A summary of the Third Global Interferon-γ Release Assay Symposium

Studies over the past several decades have dramatically increased our understanding of the immune response to Mycobacterium tuberculosis infection, and advances in proteomics and genomics have led to a new class of immune-diagnostic tests, termed interferon-γ (IFN-γ) release assays (IGRAs), which appear to obviate many of the problems encountered with the tuberculin skin test (TST). Worldwide, 2 IGRAs are currently commercially available. QuantiFERON-TB Gold In-Tube (Cellestis) is a third-generation product that uses an enzyme-linked immunosorbent assay to measure IFN-γ generated in whole blood stimulated with M. tuberculosis-specific antigens. T-Spot-TB (Oxford Immunotec) employs enzyme-linked immunosorbent spot technology to enumerate the number of purified lymphocytes that respond to M. tuberculosis-specific antigens by producing IFN-γ. These in vitro tests measure the host immune response to M. tuberculosis-specific antigens, which virtually eliminates false-positive cross reactions caused by bacillus Calmette-Guérin vaccination and/or exposure to environmental nontuberculous mycobacteria that plague the interpretation and accuracy of the tuberculin skin test (TST). The high specificity of IGRAs, together with sensitivity commensurate with or better than that of the TST, promises an accurate diagnosis and the ability to focus tuberculosis-control activities on those who are actually infected with M. tuberculosis. The Third Global Symposium was held over a 3-day period and was presented by the University of California, San Diego, Continuing Medical Education department; slides and sound recordings of each presentation are available at http://cme.ucsd.edu/igras/syllabus.html . A moderated discussion is also available at http://cme.ucsd.edu/igrasvideo . This document provides a summary of the key findings of the meeting, specifically focusing on the use of IGRAs in screening healthcare worker populations.