Induration or erythema diameter not less than 5 mm as results of recombinant fusion protein ESAT6-CFP10 skin test for detecting M. tuberculosis infection.

BACKGROUND Recombinant fusion protein ESAT6-CFP10 (EC) is a newly developed skin test reagent for detecting Mycobacterium tuberculosis (M. tuberculosis) infection. In this study, we evaluated whether induration and erythema could be used as diagnostic indicators for EC skin test to detect M. tuberculosis infection. METHODS A total of 743 tuberculosis patients and 1514 healthy volunteers underwent an EC skin test. The diameters of induration and erythema were measured with Vernier caliper, 24 h, 48 h, and 72 h after skin testing. Related indicators of EC reagent diagnostic test were tested, and the diagnostic effects of the four diagnostic indicators for EC skin test were compared. RESULTS The sensitivity of induration / erythema measurement was lower at 24 h after EC skin test than at 48 h or 72 h (P<0.01). There was no difference in consistency (P = 0.16) between induration with clinical diagnosis, and erythema with clinical diagnosis at 48 h (88.88 and 90.16%, Kappa value was 0.75 and 0.78, respectively). In patients, the sensitivity of erythema measurement was higher than induration measurement (P<0.01). In healthy volunteers, the specificity of erythema measurement was lower than induration at 24 h after skin test, but there was no difference at 48 h after skin test (P = 0.22). In BCG vaccination volunteers, the specificity of induration and erythema were higher than 90%. In addition, there was a high consistency of induration and erythema. When induration or erythema was used as a positive diagnostic indicator, the sensitivity of the EC skin test was improved, and was no different from the other three indicators in terms of specificity and consistency with clinical diagnosis. CONCLUSIONS Induration or erythema diameter not less than 5 mm could be used as a diagnostic indicator for detecting M. tuberculosis infection. TRIAL REGISTRATION Phase III clinical trial of recombinant Mycobacterium tuberculosis ESAT6-CFP10 allergen; CTR20150695 ; registered in December 16, 2015.