Gill Nelson

Oscillating migration and the epidemics of silicosis, tuberculosis, and HIV infection in South African gold miners.

BACKGROUND Hundreds of thousands of men from rural areas of South Africa and neighboring countries have come to seek work in the gold mines. They are not immigrants in the usual sense as they work for periods in the mines, go home, and then return. This is termed oscillating or circular migration. Today we have serious interrelated epidemics of silicosis, tuberculosis, and HIV infection in the gold mining industry. METHODS This article discusses the role of oscillating migration in fuelling these epidemics, by examining the historical, political, social, and economic contexts of these diseases. RESULTS The impact of silicosis, tuberculosis, and HIV infection extends beyond individual miners to their families and communities. CONCLUSION Failure to control dust and tuberculosis has resulted in serious consequences decades later. The economic and political migrant labor system provided the foundations for the epidemics seen in southern Africa today.

High Rates of Recurrence in HIV-Infected and HIV-Uninfected Patients with Tuberculosis

BACKGROUND The rate of recurrent tuberculosis disease due to reinfection, compared with the incidence of new tuberculosis, in those with and without HIV infection is not known. METHODS In a retrospective cohort study of South African gold miners, men with known dates of seroconversion to HIV (from 1991 to 1997) and HIV-negative men were followed up to 2004. Rates of tuberculosis recurrence >2 years after the first episode were used as a proxy for reinfection disease rates. RESULTS Among 342 HIV-positive and 321 HIV-negative men who had had 1 previous episode of tuberculosis, rates of recurrence were 19.7 cases per 100 person-years at risk (PYAR; 95% confidence interval [CI], 16.4-23.7) and 7.7 cases per 100 PYAR (95% CI, 6.1-9.8), respectively. The recurrence rate did not vary by duration of HIV infection. Recurrent pulmonary tuberculosis rates >2 years after the first episode were 24.4 cases per 100 PYAR (95% CI, 17.2-34.8) in HIV-positive men and 4.3 cases per 100 PYAR (95% CI, 2.2-8.3) in HIV-negative men, compared with incidence rates of new pulmonary tuberculosis of 3.7 cases per 100 PYAR (95% CI, 3.3-4.1) in HIV-positive men and 0.75 cases per 100 PYAR (95% CI, 0.67-0.84) in HIV-negative men in the same cohort. CONCLUSIONS Tuberculosis recurrence rates, likely due to reinfection, were much higher than incidence rates. The findings suggest heterogeneity in susceptibility, implying that a vaccine could still provide useful protection in the population and strengthening the case for secondary preventive therapy.

Effects of duration of HIV infection and secondary tuberculosis transmission on tuberculosis incidence in the South African gold mines.

Background:HIV increases the risk of tuberculosis directly, through immunosuppression, and indirectly, through onward transmission of Mycobacterium tuberculosis from the increased caseload. We assess the contribution of these two mechanisms by time since seroconversion to HIV. Methods:The incidence of new pulmonary tuberculosis was estimated in a retrospective cohort study of South African gold miners over 14 years. HIV tests were done in random surveys in 1992–1993, and in clinics. One thousand nine hundred fifty HIV-positive men with seroconversion intervals of less than 3 years were identified and linked to medical, demographic and occupational records. They were compared with men who were HIV-negative in a survey, with no later evidence of HIV. Analyses were censored when men were diagnosed with tuberculosis, died or left the mine. Results:Tuberculosis incidence rose soon after HIV infection, reaching 1.4/100 person-years (95% confidence interval 1.1–1.9) within 2 years, and 10.0/100 person-years (95% confidence interval 6.5–15.5) at 10 or more years. By 11 years from seroconversion, nearly half the men had had tuberculosis. Among 5702 HIV-negative men, tuberculosis incidence was 0.48/100 person-years (95% confidence interval 0.33–0.70) in 1991–1993 and doubled over the period of the study (after adjusting for age). Age-adjusted model estimates suggest that half the increase in tuberculosis incidence by time since HIV infection was attributable to increasing incidence over calendar period – the indirect effect. Conclusion:For the first time, we have shown that the increase in tuberculosis risk by time since seroconversion reflects both direct effects of HIV increasing susceptibility, and indirect effects due to onward transmission. Innovative and sustained public health measures are needed to reduce Mycobacterium tuberculosis transmission.

