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

C S Mahan, D F Johnson, C Curley, F van der Kuyp
International Journal of Tuberculosis and Lung Disease 2011, 15 (2): 174-8, i

BACKGROUND: False-positive tuberculin skin test (TST) results due to prior bacille Calmette-Guérin (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.

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