Cross-Border Dynamics of MDR/XDR-TB Epidemiology by HIV Status in Tijuana, Mexico

Funded by NIH grant 1R56-AI0831321-01; PI: Richard S. Garfein


Nearly a third of the world's population is infected with Mycobacterium tuberculosis (Mtb), resulting in 2 million deaths per year. Significant declines in TB incidence began in the US after the 1940s due to the discovery of antibiotics that cured TB, only to resurge in the 1980s with the advent of HIV/AIDS. Concurrent with the resurgence was the recognition that Mtb can become resistant to antibiotics when treatment is stopped early or taken inconsistently. Today, the threat of Mtb evolving to become multi- or even extensively drug resistant (MDR/XDR-TB) poses global challenges to TB control. Recent reports of a patient with XDR-TB boarding an international flight are a stark reminder that TB does not respect borders. The busiest border crossing in the world (over 40,000 northbound crossings daily) loosely separates the >4 million residents of San Diego, CA, USA and Tijuana, BC, Mexico, which has the highest TB incidence in Mexico. After a 1997 survey found 41% of Tijuana’s TB cases were resistant to at least one drug and 17% were resistant to isoniazid and rifampin (MDR-TB), universal drug susceptibility testing (DST) was recommended for all TB cases in Mexico, yet was rarely performed due to the cost. Consequently, the current epidemiology of drug resistant TB in Mexico is unknown, although the high proportion of Mexican-born patients among San Diego’s MDR-TB cases suggests that drug resistance in Tijuana has not declined. Increasing HIV incidence in Tijuana threatens to intensify the problem. The goal of this study is to describe the epidemiology of drug resistant TB in Tijuana in the context of HIV and the US/Mexican border. During a one-year pilot study, all newly diagnosed TB cases in Tijuana will receive DST and Mtb genotyping to address the following aims:

  1. To measure the current prevalence of MDR-TB and XDR-TB in Tijuana.
  2. To identify correlates of TB drug resistance and determine whether these drug resistant Mtb strains are being transmitted in the community.
  3. To determine whether Mtb strains that have been detected in Tijuana and California are more likely to be drug resistant in Tijuana.

These aims are consistent with the USPHS’s call for “renewed vigilance through drug-susceptibility testing, case reporting, specialty care, infection control, and expanded capacity." This study is run collaboratively between UCSD, Tijuana General Hospital, and a Mexican AIDS service organization (AFABI), to inform testing policy for MDR/XDR-TB in Mexico, highlight intervention targets for TB prevention in the US/Mexico border region, and build capacity for improved TB diagnosis and control measures.