Doenças Micobacterianas
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Discordance between Tuberculin Skin Test and Interferon Gamma Release Assay is Associated with Previous Latent Tuberculosis Infection Treatment

Divya Reddy, Max R O’Donnell, Allan M Welter-Frost, Alison Coe and C Robert Horsburgh

Background: The performance of Interferon gamma release assays (IGRA) in drug users and the impact of previous latent tuberculosis infection (LTBI) treatment on discordance of IGRA and tuberculin skin test (TST) are unclear.
Objective: To determine the prevalence and incidence of LTBI using TST and Quantiferon Gold In-Tube test (QFT-G-IT) in a cohort of persons with hepatitis C virus (HCV) and drug use history. Design: Eligible participants had baseline TST and QFT-G-IT assay and were retested with QFT-G-IT after 12 months to assess prevalence and incidence of LTBI.
Results: Of 193 HCV-infected persons enrolled, 162 (84%) were HIV infected; 132 (81%) were on anti-retroviral therapy and 131 (81%) had a CD4 count >200. 190 (98%) had a history of drug use; only 19 (10%) were active intravenous drug users. 55 (28.5%) had LTBI based on TST results and 13 (7%) were diagnosed with LTBI based on QFT-G-IT. 46/193 persons (23.8%) had positive TST with negative QFT-G-IT test. History of LTBI treatment was a strong predictor of this discordance (OR=41.5; 95%CI 16.2-106.7; p<0.0001). No QFT-G-IT conversions were detected among the 101 initially QFT-G-IT negative patients retested at one year (95% CI: 0-3.6%).
Conclusions: Intravenous drug users who are not actively using drugs have a low prevalence and incidence of LTBI by IGRA. Previous LTBI treatment is associated with a positive TST and a concurrent negative QFT-G-IT.