What is tuberculosis?

Tuberculosis (TB) is an infectious disease that mostly affects the lungs, but can also affect body parts like the spine, brain or kidneys. Everyone who is infected does not get sick. If you do get sick, you need treatment.

How common is tuberculosis?

About 33 percent of the world's population, nearly 2.5 billion people, is infected with TB. Although TB was once the leading cause of death in the United States, the number of cases fell rapidly in the 1940s and 1950s after treatments were found.

According to statistics from the Centers for Disease Control (CDC), there were 9,272 tuberculosis cases reported in the United States in 2016. For TB, there is a national incidence rate of 2.9 cases per 100,000 people.

What causes tuberculosis?

TB is caused by the bacterium Mycobacterium tuberculosis. The germs are spread through the air and usually infect the lungs, but can also infect other parts of the body. Although TB is infectious, it does not spread easily. You usually have to spend a lot of time in contact with someone who is contagious in order to catch it.

How is tuberculosis spread?

TB can be spread when a person with active TB disease releases germs into the air through coughing, sneezing, talking, singing, or even laughing. Only people with an active pulmonary infection are contagious. Most people who breathe in TB bacteria are able to fight the bacteria and stop it from growing. The bacterium becomes inactive in these individuals, and is referred to as a latent TB infection. Approximately 10 percent of the US population has latent infection.

Although the bacteria are inactive, they still remain alive in the body, and can become active later. Some people can have a latent TB infection for a lifetime, without it ever becoming active and developing into TB disease. However, TB can become active if the immune system becomes weakened and cannot stop the bacteria from growing. This is when the latent TB infection becomes TB disease.

What are the symptoms of tuberculosis?

People with inactive TB do not exhibit symptoms. However, they may have a positive skin reaction test.

Those with TB disease can show any of the following symptoms:

  • Bad cough (lasting longer than 2 weeks)
  • Pain in the chest
  • Coughing up blood or sputum (mucus)
  • Fatigue or weakness
  • Loss of appetite
  • Weight loss
  • Chills
  • Fever
  • Night sweats

Last reviewed by a Cleveland Clinic medical professional on 11/09/2018.


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