Treating populations infected with both HIV and latent TB could speed the emergence of drug-resistant TB

In 2005, 46 regional Ministers of Health in Africa declared that a dramatic rise in tuberculosis (TB) cases was cause for emergency.

In some African countries, annual TB case notifications have increased as much as four-fold over the past 15 years. The main culprit? The emergence of HIV. When individuals are infected with both HIV and TB, they are more likely to progress from latent TB infection to active TB.

To combat the problem, the World Health Organization currently recommends that as part of HIV/AIDS programs, patients infected with both HIV and TB be treated with isoniazid, an antimicrobial, as a preventive therapy to reduce the risk that TB will progress from latent infection to active disease. However, researchers from the Harvard School of Public Health (HSPH) and a team of collaborators believe that strategy has flaws. Their findings appear in the advance online edition of the May 2, 2006 issue of Proceedings of the National Academy of Sciences.

The researchers, led by Ted Cohen, doctoral student at HSPH, and senior author Megan Murray, Assistant Professor of Epidemiology, developed a mathematical model to describe the projected impact of isoniazid preventive therapy (IPT) programs on the transmission dynamics of drug-resistant TB in areas where community-wide preventive therapy may be used as a strategy to control TB. They concluded that the implementation of IPT targeted to people co-infected with HIV and TB may also have the perverse effect of speeding the emergence of drug-resistant TB.

"We're not saying isoniazid preventive therapy policies are ill-advised," said Cohen. "But we think they need to be coupled with an understanding that large-scale IPT programs should be ready to diagnose and treat individuals with drug-resistant TB as part of the programs."

This work was supported by National Institutes of Health Grants.