Journal Article

Detection of <i>Mycobacterium tuberculosis</i> Infection in United States Navy Recruits Using the Tuberculin Skin Test or Whole-Blood Interferon-γ Release Assays

Gerald H. Mazurek, Margan J. Zajdowicz, Arlene L. Hankinson, Daniel J. Costigan, Sean R. Toney, James S. Rothel, Laura J. Daniels, F. Brian Pascual, Nong Shang, Lisa W. Keep and Philip A. LoBue

in Clinical Infectious Diseases

Published on behalf of Infectious Diseases Society of America

Volume 45, issue 7, pages 826-836
Published in print October 2007 | ISSN: 1058-4838
Published online October 2007 | e-ISSN: 1537-6591 | DOI: http://dx.doi.org/10.1086/521106
Detection of Mycobacterium tuberculosis Infection in United States Navy Recruits Using the Tuberculin Skin Test or Whole-Blood Interferon-γ Release Assays

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Background. Military personnel are at risk for acquiring Mycobacterium tuberculosis infection because of activities in close quarters and in regions with a high prevalence of tuberculosis (TB). Accurate tests are needed to avoid unnecessary treatment because of false-positive results and to avoid TB because of false-negative results and failure to diagnose and treat M. tuberculosis infection. We sought to estimate the specificity of the tuberculin skin test (TST) and 2 whole-blood interferon-γ release assays (QuantiFERON-TB assay [QFT] and QuantiFERON-TB Gold assay [QFT-G]) and to identify factors associated with test discordance.

Methods. A cross-sectional comparison study was performed in which 856 US Navy recruits were tested for M. tuberculosis infection using the TST, QFT, and QFT-G.

Results. Among the study subjects, 5.1% of TSTs resulted in an induration ⩾10 mm, and 2.9% of TSTs resulted in an induration ⩾15 mm. Eleven percent of QFT results and 0.6% of QFT-G results were positive. Assuming recruits at low risk for M. tuberculosis exposure were not infected, estimates of TST specificity were 99.1% (95% confidence interval [CI], 98.3%–99.9%) when a 15-mm cutoff value was used and 98.4% (95% CI, 97.3%–99.4%) when a 10-mm cutoff value was used. The estimated QFT specificity was 92.3% (95% CI, 90.0%–94.5%), and the estimated QFT-G specificity was 99.8% (95% CI, 99.5%–100%). Recruits who were born in countries with a high prevalence of TB were 26–40 times more likely to have discordant results involving a positive TST result and a negative QFT-G result than were recruits born in countries with a low prevalence of TB. Nineteen (50%) of 38 recruits with this type of discordant results had a TST induration ⩾15 mm.

Conclusions. The QFT-G and TST are more specific than the QFT. No statistically significant difference in specificity between the QFT-G and TST was found using a 15-mm induration cutoff value. The discordant results observed among recruits with increased risk of M. tuberculosis infection may have been because of lower TST specificity or lower QFT-G sensitivity. Negative QFT-G results for recruits born in countries where TB is highly prevalent and whose TST induration was ⩾15 mm suggest that the QFT-G may be less sensitive than the TST. Additional studies are needed to determine the risk of TB when TST and QFT-G results are discordant.

Journal Article.  4896 words.  Illustrated.

Subjects: Infectious Diseases ; Immunology ; Public Health and Epidemiology ; Microbiology

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