Concordance of a positive tuberculin skin test and an interferon gamma release assay in bacille Calmette-Guerin vaccinated persons

BACKGROUND: False-positive tuberculin skin test (TST) results due to prior bacille Calmette-Guerin (BCG) vaccination may lead to unnecessary treatment of presumed latent tuberculosis infection (LTBI). Recently approved interferon-gamma release assays (IGRAs) are more specific for LTBI in this group. METHODS: A total of 316 BCG-vaccinated foreign-born individuals with a positive TST had a commercially available IGRA (QuantiFERON ® -TB Gold In-Tube) performed as part of a two-step procedure to determine the need for isoniazid therapy. Baseline demographic information and TST size were recorded and analyzed for characteristics associated with an increased likelihood of having a positive IGRA. RESULTS: Increasing age, male sex, origin from a country with a high prevalence of tuberculosis (TB), shorter time since arrival in the United States, and increasing TST size were all independently associated with a positive IGRA. CONCLUSION: Patient characteristics and TST size can help determine those at highest risk for LTBI. A two-step procedure for LTBI screening should be considered for foreign-born persons with prior BCG vaccination and a positive TST.