Chest
Volume 142, Issue 1, July 2012, Pages 55-62
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Original Research
Chest Infections
Challenges of Interferon-γ Release Assay Conversions in Serial Testing of Health-care Workers in a TB Control Program

https://doi.org/10.1378/chest.11-0992Get rights and content

Background

Clinical data with use of serial interferon-γ release assay (IGRA) testing in US health-care workers (HCWs) are limited.

Methods

A single-center, retrospective chart review was done from 2007 to 2010 of HCWs who underwent preemployment QuantiFERON-TB Gold In-Tube testing. Demographic data, bacille Calmette-Guérin history, prior tuberculin skin test result if done, and baseline and serial IGRA values were obtained. The number of IGRA converters and reverters and their subsequent management by infectious disease physicians were reviewed. Quantitative IGRA-negative values were not available.

Results

A total of 7,374 IGRAs were performed on newly hired HCWs. Of these tests, 486 (6.6%) were positive at baseline, 305 (4.1%) were indeterminate, and 6,583 (89.3%) were negative. From 2007 to 2010, 52 of 1,857 HCWs (2.8%) with serial IGRA tests were identified as converters, with a serial IGRA median value of 0.63 IU/mL. Seventy-one percent of HCWs with IGRA conversion had values ≤ 1 IU/mL. None of the converters had active TB or were part of an outbreak investigation.

Conclusions

Clinical significance of most QuantiFERON-TB Gold In-Tube conversions in serial testing remains a challenging task for clinicians. The use of a single cutoff point criterion for IGRA may lead to overdiagnosis of new TB infections. Clinical assessment and evaluation may help to prevent unnecessary therapy in these cases. The criteria for defining conversions and reversions by establishing new cutoffs needs to be evaluated further, especially in HCWs.

Section snippets

Testing

QFT-GIT is an in vitro diagnostic test using a peptide cocktail simulating early secretory antigen target-6 (ESAT-6), culture filtrate product-10 (CFP-10), and TB7.7 proteins to stimulate cells in heparinized whole blood (Cellestis International Pty Ltd). QFT-GIT with the third TB antigen TB7.7 was used beginning March 2008. These three proteins are not present in the bacille Calmette-Guérin (BCG) strains and are absent from most nontuberculous mycobacteria, with the exception of Mycobacterium

Results

There were 7,374 IGRAs (45.3%) performed on newly hired HCWs at the Cleveland Clinic. Demographic information, history of previous BCG vaccination, and previous positive TSTs in these HCWs are shown in Table 1. Among newly hired HCWs, 486 (6.6%) had positive results, 305 (4.1%) had indeterminate results, and 6,583 (89.3%) had qualitatively negative results.

All 486 HCWs with baseline positive IGRAs were offered evaluation by an ID physician, and their management is described in Figure 1. A total

Discussion

Although IGRAs are promising for serial testing, there still are limited data available on interpreting serial testing in HCWs.13, 14 The present study provides data on IGRAs among HCWs in the United States, a low-incidence country. Because exposure is a risk factor for developing TB, the ability to treat persons with LTBI is a vital component of infection control in a hospital TB program. With the implementation of IGRA testing in 2007, the Cleveland Clinic ID department evaluated > 300 HCWs,

Acknowledgments

Author contributions: Drs Fong and Miranda had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

Dr Fong: contributed to the study design, institutional review board application, data analysis, and preparation of the manuscript.

Dr Tomford: contributed to the data analysis and approval of the final manuscript.

Dr Teixeira: contributed to the study design, data analysis, and approval of the final manuscript.

Dr

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

    Funding/Support: The authors have reported to CHEST that no funding was received for this study.

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