Preventative TB trial disappoints

After seven years of research, the world's largest study of preventative tuberculosis (TB) therapy has...

An ailing patient at a medical facility. Picture: Deniz Houssein

After seven years of research, the world's largest study of preventative tuberculosis (TB) therapy has found that untargeted, community-wide distribution of TB prevention drugs did not improve TB control on South African gold mines.

Conducted among 27,000 gold-mine employees in 15 mines, the Thibela TB study tested the theory that treating an entire community with the first-line TB drug isoniazid could result in long-lasting reductions in active TB cases and TB prevalence.

Workers in eight mines were offered TB screening. Those with active TB were treated, while those without active TB - about 24,000 - were given a nine-month course of isoniazid preventative TB therapy (IPT). Workers in the remaining seven mines were screened and treated according to national guidelines whereby only high-risk individuals with HIV or silicosis would have been eligible for a six-month IPT course.

But according to results released on 8 March at the annual Conference on Retroviruses and Opportunistic Infections in Seattle, Washington, the community-wide IPT provision did not reduce TB incidence or prevalence within communities.

In people who do not have active TB, IPT applies one of the two drugs commonly used in combination to treat active TB as a preventative measure. While many people carry TB, only about 10 percent will ever develop it. However, those with compromised immune systems, such as people living with HIV or silicosis - a lung-destroying respiratory illness often contracted by miners exposed to silica dust - are much more likely to develop active TB.

Gavin Churchyard, the study's principal investigator and chief executive officer of South Africa's Aurum Institute for Health, said that while Thibela showed poor results at community level, it did underscore IPT's proven effectiveness in preventing active TB among individuals who were on the drug course but this protection waned quickly once patients stopped taking IPT.

He added that the long-running trial also revealed important insights on how to better conduct future large-scale, cluster randomized control studies and that these techniques were helping to shape studies evaluating the effects of newly introduced TB diagnostics such as GeneXpert.

Researchers are now recommending that governments such as South Africa's continue targeted IPT provision aimed at high-risk groups. However, Churchyard added that focused rollouts remain difficult when people did not know they were "high-risk", ie HIV-positive or suffering from silicosis.

Poor working and living conditions, coupled with high rates of silicosis, have fuelled TB on the mines for years, aggravated by the advent of HIV. The South African Department of Health, in its TB Strategic Plan for South Africa 2007-2011, has estimated that the country's gold-mining industry has the highest TB incidence in the world.

Silicosis is estimated to affect a third of all South African gold miners and autopsies have shown that many miners remain undiagnosed and untreated, particularly black mine workers who traditionally assumed the most dangerous jobs in the mines under apartheid.

With an HIV prevalence of about 18 percent, South Africa has had national IPT guidelines in place since 2002 but eight years later the coverage was estimated to be below 1 percent. Last year, 320,000 people were put on the preventative therapy, according to Churchyard.