Neil W. White

Tuberculosis and silica exposure in South African gold miners

Aims: 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 ∼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. Conclusion: 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.

Prevalence of Occupational Lung Disease in a Random Sample of Former Mineworkers, Libode District, Eastern Cape Province, South Africa

BACKGROUND Gold mineworkers in South Africa are exposed to high levels of silica dust as a result of which they are at risk of developing silicosis, which is a compensable disease. The incidence of tuberculosis is also high. METHODS To determine the prevalence of occupational lung disease and the previous compensation history in former migrant mineworkers, a study was undertaken in a random sample of men living in Libode, a rural district of Eastern Cape Province, South Africa. Two hundred thirty-eight ex-mineworkers were examined according to a protocol that included chest radiography and spirometry. Chest radiographs were read into the International Labour Organisation (ILO) classification for pneumoconioses by two readers. RESULTS The mean age was 52.8 years, and the mean length of service was 12.15 years. The prevalence of pneumoconiosis (> or = ILO 1/0) was 22% and 36% (variation by reader). For both readers, a significant association between length of service and pneumoconiosis and between pneumoconiosis and reduction in FVC and FEV was found. Twenty-four percent of study subjects were eligible for compensation. CONCLUSION There is a high prevalence of previously undiagnosed, uncompensated pneumoconiosis in the study group. As a result of the failure to diagnose and compensate occupational lung disease, the social and economic burden of such disease is being borne by individuals, households, and the migrant labor-sending communities as a whole.

Silicosis prevalence and exposure-response relations in South African goldminers

Aims: To measure the prevalence of silicosis among black migrant contract workers on a South African goldmine and to investigate exposure-response relations with silica dust. Methods: In a cross sectional study, 520 black goldminers (aged >37 years) were interviewed and had chest radiographs taken. Silicosis was defined as International Labour Organisation Classification radiological profusion of 1/1 or greater. Results: Mean length of service was 21.8 years (range 6.3–34.5). The mean intensity of respirable dust exposure was 0.37 mg/m3 (range 0–0.70) and of quartz 0.053 mg/m3 (range 0–0.095). The prevalence of silicosis was 18.3–19.9% depending on reader. Significant trends were found between the prevalence of silicosis and length of service, mean intensity of exposure, and cumulative exposure. Conclusion: Results confirm a large burden of silicosis among older black workers in the South African goldmining industry, which is likely to worsen as such miners spend longer periods in continuous employment in dusty jobs. An urgent need for improved dust control in the industry is indicated. If the assumption of stability of average dust concentrations on this mine over the working life of this group of workers is correct, these workers developed silicosis while exposed to a quartz concentration below the recommended occupational exposure limit (OEL) of 0.1 mg/m3. This accords with a mounting body of evidence that an OEL of 0.1 mg/m3 is not protective against silicosis.

High Prevalence of Tuberculosis in Previously Treated Patients, Cape Town, South Africa

More than half of smear-positive case-patients had previously undergone treatment.

The burden of silicosis, pulmonary tuberculosis and COPD among former Basotho goldminers

BACKGROUND The burden of silicosis, pulmonary tuberculosis and COPD is described in 624 South African gold miners 18 months after cessation of work. METHODS This was a prevalence study. Questionnaires were administered, and spirometry, chest radiography, tuberculosis investigations, and urine HIV antibody assays were performed. RESULTS Attendance was 80.1% (624/779), mean age 49.4 years, and mean employment duration 25.6 years. Most subjects had had medium (26.5%) or high (65.4%) dust-exposure jobs. Current smoking rate was 35%, with ever smoking 61%. HIV antibodies were detected in the urine in 22.3%. Prevalences were: silicosis 24.6%, past tuberculosis 26%, current tuberculosis 6.2%, airflow obstruction 13.4%, and chronic productive cough 17.7%. Almost 50% of these miners had at least one of these respiratory conditions. CONCLUSIONS A heavy burden of silicosis, tuberculosis and COPD was present in this group of former goldminers. Intensification of work place dust control measures and TB and HIV prevention activities are needed on South African gold mines. In labor sending communities investment is needed in silicosis and tuberculosis surveillance as well as HIV treatment and care.

Meteorologically estimated exposure but not distance predicts asthma symptoms in schoolchildren in the environs of a petrochemical refinery: a cross-sectional study

