Tuberculosis Tuberculosis (TB) is a slow-growing infection, usually present in the lungs, caused by breathing in air contaminated by mycobacterium tuberculosis (Mtb). It is an airborne illness, spread through tiny droplets when a person with TB coughs, sneezes, laughs, speaks, etc. For someone to develop active TB, the bacteria Mtb must enter the body and cause an infection that the immune system cannot contain. Some people are infected with TB, but the bacteria remain dormant for years and do not cause active disease. Although these latent carriers do not spread TB to others, they can eventually develop TB signs and symptoms, so medical treatment is always advised.

Early symptoms of TB include weight loss, fever, night sweats, and loss of appetite – vague signs that may go unnoticed. More debilitating symptoms include cough, chest pain, and bloody sputum.

To identify people who have been exposed to Mtb, providers inject a substance called tuberculin under the skin of the arm. If a red welt or obvious reaction forms, an infection has likely occurred. Many people heal from their initial exposure to TB, and a positive skin test or evidence of scarring on a chest x-ray may be the only clue a person has ever been exposed. However, aging, infection, poor nutrition, or conditions that compromise the immune system may coax TB into an active infection.

TB can usually be cured with appropriate antibiotics, but treatment typically includes a course of several drugs taken for several months, so complying with doctors’ orders is critical to conquering the infection. Drug-resistant TB is on the rise, and requires special TB drugs taken over a long period of time, which may lead to unwelcome side effects.

About 11,000 people are diagnosed with TB in the United States, although more than half of them were born in other countries, where they were more likely to be exposed, according to the Centers for Disease Control and Prevention.

Read more about TB from its discovery in ancient history to the latest treatment approaches from the National Institute of Allergy and Infectious Diseases .