Assessing tuberculosis infection prevalence and test concordance in high-risk groups: a cross-sectional study in Mexicali, Baja California

BACKGROUND: Despite low sensitivity and implementation challenges, the tuberculin skin test (TST) remains the standard-of-care tuberculosis (TB) infection test in Mexico. Interferon gamma release assays (IGRA) may overcome TST-related challenges. Within the confines of the local programmatic setting, this cross-sectional study evaluated the prevalence of TB infection (TBI) and concordance of TST and IGRA in three high-risk populations in Mexicali, Baja California, Mexico. METHODS: Household contacts (HHC) of individuals with TB, people who use drugs (PWUD), people deprived of liberty (PDL) and prison employees underwent evaluation for TBI using TST and QIAreach, a novel IGRA. Prevalence of infection, concordance of test results and reactivity trends of time-to-results (TTR) by TST-induration size were assessed. RESULTS: In total, 214 of 411 (52.07%) people who had TST and 269 of 460 (58.48%) people who had IGRA tested positive for TBI. Frequency of infection varied across risk groups (HHC 29 (29.6%); PWUD 67 (70.53%); PDL 111 (56.06%) and prison employees 7 (35.0%), p<0.001). Overall concordance of TST and IGRA was 74.4%. Among people without a BCG vaccination, TTR decreased as TST induration size increased (from 1200 s in 0-4 mm to 808 s in >20 mm, p=0.05). CONCLUSION: All risk groups had a high frequency of TBI, necessitating locally tailored guidelines for screening, treatment and management of TBI to optimise care for vulnerable populations.