Block 5: TB and occupation in South Africa - Goldminers in South Africa - A Case Study.

GOLDMINERS IN SOUTH AFRICA - A CASE STUDY:

The figure shows the changing relationship between occupationally related deaths from accidents and disease in the SA gold mining industry in the 1990’s. Deaths from accidents, long the focus of preventive efforts in the industry, have been superceded by deaths from diseases.

The figure above shows the causes of hospitalisation.

The South African TB incidence rates per 100 000 pop p.a. are shown in the diagram above. The figure shows that during the 1980’s and through to the present time, the incidence of TB amongst goldminers has been rising steadily and is many times that of the SA national population incidence, an effect not expected amongst healthy workers.

It is notable that rates of TB have always exceeded those observed in the general population.

This increase in TB rates is sometimes attributed solely to the HIV pandemic which has progressed in goldminers at a similar rate to the general southern African population. Other factors could be operative here.

TB rates are not only higher in gold mining than in the general population, they are also significantly higher in gold mining than in other mining populations where there is no significant silica exposure. In a comparison of comparable cohorts of gold and platinum miners, it was found that the incidence rate in goldminers was seven times higher than amongst platinum miners.

A careful study of TB in relation to cumulative dust exposure in goldminers (who do not have silicosis) has shown that this exposure is an important factor in TB risk amongst miners. The results of this study are summarised in the figure on the right.

Because TB risk in goldminers is related to cumulative silica dust exposure, it follows that high dust occupations in goldmining should have a high risk of TB.

The figure above the results of a study that has demonstrated that high dust occupations in gold mining, such as drillers and general labourers at the stopes, have the highest risk of tuberculosis.

Silica exposure alone increases the risk of TB. Presence of radiological silicosis is a factor that further increases risk of tuberculosis, associated with a 3-30 fold increased risk.

As shown in the figure on the left, silicosis is common in older goldminers. Age is a risk factor for both silicosis and tuberculosis, with prevalence and incidence increasing with age.

The following figure summarises information about risk factors for TB in goldminers and how it has changed in the 1990’s. HIV, taken alone, is the single most currently important risk factor for TB incidence. TB incidence in HIV –ve people does not seemed to have changed in the decade.

Silicosis is a risk factor for TB and the risk of TB increases with the profusion of silicotic abnormality.

Underground work has a greater risk than surface work.

HIV and silicosis are both risk factors for TB incidence. They also influence TB mortality wihilst under treatment, as shown by the figure on the left,which illustrates the results of TB treatment of a cohort of goldminers, stratified for HIV and silicosis status.