First, the air breathing path. Mycobacterium tuberculosis exists in tuberculosis focus of lung and bronchus, or in lung space and secretion of trachea-sputum. When patients talk loudly, cough and sneeze, many tiny droplets are released. Patients can release about 3500 droplets when coughing, and more droplets will be released when sneezing hard. Among them, larger water droplets quickly sink and fall to the ground, while other too small water droplets quickly evaporate in the air. Only those droplets with a diameter of 5 ~ 10 micron can float in the air for a long time. If susceptible people inhale this droplet with mycobacterium tuberculosis, they may be infected. In addition, spitting is also an important route of infection. If tuberculosis patients spit sputum containing mycobacterium tuberculosis on the ground, after the sputum is dried, the mycobacterium tuberculosis in the sputum is mixed with dust and flies in the air, which can be inhaled into the lungs by healthy people to cause infection. Air-respiratory tract infection is the main mode of transmission of tuberculosis.
Second, food infection. Tableware and leftover food used by tuberculosis patients may be contaminated by mycobacterium tuberculosis. For example, healthy people and tuberculosis patients may share tableware or eat leftovers from patients, or eat dishes and soup in bowls, and they may be infected with tuberculosis through diet. Drinking unsterilized milk or dairy products can also infect Mycobacterium bovis. Pour the sputum jar for the sterilized patient and accidentally get the sputum on his hand. If he doesn't wash his hands carefully, eating food with his hands may get infected. In rural areas, some women like to chew food with their mouths and feed it to their babies. If she is a tuberculosis injector, then the baby is likely to be infected. Under normal circumstances, the digestive tract is very resistant to mycobacterium tuberculosis. Once mycobacterium tuberculosis enters the stomach, it is easy to be killed by a large amount of gastric acid, and it is not easy to be infected unless it is swallowed in large quantities. Tuberculosis of digestive tract is mostly caused by drinking raw milk.
Third, vertical transmission. During pregnancy, the mother suffering from tuberculosis can enter the fetus through umbilical cord blood, and the fetus can also be infected by swallowing or inhaling amniotic fluid containing tuberculosis, suffering from "congenital tuberculosis".
Zhou Zhiping pointed out that in addition to the above modes of infection, Mycobacterium tuberculosis can also be directly infected through skin or mucosal wounds, but this mode of infection is relatively rare. In addition, tuberculosis is a disease that both humans and animals suffer from. Many animals, such as pigs, cats, dogs, cows, sheep and monkeys, may suffer from tuberculosis. If humans come into frequent contact with these animals, they can be infected by animals with tuberculosis, and they can also infect their own tuberculosis to raised animals.