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G Churchyard

Publications and source records attributed to G Churchyard.

6 recordsLinked to original sources
PubMed2002

Use of spoligotyping for accurate classification of recurrent tuberculosis.

The spoligotyping method has become an important tool for the tracking of Mycobacterium tuberculosis strains in different epidemiological settings. In this study, we demonstrate the ability of the spoligotyping technique to accurately determine the pathogenetic mechanism of recurrent disease. This methodology has advantages over conventional restriction fragment length polymorphism methods which may be useful in large-scale intervention studies.

Diagnostic Techniques and Procedures↗
PubMed2000

Lung function prediction equations derived from healthy South African gold miners.

OBJECTIVES: To estimate lung function prediction equations and to identify appropriate normal reference values for the population of about 250 000 of South African gold miners. METHODS: Data from a lung function screening programme conducted at a large South African gold mine from 1994 to 1998 were used to estimate the lung function prediction equations. The most reliable period of lung function testing was identified in a previous study of a temporal pattern in reliability, and lung function tests from this period were used. Miners with a history of pulmonary tuberculosis or with radiological abnormalities were excluded from the study. The prediction equations were estimated cross sectionally on 15 772 black and 2752 white miners, and published reference equations that fitted most closely the observed data were identified. RESULTS: The estimated prediction equations for forced vital capacity (FVC) are as follows: for black men, FVC (l)=- 2.901-0.025xage+4.655xheight; and for white men, FVC(l)=-4.407-0.036xage+ 5.940xheight. For forced expiratory volume in one second (FEV(1)) these equations are: for black men, FEV(1)(l)=-1.654- 0.30xage+3.665xheight; and for white men, FEV(1)(l)= -2.341- 0.038xage+4.314xheight. Units are years for age and metres for height. Knudson's and the European Community of Coal and Steel (ECCS) reference values provided the closest fit to the data on lung function of white miners, but the lower limits of normal from the ECCS equations were the closest to the observed one sided lower 95% confidence intervals (95% CIs). For black miners, reference equations that fitted best were derived by Louw et al on asymptomatic black South African men unexposed to occupational dust. There were significant differences between the two groups of miners in the estimated height adjusted mean lung function values for a 40 year old 1.7 m tall man (220 ml (5.2%) for FVC and 110 ml (3.2%) for FEV(1)); white men had higher FVC and FEV(1), but lower FEV(1)/FVC ratio. The ECCS reference values scaled by a conversion factor of 0. 93 for the FVC and 0.95 for the FEV(1) provided close fits to the data for black miners, but the rate of decline with age was higher than that in the observed data. None of the linear equations provided a good fit for the 20-29 and more than 55 years old age categories. CONCLUSION: The ECCS and Knudson equations provided the best fit to the data for white miners, whereas the equations by Louw et al estimated on asymptomatic black South African bank workers provided the best fit to the data for black miners. The ECCS reference values scaled by a factor of 0.93 for FVC and by 0.95 for FEV(1) provided close fits, but the rate of decline with age was higher than that in the data for black miners.

Adult↗
PubMed2000

Chronic pulmonary function impairment caused by initial and recurrent pulmonary tuberculosis following treatment.

