Jornal de doenças infecciosas e terapia

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Discordance between Two Interferon-Gamma Release Assays in the Diagnosis of Latent Tuberculosis Infection in Healthcare Workers

Hiroshi Fujiwara, Tomoyasu Nishimura, Osamu Iketani, Yaoko Takano, Akiko Sakai, Naomi Kondo, Kazuko Ohtake, Shuji Oguchi, Nobuko Shimizu, Ayako Shibata, Masatoshi Wakui, Mitsuru Murata, Masaaki Mori, Satoshi Iwata and Naoki Hasegawa

Background: Interferon-gamma release assays (IGRAs) more accurately diagnose Mycobacterium tuberculosis (Mtb) infection than the tuberculin skin test. To prevent outbreaks in medical facilities, early detection and treatment of Mtb infection (including latent tuberculosis infection (LTBI)) is important in healthcare workers. Therefore, the IGRAs have considerable utility for Mtb infection control in medical facilities. In Japan, two IGRAs are commercially available, QuantiFERON®-TBGold In-Tube assay (QFT-GIT) and T-SPOT®.TB (T-SPOT). However, it remains unclear if diagnostic yields of LTBI by both IGRAs are equivalent in healthcare workers.

Methods: We performed both QFT-GIT and T-SPOT simultaneously in healthcare workers with a high risk of LTBI (excluding active tuberculosis) between December 2012 and February 2013.

Results: Among 313 subjects (excluding 2 cases with indeterminate T-SPOT), 6 (1.9 %) and 12 (3.8 %) were QFT-GIT positive and T-SPOT positive, respectively. There was no significant concordance of results between the QFT-GIT and the T-SPOT (p=0.064 and Kappa=0.43, 95% confidence interval 0.082-0.78). Among 10 discordant cases between two IGRAs, 8 cases had IGRAs’ results near the cutoff values.

Conclusion: Without a diagnostic gold standard for LTBI, it is difficult for us to further assess which test is more accurate and more suitable for the diagnosis of LTBI. However, to diagnose LTBI of healthcare workers with IGRAs’ results near the cutoff values, we should consider clinical context, such as contact level, as well as the results of IGRAs.