If only "prospective contact tracking" aimed at containment is performed, it is inevitable to overlook the spread of infection below the surface. It was fortunate that the public health centers in Japan have been conducting investigations of the source of infection along with the tracing close contacts with infected people from the beginning. The Expert Meeting said that they will continue to scrutinize why they were able to investigate the source of infection in Japan first, and then speculated that it might be due to the constant effort to find the source of tuberculosis.[1][2]