Cause of death and presence of respiratory disease at autopsy in an HIV-1 seroconversion cohort of southern African gold miners

Objectives:To describe causes of death and respiratory infections in HIV-infected miners in the pre-antiretroviral era, by duration of HIV infection. Design:A retrospective cohort of 1950 gold miners with known dates of HIV seroconversion and 6164 HIV-negative miners was followed from the early 1990s to 2002. Methods:Causes of death were available from multiple sources: personnel records, clinical records, death certificates and autopsies of cardiorespiratory organs performed for compensation purposes. Results:Causes of death were known for 279 of 308 HIV-positive (91%) and 234 of 254 HIV-negative (92%) men who died while employed or within 6 months of leaving employment. The mortality rate from unnatural causes was similar in HIV-positive and HIV-negative miners and by duration of HIV infection. Among deaths from natural causes, 87% in HIV-positive and 41% in HIV-negative individuals were caused by infection (P < 0.001); 47% of HIV-positive and 26% of HIV-negative individuals had tuberculosis. The proportion of deaths from natural causes with any infection, or with specific infections (tuberculosis, cryptococcus, pneumocystis), did not vary with the duration of HIV infection. Autopsies were performed on 29% of men who died from natural causes: 83% of HIV-positive and 37% of HIV-negative men had respiratory infections (P < 0.001), half of which were clinically undiagnosed. Conclusion:Tuberculosis was the leading cause of death in HIV-positive and negative men who died from natural causes. Although the mortality rate from natural causes increased greatly with the duration of HIV infection, the pattern of disease hardly changed, suggesting that slow and fast progressors succumb to the same range of diseases.

Three decades of silicosis : disease trends at autopsy in South African gold miners

Background Eliminating silicosis is a priority of the International Labour Organization and the World Health Organization. Prevalence is particularly high in developing countries. Objectives We describe trends in silicosis among South African gold miners who had had an autopsy between 1975 and 2007 and quantify the contributions of age at autopsy and employment duration to these trends. Methods South African miners and ex-miners are eligible for autopsy examination for occupational lung disease, regardless of the clinical cause of death, and the families of deceased mine workers may receive compensation from the government of South Africa. Miners who died from external causes and who had been employed in the gold mines for > 1 year were stratified by population group because of differences in exposure, patterns of employment, and autopsy referral patterns. We extracted data from PATHAUT (Pathology Automation System) and used Stata 10 to estimate trends in relative proportions of silicosis that were standardized for age and employment duration. Results The crude proportion of silicosis for white miners was six times that of black miners in 1975. By 2007, it was 1.5 times higher for black miners. The proportion of miners with silicosis increased from 0.03 to 0.32 for black miners and from 0.18 to 0.22 for white miners. The increase can be explained by increasing age and employment duration for white miners. For black miners, it can be only partly explained by these two factors. Conclusion As miners continue to age and work for longer periods, the burden of silicosis will continue to rise. South Africa is committed to global efforts to eliminate silicosis by 2030. The autopsy database allows for disease surveillance, which is necessary to monitor the success of this initiative.

Survival from HIV-1 seroconversion in Southern Africa : a retrospective cohort study in nearly 2000 gold-miners over 10 years of follow-up

Objective:To obtain robust estimates of survival with HIV in individuals with known dates of seroconversion in Africa in the pre-antiretroviral era. Design and methods:Mortality rates were estimated in men from four South African gold mines in a retrospective cohort study with 10-year follow-up. HIV testing was carried out with counselling and consent, in random surveys in the early 1990s and in clinics. A total of 1950 HIV-positive men with seroconversion intervals < 3 years were compared with 6164 HIV-negative men with no subsequent evidence of HIV. Unique industry numbers were used to link medical records to demographic and occupational information. Follow-up after leaving the mine was conducted through employment offices across southern Africa, and using South African death registration data. Results:Follow-up was complete for 85% of those who seroconverted. Median survival was 10.5 years overall: 11.5 years for those aged 15–24 at seroconversion, 10.5 years for those aged 25–34, 9.5 years for those aged 35–44, and 6.3 years for those aged 45+ years. The relative mortality rate in comparison with HIV-uninfected miners increased quickly, reaching 13 for those HIV-infected for at least 9 years, and did not vary by age group. Excess mortality increased with age and duration of infection to > 10% per year. Adjusted to age 25–29 years at seroconversion, 5-year survival was 89% and 10-year 62%. Discussion:This study reports by far the largest cohort of individuals with known dates of seroconversion available in Africa. After adjusting for age, the survival pattern was similar to that seen in the West before antiretroviral therapy was available.

