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Free Content Two-step tuberculin skin test and booster phenomenon prevalence among Brazilian medical students

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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 ≥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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Keywords: BCG; booster; medical students; tuberculin test; tuberculosis

Document Type: Regular Paper

Affiliations: 1: Gama Filho University, Rio de Janeiro, Rio de Janeiro, Brazil; Souza Marques Foundation, Rio de Janeiro, Rio de Janeiro, Brazil; Rio de Janeiro Federal University, Rio de Janeiro, Rio de Janeiro, Brazil 2: Rio de Janeiro Federal University, Rio de Janeiro, Rio de Janeiro, Brazil 3: Ribeirão Preto School of Medicine, São Paulo University, Ribeirao Preto, São Paulo, Brazil 4: Souza Marques Foundation, Rio de Janeiro, Rio de Janeiro, Brazil 5: Gama Filho University, Rio de Janeiro, Rio de Janeiro, Brazil; Souza Marques Foundation, Rio de Janeiro, Rio de Janeiro, Brazil 6: Montreal Chest Institute, McGill University, Montreal, Quebec, Canada 7: Gama Filho University, Rio de Janeiro, Rio de Janeiro, Brazil

Publication date: December 1, 2008

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  • The International Journal of Tuberculosis and Lung Disease (IJTLD) is for clinical research and epidemiological studies on lung health, including articles on TB, TB-HIV and respiratory diseases such as COVID-19, asthma, COPD, child lung health and the hazards of tobacco and air pollution. Individuals and institutes can subscribe to the IJTLD online or in print – simply email us at [email protected] for details.

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