Background The World Health Organisation and many national guidelines for TB management recommend treatment initiation in the presence of symptoms such as cough, weight loss, night sweats and or fever, and radiological changes suggestive of TB with or without bacteriological confirmation. However, none of the studies that investigated the value of plain chest radiograph (CXR) has been done in the Southern African ex-gold miner population. Given the characteristics of this population - a high prevalence of silicosis, past TB and recurrent TB and post-TB lung destruction -application of the above recommendation may lead to unnecessary TB treatment.

Objectives To assess the performance of the screening CXR in the diagnosis of active TB disease among former gold miners from the South African mines using GeneXpert as the reference standard.

Methods We analysed the medical history information, CXR, and GeneXpert test results in a group of ex-miners examined between 2017 and 2018 at Mafeteng Occupational Health Service Centre (OHSC), Lesotho. We excluded those on TB treatment and those within twelve months of TB-treatment completion at the time of the visit. CXRs were read by a medical doctor with training and experience in the reading of pneumoconiosis and TB. A set of 300 of the CXRs were cross-read by two occupational medicine specialists with mining medicine experience, with 80–90% agreement with clinic readings.

Results We analysed information on 2572 subjects. The prevalence of active TB on GeneXpert was 3%, with CXR sensitivity 0.97 , specificity 0.41, positive predictive value 0.05, and negative predictive value 0.99.

Conclusion A CXR negative for TB is a valuable tool in ruling out active TB disease among ex-gold miners. However, its poor predictive value, given the high background prevalence of silicosis and previous TB in this population, makes bacteriological confirmation necessary before initiating TB treatment in ex-gold miners.