Background The incidence of tuberculosis has increased among South African gold miners despite comprehensive control programmes, including a radiological screening programme. No data are available as to the optimal frequency of screening. The aim of this study was to compare 6-monthly and 12-monthly radiological screening for active tuberculosis case-finding.

Methods Employees of a gold mining company were randomly assigned to the control arm (screening at baseline, 12 and 24 months) or the intervention arm (additional ‘intervention’ radiographs at 6 and 18 months after baseline). Study outcomes included proportion of tuberculosis cases detected by screening, proportion smear-positive, extent of disease and mortality.

Results 22 634 miners were randomised. Compared with 12-monthly screening, 6-monthly screening detected more tuberculosis suspects but not more cases, partly due to greater attrition between screening and further investigation after ‘intervention’ compared with routine radiographs. Tuberculosis cases detected in the 6-monthly versus the 12-monthly screening arm had less extensive disease (p=0.05) and a lower tuberculosis-specific mortality (death on tuberculosis treatment) (2.1 and 2.8 per 1000 person-years respectively, HR 0.73, 95% CI 0.50 to 1.08, p=0.1), which was most marked in the first 2 months of treatment (HR 0.48, 95% CI 0.23 to 0.98, p=0.04) when death from tuberculosis is most likely.

Discussion In settings with a high prevalence of HIV and tuberculosis despite standard tuberculosis control measures, more frequent case-finding may reduce the extent of disease, tuberculosis mortality and tuberculosis transmission through earlier detection of active tuberculosis cases. To be effective, however, all tuberculosis suspects identified through screening must be investigated for tuberculosis.