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[LUSAKA] A therapy for treating people infected with both HIV and tuberculosis (TB) could speed the emergence of drug-resistant forms of TB.

The warning comes in a study due to be published by the Proceedings of the National Academy of Sciences on 2 May.

TB is a widespread infection in developing countries and can exist in two forms: latent and active.

The World Health Organization recommends that HIV/AIDS patients take the antibiotic isoniazid to reduce the chance of latent TB becoming active.

But the researchers, led by Ted Cohen of the Harvard School of Public Health in the United States, urge caution in using this drug in areas where drug-resistant TB bacteria are already widespread.

The team developed a mathematical model that predicted that isoniazid would reduce the prevalence of TB and prevent deaths for several years, but that drug resistance would then become a major problem.

Cohen says isoniazid should be provided in combination with techniques for detecting and treating infections with drug-resistant TB.

In Zambia's main teaching hospital, at the University of Zambia, isoniazid is no longer used as a purely preventive medicine against TB, says its managing director, Tackson Lambert.

Patients with both HIV and TB, he says, are given isoniazid in combination with other drugs "because it has proved effective".

Lambert told SciDev.Net that the hospital would this year finish building a centre dedicated to research on drug resistance.

In some African countries, the annual number of TB cases has increased by up to 400 per cent over the past 15 years, due largely to the spread of HIV/AIDS.