Tuberculosis (TB) is caused by a type of bacterium called mycobacterium tuberculosis.
TB is spread when a person with an active TB infection in their lungs coughs or sneezes and someone else inhales a droplet of contaminated saliva.
However, although it is spread in the same way as a cold or the flu, TB is not as contagious. You would usually have to spend around eight hours in close contact with an infected person before you developed a TB infection yourself.
For example, TB infections usually spread between family members who live in the same house. It would be highly unlikely to become infected by sitting next to an infected person on a bus or train.
Risk factors for TB
Anyone can catch TB, but people who are particularly at risk include:
- people living in environments where the level of existing TB infection is higher than normal
- people with health conditions (such as HIV) or whose circumstances mean they are less able to fight off a TB infection
The known risk factors for an active TB infection include:
- being in close contact with someone who is infected
- having lived in, travelled to or had visitors from parts of the world where TB is common (see Tuberculosis - introduction for more details)
- being part of an ethnic minority community that originated in parts of the world where TB is still common
- having an immune system (the body’s natural defence against infection and illness) that has been weakened by HIV, diabetes or other medical conditions
- having an immune system that has been weakened by long courses of medication, such as corticosteroids, chemotherapy or tumour necrosis factor blockers (used to treat some types of arthritis)
- being very young or very old - the immune systems of people who are young or elderly tend to be weaker than those of healthy adults
- being in poor health or having a poor diet due to lifestyle and behavioural problems, such as drug misuse, alcohol misuse or homelessness
- living in poor or crowded housing conditions, such as remand centres and prisons
