Tuberculosis can be transmitted through the respiratory tract, the digestive tract, the skin, and through vertical transmission from mother to child. When a patient coughs, sneezes or speaks loudly, the exhaled gas spreads droplets of different sizes containing Mycobacterium tuberculosis into the air, and the moisture of the small droplets evaporates quickly to form a droplet nucleus with Mycobacterium tuberculosis as the core, which is suspended in the air, while the large droplets fall on the ground and dry with Mycobacterium tuberculosis attached to the dust and float in the air. When a healthy person inhales droplets or dust containing Mycobacterium tuberculosis, he or she can be infected. In addition, tuberculosis can be transmitted through the digestive tract, which is not the main route of transmission. Infection can also occur when food contaminated with Mycobacterium tuberculosis is eaten and infection develops through lymphatic follicles in the intestinal wall, or when milk contaminated with unsterilized or incompletely disinfected Mycobacterium bovis is consumed. Rarely, infection can occur through contact with skin wounds, or through vertical transmission from mother to child.