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What is latent TB?

I have heard of TB, but what is latent TB?

Tuberculosis (TB) is an illness caused by bacteria. When someone with TB in their lungs coughs or sneezes, they send TB bacteria into the air. If you breathe in these bacteria, one of three things will happen:

  • your body kills off the TB bacteria so they cannot harm you now or in the future
  • the TB bacteria make you ill – this is called ‘active TB’
  • the TB bacteria remain asleep in your body – this is called ‘latent TB’.

About active TB

When people talk about TB, they tend to mean ‘active TB’. If you have active TB, the bacteria are making you ill and you might be passing TB on to other people. Active TB can be very harmful to your health, but it can be cured with a course of medicine.

About latent TB

If you have latent TB, the TB bacteria in your body are ‘asleep’. You are not ill and you cannot pass TB on to others. However, the bacteria might ‘wake up’ in the future, making you ill with active TB. The good news is that latent TB can be treated to prevent this happening.

What are the main differences between active and latent TB?

Latent TB

  • TB bacteria are asleep in your body
  • you do not have symptoms and you feel well
  • you cannot pass TB on to others
  • it can only be detected through a blood test or TB skin test

treated with one or two medicines over three to six months

Active TB

  • TB bacteria are awake and making you ill
  • you will have symptoms that make you feel unwell
  • you can pass TB to others if it is in your lungs
  • it shows up on a chest x-ray if you have TB in the lungs

treated with four or more medicines over at least six months

How does latent TB work?

Very few people fall ill immediately after they breathe in TB bacteria. If you are in good health, your immune system – your body’s defence against illness – is likely to remove all the TB bacteria that you breathe in. If it is unable to do this, it may be able to stop you from becoming ill by forcing the bacteria into a latent (sleeping) state. The bacteria are still in your body, but they are not causing damage.

However, latent TB bacteria can ‘wake up’ and become active in the future, making you ill. This can happen many years after you first breathe in TB bacteria. Latent TB bacteria are more likely to wake up if you experience lifestyle stresses or other illnesses that weaken your immune system.

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