/ 9 March 2012

TB control in mines disappoints

Researchers are sorely disappointed by the results of a large-scale study that aimed to cut the rate of tuberculosis among South Africa’s gold miners by 60%.

With more than 24 000 participants, the Thibela TB study was the largest trial of preventative therapy carried out to date. Researchers had hoped that administering the TB-preventive drug isoniazid to an entire community of miners would improve TB control.

But, although isoniazid preventive therapy (IPT) has shown positive results in other trials, it was found to be ineffective in the context of South African mines, leaving TB researchers to pore over the reams of data gathered over a six-year period in the hope of finding new ways to tackle the country’s TB epidemic.

The Aurum Institute’s chief executive, Professor Gavin Churchyard, who led the research, presented the initial results this week at the Conference on Retroviruses and Opportunistic Infections in Seattle. He said that even though the therapy was effective in reducing the risk of TB among individuals, it did not improve TB control at a population level. The incidence of TB in South Africa’s mines is up to six times higher than it is in the general population. This week David Mametja, the head of the National TB Control Programme, said there was “a silent accident” happening daily in the country’s mines, where deaths from TB by far outstrip those from workplace accidents.

Because many mine employees come from neighbouring countries, TB in South Africa’s mines has far-reaching consequences in the Southern African Development Community. It is estimated that more than 700 000 cases in the region are linked to mining each year.

Because of their daily exposure to silica dust, gold miners are particularly susceptible to the degenerative respiratory disease silicosis, which, in turn, makes them more susceptible to TB. High rates of HIV further compound the risk.

Researchers had hoped that offering the drug to all the miners at a particular mine would bring about a 60% reduction in the incidence of TB compared with mines where the drug was offered only to at-risk individuals.

Volunteers for the study were recruited through an extensive community mobilisation programme. Miners were screened for TB and those who did not have the disease were offered the therapy for nine months. It was a radical approach to controlling rampant TB, but one that researchers believed would have rapid results.

At the outset many scientists who work in the field anticipated that the trial would be successful. A similar trial conducted in Alaskan villages in the 1960s had a profound and lasting effect on reducing TB rates in a very short period of time.

Many TB experts believed that isoniazid would prove to be the silver bullet that mine workers so desperately needed. Churchyard admitted he was one of these. “I thought I knew what the result would be and I was wrong.”

During the first six months of the programme there were 63% fewer cases of TB among the miners who were on the therapy. But the study results showed that IPT had a preventative effect only as long as the miners were taking the drug. “As soon as they stopped the therapy, the rate of TB just bounced right back,” said Churchyard.

TB prevalence at the end of the study was 2.3% in mines where workers got the therapy and 2.1% where they did not.

Two notable differences between the Alaskan study and the Thibela one were that the villages targeted in Alaska were isolated, so there was little impact from outside communities in which TB was still rife and the Alaskan trial was carried out in a pre-HIV era.

“We [in South Africa] are dealing with a highly mobile population in the era of HIV,” said Churchyard. Because miners have regular interaction with the wider communities in which they live, where TB is also poorly controlled, the rate of ongoing TB transmission remains high.

He said it was not feasible to address TB only in mines. “We have to address it more generally, otherwise it just flows back later,” he said.