Tijuana injection drug users on collision course for HIV and TB

A study by researchers from the University of California, San Diego School of Medicine, in collaboration with Mexican researchers and health officials, shows that as many as 67 percent of injection drug users in Tijuana test positive for tuberculosis (TB) infection. The analysis, which underscores the urgent need for TB screening and treatment for populations that are also at risk for HIV infection, will be published in the May issue of the International Journal of Tuberculosis and Lung Disease (IJTLD).

"While injection drug users are known to be at risk for TB, this is one of the highest infection rates ever reported among this group," said principal investigator Richard Garfein, PhD, MPH, associate professor in the Division of Global Public Health and Department of Medicine at UC San Diego. The analysis is part of a bi-national, community-based study called Proyecto El Cuete that includes more than 1,000 illicit drug injectors residing in Mexico's largest U.S. border city.

What most concerns Garfein is that injection drug users are not only likely to have weakened immune system due to illicit drug use, but are also at high risk for HIV infection. This makes the situation much worse for individuals infected with TB, because HIV further weakens a patient's immune system.

Worldwide, tuberculosis is a leading cause of death among persons with AIDS. Once a person becomes infected from breathing in TB bacteria, the immune system generally encapsulates the bacteria and prevents it from growing. When this happens, the bacteria remain alive in an inactive state called latent TB infection. But the TB bacteria can become active at a later date if the person's immune system is weakened, for example, in those with AIDS.

"Persons with latent TB infection are not sick and are not contagious," said co-investigator Dr. Rafael Laniado-Laborin, MD, chief of Tijuana General Hospital's tuberculosis clinic, adding that, in otherwise healthy individuals, the chance of the latent TB becoming active is about 10 percent over their lifetime. "However, if individuals become infected with HIV, their chance of developing active TB increases to 10 percent per year."

Once active, TB bacteria replicate in the lungs. Symptoms include coughing, which facilitates the airborne spread of bacteria to others.

"Given that two-thirds of Tijuana's injection drug users have latent TB infection, the majority of those who become HIV infected – a risk that is increasing – are also likely to develop active, contagious TB," said Garfein.