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Use of a T Cell Interferon-γ Release Assay to Evaluate Tuberculosis Risk in Newly Qualified Physicians in Singapore Healthcare Institutions

Published online by Cambridge University Press:  02 January 2015

C. B. E. Chee ,
L. K. Y. Lim ,
T. M. Barkham ,
D. R. Koh ,
S. O. Lam ,
L. Shen  and
Y. T. Wang
C. B. E. Chee*
Affiliation:
Tuberculosis Control Unit, Tan Tock Seng Hospital, Singapore
L. K. Y. Lim
Affiliation:
Tuberculosis Control Unit, Tan Tock Seng Hospital, Singapore
T. M. Barkham
Affiliation:
Department of Laboratory Medicine, Tan Tock Seng Hospital, Singapore
D. R. Koh
Affiliation:
Yong Loo Lin School of Medicine, National University of Singapore, Singapore
S. O. Lam
Affiliation:
Tuberculosis Control Unit, Tan Tock Seng Hospital, Singapore Yong Loo Lin School of Medicine, National University of Singapore, Singapore
Y. T. Wang
Affiliation:
Tuberculosis Control Unit, Tan Tock Seng Hospital, Singapore
*
Control Unit, 144 Moulmein Road, Singapore30809 ([email protected])
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Abstract

Background.

Surveillance for latent tuberculosis in high-risk groups such as healthcare workers is limited by the nonspecificity of the tuberculin skin test (TST) in BCG-vaccinated individuals. The Mycobacterium tuberculosis antigen-specific interferon-γ release assays (IGRAs) show promise for more accurate latent tuberculosis detection in such groups.

Objective.

To compare the utility of an IGRA, the T-SPOT.TB assay, with that of the TST in healthcare workers with a high rate of BCG vaccination.

Methods.

Two hundred seven medical students from 2 consecutive cohorts underwent the T-SPOT.TB test and the TST in their final year of study. Subjects with negative baseline test results underwent repeat testing after working for 1 year as junior physicians in Singapore's public hospitals.

Results.

The baseline TST result was an induration 10 mm or greater in diameter in 177 of the 205 students who returned to have their TST results evaluated (86.3%), while the baseline T-SPOT.TB assay result was positive in 9 (4.3%) of the students. Repeat T-SPOT.TB testing in 182 baseline-negative subjects showed conversion in 9 (4.9%). A repeat TST in 18 subjects with baseline-negative TST results did not reveal any TST result conversion.

Conclusions.

The high rate of positive baseline TST results in our BCG-vaccinated healthcare workers renders the TST unsuitable as a surveillance tool in this tuberculosis risk group. Use of an IGRA has enabled the detection and treatment of latent tuberculosis in this group. Our T-SPOT.TB conversion rate highlights the need for greater tuberculosis awareness and improved infection control practices in our healthcare institutions.

Type
Original Articles
Information
Infection Control & Hospital Epidemiology , Volume 30 , Issue 9 , September 2009 , pp. 870 - 875
Copyright
Copyright © The Society for Healthcare Epidemiology of America 2009

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