It is mainly transmitted by respiratory tract. It is mainly spread by droplets containing large amounts of Mycobacterium tuberculosis that are emitted by coughing, sneezing and talking loudly by TB patients. The infectiousness of tuberculosis is increased in the following cases: 1) patients with severe infectious tuberculosis; 2) patients with high bacillus excretion; 3) patients with frequent coughing; 4) close contact with patients; 5) poor ventilation of the room where patients live; 6) weak resistance of the contact person.