The main source of infection for tuberculosis is a sputum smear-positive patient with bacillary TB. With the source of infection, TB bacilli must be transmitted to others through certain means. Tuberculosis patients spread micro-foam containing TB bacteria into the air mainly through coughing or sneezing, and healthy people can be infected with TB bacteria by inhaling the micro-foam containing TB bacteria. The degree of TB transmission is mainly influenced by the amount of bacilli excreted by the TB patient, the symptoms of coughing, and the closeness of contact. Children are more likely to be infected with TB if their parents or grandparents have TB in the family. The occurrence of tuberculosis in healthy people is not necessarily affected by the infection of tuberculosis bacilli, but by two factors, namely, the virulence of the infected bacilli and the level of body resistance, and the strong virulence of tuberculosis bacilli and the low body resistance make it easy to develop tuberculosis. The first measure to prevent or reduce the occurrence of tuberculosis is not to be infected by the tuberculosis bacillus. Therefore, it is important to postpone the age of tuberculosis infection. How do you know when you have been infected with the tubercle bacillus? The main method is to perform a skin test with a pure protein derivative of tuberculin (ppd), and the skin reaction is used to determine this.