent in the men who worked in the dustiest occupations. Of the three occupational disorders, chronic airflow limitation appeared to be most relevant as it affected all of the men in this working environment, unlike silicosis, which develops in a minority of these gold miners.