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. 2012 Mar-Apr;19(2):84-8.
doi: 10.1155/2012/576324.

Use of interferon-gamma release assays in a health care worker screening program: experience from a tertiary care centre in the United States

Manish Joshi  1 , Thomas P Monson, Gail L Woods
Affiliations

Use of interferon-gamma release assays in a health care worker screening program: experience from a tertiary care centre in the United States

Manish Joshi et al. Can Respir J. 2012 Mar-Apr.

Abstract
in English, French

Background: Interferon-gamma release assays including the QuantiFERON-TB Gold In-Tube test (QFT-GIT [Cellestis Ltd, Australia]) may be used in place of the tuberculin skin test (TST) in surveillance programs for Mycobacterium tuberculosis infection control. However, data on performance and practicality of the QFT-GIT in such programs for health care workers (HCWs) are limited.

Objectives: To assess the performance, practicality and reversion rate of the QFT-GIT among HCWs at a tertiary health care institution in the United States.

Methods: Retrospective chart review of HCWs at Central Arkansas Veterans Healthcare System (Arkansas, USA) who underwent QFT-GIT testing as a part of their employee screening between November 1, 2008 and October 31, 2009.

Results: QFT-GIT was used to screen 3290 HCWs. The initial QFT-GIT was interpreted as positive for 129 (3.9%) HCWs, negative for 3155 (95.9%) and indeterminate for six (0.2%). Testing with QFT-GIT was repeated in 45 HCWs who had positive results on the initial test. The QFT-GIT reverted to negative in 18 (40.0%) HCWs, all of whom had negative TST status and initial interferon-gamma values of 0.35 IU⁄mL to 2.0 IU⁄mL.

Conclusion: The QFT-GIT test is feasible in large health care setting as an alternative to TST for M tuberculosis infection screening in HCWs but is not free from challenges. The major concerns are the high number of positive test results and high reversion rates on repeat testing, illustrating poor short-term reproducibility of positive QFT-GIT test results. These results suggest adopting a borderline zone between interferon-gamma values of 0.35 IU⁄mL to 2.0 IU⁄mL, and cautious clinical interpretation of values in this range.

HISTORIQUE :: Les tests de libération d’interféron gamma, y compris le test QuantiFERON-TB Gold In-Tube (QFT-GIT [Cellestis Ltd, Australie]), pourraitent peut-être remplacer le test cutané à la tuberculine (TCT) dans les programmes de surveillance pour contrôler l’infection au Mycobacterium tuberculosis. Cependant, les données sur le rendement et le caractère pratique du test QFT-GIT dans de tels programmes destinés aux travailleurs de la santé (TdS) sont limités.

OBJECTIFS :: Évaluer le rendement, le caractère pratique et le taux de réversion du test de QFT-GIT chez les TdS d’un établissement de soins tertiaires des États-Unis.

MÉTHODOLOGIE :: Analyse rétrospective des dossiers des TdS du Central Arkansas Veterans Healthcare System de l’Arkansas, aux États-Unis, qui ont subi le test QFT-GIT dans le cadre du dépistage des employés entre le 1er novembre 2008 et le 31 octobre 2009.

RÉSULTATS :: Le test QFT-GIT a servi au dépistage de 3 290 TdS. Le test QFT-GIT initial a été interprété comme positif auprès de 129 TdS (3,9 %), comme négatif chez 3 155 TdS (95,9 %) et comme indéterminé chez six TdS (0,2 %). Le test QFT-GIT a été repris chez 45 TdS qui avaient obtenu des résultats positifs au test initial. Il a donné des résultats négatifs chez 18 TdS (40,0 %), qui avaient tous obtenu un TCT négatif et des valeurs initiales d’interféron gamma de 0,35 UI/mL à 2,0 UI/mL.

CONCLUSIONS :: Le test QFT-GIT est faisable dans de grands établissements de santé pour remplacer le TCT dans le dépistage du M tuberculosis chez les TdS, mais il n’est pas sans défis. Les principales préoccupations sont le nombre élevé de résultats faux-positifs et le taux élevé de réversion à la reprise du test, qui démontre une mauvaise reproductibilité à court terme des résultats positifs du test QFT-GIT. Ces résultats incitent à préconiser l’adoption d’une zone seuil entre les valeurs d’interféron gamma de 0,35 UI/mL à 2,0 UI/mL et une interprétation clinique prudente des valeurs faisant partie de cette plage.

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Figures

Figure 1)
Figure 1)
The QuantiFERON-TB Gold In-Tube (QFT-GIT [Cellestis Ltd, Australia]) test results and history of tuberculin skin test (TST) status in 45 health care workers who underwent repeat testing
Figure 2)
Figure 2)
The initial and repeat interferon (IFN)-gamma values in 18 health care workers who reverted to negative on repeat QuantiFERON-TB Gold In-Tube (QFT-GIT [Cellestis Ltd, Australia]) testing. The dotted line represents the cut-off IFN-gamma value for positive tests (0.35 IU/mL). An outlier with IFN-gamma value ≥10 is not represented in this figure
Figure 3)
Figure 3)
Box-and-whisker plots showing distribution of initial interferon-gamma values in health care workers whose repeat QuantiFERON-TB Gold In-Tube test (QFT-GIT [Cellestis Ltd, Australia]) result reverted to negative (n=18) versus those who remained positive (n=27). On comparing interferon-gamma values, there was a significant difference (P=0.02) in the mean levels between the two groups
Figure 4)
Figure 4)
Box-and-whisker plots showing distribution of initial interferon-gamma values in health care workers who underwent repeat QuantiFERON-TB Gold In-Tube testing (QFT-GIT [Cellestis Ltd, Australia]) testing and had ‘negative’ tuberculin skin test status. On comparing interferon-gamma values, there was no significant difference (P=0.84) in the mean levels among the health care workers whose repeat QFT-GIT test results reverted from positive to negative (n=18) versus those that remained positive (n=13)
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References

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