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The potent role of HIV in ushering in tuberculosis (TB) infection is highlighted in a report released by the WHO today (24 March).

As many as a quarter of TB deaths occur in patients with HIV infection, according to the 2009 Global TB Control Report — twice as many as previously recorded.

Worldwide some 15 per cent of people with TB infection are also infected with HIV and Sub-Saharan Africa accounts for almost 80 per cent of these cases, the new data show.

The findings, released to coincide with World TB Day, "point to an urgent need to find, prevent and treat tuberculosis in people living with HIV…" said Margaret Chan, director-general of the WHO.

"These direct measurements provide strong evidence that the relative risk of developing TB in HIV-positive people ... is higher than previously estimated," says the report.

The figure is double the estimate that WHO published in 2008 but the report says this does not mean that the number of HIV-positive cases of TB doubled between 2006 and 2007. Rather, data gathering has improved because more countries are making direct measurements of the prevalence of HIV in TB patients.

The findings highlight the need to better understand the relationship between the two infections, say researchers in South Africa.

"Three quarters of all TB patients in South Africa are HIV positive," says Salim Karim, director of the Centre for AIDS Programme of Research in South Africa (CAPRISA) based in Durban, South Africa.

There are several challenges to treating the co-infection. Antiretroviral drugs used for HIV/AIDS lead the body to break down certain TB drugs more quickly, which weakens their effect. And patients suffer from side effects when they take up to seven different drugs for TB and HIV.

Karim, who will be leading research into recurrent TB infections to ascertain whether they are the result of a relapse or a re-infection with a different strain of TB, told SciDev.Net that there are 700,000 people on AIDS treatment programmes in South Africa who are at a high risk of TB re-infection.

In much of South Africa the clinics are "overcrowded and poorly ventilated" — so people with the most highly infectious cases of TB are put close to people who carry a high risk of contracting TB, he says.

The WHO report says that overall TB infection rates have remained broadly stable, with just below 9.3 million new cases in 2007, while the proportion of people with TB continued to decline. Co-infection and the growth in drug-resistant forms of tuberculosis present the greatest challenges to combating TB.

The report also says there are concerns that the global financial crisis will exacerbate deficits in funding for TB.

Link to full report