TB is the common name for tuberculosis, a bacterial infection, according to WebMD. The infection usually develops in the lungs; however, it can travel through blood and the lymph nodes to other parts of the body. Most people carry the TB bacterium without developing any symptoms.
WebMD further mentions that tuberculosis usually develops in people with weakened immune systems, such as the elderly or HIV-positive patients. TB causes the death of infected tissue, and, if left untreated, it can be fatal. Symptoms include fatigue, difficulty breathing, chest pain, weight loss, mild fever, sweating during the night and coughing, which can also bring up bloody mucus.