Poor correlation between tuberculin skin tests and interferon-γ assays in close contacts of patients with multidrug-resistant tuberculosis

Background and Objective: The results of tuberculin skin tests (TST) and QuantiFERON TB-Gold In-Tube (QFT-GIT) assays were compared in close contacts of patients with multidrug-resistant tuberculosis (MDR-TB). Methods: Close contacts of patients with bacteriologically confirmed MDR-TB (n = 101) were assessed. Most contacts were members of the households of patients, and 79 (78.2%) had received Bacille Calmette-Guerin (BCG) vaccination. Samples from each contact were tested using the TST and the QFT-GIT assay on the same day, and the concordance between these results was assessed using kappa (κ) coefficients. Results: Forty-eight subjects (47.5%) showed positive responses on TST, using a 10-mm induration cut-off, and 54 (53.5%) were positive for the QFT-GIT assay. Of the 48 individuals who were TST positive, 34 (70.8%) were positive for the QFT-GIT assay. Of the 53 subjects who were TST negative, 33 (62.5%) were negative for the QFT-GIT assay. The overall agreement between the two tests (κ coefficient) was 0.33. The κ coefficient was higher in the 22 subjects who had not received BCG vaccination (κ = 0.48) than in the 79 subjects who had received BCG vaccination (κ = 0.29). Conclusion: The TST and QFT-GIT assays showed poor correlation in close contacts of patients with MDR-TB, especially those contacts who had received BCG vaccination. There was a discrepancy between results of TSTs and QFT-GIT assays in close contacts of patients with multidrug-resistant tuberculosis, particularly those who had received BCG vaccination. These findings were similar to those from studies reporting poor correlation between these tests in close contacts of South Korean patients with drug-susceptible tuberculosis.