Biomedical subjects

B G Williams

Publications and source records attributed to B G Williams.

At least 19 recordsLinked to original sources

PubMed2005

The impact of HIV/AIDS on the control of tuberculosis in India.

Epidemics of HIV/AIDS have increased the tuberculosis (TB) case-load by five or more times in East Africa and southern Africa. As HIV continues to spread, warnings have been issued of disastrous AIDS and TB epidemics in "new-wave" countries, including India, which accounts for 20% of all new TB cases arising in the world each year. Here we investigate whether, in the face of the HIV epidemic, India's Revised National TB Control Program (RNTCP) could halve TB prevalence and death rates in the period 1990-2015, as specified by the United Nations Millennium Development Goals. Using a mathematical model to capture the spatial and temporal variation in TB and HIV in India, we predict that, without the RNTCP, HIV would increase TB prevalence (by 1%), incidence (by 12%), and mortality rates (by 33%) between 1990 and 2015. With the RNTCP, however, we expect substantial reductions in prevalence (by 68%), incidence (by 41%), and mortality (by 39%) between 1990 and 2015. In India, 29% of adults but 72% of HIV-positive adults live in four large states in the south where, even with the RNTCP, mortality is expected to fall by only 15% between 1990 and 2015. Nationally, the RNTCP should be able to reverse the increases in TB burden due to HIV but, to ensure that TB mortality is reduced by 50% or more by 2015, HIV-infected TB patients should be provided with antiretroviral therapy in addition to the recommended treatment for TB.

AIDS-Related Opportunistic Infections↗

PubMed2005

Risk factors of sexually transmitted infections among migrant and non-migrant sexual partnerships from rural South Africa.

In October 1998, cohorts of circular migrant men and their non-migrant sexual partners, and non-migrant men and their non-migrant sexual partners from rural South Africa were recruited and followed-up every 4 months until October 2001. At each visit, information on sociodemographic, sexual behaviour, sexually transmitted infections (STIs) and HIV was collected. In total, 553 individuals aged between 18 and 69 years were recruited. A man and his sexual partner(s) form a sexual partnership. Migration status, age, marital status, age at sexual debut, recent sexual partners and HIV status were found to be important determinants of STI. The risk of STI varies (sigma2 = 1.45, P < 0.001) significantly across sexual partnerships even after controlling for important determinants. The variance implies substantial correlation (0.59) between members of the same sexual partnership. Ignoring this correlation leads to incorrect inference. Migration contributes significantly to the spread of STIs. Community interventions of HIV/STI should target co-transmitter sexual partnerships rather than high-risk individuals.

Adolescent↗

PubMed2005

Tuberculosis deaths in countries with high HIV prevalence: what is their use as an indicator in tuberculosis programme monitoring and epidemiological surveillance?

Although the reduction of tuberculosis deaths is one of the aims of tuberculosis control, it has not always been a priority for National Tuberculosis Programmes (NTPs). The usual explanation is that death as a treatment outcome not associated with ongoing tuberculosis transmission is not relevant to the public health objective of cutting the cycle of disease transmission. However, death as an adverse outcome for tuberculosis patients and their families is an important indicator in NTP monitoring. Global health targets agreed as part of the Millennium Development Goals include the reduction of tuberculosis deaths. Tuberculosis deaths as an indicator of the impact of tuberculosis control measures are therefore important in the epidemiological surveillance of progress towards these targets. These considerations are particularly important in countries with high human immunodeficiency virus (HIV) prevalence where HIV has exacerbated the tuberculosis epidemic and is now the single best predictor of tuberculosis incidence. Tuberculosis deaths are also closely linked to HIV prevalence. Routine NTP data on tuberculosis cohort deaths are important in programme monitoring, and improvements in recording and reporting of deaths would help to overcome limitations in their accuracy. As routine NTP data on tuberculosis cohort deaths are insufficient as an indicator in epidemiological surveillance regarding the impact of NTPs on tuberculosis mortality, measuring progress towards targets for reduced tuberculosis deaths depends on improved national vital registration systems for a more accurate determination of tuberculosis mortality.

Environmental Monitoring↗

PubMed2004

Monitoring trends in under-5 mortality rates through national birth history surveys.

