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

SummaryObjectiveTo 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 chemoprophylaxis.DesignThis 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.ResultsA total of 116 subjects were enrolled in the study, having a mean CD4 count of 393 cells/μl (range 100–977). The tuberculin skin text (TST; 5 mm cutoff) and QFT-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 1.62–26.3). 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/μl and 560 cells/μl, respectively, p = 0.03).ConclusionsIn this population of HIV-infected individuals, QFT-G and TST showed an acceptable level of agreement, although QFT-G appears less affected by more advanced immunosuppression.