Tuberculosis (TB)

What is latent TB infection?

In most people who breathe in TB bacteria and become infected, the body is able to fight the bacteria to stop them from growing. The bacteria become inactive, but they remain alive in the body and can become active later. This is called latent TB infection. People with latent TB infection

  • have no symptoms

  • don't feel sick

  • can't spread TB to others

  • usually have a positive skin test reaction

  • can develop active TB disease if they do not receive treatment for latent TB infection.

Many people who have latent TB infection never develop active TB disease. In these people, the TB bacteria remain inactive for a lifetime without causing disease. But in other people, especially people who have weak immune systems, the bacteria become active and cause TB disease.

What is active TB disease?

TB bacteria become active if the immune system can't stop them from growing. The active bacteria begin to multiply in the body and cause active TB disease. The bacteria attack the body and destroy tissue. If this occurs in the lungs, the bacteria can actually create a hole in the lung. Some people develop active TB disease soon after becoming infected, before their immune system can fight the TB bacteria. Other people may get sick later, when their immune system becomes weak for another reason.

Babies and young children often have weak immune systems. People infected with HIV, the virus that causes AIDS, have very weak immune systems. Other people can have weak immune systems, too, especially people with any of these conditions:

  • substance abuse

  • diabetes mellitus

  • silicosis

  • cancer of the head or neck

  • leukemia or Hodgkin's disease

  • severe kidney disease

  • low body weight

  • certain medical treatments (such as corticosteroid treatment or organ transplants)

  • specialized treatment for rheumatoid arthritis or Crohn’s disease.

Symptoms of TB depend on where in the body the TB bacteria are growing. TB bacteria usually grow in the lungs. TB in the lungs may cause symptoms such as:

  • a bad cough that lasts 3 weeks or longer

  • pain in the chest

  • coughing up blood or sputum (phlegm from deep inside the lungs).

Other symptoms of active TB disease are:

  • weakness or fatigue

  • weight loss

  • no appetite

  • chills

  • fever

  • sweating at night .

The Difference Between Latent TB Infection and Active TB Disease

A person with latent TB infection:

  • Has no symptoms

  • Does not feel sick

  • Cannot spread TB to others

  • Usually has a positive skin test or QuantiFERON-TB® Gold test

  • Has a normal chest x-ray and sputum test

A person with active TB disease:

  • Has symptoms that may include:

    • a bad cough that lasts 3 weeks or longer
    • pain in the chest
    • coughing up blood or sputum
    • weakness or fatigue
    • weight loss
    • no appetite
    • chills
    • fever
    • sweating at night
  • May spread TB to others

  • Usually has a positive skin test or QuantiFERON-TB® Gold test

  • May have an abnormal chest x-ray, or positive sputum smear or culture

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Important disclaimer: The information on pkids.org is for educational purposes only and should not be considered to be medical advice. It is not meant to replace the advice of the physician who cares for your child. All medical advice and information should be considered to be incomplete without a physical exam, which is not possible without a visit to your doctor.


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