title: Single-step QuantiFERON screening of adult contacts: a prospective cohort study of tuberculosis risk.
abstract: BACKGROUND
  The efffectiveness of tuberculosis (TB) contact screening programmes using interferon γ release assays remains uncertain as prospective contact TB risk is not well characterised.
  
  
  OBJECTIVE
  To quantify 2-year TB risk and evaluate screening performance with single-step QuantiFERON TB Gold-In Tube (QFT) in adult contacts. To compare TB risk between QFT tested subgroups stratified by exposure type (smear positive pulmonary (SP) versus non-smear positive (NSP) TB) and age (younger (16-35 years) versus older (≥36 years)).
  
  
  METHODS
  Screening involved QFT testing in older contacts of SP and all younger contacts, 8-12 weeks after index notification. Chemoprevention (3RH) was offered to QFT positive (+) younger adults. TB risk was determined in a prospective cohort study.
  
  
  RESULTS
  43 TB events occurred in 1769 adult contacts observed for median 717 days (2-year rate (95% CI)=2·5% (1.7 to 3.2)). Index-contact strain matching was demonstrable for 18 of 22 (82%) paired samples. No contacts (0/98) receiving 3RH developed TB. 215 of 817 appropriately tested adults (26.3%) were QFT+. 14 of 112 untreated QFT+ adults developed TB (2-year rate (95% CI)=13·4% (7.7 to 21.1)). The model required 35 contacts screened with QFT to identify one contact developing TB at 2 years. TB rates were comparable in QFT+ contacts of SP and NSP (rate ratio (RR)=0.98, p=0·962). For QFT+ older contacts, the disease rate was lower (8.9% (3.3 to 19.1)) and similar to the overall group rate (RR=1.4, p=0.503).
  
  
  CONCLUSIONS
  QFT based single-step contact screening is effective in young adults.
authors.affiliation: Department of Respiratory Medicine, Institute for Lung Health, Glenfield Hospital, Leicester, UK. ph62@le.ac.uk
authors.forename: Pranabashis
authors.initials: P
authors.lastname: Haldar
authors.forename: Helen
authors.initials: H
authors.lastname: Thuraisingam
authors.forename: Hemu
authors.initials: H
authors.lastname: Patel
authors.forename: Nelun
authors.initials: N
authors.lastname: Pereira
authors.forename: Robert C
authors.initials: RC
authors.lastname: Free
authors.forename: James
authors.initials: J
authors.lastname: Entwisle
authors.forename: Martin
authors.initials: M
authors.lastname: Wiselka
authors.forename: Edwyn Wren
authors.initials: EW
authors.lastname: Hoskyns
authors.forename: Philip
authors.initials: P
authors.lastname: Monk
authors.forename: Michael R
authors.initials: MR
authors.lastname: Barer
authors.forename: Gerrit
authors.initials: G
authors.lastname: Woltmann
mesh_terms: D000293:Adolescent; D000328:Adult; D000465:Algorithms; D016001:Confidence Intervals; D016358:Contact Tracing; D004739:England / Q000453:epidemiology; D005260:Female; D005838:Genotype; D006801:Humans; D059425:Interferon-gamma Release Tests; D053208:Kaplan-Meier Estimate; D055985:Latent Tuberculosis / Q000175:diagnosis* / Q000453:epidemiology* / Q000382:microbiology; D008137:Longitudinal Studies; D008297:Male; D009169:Mycobacterium tuberculosis / Q000235:genetics; D016017:Odds Ratio; D011446:Prospective Studies; D012307:Risk Factors; D012680:Sensitivity and Specificity; D013183:Sputum / Q000382:microbiology; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis* / Q000453:epidemiology* / Q000382:microbiology; D055815:Young Adult