What causes TB?

• TB is caused by the bacterium Mycobacterium tuberculosis.
• TB in the lungs or throat 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. When infectious people cough, sneeze, talk, laugh or spit, droplets containing bacteria are sprayed into the air. People nearby may inhale these bacteria and become infected. Bacteria can stay air-borne for a long time, and can remain active in house dust for weeks.
• However, transmission usually occurs only after substantial exposure to someone with active TB. People with TB disease are most likely to spread it to those they spend time with daily, such as family members and co-workers. You are unlikely to get TB from someone coughing in a public place. You cannot get TB from handshakes, toilet seats, or sharing eating utensils, bedclothes or clothing with people who have TB.
• Infection can also be acquired from contact with an infected cow or through drinking contaminated milk. However, this is an extremely rare way of getting TB. Most milk is pasteurized, and dairy herds are usually kept under veterinary control.

- 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