title: T-Spot.TB outperforms tuberculin skin test in predicting development of active tuberculosis among household contacts.
abstract: OBJECTIVE
  In Hong Kong, neonatal Bacillus Calmette-Guerin (BCG) vaccination is practiced with 99% coverage. This study was to compare the performance of T-Spot.TB and tuberculin skin test (TST) in predicting tuberculosis (TB) among household contacts.
  
  
  METHODS
  From 1 March 2006 to 31 July 2010, 1049 asymptomatic household contacts of smear-positive patients were simultaneously tested with T-Spot.TB and TST, and then followed for up to 5 years for development of TB. Attending clinicians and subjects were blinded to the results of T-Spot.TB.
  
  
  RESULTS
  T-Spot.TB gave a significantly higher positive rate (32.7% vs 22.1%) and better association with exposure time than TST at the 15 mm cut-off. Agreement between T-Spot.TB and TST using cut-offs of 5, 10 and 15 mm were relatively poor (kappa 0.25-0.41) irrespective of presence or absence of BCG scar. Only T-Spot.TB positivity was negatively associated with BCG scar. Both T-Spot.TB (incidence rate ratio between test-positive and test-negative subjects, IRR: 8.2) and TST (IRR: 4.1, 6.1 and 2.8, using cut-offs of 5 mm, 10 mm and 15 mm, respectively) helped to predict TB. Using a TST cut-off of 15 mm, 56% of future TB cases and 62.5% of bacteriologically confirmed cases were missed. Lowering the TST cut-off to 10 mm or 5 mm could achieve sensitivity comparable with that of T-Spot.TB, but at the expense of lower specificities, with more positive tests (thus requiring treatment) per case of TB predicted.
  
  
  CONCLUSIONS
  T-Spot.TB outperformed TST in predicting TB among household contacts in a high-income area with widespread BCG vaccination coverage.
authors.affiliation: Tuberculosis and Chest Service, Centre for Health Protection, Department of Health, Hong Kong, China.
authors.forename: Chi Chiu
authors.initials: CC
authors.lastname: Leung
authors.forename: Wing Cheong
authors.initials: WC
authors.lastname: Yam
authors.forename: Pak Leung
authors.initials: PL
authors.lastname: Ho
authors.forename: Wing Wai
authors.initials: WW
authors.lastname: Yew
authors.forename: Chi Kuen
authors.initials: CK
authors.lastname: Chan
authors.forename: Wing Sze
authors.initials: WS
authors.lastname: Law
authors.forename: Shuk Nor
authors.initials: SN
authors.lastname: Lee
authors.forename: Kwok Chiu
authors.initials: KC
authors.lastname: Chang
authors.forename: Lai Bun
authors.initials: LB
authors.lastname: Tai
authors.forename: Cheuk Ming
authors.initials: CM
authors.lastname: Tam
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D005260:Female; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D014374:Tuberculin Test / Q000379:methods*; D014376:Tuberculosis / Q000175:diagnosis* / Q000453:epidemiology / Q000635:transmission; D055815:Young Adult
keywords: contact screening; interferon-gamma release assay; latent tuberculosis infection; sensitivity; specificity