Tuberculosis and silica exposure in South African gold miners.
OBJECTIVE
To examine the effect of silica exposure, in the absence of silicosis, on the prevalence of pulmonary tuberculosis (PTB), which is epidemic among South African gold miners.


METHODS
Cross-sectional study of 520 gold miners over 37 years of age. Length of service, and cumulative and average dust and quartz exposure indices were derived for each miner. Chest radiographs were read for PTB by two NIOSH "B" readers. PTB was defined as a self-reported history of PTB or PTB on chest radiograph. Logistic regression was used to adjust for age, smoking, and silicosis. PTB effects of different exposure metrics for silica, scaled on their interquartile range (IQR), were compared.


RESULTS
Means (ranges) were: age 46.7 (37.1-59.9) years; length of service 21.8 (6.3-34.5) years; average intensity of respirable quartz 0.053 (0-0.095) mg/m3. PTB prevalence was 19.4% (95% CI 16.0 to 22.8) on history alone, and 35.2% (95% CI 31.1 to 39.3) on history or on chest radiograph. Length of service was poorly predictive of PTB, while all exposure indices which included dust or quartz yielded prevalence odds ratios (PORs) of approximately 1.4 (95% CI approximately 1.1 to 1.8) for changes of one interquartile range in exposure. Controlling for silicosis--by adjustment or restriction--did not modify these results. Drillers and winch operators had the highest PTB prevalences and the highest dust and silica exposures.


CONCLUSIONS
Older in-service gold miners in South Africa have a high prevalence of PTB, which is significantly associated with dust and silica exposure, even in the absence of silicosis. Limitations include a survivor workforce and the use of cumulative exposures based on current exposures. Dust control is an important component in control of the PTB epidemic in South African gold mines.
School of Public Health and Family Medicine, University of Cape Town, Cape Town, South Africa. jim@cormack.uct.ac.za
J M
JM
teWaternaude
R I
RI
Ehrlich
G J
GJ
Churchyard
L
L
Pemba
K
K
Dekker
M
M
Vermeis
N W
NW
White
M L
ML
Thompson
J E
JE
Myers
D000328:Adult; D003430:Cross-Sectional Studies; D004391:Dust; D006046:Gold; D006801:Humans; D008875:Middle Aged; D008906:Mining; D009784:Occupational Diseases / Q000209:etiology*; D016273:Occupational Exposure / Q000009:adverse effects*; D016017:Odds Ratio; D015995:Prevalence; D012044:Regression Analysis; D012822:Silicon Dioxide / Q000633:toxicity*; D013019:South Africa / Q000453:epidemiology; D014397:Tuberculosis, Pulmonary / Q000453:epidemiology*
D004391:Dust; D006046:Gold; D012822:Silicon Dioxide