People who have active TB – TB that the immune system has not been able to control – in their lungs can transmit the disease to other people. TB is spread through the air when a person with active TB coughs. You need to be in close contact with TB in an enclosed space to have a real risk of infection. Close contacts include partners of people with TB, people who live in the same house, and frequent visitors to the house.

If you have been diagnosed with TB, a nurse will usually arrange for close contacts to be screened for TB as well.  It is unlikely they will have been infected, but it is important they are contacted. 

Once you start treatment for TB, you soon stop being infectious.  In the meantime you should make sure you cover your mouth when you cough and wash your hands afterwards.  Talk to your nurse or doctor if you have concerns about transmitting TB.

Rarely, TB can affect the larynx (the part of the throat that contains the vocal cords), and active TB here can be spread when a person coughs, shouts, or sneezes. Occasionally, TB can be spread from open wounds and ulcers.

However, not everybody who has active TB in their lungs is infectious and TB that affects the bones or lymph glands is not infectious.

In the UK, there have been cases of HIV-positive people becoming infected with TB on hospital wards. This happened before it was realised that TB was a major health concern for people with HIV, and it is now standard practice for HIV-positive people with TB to be cared for in single rooms rather than wards, and for these rooms to have "negative pressure" meaning that the air is gently sucked out of the room and expelled outside the building so it cannot escape into the rest of the hospital.

If a patient in hospital has a risk of spreading TB they may be asked to wear a mask, as might the staff looking after them and their visitors.