Performance of Tuberculin Skin Testing Compared With Interferon-Gamma Release Assays Foreign-Born Individuals

Area of Science:

• Infectious Diseases
• Public Health
• Clinical Microbiology

Background:

• Foreign-born individuals entering correctional facilities represent a population at higher risk for tuberculosis (TB).
• The Bacillus Calmette-Guérin (BCG) vaccine, commonly administered to foreign-born individuals, can interfere with the interpretation of the tuberculin skin test (TST).
• Interferon gamma release assays (IGRAs) are an alternative diagnostic tool for latent TB infection (LTBI).

Purpose of the Study:

• To determine the prevalence of Mycobacterium tuberculosis infection among foreign-born individuals admitted to prison.
• To evaluate the performance of the TST in BCG-vaccinated individuals, using IGRAs as the reference standard.
• To assess the positive predictive value (PPV) of the TST in BCG-vaccinated individuals based on induration size.

Main Methods:

• A prospective observational study was conducted in prisons in Catalonia, Spain.
• Foreign-born individuals were screened for active TB and underwent TST if eligible.
• BCG vaccination status was determined, and TST results were compared with IGRA results in vaccinated individuals.

Main Results:

• Out of 1075 individuals, 3.0% had a prior TB diagnosis. Of the remaining, 86.4% were BCG-vaccinated.
• Overall TST positivity was 45.2%, with no significant difference between vaccinated and unvaccinated individuals (46.1% vs. 39.9%).
• Among BCG-vaccinated individuals with a positive TST, the overall TST PPV was 65%, increasing with induration diameter (51.6% for 10-14 mm to 81.8% for ≥20 mm).

Conclusions:

• A high prevalence of M. tuberculosis infection exists among foreign-born individuals entering prison.
• The TST demonstrates limited predictive value in BCG-vaccinated individuals, especially with smaller indurations.
• IGRA-based screening strategies are recommended for LTBI detection in this high-risk population.