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Thorax 68:240-246 doi:10.1136/thoraxjnl-2011-200956
  • Tuberculosis
  • Original article

Single-step QuantiFERON screening of adult contacts: a prospective cohort study of tuberculosis risk

  1. Gerrit Woltmann1,*
  1. 1Department of Respiratory Medicine, Institute for Lung Health, Glenfield Hospital, Leicester, UK
  2. 2Department of Infection, Immunity and Inflammation, University of Leicester, Leicester, UK
  3. 3Department of Microbiology, Leicester Royal Infirmary, Leicester, UK
  4. 4Department of Infectious Diseases, Leicester Royal Infirmary, Leicester, UK
  5. 5Department of Paediatrics and Neonatal Medicine, Leicester Royal Infirmary, Leicester, UK
  6. 6Health Protection Agency, East Midlands South Health Protection Unit, Leicester, UK
  7. *Cosenior authorship for manuscript.
  1. Correspondence to Dr Pranab Haldar, Department of Respiratory Medicine, Glenfield Hospital, Groby Road, Leicester, LE3 9QP, UK; ph62{at}le.ac.uk
  • Received 16 August 2011
  • Revised 6 August 2012
  • Accepted 9 August 2012
  • Published Online First 6 September 2012

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.

Objectives 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.

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