Definition

Tuberculosis (TB) is a contagious infectious disease which can have either active or inactive forms. Although it can affect many organ systems, it primarily affects the lungs in most patients. In many patients, TB causes no symptoms, while in others it is fatal.

Causes

TB is a bacterial infection caused by Mycobacterium tuberculosis. When someone 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

Spores in lungs

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Risk Factors

A risk factor is something that increases your chance of getting a disease or condition.

People who have weakened immune systems or chronic diseases are at highest risk for developing active TB. These include:

  • HIV infection
  • Malnutrition
  • IV drug use
  • Alcoholism
  • Leukemia, lymphoma, and other cancers
  • Poorly controlled diabetes mellitus
  • Severe kidney disease
  • 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

Symptoms

Most people infected with TB have no symptoms. The bacteria lie dormant in the lungs and may remain there permanently without causing illness. During the dormant stage, the infected person cannot spread TB to others. Once the bacteria become active, the infection can spread.

Symptoms of active TB include:

  • 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

Diagnosis

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 to 3 days, a raised, firm welt appears at the injection site that is 10 millimeters (mm) or greater in diameter. (Under some circumstances the cut-off may be 5 mm or 15 mm.) This means you were exposed to TB at some point, even if you never became ill. Your doctor will then order a chest x-ray to look for signs of lung infection. People at high risk of TB should be screened regularly with skin testing.

In addition, a new blood test has also become available to help screen for TB.

If you have symptoms of active TB, your doctor may order:

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

Treatment

Medication can help prevent TB from becoming active and it can help cure active TB. It is extremely important that you take ALL medication exactly as prescribed. You must 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 extremely difficult to cure.

For Inactive TB

People who have a positive tuberculin skin test but no signs of active TB may need to take medication to help prevent active TB. The drug isoniazid (INH) is usually prescribed for at least six months, many times longer.

For Active TB

Your doctor may prescribe a combination of the following drugs:

  • Isoniazid (INH)
  • 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 for the full time that your doctor recommends (in many cases this can be six months, in some cases this may be up to two years).

Prevention

If you have a positive skin test, you may be able to prevent active TB from developing by taking medication (see above). There is a vaccine for TB called Bacillus Calmette-Guerin (BCG) vaccine, which is not routinely used in the United States because of the unreliable protection it provides.

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