A comparative study of two different methods for the detection of latent tuberculosis in HIV-positive individuals in Chile

Objective: To compare the performance of two tests for diagnosing latent tuberculosis (TB) infection in the HIV-positive population in Chile, in order to better identify the subjects who might benefit from TB chemoprophytaxis. Design: This was a cross-sectional study among individuals attending three HIV outpatient clinics in Santiago, tested with a 2-TU purified protein derivative, QuantiFERON -TB Gold 'in-tube' (QFT-G), and a chest X-ray. Results: A total of 116 subjects were enrolled in the study, having a mean CD4 count of 393 celts/mu l (range 100-977). The tuberculin skin text (TST; 5 mm cutoff) and QFF-G results were positive in 10.9% and 14.8% of the individuals, respectively, with moderate agreement between both tests (kappa = 0.59). A history of both known TB exposure (odds ratio (OR) 3.46, 95% confidence interval (CI) 1.02-11.22) and past TB (OR 4.31, 95% CI 1.13-15.5) were associated with a positive QFT-G result. Only past TB was significantly associated with a positive TST result (OR 6.63, 95% CI 1.6226.3). Among the subjects with TST < 5 mm, 8.2% were positive by QFT-G test. These individuals had a lower mean CD4 cell count than those detected positive by both tests (328 cells/mu l and 560 cells/mu l, respectively, p=0.03). Conclusions: In this population of HIV-infected individuals, QFT-G and TSTshowed an acceptable level of agreement, although QFT-G appears less affected by more advanced immunosuppression. (C) 2008 International Society for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.