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