Interpreting Tuberculin Skin Tests in a Population With a High Prevalence of HIV, Tuberculosis, and Nonspecific Tuberculin Sensitivity

摘要

Understanding the epidemiology and clinical course of tuberculosis is hampered by the absence of a perfect testnfor latent tuberculosis infection. The tuberculin skin test (TST) is widely used but suffers poor specificity in thosenreceiving the bacille Calmette-Gue′ rin vaccine and poor sensitivity in individuals with human immunodeficiencynvirus (HIV) infections. TST responses for a target population in Harare, Zimbabwe (HIV prevalence, 21%), recruitednin 2005–2006, were interpreted by using a separate calibration population in Harare, for which interferon-gammanrelease assays (enzyme-linked immunosorbent spot (ELISpot)) results were also known. Statistical fitting of thenresponses in the calibration population allowed computation of the probability that an individual in the targetnpopulation with a given TST and HIV result would have tested ELISpot positive. From this, estimates of thenprevalence of tuberculosis infection, and optimal TST cutpoints to minimize misdiagnosis, were computed forndifferent assumptions about ELISpot performance. Different assumptions about the sensitivity and specificity ofnELISpot gave a 40%–57% prevalence of tuberculosis infection in the target population (including HIV-infectednindividuals) and optimal TST cutpoints typically in the 10 mm–20 mm range. However, the optimal cutpoint for HIVinfectednindividuals was consistently 0 mm. This calibration method may provide a valuable tool for interpretingnTST results in other populations.