Evaluation of a new interferon-gamma release assay and comparison to tuberculin skin test during a tuberculosis outbreak

Summary Background The tuberculin skin test (TST) is commonly used for the diagnosis of latent tuberculosis infection (LTBI) in non-bacille Calmette–Guerin (BCG) vaccination settings. In recent years, attention has been drawn to interferon-gamma release assays (IGRAs), especially in BCG-vaccinated populations. In this study, we evaluated the TST and a new whole blood IGRA in BCG-vaccinated individuals during a tuberculosis (TB) outbreak in China. Methods A TB outbreak occurred at a university in Dalian, China from March to November 2010. The TST and a whole blood IGRA were used to screen for TB infection. The correlation between exposure levels, TST, and the IGRA were evaluated. Results We found that agreement between the IGRA and TST was poor (kappa 0.182–0.290). IGRA positivity was associated with the level of exposure, and IGRA positivity and the level of exposure were risk factors for TB incidence. Neither the IGRA nor the TST alone picked up all TB incidences. However, if a 10mm cutoff for the TST was used in the highest risk exposure group and IGRA positivity was used in the other risk groups, 19 of the 20 (95%) TB cases were identified. Conclusions A recommended preventive treatment regimen for China should be based on the level of exposure in conjunction with IGRA and TST test results.