There are three types of tuberculosis: first, active tuberculosis; second, inactive tuberculosis; and third, people with latent Mycobacterium tuberculosis infection. Of these, only active tuberculosis is infectious, while the other two, inactive tuberculosis and Mycobacterium tuberculosis latent infection, are not infectious. Because both of these do not carry bacteria in their sputum and only active TB carries bacteria in their sputum, only active TB is infectious. Because tuberculosis is transmitted by spreading microdroplets of Mycobacterium tuberculosis into the air, sputum with bacteria can spread microdroplets of Mycobacterium tuberculosis into the air by coughing, sneezing, laughing, or talking loudly, and can be inhaled by others to cause others to become infected. Therefore, patients with active tuberculosis should take anti-tuberculosis drugs as soon as possible, and the infectiousness will gradually disappear in 2-3 weeks after taking anti-tuberculosis drugs.