Optimal testing strategies for diagnosing latent tuberculosis infection and the administration of isoniazid preventive therapy (IPT) remain uncertain among human immunodeficiency virus (HIV)-infected patients. A 4-year prospective study was conducted among Thai HIV-infected patients who underwent simultaneous tuberculin skin test (TST) and QuantiFERON-TB Gold In-Tube Test (QFT-IT) at care entry. Based on baseline test results, patients were categorized into the following 4 groups: i) QFT-IT-positive, TST-reactive; ii) QFT-IT-positive, TST-non-reactive; iii) QFT-IT-negative, TST-reactive; and iv) QFT-IT-negative, TST-non-reactive. The QFT-IT-positive patients were offered 9-month IPT and were QFT-IT tested annually. Of the 150 enrolled patients, 8, 12, 16, and 114 patients were assigned to groups 1, 2, 3, and 4, respectively. Sixteen of 19 QFT-IT-positive patients (84%) completed IPT. The incidence of tuberculosis was significantly higher in patients who declined IPT than in those underwent treatment (11.11 vs. 0 case/100 patient-year; P ＜ 0.001). Among the 16 patients completing IPT, 11 (69%) and 2 (12%) had QFT-IT reversion at 1 and 2 years after IPT, respectively. The remaining 3 (19%) did not demonstrate any reversion, and their baseline interferon-γ (IFN-γ) levels were above 1.2 IU/mL. Initial QFT-IT-guided IPT was effective in preventing tuberculosis. Serial QFT-IT for evaluating IPT effectiveness had limitations because of delayed or lack of reversion, especially for patients with high baseline IFN-γ levels.
Keywords: QuantiFERON-TB Gold In-Tube Test; Thailand; human immunodeficiency virus; isoniazid preventive therapy (IPT); latent tuberculosis infection.