Value of adding an IGRA to the TST to screen for latent tuberculous infection in Greek health care workers.

Abstract

Ioannina University Hospital, Ioannina, Greece. To evaluate the value of adding an interferon-gamma release assay (IGRA) to the tuberculin skin test (TST) for detecting latent tuberculous infection (LTBI) in a Greek university hospital among health care workers (HCWs) predominantly vaccinated with bacille Calmette-Guérin (BCG). Of 788 HCWs enrolled, 68.1% were BCG-vaccinated. A TST ⩾ 10 mm was considered positive and was followed by the QuantiFERON-TB(®) Gold In-Tube assay (QFT-GIT) in a two-step strategy. Of the enrolled HCWs, 36.4% were TST-positive, of whom only 14.4% were IGRA-positive. Agreement between the tests was poor (κ = 0.019; 95%CI -0.014-0.05, P = 0.355). Both TST and IGRA positivity increased with TST diameter, from 5.7% in TST 10-14 mm to 48.8% in TST ⩾20 mm. TST-positive, IGRA-negative results were most likely in younger, recently BCG-vaccinated HCWs (84.6% in those aged 20-29 years) and less likely in older HCWs (45% in those aged 50-59 years). The two-step strategy would have been more cost saving compared to the TST-only approach if adherence to LTBI treatment in our cohort had been ⩾24%. Poor overall agreement between TST and QFT-GIT was found. Use of IGRA as a second step in TST-positive cases offers an appropriate tool for LTBI detection among BCG-vaccinated HCWs in low-TB-incidence settings.