TB is spread from person to person through the air. When people with lung TB are caught, sneezed or spit, they propel the TB germs into the air. A person needs to inhale only a few of these grams to become infected. Although TB is spread in a similar way to a cold or flu, it is not as contagious. You would have to spend prolonged periods in close contact with an infected person to catch the infection yourself.
However, not everyone infected with TB bacteria becomes sick . People who are infected, but not sick, have what is called latent TB infection . People who have latent TB infection do not feel sick, do not have any symptoms, and cannot spread TB to others. But some people with latent TB infection go on to get TB disease.