This will be revealed in one of the first poster presentations at the 16th International AIDS conference which gets into full swing tomorrow in Toronto, Canada.

The study by Johns Hopkins University and Brazilian scientists reviewed the medical records of over 11 000 HIV-positive men and women in Rio de Janeiro, Brazil and found the risk of developing TB disease was reduced by two thirds (67 percent) among those treated with both Isoniazid and triple therapy or HAART,.

TB disease remains the leading cause of death in South Africa and the rest of the world among those with HIV and AIDS.

In South Africa about 279 000 people were diagnosed with TB in 2004 – up from 185 000 cases detected a year earlier. It is widely accepted that HIV is fuelling the TB epidemic in South Africa.

The study found that on its own Isoniazid, dispensed in the South African public health system, reduced the frequency of disease from TB by 32 percent.  Scientists have known for years that HAART on its own reduced the risk of TB (by 51 percent in this survey), but they did not know until now the drugs’ combined effects.

In the Johns Hopkins survey, sicker patients – those with immune cell CD4 counts of less than 350 – were found to benefit more, with a 66 percent reduced risk of TB, compared to those with higher CD4 counts, whose risk went down by 56 percent.

Study senior author Dr Richard Chaisson, a professor of infectious diseases at Johns Hopkins and founding director of its Center for Tuberculosis Research, said that while Isoniazid treatment is recommended by the World Health Organization to prevent TB in HIV patients, most doctors fail to prescribe the drug, which costs less than U$1 (R7) for a full course of therapy.

The study team will continue to monitor how well the drugs, both in combination and alone, help reduce the number of new cases of TB disease within the HIV-infected population of Rio de Janeiro.

Their research is part of three ongoing studies by the Consortium to Respond Effectively to the AIDS/TB Epidemic (CREATE) which is funded by the Bill and Melinda Gates Foundation.

The goal of researchers in CREATE is to develop novel strategies to detect and treat latent TB infection and active TB disease in patients also infected with HIV.

Worldwide, each year, more than 9 million new cases of TB are diagnosed, and more than 2 million people die from the disease, caused by TB.