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TB: About Active TB Disease and Latent TB Infection (LTBI)

Chest X-ray showing Tuberculosis (Tb)

Active tuberculosis (TB) disease

Tuberculosis, or TB, is a disease caused by bacteria called Mycobacterium tuberculosis. The bacteria can attack any part of the body, but usually attack the lungs. People who are infected with TB do not always feel sick.

Latent tuberculosis infection (LTBI)

People with latent TB do not have any symptoms and cannot spread TB. If they do not get treatment, however, they may develop active TB disease in the future, spread the disease to others, and feel quite ill.

People with active TB disease can be treated and cured if they get medical help. Even better, people who have latent TB infection, but are not yet sick, can take medicine so they will never develop active TB disease.

Frequently asked questions

TB is spread from one person to another.

The bacteria that cause TB are spread through the air when a person with active TB disease of the lungs or throat:

  • Coughs
  • Speaks
  • Laughs
  • Sings

When this happens, people nearby may breathe in these bacteria and become infected with TB. Only those with active TB disease can spread the bacteria to others. A person who has been infected with the bacteria may develop active TB disease weeks or years after infection depending on their immune system. Many people with latent TB infection never develop active TB disease.

TB is not spread by

  • Touching an object that someone infected with TB has touched
  • Shaking someone's hand
  • Sharing food or drink
  • Sharing toothbrushes
  • Kissing

Signs and symptoms of active TB disease depend on where in the body the bacteria are growing. TB bacteria most often grow in the lungs.

Signs and symptoms of active TB disease

Signs and symptoms in the lungs include:

  • A bad cough, lasting three weeks or longer
  • Pain in the chest
  • Coughing up blood or phlegm from deep inside the lungs (sputum)
  • Weakness or fatigue
  • Weight loss
  • No appetite
  • Fever, chills, sweating at night

People with latent TB infection will not feel sick and will not have these signs and symptoms.

If you believe you may have been exposed to someone with active TB disease, contact your doctor or local health department. They will help you get a TB skin test or a TB blood test. A person who has been exposed to TB bacteria may become infected. A person with latent TB infection (LTBI) cannot spread the bacteria to others right away. Only those who develop active TB disease can spread the bacteria to others.

Bovine TB is a chronic disease of animals caused by bacteria Mycobacterium bovis, which is closely related to the bacteria that causes human TB. People may get bovine TBs after close contact with infected animals or after eating unpasteurized dairy products from infected animals. See the Department of Agriculture, Trade, and Consumer Protection (DATCP) for more information about bovine TB in Wisconsin. View recommendations on safe handling of animal carcasses from herds with infected animals. (PDF)


Department of Health Services resources

CDC (Centers for Disease Control and Prevention) resources

Other resources

Questions about TB? Contact Us!
Phone: 608-261-6319 ǀ Fax: 608-266-0049

Last revised December 22, 2023