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Middlesex-London Health Unit

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Inactive Tuberculosis (TB)

Inactive TB

Active TB

TB germs in your body are not growing TB germs in your body are growing
Positive TB skin test Positive TB skin test
No TB symptoms May be sick with TB symptoms
Chest X-ray shows no active TB  Abnormal chest X-ray or CT scan
No TB germs in sputum test Sputum test shows TB germs
Not contagious.  People cannot catch TB from you Contagious if TB germs are found in lung or airway.
Medicationcan be taken to prevent Inactive TB from becoming Active TB Many medicationsmust be taken to stop symptoms and the spread of TB

Table of Contents

What is inactive TB?

Breathing in TB germs does not usually make a person ill because the body’s immune system is able to control the infection. The TB germs remain in the person’s body, but are inactive and not growing. Inactive TB is also known as TB infection or latent TB. People with inactive TB are not sick and cannot spread TB to others.

1 out of 3 people in the world has inactive TB.

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Is inactive TB contagious?

Inactive TB is not contagious and cannot be spread to others. TB can only be spread when inactive TB becomes active. Inactive TB can turn into active TB when the person’s immune system can no longer control the TB germ. The following people with inactive TB are most likely to get active TB:

  • very young children
  • elderly people
  • People who have a lot of stress
  • People who do not have a good immune system
  • People with certain medical conditions

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How is inactive TB treated?

Inactive TB treatment is not mandatory; however it can reduce the risk of developing active TB to less than 1% in some cases. Certain long term medical conditions increase your chances of developing active TB disease, making prevention even more important. People who develop active disease have no choice but to take many medications for at least 6 months. If you have inactive TB, your doctor may recommend you take one TB medicine for 4 to 12 months to reduce the chance of your inactive TB turning into active TB. This is sometimes called latent TB treatment or TB prophylaxis.

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How do I find out if I have inactive TB?

A TB skin test (TST) is the most common way to diagnosis inactive TB. A small amount of liquid, called tuberculin, is injected under the skin on your forearm. Two to three days later, you must return to have your arm checked. If there is a reaction (induration), it will be measured to see if it is considered positive for TB. 

A positive reaction usually means that you have been infected with the TB bacteria at some time in your life.  A doctor will do further tests such as a chest x-ray and sputum samples, to make sure you do not have active TB and to discuss treatment options.  Both inactive and active TB can cause a positive reaction.

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Can inactive TB turn into active TB? 

Most people with inactive TB never develop active TB. For healthy people with inactive TB, the risk of developing active TB is about 5% within the first 2 years of becoming infected.  After this, there is a 5% chance of developing active TB in the rest of a person’s lifetime. If you have inactive TB, it is important that you tell a doctor if you think you are having symptoms of active TB. A doctor can do tests such as a chest x-ray and sputum samples, to make sure you do not have active TB. 

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Date of creation: February 26, 2013
Last modified on: October 31, 2022


1Public Health Agency of Canada and the Canadian Lung Association/Canadian Thoracic Society. Canadian Tuberculosis Standards, 8th edition 2022