Journal Article

Predictors of Positive Tuberculin Skin Test (TST) Results after 2-Step TST among Health Care Workers in Manitoba, Canada

Allen Kraut, Michael Coodin, Rose Plessis and Daria McLean

in Clinical Infectious Diseases

Published on behalf of Infectious Diseases Society of America

Volume 39, issue 11, pages e113-e118
Published in print December 2004 | ISSN: 1058-4838
Published online December 2004 | e-ISSN: 1537-6591 | DOI: http://dx.doi.org/10.1086/425916
Predictors of Positive Tuberculin Skin Test (TST) Results after 2-Step TST among Health Care Workers in Manitoba, Canada

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Background. Baseline 2-step tuberculin skin testing (TST) is recommended for health care workers (HCWs) to identify cases of the “boosting phenomenon” (i.e., a negative initial TST result followed by a positive result) and to track the risk of acquiring occupational tuberculosis. However, the 2-step TST has been shown to be insufficient to identify all cases of the booster phenomenon in older adults and refugees. The objective of this study was to identify whether a history of bacille Calmette-Guérin (BCG) vaccination and foreign birth—variables that are known to be associated with the booster phenomenon—remain predictors of a positive TST result in a group of HCWs documented to have negative 2-step TST results (i.e., 2 TSTs done 7–28 days apart with indurations <10 mm in diameter).

Methods. We performed a retrospective analysis of an employee database in a tertiary care hospital in Winnipeg, Canada. The study population was comprised of 698 HCWs with negative 2-step TST results who underwent a TST 0–2 years after completion of the 2-step procedure.

Results. Forty-six HCWs (6.6%) had a positive TST result 0–2 years after the 2-step test. In a multiple logistic regression analysis controlling for age, BCG vaccination, foreign birth, sex, and work setting, only history of BCG vaccination (odds ratio [OR], 8.38; 95% confidence interval [CI], 4.04–17.4), foreign birth (OR, 3.19; 95% CI, 1.53–6.62), and high-risk work setting (OR, 2.93; 95% CI, 1.44–5.95) were associated with a positive TST result.

Conclusions. Even for HCWs with negative results of 2-step TST, foreign birth and history of BCG vaccination are associated with a positive result of a future TST. Some positive TST results in such HCWs are related to nonoccupational factors, including delayed boosting, rather than to conversion due to recent tuberculosis contact.

Journal Article.  3361 words.  Illustrated.

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

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