BACKGROUND: We assessed whether Demographic and Health Surveys (DHS), a large and high-quality source of under-5 mortality estimates in developing countries, would be able to detect reductions in under-5 mortality as established in global child health goals. METHODS AND RESULTS: Mortality estimates from 41 DHS conducted in African countries between 1986 and 2002, for the interval of 0-4 years preceding each survey (with a mean time lag of 2.5 years), were reviewed. The median relative error on national mortality rates was 4.4%. In multivariate regression, the relative error decreased with increasing sample size, increasing fertility rates, and increasing mortality rates. The error increased with the magnitude of the survey design effect, which resulted from cluster sampling. With levels of precision observed in previous surveys, reductions in all-cause under-5 mortality rates between two subsequent surveys of 15% or more would be detectable. The detection of smaller mortality reductions would require increases in sample size, from a current median of 7060 to over 20,000 women. Across the actual surveys conducted between 1986 and 2002, varying mortality trends were apparent at a national scale, but only around half of these were statistically significant. CONCLUSIONS: The interpretation of changes in under-5 mortality rates between subsequent surveys needs to take into account statistical significance. DHS birth history surveys with their present sampling design would be able to statistically confirm under-5 mortality reductions in African countries if true reductions were 15% or larger, and are highly relevant to tracking progress towards existing international child health targets.

Africa↗

PubMed2003

Experiences of men with breast cancer: an exploratory focus group study.

Management and care of men with breast cancer is based on that developed for women. Our study reports that men have specific issues regarding certain aspects of their breast cancer experience, including diagnosis, disclosure, support and gender-specific information, and offers suggestions for improved patient care.

Adult↗

PubMed2002

Relative risk of HIV infection among young men and women in a South African township.

The prevalence of HIV infection in Africa is substantially higher among young women than it is among young men. Biological explanations of this difference have been presented but there has been little exploration of social factors. In this paper we use data from Carletonville, South Africa to explore various social explanations for greater female infection rates. This paper reports on data from a random sample of 507 people between 13 and 24 years old. Subjects were tested for HIV, as well as other sexually transmitted infections (STIs), and answered a behavioural questionnaire. The age-prevalence of HIV infection differs between men and women with considerably higher rates of increase with age among young women. The age of sexual debut did not differ significantly between men and women (15.9 and 16.3 years, respectively) and below the age of 20 years there was no difference in the number or distribution of the number of sexual partners reported by men or women. The risk of infection per partnership was substantially higher among women than among men. Women have sexual partners who are, on average, about five years older than they are with some variation with age. Scaling the age-prevalence curve for men by the age of their sexual partners gives a curve whose shape is indistinguishable from that for women but is about 30% lower for men than for women. In terms of social explanations for HIV rates among women, the data indicates that this difference can be explained by the relative age of sexual partners, but not by other factors explored. In addressing the epidemic among young women it will be essential to deal with the social factors that lead young women to select their partners from older-age cohorts and that shape their sexual networking patterns.

Age Factors↗

PubMed2001

The landing of the NEAR-Shoemaker spacecraft on asteroid 433 Eros.

The NEAR-Shoemaker spacecraft was designed to provide a comprehensive characterization of the S-type asteroid 433 Eros (refs 1,2,3), an irregularly shaped body with approximate dimensions of 34 x 13 x 13 km. Following the completion of its year-long investigation, the mission was terminated with a controlled descent to its surface, in order to provide extremely high resolution images. Here we report the results of the descent on 12 February 2001, during which 70 images were obtained. The landing area is marked by a paucity of small craters and an abundance of 'ejecta blocks'. The properties and distribution of ejecta blocks are discussed in a companion paper. The last sequence of images reveals a transition from the blocky surface to a smooth area, which we interpret as a 'pond'. Properties of the 'ponds' are discussed in a second companion paper. The closest image, from an altitude of 129 m, shows the interior of a 100-m-diameter crater at 1-cm resolution.

Journal Article↗

PubMed2001

The epidemiology of human immunodeficiency virus in South Africa.

We review the epidemiology of human immunodeficiency virus (HIV) in South Africa where the prevalence of HIV infection is among the highest in the world. The epidemic reached South Africa relatively recently but the prevalence of infection has increased rapidly and there are significant differences among provinces. Although few 15-year-old people are infected the prevalence increases rapidly with age thereafter, especially among women. The prevalence of herpes simplex virus type 2 exceeds that of HIV and curable sexually transmitted infections are common. 'Circular migration' may help to explain the high rates and rapid spread of HIV in the region. The incidence of tuberculosis has increased dramatically as a result of the HIV epidemic. Antiretroviral therapy for the prevention of vertical transmission has been shown to be effective in local conditions but transmission through breast-feeding remains problematical. While some epidemiological models have been developed, much more needs to be done in this regard in order to plan, coordinate and evaluate an effective response to the epidemic. We conclude by discussing some of the research that is needed and steps that could be taken to reduce the continued spread of the infection.

