IFNG and tuberculosis: Based on the magnitude of IFN-γ response to ESAT-6, the spouses who have been exposed to TB patients were divided into two groups; one is considered as a group of exposure with low possibility of infection (S1; <62.5 pg/mL) and the other is a group of exposure with high possibility of infection without active diseases (S2; >62.5 pg/mL).