The conventional diagnosis of tubercle infection in contact investigation was mainly based on the tuberculin reaction. However, in Japan, due to the influences of BCG vaccination, over diagnosis could not be avoided in diagnosis using the tuberculin reaction. Shimouchi et al. evaluated the results of tuberculosis contact group investigation in Osaka City, and reported that the accuracy of diagnosis was a problem since the diagnosis of tubercle infection was based only on the tuberculin reaction.
However, due to the introduction of QuantiFERON-TB Gold (QFT-2G) or QuantiFERON-TB Gold In- Tube (QFT-3G), the accuracy of the diagnosis of tubercle infection has markedly increased. Mori et al.reported that the sensitivity and specificity of QFT-2G were 89 and 98%, respectively, although the subjects consisted of patients with active tuberculosis because of the absence of a gold standard for the diagnosis of infection. Similarly, although the subjects consisted of patients with active tuberculosis, Harada et al.reported a sensitivity and specificity of QFT-3G of 92.6 and 98.8%, respectively.