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.