TB Basics

Tuberculosis (TB) is caused the bacterium Mycobacterium tuberculosis. It spreads from person to person through the air. The germs enter the air when a person with active TB disease of the lungs or throat coughs, sneezes, or sings. People who breathe in air containing the germs can become infected. A person is more likely to become infected with TB if they have had repeated or prolonged contact with a person with active TB disease.

The bacteria usually attack the lungs, but TB bacteria can attack any part of the body such as the kidneys, spine, lymph nodes, and brain. Not everyone infected with TB bacteria becomes sick. Many people with healthy immune systems can fight off TB germs and not get sick. As a result, two TB-related conditions exist: latent TB infection (LTBI) and active TB disease. If not treated properly, TB disease can be fatal. There are safe and effective treatments to cure both TB infection and TB disease.

Latent TB Infection and TB Disease

Not everyone infected with TB bacteria becomes sick.

People with latent TB infection (LTBI) have live TB bacteria in their body, but their immune system can fight the germs and prevent them from multiplying. The germs are considered inactive. People with LTBI do not feel ill and do not have symptoms of TB disease. They cannot spread the infection to others.

While some people can live their whole life with LTBI, others will develop TB disease if their body is no longer able to prevent the TB germs from multiplying. When this happens, the germs become active and make the person sick. This can occur months or years after infection. Treatment for LTBI is available. People can take medication to prevent them from ever progressing to TB disease. Learn more about latent TB infections.

People with active TB disease have live bacteria in their body that are multiplying and causing disease. People with active TB disease are usually sick and have TB symptoms. The types of symptoms a person has depends on which part of their body is affected. TB disease of the lungs is the most common, but TB can affect any part of the body. People with TB disease in their lungs or throat can spread the infection to others. People with TB disease, regardless of the site of disease, require treatment. Without treatment, the condition can be fatal. With the appropriate treatment, TB disease can be cured. Learn more about active TB disease (CDC).

Comparing LTBI and TB Disease

Latent TB Infection (LTBI)	Active TB Disease
A small amount of TB germs are in the person’s body that are alive but inactive	A large amount of active TB germs are in the person’s body
Does not feel sick, has no symptoms	Usually feels sick and has symptoms that may include: • a bad cough that lasts 3 weeks or longer • pain in the chest • coughing up blood or sputum (mucus from deep in the chest) • weakness or fatigue • no appetite • chills • fever • night sweats • other symptoms depending on the site of disease
Cannot spread the germs to others	Can spread the germs to others
Usually has a positive skin or blood test indicating TB infection	Usually has a positive skin or blood test indicating TB infection
Has a normal chest x-ray	May have an abnormal chest x-ray
Will have negative TB culture results from sputum (mucus from deep in the chest) or other sample from the body	May have positive TB culture result from sputum (mucus from deep in the chest) or other sample from the body
Should consider treatment for LTBI to prevent active TB disease	Needs treatment for active TB disease