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Tuberculosis (TB) is a contagious infectious disease. It can have either active or inactive forms. Although it can affect many organ systems, it mostly affects the lungs.


TB is caused by the bacterium Mycobacterium tuberculosis. When a person with active TB of the lungs coughs or sneezes, people nearby may inhale the bacteria. TB is easily spread in crowded conditions and among people who are ill or have weakened immune systems.

Pathway to the Lungs

Air pathway breathing

Mycobacterium tuberculosis is inhaled through the mouth and nose and travels down into the lungs causing TB.

© 2008 Nucleus Medical Art, Inc.

Risk Factors

These factors increase your chance of developing TB. Tell your doctor if you have any of these risk factors:

  • Weakened immune system or chronic diseases (highest risk)
  • HIV infection
  • Malnutrition
  • Intravenous drug use
  • Alcoholism
  • Leukemia, lymphoma, and other cancers
  • Poorly controlled diabetes mellitus
  • Severe kidney disease
  • Corticosteroids
  • Some medications used for treating rheumatoid arthritis and other diseases including etanercept, infliximab, and adalimumab
  • Suppressed immune system caused by medications, such as drugs to prevent rejection of a transplanted organ
  • Other risks factors include:
    • Silicosis (an occupational lung disease)
    • Living in crowded, indoor conditions, such as:
      • Homeless shelters
      • Dormitories
      • Military barracks
    • Age (infants, young children, and elderly people)


TB causes no symptoms in most patients, while in others it is fatal. The bacteria lie dormant in the lungs. Bacteria may remain there permanently without causing illness. During this time, the infected person cannot spread TB to others. The infection spreads once the bacteria are active.

If you have any of these symptoms do not assume it is due to TB. These symptoms may be caused by other conditions. Tell your doctor if you have any of these:

  • Severe cough that lasts more than two weeks
  • Coughing up blood and sputum (mucus from deep in the lungs)
  • Pain in the chest
  • Weakness or fatigue
  • Unexplained weight loss
  • Chills
  • Fever
  • Night sweats
  • Loss of appetite


A skin test is used to screen for TB. A small amount of tuberculin test fluid is injected into the skin of the lower part of your arm. The test is positive if, after 2-3 days, a raised, firm welt appears at the injection site. The welt is 10 millimeters (mm) or greater in diameter (5 mm or 15 mm under some situations).

A positive test means you were exposed to TB, even if you never became ill. People at high risk for TB should have a skin test regularly. Also, a new blood test is available to screen for TB. Talk to your doctor to learn more.

If you have symptoms or signs of active TB, your doctor may order the following:

  • Chest x-ray
  • Samples of your sputum to be tested for the bacterium


Medication can prevent TB from becoming active. It can also help cure active TB. It is very important that you take all medication exactly as prescribed. Take all the medication, even if the symptoms go away. If you do not finish your medication, you may develop drug-resistant TB, which is very difficult to cure.

For Inactive TB

People who have a positive skin test but no signs of active TB may need to take medication to prevent active TB. The drug isoniazid is usually given for six months or longer.

For Active TB

Your doctor may give you a combination of the following drugs:

  • Isoniazid
  • Rifampin
  • Pyrazinamide
  • Ethambutol
  • Streptomycin
  • Under special circumstances, other drugs may be used

If you have active TB, you will need to be isolated from friends, family, and coworkers until your doctor says you are no longer contagious (usually after the first several weeks of medication use). This will help prevent the spread of TB. You can resume your normal activities after you get your doctor’s approval. You will need to keep taking the drugs until your doctor tells you to stop. This can be six months, but in some cases this may be up to two years.


If you have a positive skin test, you might prevent active TB from developing by taking medication. There is a vaccine, but it is not routinely used in the US because of the unreliable protection it provides. Talk to your doctor to learn more.

If you have active TB, you can prevent its spread by:

  • Avoiding contact with people until your doctor says you are no longer contagious
  • Taking all medication as prescribed for the full course of treatment


American Lung Association

National Institute of Allergy and Infectious Disease


The Canadian Lung Association

Health Canada


Division of Tuberculosis Elimination. Centers for Disease Control website. Available at: Accessed July 9, 2008.

Harrison TR, Braunwald E, Fauci AS, Kasper DL, Hauser SL, Longo DL, et al. Harrison's Guide to Internal Medicine. 16th ed. New York, NY: McGraw Hill; 2001.

Last reviewed March 2008 by David Horn, MD, FACP

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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