Setting: A medical facility for approximately 90 000 gold miners emplo
yed on 24 South African gold mines. Objective: To establish the long-t
erm risk attributable to silicosis of relapse from pulmonary tuberculo
sis treated,vith short-course chemotherapy. Design: A consecutive samp
le of gold miners with pulmonary tuberculosis allocated to receive rif
ampicin, isoniazid, pyrazinamide and streptomycin given on weekdays fo
r 5 months. Radiographs were assessed at the time of diagnosis for the
presence of silicosis. All of the men were followed for at least 5 ye
ars after completing their treatment, or until they left mine service
or suffered a relapse of tuberculosis. Results: The sample included 54
9 men of whom 167 had silicosis. The incidence density for relapse in
silicosis was 1.55 (95% CI 0.97, 2.48) times that for the men without
silicosis. There was no difference in the pattern of relapse over time
between the two groups: the mean period to relapse in the men with si
licosis was 2.6 years (SD 1.89 years) and for the men without silicosi
s was 3.1 years (SD 2.23 years) (P = 0.6). Conclusion: Silicosis cause
s a small increase in the risk of relapse of tuberculosis. Relapses in
both groups were not confined to the first 2 years after completion o
f treatment.