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Infect Control Hosp Epidemiol. 2009 Sep;30(9):870-5. doi: 10.1086/599284.

Use of a T cell interferon-gamma release assay to evaluate tuberculosis risk in newly qualified physicians in Singapore healthcare institutions.

Author information

1
Tuberculosis Control Unit, Singapore. cynthia_chee@ttsh.com.sg

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-gamma 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.

PMID:
19637958
DOI:
10.1086/599284
[Indexed for MEDLINE]

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