How is tuberculosis spread? 1. Respiratory transmission Tuberculosis bacteria are spread from one person to another by airborne transmission. In the lung lesions or cavities of TB patients, a large number of TB bacteria are present. These TB bacilli are discharged with the destroyed lung tissue and sputum through the fine bronchi, bronchioles, and large trachea to form sputum containing a large number of TB bacilli, which is sprayed out of the body through the nose and mouth by coughing, sneezing, talking loudly or singing, etc., forming an aerosol or called droplets in the air, with the larger droplets quickly falling to the ground and the smaller droplets quickly evaporating into ‘ microdroplet nuclei’ containing TB bacilli and remain suspended in the air for a long time. If the air is not circulated and the microdroplet nuclei containing the bacilli are inhaled into the alveoli by a healthy person nearby, they may cause infection and develop into tuberculosis, which then spreads to all organs of the body through the lymphatic and vascular systems. Thus, the degree of contagiousness is related to the severity of the disease of the infected patient, the amount of bacilli excreted, the frequency of coughing, the ventilation of the house where the patient lives, and the closeness and resistance of the contact person. The above is called ‘cough transmission’, which has been scientifically tested and is the most important mode of transmission. There is also the possibility of ‘dust transmission’ through spitting, but this is a secondary mode of transmission. 2. Gastrointestinal transmission Infection from eating food, milk, etc. contaminated with TB bacilli. It should be noted that TB is not transmitted in the following cases 1. shaking someone’s hand, i.e. shaking hands 2. sharing food or drinks 3. sheets or toilet seats that are touched 4. sharing toothbrushes 5. kissing Transmission of tuberculosis bacteria