Adolescent↗

PubMed2001

Imaging of small-scale features on 433 Eros from NEAR: evidence for a complex regolith.

On 25 October 2000, the Near Earth Asteroid Rendevous (NEAR)-Shoemaker spacecraft executed a low-altitude flyover of asteroid 433 Eros, making it possible to image the surface at a resolution of about 1 meter per pixel. The images reveal an evolved surface distinguished by an abundance of ejecta blocks, a dearth of small craters, and smooth material infilling some topographic lows. The subdued appearance of craters of different diameters and the variety of blocks and different degrees of their burial suggest that ejecta from several impact events blanketed the region imaged at closest approach and led to the building up of a substantial and complex regolith consisting of fine materials and abundant meter-sized blocks.

Journal Article↗

PubMed2001

A mouse genetic locus with death clock and life clock features.

A senility syndrome, with weight loss and priapism, occurs in CBAT6/T6 mice, an exceptionally long-lived strain. Instead of dying at the expected time, these mice get senile weight loss and priapism and go on living. We have postulated that a mutant death clock kills the wrong neurons. Crosses with the NZW and C57BL/6 strains show causation by a single genetic locus (Priap1), with a pronounced gene dosage effect on timing. We report here that various cancers were the cause of death in 31 of 32 NZW mice, compared to only five of 22 CBAT6/T6 mice, a highly significant difference (P<0.001). The longevity of (CBAT6/T6xNZW)F1 hybrids, and the segregation of longevity with priapism and senile weight loss in (CBAT6/T6xNZW) F2 hybrids, indicates that Priap1, or a linked gene, inhibits the cancers that usually shorten the lives of NZW mice. If a timer gene is involved, the cancer resistance action could be because the locus impedes the normal mid-life regression of anti-cancer defence. The priapism suggests loss of the medullary reticular formation neurons which normally inhibit male spinal sexual reflexes. In this region of the medulla there are also the respiratory and cardiac control centres, where apoptotic neuron destruction by the wild-type locus could govern maximal life-span. The CBAT6/T6 locus may be a mutant life-stage control clock. Its discovery could be the revelation of a new, major class of aetiology of disease.

Aging↗

PubMed2001

Occupational lung diseases among former goldminers in two labour sending areas.

OBJECTIVES: To compare and contrast the prevalence of pneumoconiosis in two groups of former migrant mineworkers in southern Africa, and to examine the effectiveness of the South African compensation system for occupational lung diseases. DESIGN: Comparison of two cross-sectional studies and follow-up data on compensation results. SETTING: The village of Thamaga, Botswana and the rural area of Libode, Eastern Cape, South Africa. SUBJECTS: Two hundred and thirty-four former underground mineworkers in Thamaga, and 238 in Libode. MAIN OUTCOME MEASURES: Prevalence and severity of pneumoconiosis, prevalence of radiological signs of tuberculosis (TB), Medical Bureau for Occupational Diseases (MBOD) certification committee decisions, and compensation results. RESULTS: Prevalence of pneumoconiosis > or = 2/1 was 15.4% in Libode and 13.6% in Thamaga. Significantly more Libode than Thamaga subjects (51.1% versus 29.0%) reported past TB treatment. Radiological signs of pulmonary TB were also more prevalent in Libode (33.3% v. 23.9%). Twenty-six per cent of Libode men and 16.1% of Thamaga men were certified with compensable disease. Libode payments were finalized within 30 months, whereas Thamaga cases only began receiving payments 52 months after medical examination, with 11 cases still pending 66 months after medical examination. CONCLUSION: There was a high prevalence of pneumoconiosis in both study groups. Many men were eligible for compensation but were previously uncompensated. The higher rate of compensable disease in the Libode group may relate to the higher prevalence of TB, as well as more active follow-up by the study group, including a large number of appeals. Socio-political changes in South Africa between 1994 and 1996 may also have influenced compensation results.

Cross-Sectional Studies↗

PubMed2001

Psychometric properties of the California Critical Thinking Tests.

