It usually affects the lungs and is caught from other people. Your body’s natural defences, its immune system, usually control or destroy the germs once they are inhaled leaving them inactive. This is called latent TB.
If you develop TB symptoms this is known as active TB. Some people go on to develop active TB weeks or months later. In others TB can remain latent for many years before becoming active. This is more likely if your body is weakened by other medical problems.
You are most at risk of developing active TB if your immune system is damaged or if it works less well following an organ transplant or treatment for conditions such as cancer and rheumatoid arthritis.
Find out more: http://www.blf.org.uk/Page/Tuberculosis-health-information