Trends in lung cancer mortality in South Africa: 1995-2006

BackgroundCancer remains a major cause of morbidity and mortality worldwide. In developing countries, data on lung cancer mortality are scarce.MethodsUsing South Africas annual mortality and population estimates data, we calculated lung cancer age-standardised mortality rates for the period 1995 to 2006. The WHO world standard population was used as the reference population. Scatter plots and regression models were used to assess linear trends in mortality rates. To better characterise emerging trends, regression models were also partitioned for defined periods.ResultsLung cancer caused 52,217 deaths during the study period. There were 4,525 deaths for the most recent year (2006), with men accounting for 67% of deaths. For the entire South African population, the age-standardised mortality rate of 24.3 per 100,000 persons in 1995 was similar to the rate of 23.8 per 100,000 persons in 2006. Overall, there was no significant decline in lung cancer mortality in South Africa from 1995 to 2006 (slope = -0.15, p = 0.923). In men, there was a statistically non-significant annual decline of 0.21 deaths per 100,000 persons (p = 0.433) for the study period. However, from 2001 to 2006, the annual decline of 1.29 deaths per 100,000 persons was statistically significant (p = 0.009). In women, the mortality rate increased significantly at an annual rate of 0.19 per 100,000 persons (p = 0.043) for the study period, and at a higher rate of 0.34 per 100,000 persons (p = 0.007) from 1999 to 2006.ConclusionThe more recent declining lung cancer mortality rate in men is welcome but the increasing rate in women is a public health concern that warrants intervention. Smoking intervention policies and programmes need to be strengthened to further reduce lung cancer mortality in men and to address the increasing rates in women.

Quantitative neuropathology associated with chronic manganese exposure in South African mine workers

Manganese (Mn) is a common neurotoxicant associated with a clinical syndrome that includes signs and symptoms referable to the basal ganglia. Despite many advances in understanding the pathophysiology of Mn neurotoxicity in humans, with molecular and structural imaging techniques, only a few case reports describe the associated pathological findings, and all are in symptomatic subjects exposed to relatively high-level Mn. We performed an exploratory, neurohistopathological study to investigate the changes in the corpus striatum (caudate nucleus, putamen, and globus pallidus) associated with chronic low-level Mn exposure in South African Mn mine workers. Immunohistochemical techniques were used to quantify cell density of neuronal and glial components of the corpus striatum in eight South African Mn mine workers without clinical evidence of a movement disorder and eight age-race-gender matched, non-Mn mine workers. There was higher mean microglia density in Mn mine workers than non-Mn mine workers in the globus pallidus external and internal segments [GPe: 1.33 and 0.87 cells per HPF, respectively (p=0.064); GPi: 1.37 and 0.99 cells per HPF, respectively (p=0.250)]. The number of years worked in the Mn mines was significantly correlated with microglial density in the GPi (Spearmans rho 0.886; p=0.019). The ratio of astrocytes to microglia in each brain region was lower in the Mn mine workers than the non-Mn mine workers in the caudate (7.80 and 14.68; p=0.025), putamen (7.35 and 11.11; p=0.117), GPe (10.60 and 16.10; p=0.091) and GPi (9.56 and 12.42; p=0.376). Future studies incorporating more detailed occupational exposures in a larger sample of Mn mine workers will be needed to demonstrate an etiologic relationship between Mn exposure and these pathological findings.