BACKGROUND: A study was undertaken to establish the chronic effect of initial and recurrent treated pulmonary tuberculosis on impairment of lung function. METHODS: A total of 27 660 black South African gold miners who had reliable pulmonary function tests from January 1995 to August 1996 were retrospectively followed for the incidence of pulmonary tuberculosis to 1970. The lung function measurements in 1995-6 were related to the number of previous episodes of tuberculosis and to the time that had lapsed from the diagnosis of the last episode of tuberculosis to the lung function test. Miners without tuberculosis or pneumoconiosis served as a comparison group. RESULTS: There were 2137 miners who had one episode of tuberculosis, 366 who had two, and 96 who had three or more episodes. The average time between the diagnosis of the last episode of tuberculosis and the lung function test was 4.6 years (range one month to 31 years). The loss of lung function was highest within six months of the diagnosis of tuberculosis and stabilised after 12 months when the loss was considered to be chronic. The estimated average chronic deficit in forced expiratory volume in one second (FEV(1)) after one, two, and three or more episodes of tuberculosis was 153 ml, 326 ml, and 410 ml, respectively. The corresponding deficits for forced vital capacity (FVC) were 96 ml, 286 ml, and 345 ml. The loss of function due to tuberculosis was not biased by the presence of HIV as HIV positive and HIV negative subjects had similar losses. The percentage of subjects with chronic airflow impairment (FEV(1) <80% predicted) was 18.4% in those with one episode, 27.1% in those with two, and 35.2% in those with three or more episodes of tuberculosis. CONCLUSIONS: Tuberculosis can cause chronic impairment of lung function which increases incrementally with the number of episodes of tuberculosis. Clearly, prevention of tuberculosis and its effect on lung function is important and can be achieved by early detection and by reduction of the risk of tuberculosis through intervention on risk factors such as HIV, silica dust exposure, silicosis, and socioeconomic factors.

Adult↗
PubMed1999

Assessment of reliability of lung function screening programs or longitudinal studies.

The aim was to determine reliability of lung function measurements performed according to recommendations of the American Thoracic Society (ATS) at a screening program in a large South African gold mine and to determine the usefulness of the reliability coefficient G for monitoring the reliability of lung function measurements in a mass screening program. The reliability coefficient G estimates the amount of random error of measurement, relative to the total variation in a measurement. The coefficient G was calculated as a correlation coefficient between two consecutive lung function tests performed within 6 mo, over a period of 43 mo on 3,378 miners. There was significant temporal variability in the reliability. For FEV(1), the coefficient G showed increased variability over the first 5 mo and stabilized at a value of 0.93 for the next 23 mo, after which it systematically declined over the next 15 mo. We estimated that in a large screening program, an optimal sample size of around 900 miners, examined randomly throughout the year, on a yearly basis, would provide a sufficient sample to examine monthly or quarterly fluctuation in the reliability. The value of the reliability coefficient G did not change when the time between two consecutive tests increased up to 15 mo. In conclusion, monitoring of lung function reliability in a screening program by the reliability coefficient G should improve data quality, and provide a measure on which the confidence in a decision-making process could be based when examining temporal changes in lung function for individual subjects.

Adult↗
PubMed1997

Variation in incidences of tuberculosis in subgroups of South African gold miners.

OBJECTIVES: To determine risk factors and to identify groups at high risk of tuberculosis (TB) among South African gold miners. METHODS: A retrospective cohort analysis was carried out with hospital and personnel databases on a random sample of the workforce of Freegold Mines, served by Ernest Oppenheimer Hospital, Welkom, South Africa. The outcome measure of interest was a reported first episode of TB while employed at Freegold. A person-years analysis was carried out to estimate incidence ratios between different categories of age group, period, cumulative service, mining occupation, and silicosis status. A separate analysis was carried out on a subgroup of men (non-random) whose HIV status was known. RESULTS: The main finding of the study was that TB was more strongly associated with age than expected with a rate ratio of reported incidence of 21 for the oldest age group compared with the youngest, after adjustment for period, cumulative service, occupation, and silicosis status. There was also a significant association between TB and occupations such as drilling with a rate ratio of 2.3 compared with low dust surface and maintenance workers, after adjustment for age, period, cumulative service, and silicosis. Analysis of the HIV tested subgroup showed that these results are unlikely to be the result of confounding due to HIV infection. Prevalence of HIV in this group has been rising sharply since 1991, but the increase was slowing towards the end of the study period. CONCLUSION: A profile of mineworkers who are at high risk of TB can be defined by age, mining occupation, silicosis status, and HIV infection with predicted rates of 100/1000 person-years. TB screening programmes should take special cognisance of high risk groups of gold miners.

Adolescent↗