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Original Research: Chest Infections |

Monthly Follow-ups of Interferon-γ Release Assays Among Health-care Workers in Contact With Patients With TBMonthly Follow-ups of Interferon-03B3 Release Assays

Jong Sun Park, MD; Ji Sun Lee; Min Young Kim, RN; Chang Hoon Lee, MD; Ho Il Yoon, MD; Sang-Min Lee, MD; Chul-Gyu Yoo, MD; Young Whan Kim, MD; Sung Koo Han, MD; Jae-Joon Yim, MD
Author and Funding Information

From the Division of Pulmonary and Critical Care Medicine (Drs Park and Yoon), Department of Internal Medicine, Seoul National University Bundang Hospital; the Division of Pulmonary and Critical Care Medicine (Drs S.-M. Lee, Yoo, Y. W. Kim, Han, and Yim and Mss J. S. Lee and M. Y. Kim), Department of Internal Medicine and Lung Institute of Medical Research Center, Seoul National University College of Medicine; and the Division of Pulmonary and Critical Care Medicine (Dr C. H. Lee), Department of Internal Medicine, Seoul Metropolitan Government Seoul National University Boramae Medical Center, Seoul, South Korea.

Correspondence to: Jae-Joon Yim, MD, Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine and Lung Institute of Medical Research Center, Seoul National University College of Medicine, 101 Daehangno, Jongno-gu, Seoul 110-744, South Korea; e-mail: yimjj@snu.ac.kr


For editorial comment see page 1366

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.

Funding/Support: This study was supported by the Seoul National University Hospital Research Fund [04-2010-1120].


Chest. 2012;142(6):1461-1468. doi:10.1378/chest.11-3299
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Background:  Interferon-γ (IFN-γ) release assays (IGRAs), which can overcome several limitations of the tuberculin skin test in detecting latent TB infection, were introduced recently in routine clinical practice. However, IGRAs are highly dynamic tests, and the T-cell responses tend to fluctuate over time. We wanted to evaluate the conversion and reversion rates of monthly IGRAs over 1 year among health-care workers (HCWs) in contact with patients with TB in South Korea, a country with an intermediate TB burden.

Methods:  Forty-nine HCWs in contact with patients with active pulmonary TB were prospectively enrolled. Interviews on exposure to patients with active TB, a physical examination, and a QuantiFERON TB Gold In-Tube assay (QFT-GIT) were carried out monthly for 1 year.

Results:  Among 48 participants, 25 (52%) showed inconsistent results in serial testing. When an increase from< 0.35 IU/mL to ≥ 0.70 IU/mL was applied as the definition of a conversion, inconsistent IGRA results were identified in 13 participants (27.0%). Consistency in QFT-GIT results was associated with age, length of service, and baseline IFN-γ levels, but not with the profession of the participant, degree of TB exposure, or wearing of an N95 mask. In five participants, fluctuations in IFN-γ levels showed levels > 0.70 IU/mL two or more times.

Conclusions:  Fluctuation in IGRA findings was common when HCWs in contact with patients with TB were tested monthly. This could be a result of poor reproducibility of the assay, repeated infection and true reversion, or periodic secretion of antigens from Mycobacterium tuberculosis.

Trial registry:  ClinicalTrials.gov; No.: NCT01121068; URL: www.clinicaltrials.gov

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