Silicosis in Zambian ex-copper miners: A cross-sectional study

Dust exposure in copper mining, an important industry in Africa, poses a risk of silicosis and pulmonary tuberculosis (TB). Despite a number of reports on silicosis in Zambian copper miners since the 1960s, there has been no published report on silicosis prevalence.

To determine the prevalence of silicosis and related radiological abnormalities in Zambian copper miners.

A cross-sectional analysis was conducted of 496 ex-copper miners' chest X-rays (CXRs) taken at the Occupational Health and Safety Institute in Kitwe, Zambia, between October 2019 and September 2020. Two experienced readers classified anonymised CXRs by consensus using the International Labour Organization (ILO) classification system for pneumoconiosis. The association between CXR outcomes and occupational variables, adjusting for age, was analysed using logistic regression.

A total of 472 records were analysable. Of the miners, 82% were from seven companies across six mining districts, with most having worked in Kitwe and Chingola. Median service length was 25.4 years and median age 62.8 years. Silicosis of nodular profusion >ILO 1/0 was found in 8.3% (95% confidence interval (CI) 5.9 - 11.1), with ILO categories 1 and >2 comprising 4.9% and 3.4%, respectively. Silicotuberculosis was present in 4.0%. Exposure-response relationships between silicosis and occupational metrics were weak with wide CIs. Other CXR abnormalities were features suggestive of TB (16.5%; 95% CI 13.3 - 20.2) and cardiomegaly (19.3%; 95% CI 15.8 - 23.1). Adjusting for age, TB was strongly associated with silicosis (odds ratio (OR) 6.0; 95% CI 3.0 - 11.9) but unrelated to service length. Cardiomegaly was associated with service length after adjustment for age (OR 1.38; 95% CI 0.94 - 2.10).

The prevalence of silicosis in Zambian copper miners has not changed since the last (unpublished) study in 2012. Best-practice measurement of silica exposure in all copper mines and comprehensive surveillance of ex-miners for silicosis and TB are needed. The unexpected association of cardiomegaly with length of service warrants investigation of possible occupational risk.

What the study adds. Although there have been previous reports on silicosis in Zambia, this is the first study of the prevalence of silicosis published in the open literature. It shows a persistence since 2012 of silicosis prevalence among ex-copper miners of 8%, with a substantial proportion of radiologically advanced disease.Implications of the findings. Zambia has a large and growing copper mining industry. Silicosis is a strong risk factor for pulmonary tuberculosis (TB), contributing to the elevated burden of TB among miners in Zambia. A multidisciplinary response of best-practice measurements of silica dust on all copper mines and countrywide medical surveillance of ex-miners for silicosis and TB is needed as a basis for primary prevention.