TB disease is contagious when people with TB get sputum or saliva from their mouths that contain M. tuberculosis into the air - for example when coughing, sneezing, talking, singing, or even laughing - and then being inhaled by others.
Germs that come out of their cough with tuberculosis can survive in humid air that is not exposed to sunlight for hours. As a result, everyone who is close to and interacting with TB sufferers has the potential to inhale it and eventually get infected.