Tuberculosis FACT SHEETS

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Latent TB infection progressing to TB disease

Why does latent TB infection progress to active TB disease?

Latent tuberculosis (TB) infection may develop into active TB disease if your body’s defence (immune) system can’t stop the TB germs (bacteria) from growing. You are at the highest risk (about five per cent) of active TB disease within the first two years of becoming infected. After the first two years, there is only another five per cent chance of you developing active TB disease in your lifetime.

Who is more likely to get active TB disease?

You are at a greater risk of developing active TB disease if your body’s defence system gets weak. The following conditions can weaken your body’s defence system:

• HIV infection and AIDS (increases your risk of TB disease from 10 per cent over a lifetime to 10 per cent each year);
• organ transplants (because the patient is treated with immunity-suppressing drugs);
• a type of lung disease called silicosis;
• chronic kidney failure requiring dialysis;
• cancer of the head and neck;
• having been infected with TB bacteria within the past two years;
• a chest x-ray showing signs of old TB;
• treatment with steroids known as glucocorticoids;
• treatment with tumour necrosis factor (TNF)-alpha inhibitors (e.g., for auto-immune disorders such as rheumatoid arthritis);
• diabetes mellitus (all types);
• being underweight (for most people, this is a body mass index equal to or less than 20);
• being under five years of age when first infected with the TB bacteria; and
• cigarette smoking (one pack per day or more).

What can I do to prevent active TB disease?

If you have latent TB infection it is important to protect your immune system from becoming weak. TB drugs (antibiotics) will help your immune system fight the TB germs and prevent TB disease. Talk to your health-care professional to find out if you need to take TB drugs. It’s also important to find out if you have HIV. If you do, you need to take special precautions.

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