Effect of HIV on work-related injury rates in South African gold miners

Objective:Work-related injuries have severe, well-documented economic and social impacts, and injury is a leading cause of death in working adults. As adults of working age are one of the groups most affected by the HIV epidemic, the interaction between work-related injuries and HIV is important. The objective was to calculate the effect of HIV on the rate and severity of work-related injuries by duration of infection. Design and methods:A large, retrospective seroincident cohort of South African gold miners was studied. Data routinely collected by the mines, and assurance company injury data were analysed. HIV-positive and negative miners were compared, allowing the calculation of injury rates and rate ratios. Severity of injuries was measured by the number of days away from work, percentage of permanent disability, and fatalities. Results:Results were available for 1661 HIV-positive and 6166 HIV-negative miners over 10 years. HIV infection increased the rate of work-related injuries overall (adjusted rate ratio, 1.3; 95% confidence interval, 1.1–1.4), but had less effect on severe injuries. Injury rates in HIV-positive men prior to the first positive test were similar to those in HIV-negative men. The injury rate rose soon after the first HIV positive test. After seroconversion there was only weak evidence of an increase in injury rates by duration of infection. Conclusion:This is the first study to demonstrate an increase in injury rates in HIV-positive individuals. The increase may reflect direct effects of HIV infection as well as behaviour change once HIV is diagnosed.

Occupational respiratory diseases in the South African mining industry

Background : Crystalline silica and asbestos are common minerals that occur throughout South Africa, exposure to either causes respiratory disease. Most studies on silicosis in South Africa have been cross-sectional and long-term trends have not been reported. Although much research has been conducted on the health effects of silica dust and asbestos fibre in the gold-mining and asbestos-mining sectors, little is known about their health effects in other mining sectors. Objective : The aims of this thesis were to describe silicosis trends in gold miners over three decades, and to explore the potential for diamond mine workers to develop asbestos-related diseases and platinum mine workers to develop silicosis. Methods : Mine workers for the three sub-studies were identified from a mine worker autopsy database at the National Institute for Occupational Health. Results : From 1975 to 2007, the proportions of white and black gold mine workers with silicosis increased from 18 to 22% and from 3 to 32% respectively. Cases of diamond and platinum mine workers with asbestos-related diseases and silicosis, respectively, were also identified. Conclusion : The trends in silicosis in gold miners at autopsy clearly demonstrate the failure of the gold mines to adequately control dust and prevent occupational respiratory disease. The two case series of diamond and platinum mine workers contribute to the evidence for the risk of asbestos-related diseases in diamond mine workers and silicosis in platinum mine workers, respectively. The absence of reliable environmental dust measurements and incomplete work history records impedes occupational health research in South Africa because it is difficult to identify and/or validate sources of dust exposure that may be associated with occupational respiratory disease.BACKGROUND Crystalline silica and asbestos are common minerals that occur throughout South Africa, exposure to either causes respiratory disease. Most studies on silicosis in South Africa have been cross-sectional and long-term trends have not been reported. Although much research has been conducted on the health effects of silica dust and asbestos fibre in the gold-mining and asbestos-mining sectors, little is known about their health effects in other mining sectors. OBJECTIVE The aims of this thesis were to describe silicosis trends in gold miners over three decades, and to explore the potential for diamond mine workers to develop asbestos-related diseases and platinum mine workers to develop silicosis. METHODS Mine workers for the three sub-studies were identified from a mine worker autopsy database at the National Institute for Occupational Health. RESULTS From 1975 to 2007, the proportions of white and black gold mine workers with silicosis increased from 18 to 22% and from 3 to 32% respectively. Cases of diamond and platinum mine workers with asbestos-related diseases and silicosis, respectively, were also identified. CONCLUSION The trends in silicosis in gold miners at autopsy clearly demonstrate the failure of the gold mines to adequately control dust and prevent occupational respiratory disease. The two case series of diamond and platinum mine workers contribute to the evidence for the risk of asbestos-related diseases in diamond mine workers and silicosis in platinum mine workers, respectively. The absence of reliable environmental dust measurements and incomplete work history records impedes occupational health research in South Africa because it is difficult to identify and/or validate sources of dust exposure that may be associated with occupational respiratory disease.