The evaluation of critical thinking, as with any other measure, must employ instruments that meet appropriate psychometric standards. Therefore, the purpose of this study was to investigate the psychometric properties of the two California Critical Thinking Tests. Two samples of undergraduate students enrolled in a southern comprehensive university took the California Critical Thinking Skills Test (TST) and the California Critical Thinking Dispositions Inventory (TDI). A portion of the participants, who were nursing students, were retested on the TST and TDI two weeks after the initial testing. Some participants also completed the Watson-Glaser Critical Thinking Appraisal (WGCTA). In both samples the TST had neither sufficient psychometric properties to assess individual abilities nor sufficient stability reliability. In particular, the analysis subscale of the TST demonstrated exceptional weakness in all administrations. In contrast, the TDI demonstrated very good reliability estimates in all administrations of the test. The data did not conform to the subscale structure during factor analysis. Whereas the TST needs further refinement, the TDI demonstrated sufficient reliability for use in attitudinal research.

Adolescent↗

PubMed2000

HIV infection and silicosis: the impact of two potent risk factors on the incidence of mycobacterial disease in South African miners.

OBJECTIVE: To investigate the combined effects of HIV infection and silicosis on mycobacterial disease. DESIGN AND SETTING: A retrospective cohort of 1374 HIV-positive and 2648 HIV-negative miners who attended a South African gold mining hospital and primary health clinics. PARTICIPANTS: Miners who had been tested for HIV, with consent, at primary health clinics during 1991-1996, predominantly because of a symptomatic sexually transmitted disease. RESULTS: Tuberculosis (TB) incidence was 4.9 and 1.1 per 100 person-years in HIV-positive and HIV-negative miners respectively. The incidence of Mycobacterium kansasii disease was also high (0.32 and 0.10 per 100 person-years, respectively). Silicosis was highly prevalent, implying inadequate dust control, and was a significant TB risk factor among both HIV-positive and HIV-negative men (adjusted incidence rate ratios 1.4-2.5 according to radiological severity). The data were consistent with the risks of silicosis and HIV combining multiplicatively, but did not fit an additive model. The incidence of HIV-associated TB increased significantly during the study, with no corresponding change in HIV-negative rates, to reach 16.1 per 100 person-years among HIV-positive silicotics. CONCLUSIONS: The risks of silicosis and HIV infection combine multiplicatively, so that TB remains as much a silica-related occupational disease in HIV-positive as in HIV-negative miners, and HIV-positive silicotics have considerably higher TB incidence rates than those reported from other HIV-positive Africans. The increasing impact of HIV over time may indicate epidemic TB transmission with rapid disease development in HIV-infected miners. Similar but currently unrecognized interactions may be contributing to TB control problems in other industrializing countries affected by the HIV epidemic.

AIDS-Related Opportunistic Infections↗

PubMed2000

Criteria for the control of drug-resistant tuberculosis.

Antibiotic resistance is a growing impediment to the control of infectious diseases worldwide, tuberculosis (TB) being among them. TB kills two million people each year and foci of multidrug-resistant TB (MDR-TB) have been identified in Eastern Europe, Africa, Asia, and Latin America. A critical question for health policy is whether standardized short-course chemotherapy for TB, based on cheap first-line drugs, can prevent and reverse the spread of drug resistance. Here we use mathematical modeling, in conjunction with treatment results from six countries, to show that best-practice short-course chemotherapy is highly likely to bring strains resistant to either of the two key drugs isoniazid and rifampicin under control and to prevent the emergence of MDR-TB. However, it is not certain to contain MDR-TB once it has emerged, partly because cure rates are too low. We estimate that approximately 70% of prevalent, infectious MDR-TB cases should be detected and treated each year, and at least 80% of these cases should be cured, in order to prevent outbreaks of MDR-TB. Poor control programs should aim to increase case detection and cure rates together for three reasons: (i) these variables act synergistically; (ii) when either is low, the other cannot succeed alone; and (iii) the second-line drugs needed to raise MDR-TB cure rates are few and extremely costly. We discuss the implications of these results for World Health Organization policy on the management of antibiotic resistance.

Antitubercular Agents↗

PubMed1999

Imaging of asteroid 433 eros during NEAR's flyby reconnaissance

During the 23 December 1998 flyby of asteroid 433 Eros, the Near-Earth Asteroid Rendezvous (NEAR) spacecraft obtained 222 images of Eros, as well as supporting spectral observations. The images cover slightly more than two-thirds of Eros (best resolution is approximately 400 meters per pixel) and reveal an elongated, cratered body with a linear feature extending for at least 20 kilometers. Our observations show that Eros has dimensions of 33 x 13 x 13 kilometers. The volume, combined with the mass determined by the NEAR radio science experiment, leads to a density of 2.5 +/- 0.8 grams per cubic centimeter. This relatively high density, and the presence of an extensive linear feature, suggest that Eros may be a structurally coherent body.

Journal Article↗

PubMed1999

Nontuberculous mycobacteria: defining disease in a prospective cohort of South African miners.

