An evaluation of mortality rates and their determinants in a South African cohort of former asbestos miners

Williams-Mohamed, Yumna

An evaluation of mortality rates and their determinants in a South African cohort of former asbestos miners

Thesis / Dissertation

2026

Publisher

University of Cape Town

Department

Department of Public Health and Family Medicine

Faculty

Faculty of Health Sciences

Abstract

Background: There is a well-established causal link between occupational asbestos exposure and lung diseases such as pneumoconiosis and mesothelioma. Higher mortality rates in former asbestos miners compared to the general population are thus anticipated. However, no local, large-scale studies have been conducted to evaluate the all-cause mortality experience in this subpopulation. We investigated all-cause mortality among a cohort of former South African asbestos miners captured on 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 modelled 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). Radiological abnormalities based on ILO profusion category were strong predictors of mortality with adjusted hazard ratios (aHRs) ranging from 1.13 (95% CI: 1.05-1.23) to 2.34 (95% CI: 1.52-3.58). Other significant predictors were a BMI less than 18.5 kg/m2 (aHR=1.46; 95% CI: 1.35-1.58), history of previous smoking (aHR=1.43; 95% CI: 1.35-1.53), costophrenic angle obliteration (aHR=1.27; 95% CI: 1.14-1.41), and reduced forced expiratory volume in one second and forced vital capacity (aHR=1.60; 95% CI:1.41-1.81 and aHR=1.26: 95% CI: 1.12-1.42, respectively, for z-scores less than -3.0). The SMR decreased with time. Conclusion: Interpretation of mortality in this cohort was limited by incomplete data, preventing firm conclusions. However, radiologic and spirometric measures emerged as significant predictors of mortality, potentially enabling risk stratification and guiding targeted interventions. Such interventions include early management of respiratory complications and smoking cessation, which could mitigate mortality risk.