The purpose of this study is to add new indications for Vaccae, mainly to prevent Tuberculosis for high risk groups of Tuberculosis Infection . In December 2012, China Food and Drug Administration approved of the plan "Phase III Clinical Study of Efficacy and Safety of Mycobacterium Vaccae to Prevent Tuberculosis in high risk groups of Tuberculosis Infection". In the test, 10,000 cases whose skin tests of PPD are strongly positive are enrolled. Using random, double-blind, and placebo-controlled methods, the study is carried out to evaluate the efficacy and safety of Vaccae in preventing Tuberculosis. Meanwhile, in this test, TB incidence and degree of pathological changes of experimental group are lower than that of control group, and no drug-related SAEs are reported in treatment groups.