BackgroundCommunity concern about asthma prompted an epidemiological study of children living near a petrochemical refinery in Cape Town, South Africa. Because of resource constraints and the complexity of refinery emissions, neither direct environmental measurements nor modelling of airborne pollutants was possible. Instead a meteorologically derived exposure metric was calculated with the refinery as the putative point source. The study aimed to determine whether (1) asthma symptom prevalences were elevated compared to comparable areas in Cape Town and (2) whether there was an association between asthma symptom prevalences and the derived exposure metric.MethodsA cross-sectional study was carried out of all consenting school children aged 11 to 14 years attending schools in a defined area, utilizing the International Study of Asthma and Allergy in Childhood (ISAAC) written and video questionnaires. Information was collected on potential confounders, e.g. parental history of atopic disease, active and passive smoking by the participant, birth order, number of children in the home and distance from a major road. The exposure metric combined residential distance of each child from the refinery with a wind vector in the form of wind speed, wind direction and proportion of the year blown.ResultsA total of 2,361 children from 17 schools met the criteria for inclusion. In multivariate analysis, meteorologically estimated exposure (MEE), but not simple distance from the refinery, was positively associated with having to take an inhaler to school [odds ratio per interquartile range (OR) 1.22, 95% confidence interval (CI) 1.06-1.40], and with a number of video elicited asthma symptoms, including recent waking with wheezing (OR 1.33, 95% CI 1.06-1.66) and frequent wheezing at rest (OR 1.27, 95% CI 1.05 - 1.54). Symptom prevalences were higher than in other areas of the city, with frequent waking with wheezing being in great excess (OR 8.92, 95% CI 4.79-16.63).ConclusionThe results support the hypothesis of an increased prevalence of asthma symptoms among children in the area as a result of refinery emissions and provide a substantive basis for community concern. The methodology also provides a low cost means of testing hypotheses about point source pollutant effects on surrounding populations of children.

Incidence of tuberculosis and HIV and progression of silicosis and lung function impairment among former Basotho gold miners.

BACKGROUND Pulmonary tuberculosis and HIV incidence, mortality, and the progression of silicosis and lung function impairment are described over a 1-year period in migrant ex-gold miners from Lesotho. METHODS Seven hundred seventy-nine Basotho miners were followed for 1 year starting 18 months after lay-off from a South African gold mine in 1998. At baseline and follow-up, they underwent a respiratory symptom interview, physical examination, HIV test, chest radiograph, and spirometry. RESULTS Five hundred thirteen of 779 (65.9%) participants attended both baseline and follow-up visits. HIV incidence was 5.4/100 person-years (95% CI: 3.4-8.2). Prevalence of silicosis (ILO score > or =1/1) was 26.6% at baseline and 27.0% at follow-up. Active tuberculosis diagnosed at baseline was a strong predictor of radiological progression of silicosis. Lung function as measured by FEV(1) declined an average of 91 ml between visits (95% CI: 67-116 ml). Calculated minimum incidence of tuberculosis was 3,085/100,000/years (95% CI: 1,797-4,940) at follow-up. Of those seen at baseline, 18 died before their scheduled follow-up visit (mean age: 51 years). CONCLUSIONS High rates of mortality and of HIV infection and pulmonary tuberculosis were found in this cohort after leaving the South African goldmines. Continuing lung function loss was also apparent. A partnership between the South African mining industry and governments in labor-sending areas of Southern Africa is needed to provide continuity of care and access to HIV and tuberculosis treatment and prevention services. Active silicosis surveillance and an improved statutory compensation system are also needed. These findings can serve as a baseline against which the impact of such interventions can be assessed.

Excess lung function decline in gold miners following pulmonary tuberculosis

Background Few if any studies of the association between pulmonary tuberculosis (TB) and lung function loss have had access to premorbid lung function values. Methods Using a retrospective cohort design, the study recruited employed South African gold miners who had undergone a pulmonary function test (PFT) between January 1995 and August 1996. The ‘exposed’ group comprised 185 miners treated for pulmonary TB after the initial PFT and the ‘unexposed’ group comprised 185 age-matched miners without TB. All participants had a follow-up PFT between April and June 2000. The outcome of interest was decline in lung function during the follow-up period as measured by forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV1). Results After controlling for age, height, baseline lung function, silicosis, years of employment, smoking and other respiratory diagnoses, pulmonary TB during the follow-up period was associated with a mean excess loss of 40.3 ml/year in FEV1 (95% CI 25.4 to 55.1) and 42.7 ml/year in FVC (95% CI 27.0 to 58.5). Lung function loss was greater among those with more severe or later clinical presentation of TB. Breathlessness was twice as common among TB cases (OR 2.20, 95% CI 1.18 to 4.11). Conclusion There is a need for greater clinical recognition of the long-term respiratory consequences of treated pulmonary TB. Early detection of TB would help to reduce these sequelae and remains a priority, particularly in a workforce already subject to silica dust disease. However, strategies such as dust control, worker education about TB and dust and TB preventive therapy are also needed to avert the disease itself.

Costs of occupational lung disease in South African gold mining

Abstract This paper analyses the costs of gold mining related occupational lung disease to the mining industry, the state health services and the mine labour sending communities. The extent of the liability of unpaid occupational lung disease compensation is estimated. It is shown that there is a high prevalence of uncompensated occupational lung disease in ex-mine-workers and that much of the cost of this disease is being externalised from the industry. The total cost, both internalised and externalised, of gold mining related lung disease represents 6 per cent of the 1996 wage bill and 2.6 per cent of the gold mining industrys contribution to South Africas GDP in 1996. Better information on costs is critical for planning profitable and safe gold mining and also for the planning and budgeting of health care services.