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Published on: August 11, 2018
Two-step tuberculin skin test and booster phenomenon prevalence among Brazilian medical students
E G Teixeira1, A Kritski, A Ruffino-Netto
1Gama Filho University, Rio de Janeiro, Rio de Janeiro, Brazil. elenygt@globo.com
Setting:
Five medical schools in three cities in Rio de Janeiro State, Brazil, with different tuberculosis (TB) incidence rates.
Objective:
To evaluate the prevalence of the booster phenomenon and its associated factors in a young universally BCG-vaccinated TB-exposed population.
Design:
A two-step tuberculin skin test (TST) was performed among undergraduate medical students. Boosting was defined as an induration > or =10 mm in the second TST (TST2), with an increase of at least 6 mm over the first TST (TST1). The association of boosting with independent variables was evaluated using multivariate analysis.
Results:
Of the 764 participants (mean age 21.9 +/- 2.7 years), 672 (87.9%) had a BCG scar. The overall booster phenomenon prevalence was 8.4% (95%CI 6.5-10.6). Boosting was associated with TST1 reactions of 1-9 mm (aOR 2.5, 95%CI 1.04-5.9) and with BCG vaccination, mostly after infancy, i.e., after age two years (aOR 9.1, 95%CI 1.2-70.7).
Conclusion:
The prevalence of the booster phenomenon was high. A two-step TST in young BCG-vaccinated populations, especially in those with TST1 reactions of 1-9 mm, can avoid misdiagnosis as a false conversion and potentially reduce unnecessary treatment for latent TB infection.
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