An Evaluation of Mortality Rates and Their Determinants in a Cohort of Former Asbestos Miners in South Africa

Abstract

Background: A causal association between occupational asbestos exposure and lung disease, including pneumoconiosis and mesothelioma, is well established. Elevated mortality among former asbestos miners is expected. However, large-scale South African studies examining all-cause mortality in this population are lacking. We assessed all-cause mortality among former asbestos miners recorded in the Asbestos and Kgalagadi Relief Trusts' Inyosi database.

Methods: All-cause standard mortality ratios (SMRs) and crude mortality rates (CMRs) were calculated for 11,343 ex-miners. Mortality predictors were modeled using Cox regression analysis, and mortality trends were assessed by examining annual all-cause CMRs and SMRs over the 20-year study period.

Results: The cohort's all-cause mortality exceeded that of the general population by 4% (SMR = 1.04; 95% CI: 1.01-1.07), with excess mortality confined to women (SMR = 1.17; 95% CI: 1.09-1.25). Increasing ILO radiographic profusion category strongly predicted mortality, with adjusted hazard ratios (aHRs) ranging from 1.13 (95% CI: 1.05-1.23) to 2.42 (95% CI: 1.58-3.71). Severely reduced lung function was also associated with increased risk, including forced expiratory volume in 1 s and forced vital capacity z-scores below -3.0 (aHR = 1.60; 95% CI: 1.41-1.81 and aHR = 1.26; 95% CI: 1.12-1.42, respectively). Additional predictors included body mass index less than 18.5 kg/m² (aHR = 1.46; 95% CI: 1.36-1.58) and previous smoking (aHR = 1.43; 95% CI: 1.35-1.53). SMRs declined over time.

Conclusion: Radiological and spirometric indicators were key predictors of mortality. These findings support risk stratification and targeted interventions, particularly early management of respiratory complications and smoking cessation, to reduce mortality. The excess female mortality highlights the occupational hazards of aboveground asbestos activities, gender‑specific work practices, and insufficient control measures in this setting. Although standardized mortality was only modestly elevated, interpretation was limited by incomplete data.

Keywords: asbestos miners; asbestos‐related disease; determinants; mortality rates; predictors; risk factors.