title: The tuberculin skin test is unreliable in school children BCG-vaccinated in infancy and at low risk of tuberculosis infection.
abstract: BACKGROUND
  The tuberculin skin test (TST) is often used to screen for latent tuberculosis infection (LTBI) in school children, many of whom were bacille Calmette-Guérin (BCG)-vaccinated in infancy. The reliability of the TST in such children is unknown.
  
  
  METHODS
  TSTs performed in low-risk BCG-vaccinated and -nonvaccinated grade 1 and grade 6 First Nations (North American Indian) school children in the province of Alberta, Canada, were evaluated retrospectively. To further assess the specificity of the TST, BCG-vaccinated children with a positive TST (≥10 mm of induration) and no treatment of LTBI were administered a QuantiFERON-TB Gold In-Tube test (QFT-GIT, Cellestis International).
  
  
  RESULTS
  A total of 3996 children, 2063 (51.6%) BCG-vaccinated and 1933 (48.4%) BCG-nonvaccinated, were screened for LTBI. Vaccinated children were more likely than nonvaccinated children to be TST positive (5.7% vs. 0.2%, P < 0.001). Vaccinated children with a positive TST were more likely to have a recent past TST as compared with those with a negative TST (6.8% versus 2.8%, P = 0.01). Among 65 BCG-vaccinated TST-positive children who underwent a QFT-GIT, only 5 (7.7%; 95% CI: 2.5%, 17.0%) were QFT-GIT positive. A TST of ≥15 mm was more likely to be associated with a positive QFT-GIT than a TST of 10 to 14 mm, 16.0% (95% CI: 4.5%, 36.1%) versus 2.5% (95% CI: 0.1%, 13.2%), P = 0.047.
  
  
  CONCLUSIONS
  The TST is unreliable in school children, BCG-vaccinated in infancy, and who are at low risk of infection. The QFT-GIT is a useful confirmatory test for LTBI in BCG-vaccinated TST-positive school children.
authors.affiliation: First Nations and Inuit Health, Alberta Region, Canada.
authors.forename: Sandy
authors.initials: S
authors.lastname: Jacobs
authors.forename: Andrea
authors.initials: A
authors.lastname: Warman
authors.forename: Ruth
authors.initials: R
authors.lastname: Richardson
authors.forename: Wadieh
authors.initials: W
authors.lastname: Yacoub
authors.forename: Angela
authors.initials: A
authors.lastname: Lau
authors.forename: Denise
authors.initials: D
authors.lastname: Whittaker
authors.forename: Sandy
authors.initials: S
authors.lastname: Cockburn
authors.forename: Geetu
authors.initials: G
authors.lastname: Verma
authors.forename: Jody
authors.initials: J
authors.lastname: Boffa
authors.forename: Gregory
authors.initials: G
authors.lastname: Tyrrell
authors.forename: Dennis
authors.initials: D
authors.lastname: Kunimoto
authors.forename: Jure
authors.initials: J
authors.lastname: Manfreda
authors.forename: Deanne
authors.initials: D
authors.lastname: Langlois-Klassen
authors.forename: Richard
authors.initials: R
authors.lastname: Long
mesh_terms: D000293:Adolescent; D001500:BCG Vaccine / Q000276:immunology; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D055985:Latent Tuberculosis / Q000276:immunology / Q000517:prevention & control; D008297:Male; D009169:Mycobacterium tuberculosis / Q000276:immunology; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014374:Tuberculin Test; D014376:Tuberculosis / Q000276:immunology / Q000517:prevention & control*; D014611:Vaccination
chemical_list: D001500:BCG Vaccine