Pulmonary tuberculosis (TB) is caused by the bacterium Mycobacterium tuberculosis (M. tuberculosis). TB is contagious. This means the bacteria is easily spread from an infected person to someone else. You can get TB by breathing in air droplets from a cough or sneeze of an infected person. The resulting lung infection is called primary TB.

Most people recover from primary TB infection without further evidence of the disease. The infection may stay inactive (dormant) for years. In some people, it becomes active again (reactivates).

Most people who develop symptoms of a TB infection first became infected in the past. In some cases, the disease becomes active within weeks after the primary infection.

Source:https://medlineplus.gov/ency/article/000077.htm