Background and objective: China is a country with a high prevalence of latent tuberculosis (TB) infection (LTBI) and has a policy of routine bacillus Calmette-Guérin (BCG) vaccination. The purified protein derivative (PPD) skin test cannot distinguish TB infection from BCG vaccination, and the diagnosis of LTBI lacks an accepted standard method. The primary objective of this study was to assess the potential of a highly sensitive whole-blood interferon (IFN)-γ release assay that uses recombinant culture filtrate protein (CFP)-10/early secretory antigenic target (ESAT)-6 fusion protein (rCFP-10/ESAT-6) as a stimulus for diagnosis of LTBI.
Methods: Between December 2009 and March 2010, a total of 892 new recruits to the army in Beijing, China, were interviewed and routinely examined by chest radiographs. IFNγ released from whole blood in response to stimulation with rCFP-10/ESAT-6 was detected with an enzyme-linked chemiluminescent immunoassay. The recruits were also intradermally injected with PPD to assess 72-hour skin induration (the PPD skin test).
Results: Of the 892 participants, 450 (50.4%) had a positive PPD skin test and 244 (27.4%) had a positive whole-blood IFNγ release assay. Of 442 PPD-negative subjects, 88 (19.9%) had a positive whole-blood IFNγ test. Of 450 PPD-positive subjects, 156 (34.7%) had a positive whole-blood IFNγ test. Of 132 strongly PPD-positive subjects, 62 (47.0%) had a positive whole-blood IFNγ test. The agreement between the two tests was 57.2%. Of the 892 participants, 579 (64.9%) had clear vaccination scars on their arms, and of these, 382 (66.0%) had positive PPD skin responses and 162 (28.0%) were positive for the whole-blood IFNγ test.
Conclusion: The new whole-blood IFNγ release assay might be a better indicator of LTBI than the PPD test in China.