Latent tuberculosis infection

The germs that cause tuberculosis (TB) disease can make you very sick. But if your body can suppress the germs, you will stay well. This is called latent tuberculosis infection (LTBI).


TB disease

TB is a condition that usually affects the lungs. TB can also affect other parts of the body such as the glands, bones or brain.

TB is caused by a bacterium (germ). When someone with TB in their lungs coughs or sneezes, the germs can pass into the air. These germs may be breathed in by other people. The germs can then damage the lungs or other parts of the body and make the person very sick. This is called TB disease.

TB disease can be cured by medication.

You can find out more at Tuberculosis disease.

Latent TB infection

People with LTBI are well. They cannot pass on TB germs to others.

Latent TB infection (LTBI) is different from TB disease.

In people with LTBI, the body’s immune system is able to suppress the TB germs, causing the germs become inactive (latent). As long as the germs are inactive, the person stays perfectly well.

If I am not sick, why do I need treatment?

Sometimes, after months or years, the germs can become active. The active germs can cause TB disease in the lungs or other parts of the body. If you get TB disease you can become very sick, and you can pass on TB germs to your family and others.

Babies and children with LTBI are at greatest risk of developing TB disease.

If you have LTBI, the doctor may recommend treatment to kill the inactive germs.

Even though you feel well and healthy, the doctor may still advise treatment to make sure you do not develop TB disease.

Your doctor will discuss with you the sort of treatment you need.

If you have latent TB infection, remember…

  • you do not have TB disease
  • you cannot pass the germs on to someone else
  • you need to continue treatment even though you feel well.

If you want more information, speak with your doctor or nurse.


There are no signs of illness. A skin test can tell if you have LTBI. People with LTBI are not sick.


The type of treatment for LTBI usually depends on a person's age and other health problems.

Children are examined by a children’s doctor (paediatrician). The paediatrician will assess the best treatment for the child.

Adults will be seen by a doctor who specialises in the treatment of LTBI. The doctor will assess what treatment is best for you.

The doctor may offer you medicine. You will need to take the medicine for several months. The duration of treatment depends on the type of medicine used. During this time a doctor or nurse will see you every month. Even though you feel perfectly well, you need to take your medicine every day – or exactly as your doctor advises.

If you don't take your medicine regularly, it may not kill the inactive germs.

If the doctor does not offer you medicine, the doctor or nurse will tell you about the early signs of TB disease. If you think you have any of these signs in the future, see your doctor or nurse without delay.

Medicines used for latent TB

Isoniazid or INH is the usual medicine given for LTBI, although other medicines may be offered. The medicine kills the inactive TB germs.

You need to take INH every day for 6 to 9 months. Take the medicine when your stomach is empty, for example:

  • 1 hour before breakfast each morning


  • 2 hours after a meal at night.

Your doctor may also give you pyridoxine (a vitamin). This medicine helps to prevent side effects from INH in adults.

Talk with your doctor or nurse if you are worried about LTBI, your treatment or side effects.

Side effects of INH

INH can sometimes have side effects in adults. Side effects in children are very rare.

Side effects may be:

  • nausea (feeling sick), vomiting, a painful stomach
  • skin rash and/or itchiness of the skin
  • numbness and tingling in the hands and feet
  • hepatitis (inflammation of the liver). Signs of hepatitis are yellow skin, yellow in the white part of the eyes and dark urine.

Your doctor or nurse will test your blood regularly to check that your liver is healthy.

If you think you have any side effects, stop taking the medicine and phone your doctor or nurse right away.

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