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

Full 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.

Author information

Author/s: Chee, C B E (CB); Lim, L K Y (LK); Barkham, T M (TM); Koh, D R (DR); Lam, S O (SO); Shen, L (L); Wang, Y T (YT);

Affiliation: Tuberculosis Control Unit, Singapore. cynthia_chee(-atsign-)ttsh.com.sg

Journal and publication information

Publication Type: Evaluation Studies; Journal Article; Research Support, Non-U.S. Gov't

Journal: Infection control and hospital epidemiology : the official journal of the Society of Hospital Epidemiologists of America (Infect Control Hosp Epidemiol), published in United States. (Language: eng)

Reference: 2009-Sep; vol 30 (issue 9) : pp 870-5

Dates: Created 2009/08/05; Completed 2009/10/16;

PMID: 19637958, status: MEDLINE (last retrieval date: 10/16/2009, IMS Date: )

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