title: Two-step tuberculin skin test and booster phenomenon prevalence among Brazilian medical students.
abstract: METHODS
  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.
  
  
  METHODS
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Gama Filho University, Rio de Janeiro, Rio de Janeiro, Brazil. elenygt@globo.com
authors.forename: E G
authors.initials: EG
authors.lastname: Teixeira
authors.forename: A
authors.initials: A
authors.lastname: Kritski
authors.forename: A
authors.initials: A
authors.lastname: Ruffino-Netto
authors.forename: R
authors.initials: R
authors.lastname: Steffen
authors.forename: J R
authors.initials: JR
authors.lastname: Lapa E Silva
authors.forename: M
authors.initials: M
authors.lastname: Belo
authors.forename: R R
authors.initials: RR
authors.lastname: Luiz
authors.forename: D
authors.initials: D
authors.lastname: Menzies
authors.forename: A
authors.initials: A
authors.lastname: Trajman
mesh_terms: D001500:BCG Vaccine; D001938:Brazil / Q000453:epidemiology; D005260:Female; D006801:Humans; D007117:Immunization, Secondary; D008297:Male; D015999:Multivariate Analysis; D015995:Prevalence; D013337:Students, Medical; D014374:Tuberculin Test / Q000379:methods*; D014376:Tuberculosis / Q000453:epidemiology; D014611:Vaccination; D055815:Young Adult
chemical_list: D001500:BCG Vaccine