A gold mining work force was followed prospectively over 1 yr for sputum nontuberculous mycobacterial (NTM) isolates. NTM were isolated from 118 men, of whom 32 (27%) met the American Thoracic Society (ATS) case-definitions for pulmonary NTM disease (23 M. kansasii, seven M. scrofulaceum, one M. avium, and one M. abscessus). Determining isolate significance was difficult because most men had been started on presumptive TB treatment before isolate identification (70%). Histologic criteria were considered inappropriate for this high M. tuberculosis incidence population, particularly for patients who had stabilized on presumptive TB treatment. Among men not meeting case-definitions, indicators of disease were significantly more prevalent for M. kansasii than for M. fortuitum, the local laboratory contaminant (ORs: 6.5 for cough, 7. 2 for smear-positivity, 36.0 for radiologic changes, and 14.3 for presumptive TB treatment), suggesting underdiagnosis of M. kansasii disease. Of 53 men with definite or possible M. kansasii disease, 18 (34%) were HIV-positive. HIV-associated M. kansasii disease occurred at an early stage of immunosuppression (median CD4 count, 381 x 10(6)/L) with a good outcome (83% cured after 12 mo of treatment). ATS case-definitions for NTM disease are difficult to apply in this population, and treatment decisions should be guided by the pathogenic potential of the isolate.

Adult↗

PubMed1999

Mycobacterium kansasii and M. scrofulaceum isolates from HIV-negative South African gold miners: incidence, clinical significance and radiology.

SETTING: A South African gold mining hospital. OBJECTIVE: To investigate the clinical significance of non-tuberculous mycobacteria (NTM) isolates, and estimate NTM disease incidence in human immunodeficiency virus (HIV) negative miners. DESIGN: Retrospective case series describing clinical and radiological features associated with NTM sputum isolates from HIV-negative miners between January 1993 and July 1996, and a comparison group with Mycobacterium tuberculosis infection. RESULTS: Of miners with NTM isolates, 90% had been HIV-tested and 81% were HIV-negative. M. kansasii and M. scrofulaceum accounted for 202 (68%) and 41 (14%) isolates respectively. More than 80% of miners with M. kansasii or M. scrofulaceum were smear positive, and new cavitation was present in 78% and 74% respectively. Treatment failure occurred in 3% of M. kansasii and 12% of M. scrofulaceum patients. A normal pre-morbid radiograph was significantly less common in NTM than M. tuberculosis patients (odds ratio 0.26 and 0.10 for M. kansasii and M. scrofulaceum, respectively). NTM disease incidence, defined as NTM isolate plus new cavitation, was estimated at 66 and 12 per 100000 person-years for M. kansasii and M. scrofulaceum, respectively. CONCLUSIONS: M. kansasii and M. scrofulaceum disease are common in HIV-negative South African gold miners. Most isolates are associated with new cavitation against a background of silicosis or old TB scarring.

Adult↗

PubMed1998

Prospects for worldwide tuberculosis control under the WHO DOTS strategy. Directly observed short-course therapy.

BACKGROUND: WHO advocates the use of directly observed treatment with a short-course drug regimen as part of the DOTS strategy, but the potential effect of this strategy worldwide has not been investigated. METHODS: We developed an age-structured mathematical model to explore the characteristics of tuberculosis control under DOTS, and to forecast the effect of improved case finding and cure on tuberculosis epidemics for each of the six WHO regions. FINDINGS: In countries where the incidence of tuberculosis is stable and HIV-1 absent, a control programme that reaches the WHO targets of 70% case detection and 85% cure would reduce the incidence rate by 11% (range 8-12) per year and the death rate by 12% (9-13) per year. If tuberculosis has been in decline for some years, the same case detection and cure rates would have a smaller effect on incidence. DOTS saves a greater proportion of deaths than cases, and this difference is bigger in the presence of HIV-1. HIV-1 epidemics cause an increase in tuberculosis incidence, but do not substantially reduce the preventable proportion of cases and deaths. Without greater effort to control tuberculosis, the annual incidence of the disease is expected to increase by 41% (21-61) between 1998 and 2020 (from 7.4 million to 10.6 million cases per year). Achievement of WHO targets by 2010 would prevent 23% (15-30) or 48 million cases by 2020. INTERPRETATION: The potential effect of chemotherapy (delivered as DOTS) on tuberculosis is greater in many developing countries now than it was in developed countries 50 years ago. To exploit this potential, case detection and cure rates urgently need to be improved in the main endemic areas.

Communicable Disease Control↗