TB is caused by the bacterium Mycobacterium tuberculosis. TB in the lungs can be infectious i.e. the bacteria can be spread to other people. TB in other parts of the body is usually not infectious.
TB is spread mainly through the air via droplets (called aerosols), that are produced when infectious people cough, sneeze, talk, laugh or spit. These aerosols contain millions of bacteria that are sprayed into the air. People nearby may inhale these bacteria and become infected.
TB bacteria can stay air-borne for a long time (up to eight hours) in closed spaces such as classrooms, movie theatres and aeroplanes. They can also remain active in house dust for weeks. This means that risk of transmission is higher in confined spaces with minimal ventilation.
Someone with TB disease is most likely to spread it to people they spend time with daily, such as family members, friends and co-workers.
While it needs as few as 1–10 bacteria to establish infection, transmission usually only occurs after substantial exposure to someone with active TB.
You cannot get TB from:
- Handshakes or toilet seats
- Sharing eating utensils, bedclothes or clothing with people who have TB
You are unlikely to get TB from someone coughing in a public place.
Reviewed by Dr AW Dreyer, Pathologist and Clinical Microbiologist, Centre for Tuberculosis, National Institute for Communicable Diseases February 2015.
Previously reviewed by Joanna Evans, PhD, Molecular Mycobacteriology Research Unit, Division of Medical Microbiology Institute of Infectious Diseases and Molecular Medicine, University of Cape Town, February 2011.