Pulmonary tuberculosis (TB) is a disease which is both curable and preventable, with
recognised complications such loss of lung function and progressive massive fibrosis (PMF).
It is a major cause of pulmonary disability and mortality in the South Africa mining industry.
Tuberculosis has a high social and economic cost, both for the individual concerned and for
the industry as a whole. However, notwithstanding the extensive literature on TB in the
mining industry, given the size and economic importance of coal mining in South Africa, there
is surprisingly scanty information available on TB and other occupational lung diseases in
A strong correlation was reported in Canada, the USA and China between coal usage and
TB. This highlights the possibility of the direct impact of coal usage on TB. Although black
miners have historically done jobs with the highest exposure in the coal mining industry,
there have been remarkably few studies reporting the prevalence of TB and the exposure
response relationship in black coal miners in South Africa.
Dust exposure in coal mines is a risk factor for occupational lung diseases such as coal
workers' pneumoconiosis (CWP), chronic obstructive airways disease (COAD) and lung
function deficiency. However, there are still doubts and debates about the risk in such work
of tuberculosis. The aim of this study was to fill the gap in the literature by determining the
prevalence and exposure response relationship of TB to coal dust exposure.
To determine, within a sample of coal miners:
. Prevalence of tuberculosis (TB)
. Prevalence of coal workers' pneumoconiosis and past TB
. Association of outcome variables with exposure variables and underground coalmine
workers' exposure as compared to that of surface workers
. Association of TB with coal workers' pneumoconiosis and past TB
. Exposure response relationship of TB, coal workers' pneumoconiosis and past TB to
respirable coal dust.
A cross-sectional study of 344 employed black male coal miners at a coal mining complex
with fourteen mine shafts at Secunda in Mpumalanga, was done. The records from 1
January 2000 to 31 December 2005 were reviewed.
The main outcome measure was the prevalence of current TB in coal miners. The sample
consisted of 220 underground and 124 surtace coal miners. The exposure variables
considered were lifetime mean exposure level (LMEL) (mgim3), cumulative dust exposure
(CDE) in mg-years/m3, and coal mining years. Information was collected from multiple
sources including hospital files, surveillance records and medical records, and crossvalidated
with the information from the human resources department.
Information was collected on the demographic profile, exposure, underground or surface
work, area of work, smoking history, HIV status from medical records, dust exposure
intensity, length of service, TB diagnosis and the methods of diagnosis and outcome of the
treatment, and previous TB and CWP. Participants with current TB were either sputum
culture positive or sputum culture negative TB.
The mean age of the sample was 45.2 years, (range 2844 years; SD = 8.2).The mean
duration of service was 16.1 years (range 4.1-27.7 years; SD 5.9). There were 34 (9.9%)
cases of current TB in total, of which 31 were underground coal miners and three were
surface coal miners.
The prevalence of current TB reported by this study was 9.97o, with a mean age of 46J
years and length of service of 16.2 years. The prevalence of current TB among the
underground and surface workers was 14.1o/o and 2.4o/o rcspectively. The prevalence of
CWP was 3.8o/o, with a mean age of 51.3 years and a mean length of service of 2Q.l years.
The prevalence of past TB was also 3.8o/o, with a mean age and length of service of 44.9 and
1 6. 1 years respectively.
Underground coal mines workers' exposure to coal dust was high, with a lifetime mean
exposure level (LMEL) and cumulative dust exposure (CDE) of 2.4 mg/m3 and 33.4 mgyears/
m3 respectively. The difference in LMEL and CDE among underground vs. surface
workers was significant, with underground exposure being higher than surface exposure,
namely p<0.001 and p<0.001 respectively. The difference in length of service between
underground and surface participants was not significant.
The difference in exposure to coal dust (LMEL and CDE) among participants with current
and previous TB, compared to those without current and previous TB, was statistically
significant, p<0.008 and p<0.04. The difference between the coal dust exposure indices
(LMEL, CDE exposure duration) for participants with and without CWP was significant.
However, the difference between participants with current TB and previous TB compared to
those with non-current TB and without previous TB in age and length of service years was
not significant. This also applied to HIV status and smoking: the difference between
participants with and without current TB was not significant.
There was a strong significant association of underground mine work with current TB, with a
prevalence odds ratio (POR) of 6.62 (p<0.001).This showed that the association of exposure
to coal dust with current TB was strong and significant as underground mine workers were
exposed to higher coal dust concentrations than surface workers. Workers with current TB
were more likely to have co-existing CWP, with a POR of 1.7 (95Vo Cl:0.f7.1).
The exposure-response relationship of LMEL and CDE in participants with current TB and
CWP was significant. A significant trend was observed of increasing of LMEL and CDE with
an increase in the prevalence of current TB, CWP and past TB.
There was a possible dose response relationship between coal dust exposure and the risk of
development of pulmonary TB. The study showed that coal dust exposure was associated
with pulmonary TB, and a dose response relationship with the trend of increasing coal dust
exposure. lt has been shown that there is a more significant and stronger association of
underground coal mine work with current TB than there is in surface work.
This study has shown a significant exposure response relationship in the exposure indices
(CDE and LMEL), age and length of service for CWP. This study found a high prevalence of
pulmonary TB of 9.9% in black migrant coal mine workers who historically held jobs in the
dustiest areas in the mining industry. The limitations of the study include the use of
cumulative exposure calculated from current exposure, and the secondary healthy worker
effect or survivor workforce. Dust control and HIV/AIDS programmes should be an integral
part of a TB and occupational lung disease control strategy in the mining industry.||en