I. What is the source of infection of tuberculosis? The main source of TB infection is secondary TB patients with Tu-Yang or Pei-Yang, and untreated patients with bacillary TB are the most infectious. How is tuberculosis transmitted? 1. Air-respiratory transmission is the most important route of transmission of TB. If a patient speaks loudly, coughs or sneezes, many droplets with tuberculosis bacilli will be released, and if a susceptible person inhales such droplets, he or she can be infected. If a tuberculosis patient spits on the ground, the sputum will dry and the tuberculosis bacilli will be mixed with dust and fly in the air, which can be inhaled by healthy people. Bacterial droplets must be small (1-10μm) to float in the air without falling; it is possible to enter the deep part of human respiratory tract. Because the diameter of the terminal fine bronchus is very thin, about 0.2mm. 2, through the digestive tract infection TB patients with tableware, leftover food may be contaminated with tuberculosis bacilli. It is also possible to get infected with Mycobacterium tuberculosis by drinking unsterilized milk or dairy products, or by not washing hands carefully after touching the spittoon used by the patient. 3.Vertical transmission of tuberculosis from a mother with tuberculosis during pregnancy, the tuberculosis bacilli in her body can enter the fetus through the blood of the umbilical cord. In addition to these modes of transmission, Mycobacterium tuberculosis can also be directly infected by wounds on the skin or mucous membranes. Since Mycobacterium tuberculosis cannot penetrate the skin, this mode of infection is relatively rare, but it should be noted. Are all tuberculosis diseases infectious? Not all types of tuberculosis are infectious, and not all tuberculosis patients are infectious at any time during their illness. Relatively speaking, some types of tuberculosis are often infectious, while extrapulmonary tuberculosis (such as bone tuberculosis and meningeal tuberculosis) is not infectious. Because the lungs are connected to the outside world, when TB disease develops, worsens or forms a cavity, the TB bacteria in the lesion multiply and are expelled through the bronchi, causing transmission of the TB bacteria. Only such a TB patient is infectious. However, when the patient is cured, he or she no longer becomes infectious. The easiest and most reliable way to measure and determine whether a patient is infectious is to smear the patient’s sputum and conduct a microscopic examination. If the sputum smear is found to be positive for antacid bacilli, the patient is considered infectious, or “infectious”. The most infectious time for infectious tuberculosis is before detection and treatment. Therefore, early detection and proper and timely treatment of the source of infection should be emphasized.