JOHANNESBURG, 26 March 2009 (IRIN) - Findings from an ongoing South African study into preventative tuberculosis (TB) therapy suggest that prevention really may be the best medicine.

In the Thibela TB study, one of the largest of its kind, almost 40,000 gold miners in South Africa received a nine-month course of isoniazid, a standard first-line TB drug. None of the miners was actually suffering from TB, but the high prevalence of both HIV and silicosis in South African mines makes miners extremely vulnerable to the disease.

Isoniazid preventive therapy (IPT) is usually given to people living with HIV to reduce their risk of developing TB, but the Thibela study is testing the theory that treating an entire community with the drug could have a significant impact on TB rates for a period of about 10 years.

The study, which is being conducted in three of the country's nine provinces, is only expected to conclude in 2012, but preliminary findings released on Wednesday suggest that isoniazid has already been effective in reducing TB incidence among participants.

"We've had very few subsequent infections in those taking the preventative treatment," said Dr Dave Clark, deputy CEO of the Aurum Institute, the health research NGO conducting the study.

The results could also influence case management of HIV-positive people in South Africa, who are around 20 times more likely to develop TB than those who are HIV-negative – 75 percent of new TB patients are HIV-positive.

The World Health Organization (WHO) has recommended IPT for people living with HIV in countries with a high prevalence of TB, but less than one percent of HIV-positive people in South Africa are receiving it, according to Clark.

Although many feared the preventative treatment would increase the incidence of drug-resistant TB, the number of such cases in the study has been negligible. Most patients also showed a surprising wiliness to adhere to treatment.

"Asking mineworkers, who are ostensibly well, to adhere to treatment is difficult," Clark said. "We've had an 80 percent success rate to date with adherence, and it's caught on. We've had cases where workers have asked, 'Is this something we can take back to our communities, to our wives?'"

Findings from the study might also influence the way health workers and policy-makers handle epidemics other than TB. "If this methodology can work in this setting, there is huge potential that the approach would work in the case of other diseases, such as diabetes and hypertension," said Clark. 

In the latest global TB control report released by WHO on Tuesday, South Africa's incidence of TB ranks second only to Swaziland's, the highest in the world. South Africa also has the world's fourth highest burden of multidrug-resistant (MDR) TB.

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