Distribution of IFN-γ responses in the baseline and the follow-up QFT-GIT. The responses of four subjects with indeterminate QFT-GIT results are not shown. The vertical and the horizontal dashed lines represent the QFT-GIT's diagnostic cut-off of 0.35 IU/ml. IFN-γ responses ≥ 10 IU/ml are shown as 10 IU/ml, IFN-γ responses < 0.00 IU/ml are shown as 0.00 IU/ml. IFN = interferon; QFT-GIT = QuantiFERON®-TB Gold In-Tube.