TB infection usually occurs initially in the upper part of the lungs. The body's immune system, however, can stop the bacteria from continuing to reproduce. Thus, the immune system can make the lung infection inactive. On the other hand, if the body's immune system cannot contain the TB bacteria, the bacteria will reproduce nin the lungs and spread elsewhere in the body.

It may take many months from the time the infection initially gets into the lungs until symptoms develop. The usual symptoms that occur with an active TB infection are a generalized tiredness or weakness, weight loss, fever, and night sweats. If the infection in the lung worsens, then further symptoms can include coughing, chest pain, coughing up of sputum and/or blood, and shortness of breath. If the infection spreads beyond the lungs, the symptoms will depend upon the organs involved.

Tuberculosis is a very serious disease that affects lungs in the first place. It is contagious, which means that it can be spread from one person to another, and for something like that to happen, even a tiny little droplet released into the air is enough. A number of infected people has been constantly increasing over the past three decades, and even though the treatment is possible and constantly advancing, a significant number of cases ends fatally every year, particularly in Africa and Asia.