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Public Health - Seattle & King County

Tuberculosis (TB) facts

What is it?

Tuberculosis, also called TB, is an infectious disease caused by a bacterium named Mycobacterium tuberculosis. TB usually involves the lungs (pulmonary TB) but can infect almost any organ in the body. TB is almost always curable with antibiotics that are readily available in countries such as the U.S.


These symptoms usually come on gradually over a period of weeks. The most common symptoms are:

  • cough, (usually for more than 3 weeks)
  • coughing up blood or sputum (phlegm from deep inside the lungs) pain in the chest
  • fatique
  • weight loss
  • fever
  • night sweats

How is it spread?

TB spreads when someone who has pulmonary TB coughs. TB bacteria from that person's lungs are then expelled into the air, and may be inhaled into the lungs of another person. TB is not very infectious; it's much harder to catch than the common cold. Usually a lot of time needs to be spent with a person with pulmonary TB for someone to catch TB. It's not possible to get TB from sharing a glass with a person with TB or touching a doorknob after someone with TB has used it. Also, once a person with TB is on medication he or she quickly becomes non-contagious. People on medication can quickly resume their normal patterns of life without fear of spreading TB to others.


To treat TB several antibiotics need to be taken together over a period of usually 6 months to a year. For this treatment to work it's vital that these medicines be taken regularly and that the treatment be completed. Lengthy treatment is necessary because it is difficult to eradicate TB bacteria from the body.

What is TB infection and how do you treat it?

TB infection means someone has bacteria sleeping in their body. They're not sick or contagious because the bacteria are dormant. TB infection is detected when someone has a positive skin test but a normal chest x-ray and no other sign of tuberculosis disease. To kill these sleeping bacteria and to prevent the development of active disease, persons with TB infection are often advised to take several months of treatment, usually with only one or two medications.

What is the difference between TB infection and TB disease?

People with TB disease are made sick by germs that are active in their body. Often they have several symptoms of TB like persistent cough, fever and weight loss. If the disease is in their lungs they can give the disease to other people. Permanent damage and death can result from this disease. Medications to cure TB are almost always effective.

People who have TB infection have the germ that can cause TB inside their body. However, they are not sick because the germ is inactive inside their body. They can not make other people sick. These people may develop TB in the future. Medication is often given to these people to prevent them from developing TB disease.

What is the TB skin test?

The TB skin test is performed by injecting a small amount of testing liquid into the skin of the forearm. The test needs to be read 48 to 72 hours later by someone trained in reading skin tests. If it's positive then a chest x-ray is done to rule out active disease. If the chest x-ray is normal then the person is likely to have TB infection. Once a skin test is positive it will most likely stay positive and should not be repeated. Unless a person develops symptoms one chest x-ray is all that's needed.

How important is TB today?

Tuberculosis kills more people today than any other infectious disease. About 2 million people a year die from TB worldwide. However, death from TB is rare in the United States. King County reports 120-150 cases of people with active TB per year and of these people the cure rate is almost one hundred percent.

TB facts in other languages:

For King County health care providers: