Tuberculosis (TB) is an infection with a germ (bacterium) called Mycobacterium tuberculosis. If you have symptoms or a doctor can find unusual signs when examining you, this is known as active TB. If you have TB infection without any signs or symptoms, this is known as latent TB.
How infectious is it?
You have to be in contact with someone who has active TB for a considerable amount of time to catch TB. This usually means living in the same house or coming from the same family as the infected person.
How do you catch it?
The TB germs (bacteria) usually settle in the lung. They say that coughs and sneezes spread diseases and this is certainly true of TB. Droplets of TB bacteria are propelled into the air and you can catch the infection by breathing them in.
In most cases, you won't notice anything and your immune system will deal with the invaders.
If your immune system can't cope (this can happen in undernourished children or newborn babies), symptoms develop 6-8 weeks later.
If your immune system goes wonky, TB can suddenly reactivate many years later. This can happen when you become very old or weak, don't eat enough, drink too much, take medicines that affect your kidneys, or develop another condition such as diabetes or AIDS.
How common is it?
It's at its most common in developing countries where people have a poor diet, poor housing, poor health and a high incidence of AIDS. Worldwide, the number of deaths from TB is falling but it still causes 2 million deaths a year.
The UK saw the number of cases increase from an all-time low in the 1980s but in recent years the number has come down again. It's thought this has been helped by dealing with social problems and testing immigrants as they enter the country.
In England, just under 6,000 new cases were reported in 2015. Rates of TB vary in different parts of the UK, with some London boroughs having very high rates.
Who gets it?
It can affect anyone. People who are in close contact with a person who has active TB of the lungs or voice box (larynx) are mostly at risk. You will also be at higher risk if you come from a country where TB is common or if you are very young or very old. You will also have a higher risk if you have problems with your immune system, have a poor diet, are homeless or have an alcohol or drug dependency problem.
Are precautions needed to stop others catching it?
If you have active TB, you will be infectious to other people until you have taken a couple of weeks' treatment. Stay at home and steer clear especially of anyone who is at increased risk of catching the infection, such as babies, the elderly or people with HIV,
Do family, friends or colleagues need tests?
If you have TB of the lung or voice box, anyone who comes into close and prolonged contact with you needs testing. The usual tests available for contacts are a chest X-ray and/or tuberculin skin test (Mantoux test). If these show possible TB, other tests may need to be done.
It may be difficult to diagnose babies and children under the age of 2 years. They may be put on treatment whilst awaiting results of tests.
Further reading and references
Tuberculosis; NICE Guideline (January 2016)
Tuberculosis (TB); World Health Organization
Tuberculosis; NICE CKS, January 2015 (UK access only)
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