title: The tuberculin skin test versus QuantiFERON TB Gold® in predicting tuberculosis disease in an adolescent cohort study in South Africa.
abstract: METHODS
  This study was conducted in a high tuberculosis (TB) burden area in Worcester, South Africa, with a notified all TB incidence rate of 1,400/100,000.
  
  
  OBJECTIVE
  To compare the predictive value of a baseline tuberculin skin test (TST) with that of the QuantiFERON TB Gold (In-tube) assay (QFT) for subsequent microbiologically confirmed TB disease among adolescents.
  
  
  METHODS
  Adolescents aged 12-18 years were recruited from high schools in the study area. At baseline, blood was drawn for QFT and a TST administered. Participants were followed up for up to 3.8 years for incident TB disease (median 2.4 years).
  
  
  RESULTS
  After exclusions, 5244 (82.4%) of 6,363 adolescents enrolled, were analysed. The TB incidence rate was 0.60 cases per 100 person years (pyrs) (95% CI 0.43-0.82) for baseline TST positive (≥ 5 mm) participants and 0.64 cases per 100 pyrs (95% CI 0.45-0.87) for baseline QFT positive participants. TB incidence rates were 0.22 per 100 pyrs (0.11-0.39) and 0.22 per 100 pyrs (0.12-0.38) among those with a negative baseline TST and QFT respectively. Sensitivity for incident TB disease was 76.9% for TST and 75.0% for QFT (p = 0.81). Positive predictive value was 1.4% for TST and 1.5% for QFT.
  
  
  CONCLUSIONS
  Positive TST and QFT tests were moderately sensitive predictors of progression to microbiologically confirmed TB disease. There was no significant difference in the predictive ability of these tests for TB disease amongst adolescents in this high burden setting. Therefore, these findings do not support use of QFT in preference to TST to predict the risk of TB disease in this study population.
authors.affiliation: South African Tuberculosis Vaccine Initiative, Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Cape Town, South Africa.
authors.forename: Hassan
authors.initials: H
authors.lastname: Mahomed
authors.forename: Tony
authors.initials: T
authors.lastname: Hawkridge
authors.forename: Suzanne
authors.initials: S
authors.lastname: Verver
authors.forename: Deborah
authors.initials: D
authors.lastname: Abrahams
authors.forename: Lawrence
authors.initials: L
authors.lastname: Geiter
authors.forename: Mark
authors.initials: M
authors.lastname: Hatherill
authors.forename: Rodney
authors.initials: R
authors.lastname: Ehrlich
authors.forename: Willem A
authors.initials: WA
authors.lastname: Hanekom
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Hussey
mesh_terms: D000293:Adolescent; D002648:Child; D015331:Cohort Studies; D003710:Demography; D004781:Environmental Exposure; D005260:Female; D006801:Humans; D015994:Incidence; D008137:Longitudinal Studies; D008297:Male; D011237:Predictive Value of Tests; D011933:Reagent Kits, Diagnostic; D012307:Risk Factors; D012680:Sensitivity and Specificity; D013019:South Africa / Q000453:epidemiology; D013997:Time Factors; D014374:Tuberculin Test / Q000379:methods*; D014376:Tuberculosis / Q000175:diagnosis* / Q000453:epidemiology*
chemical_list: D011933:Reagent Kits, Diagnostic