The Epidemiology of Tuberculosis in Gold Miners with Silicosis

The elevated risk of tuberculosis in subjects with silicosis is widely accepted but has not been quantified in a population with a high prevalence of tuberculosis. In this study, a cohort of 1,153 older gold miners with and without silicosis who had not had tuberculosis have been followed for 7 yr by a routine mine surveillance program for detection of tuberculosis. One hundred seventy-eight of the men developed tuberculosis. The annual incidence of tuberculosis was 981/100,000 in the 335 men without silicosis and 2,707/100,000 in the 818 men with silicosis. The relative risk for tuberculosis was 2.8 (95% CI, 1.9 to 4.1) for men with silicosis compared with that in the men without silicosis. The incidence of tuberculosis increased from 1% per annum (pa) for the men without silicosis to 2.2% pa for the men with silicosis with Category 1 nodule profusion, 2.9% pa for those with Category 2, and 6.3% pa for those with Category 3 silicosis. This study has confirmed and quantified the high risk of pulmonary and of extrapulmonary tuberculosis in men with silicosis. The incidence of tuberculosis during this 7-yr study suggests that one quarter of these men with silicosis will have developed tuberculosis by 60 yr of age.