Supplemental use of an interferon-gamma release assay in a state-wide tuberculosis contact tracing program in Victoria: a six-year review

Abstract

Introduction: Tuberculin skin testing (TST) has been the accepted Australian standard for investigating contacts following exposure to infectious tuberculosis (TB). In recent years, the availability of the interferon-gamma release assays (IGRA) has introduced a potential alternative test but data on its use in this context are limited.
Methods: A prospective longitudinal cohort study was conducted from 2008–2013 to review the use of IGRA and subsequent TB disease following testing in a state-wide contact tracing program. Additional information on the experience and acceptability of IGRA in this context was also obtained through program staff surveys following implementation.
Results: IGRA testing was performed on 643 contacts, with a mean follow-up of 3.7 years. IGRA was primarily used to supplement TST, most commonly due to borderline TST reactivity in individuals who had bacille Calmette-Guérin vaccination. Where both TST and IGRA were performed, correlation of test results was poor (kappa=0.35). The negative predictive value for later development of active TB was 99.5%.
Conclusions: Our experience suggests that IGRA are able to be incorporated safely and effectively as a supplement to TST-based contact tracing. Commun Dis Intell 2015;39(2):E191–E196.