A positive sputum culture of Mycobacterium tuberculosis is infectious. This is because Mycobacterium tuberculosis can invade the human body and cause it to have tuberculosis. By coughing, sneezing, laughing, talking and singing, a patient with tuberculosis can spread microscopic droplets of Mycobacterium tuberculosis into the air, where they can survive for several hours and be infected with tuberculosis when inhaled by others. In addition, a large number of Mycobacterium tuberculosis bacteria are found in the sputum spit out by patients with tuberculosis, and they can survive for 6-8 months in dry sputum. Patients with tuberculosis should also do a good job of coughing and not spitting to avoid transmitting Mycobacterium tuberculosis to others.