The pathways of invasion of the tuberculosis bacilli into the host are multiple: 1. Inhalation of microdroplet nuclei containing human or bovine bacilli, which can form primary foci and corresponding regional lymph node tuberculosis in the lungs of hosts not previously infected with tuberculosis, constituting the primary syndrome; 2. Drinking unboiled milk from tuberculous cows infected with bovine bacilli; 3. TB lesions in the skin and mucous membranes and lymphatic TB in the corresponding areas; 4. I. Airborne transmission: TB is mainly transmitted through the air. People are infected by xiru infectious TB patients who cough, talk, sing, and sneeze with bacterium-containing droplets. In places with poor air circulation (such as Internet cafes and crowded dormitories for students), the chance of infection is higher because of the high bacterial content. Research found that: 1 particle of 5 microns in diameter contains 1-10 tuberculosis bacilli, infection will occur when inhaling between 5-200 Second, the factors affecting the infection: 1, the amount of bacilli excretors The most important is the scope of the lung lesions and the nature of the lesions of the excretors. Wide range of lesions, the chance of transmission, cavity patients have the strongest potential for infection. Sputum smear negative person does not necessarily not excretor bacteria (this is related to sputum examination specimen and test sensitivity) 2, chemotherapy regimen Inappropriate regimen can lead to the development of drug-resistant bacteria 3, exposure time and frequency Too long exposure, frequency of exposure and proximity in the infected environment is positively correlated with the risk of infection. If the host has been vaccinated with BCG or has had previous non-tuberculous mycobacterial infections, tuberculosis should not occur.