The influence of silicosis on deteriorating lung function in gold miners.

STUDY OBJECTIVE To reexamine the symptoms, lung function, and chest radiographs of older gold miners who continued to work in or around gold mines 5 years after their enrollment in the cohort. DESIGN A follow-up study of a stratified sample of a cohort of gold miners. SETTING A health-care center for 24 gold mines in Welkom, South Africa. POPULATION A stratified, random sample of 242 miners who were part of a cohort of 1,197 gold miners who had been employed underground in gold mines for a mean period of 29 years. No silicosis was apparent on entry in 59 men, 78 had silicosis with category 1 nodule profusion, 73 had category 2, and 32 had category 3. MEASUREMENTS The men were assessed with questionnaires, lung function tests, and chest radiographs approximately 4.5 years after their initial assessment. RESULTS Radiologic features of silicosis had progressed an average of one subcategory (eg, 2/1 to 2/2) in the follow-up period. Lung function deteriorated more rapidly in the men with silicosis and the deterioration increased in proportion to the degree of silicosis at the start of the study. Thus, the annual loss of FEV1 was 37 mL in those without silicosis, 57 mL in those with category 1, 100 mL with category 2, and 128 mL in the men with category 3 nodule profusion (p=0.000001). A similar pattern of loss was noted for the FVC (p=0.00003) and the single-breath lung diffusion (p=0.004). These changes remained significant after controlling for age, original lung function, and for smoking. CONCLUSIONS The men with silicosis suffered a substantial loss of lung function during the period of follow-up that was directly in proportion with the nodule profusion on their initial chest radiographs.