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Am Fam Physician. 2014;89(11):online

See related article on latent tuberculosis.

What is latent tuberculosis?

Tuberculosis (too-BERK-yoo-LOW-sis), also called TB for short, is a lung disease caused by a germ. Latent TB means a person is infected with the germ, but they are not sick. Some people with latent TB can get sick later in life. This is called active TB.

How is it spread?

People who have active TB spread the germ when they cough or sneeze. Other people get infected when they breathe it in. One of these things can happen when a person breathes in the TB germ:

  • Their immune system completely destroys the germ.

  • Their immune system does not destroy the germ, but they do not get sick. These people will have latent TB.

  • They get sick and have active TB.

How do I know if I have latent TB?

There are two types of tests for TB. The most common is the TB skin test. Your doctor uses a needle to inject fluid just under the skin of your forearm. Two or three days later you go back to have your arm checked. If you have a raised red area or bump, that means you might have TB. Your doctor will do more tests to make sure. The other type of TB test uses a sample of your blood. It is more expensive, but you do not need to go back to the doctor to get the results. These tests may be more accurate than skin tests in some people, especially those who were not born in the United States and people who got the TB shot when they were younger.

Should I get tested?

TB tests are done on people who are most likely to be exposed to the TB germ. This includes people who:

  • Have had contact with someone who has active TB

  • Work in the health care field

  • Take certain medicines that make it hard for their immune system to fight off infections

  • Have conditions that weaken their immune system, such as human immunodeficiency virus (HIV)

What are the symptoms?

People with latent TB do not have symptoms. Your doctor will check to see if you have any symptoms of active TB. These include coughing for more than three weeks, fever, coughing up blood, weight loss, and sweating at night.

How is latent TB treated?

People with latent TB have to take medicines so that they won't get active TB later in life. It is important to take your medicine exactly the way your doctor tells you to, and to visit your doctor regularly to check for side effects. The medicines used to treat TB can hurt your liver, so you need to avoid things that make your liver work harder, such as alcohol, acetaminophen (one brand: Tylenol), and certain other medicines. Talk to your doctor about all medicines before you take them.

Where can I get more information?

Your doctor

American Lung Association

Centers for Disease Control and Prevention

National Library of Medicine

World Health Organization

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