Tuberculosis (TB) is caused by a type of bacterium called Mycobacterium. There are different species of Mycobacterium, but the one which causes most cases of TB in humans is called Mycobacterium tuberculosis.
TB is often thought of as an ‘old’ infectious disease that does not affect people in the UK any longer. However, it has been on the increase in some areas of the UK since 1990. About 9000 cases are currently reported each year, mostly from big cities, particularly London. Groups most at risk are young adults, people from countries where there are high rates of TB (more than 40 cases of TB per year for every 100,000 people), and people with social risk factors (such as homelessness, alcohol misuse or being in prison). If TB is not treated it can be fatal, even in people with no other health issues. Around 350 people a year in the UK die from TB-related causes. The most severe forms of the disease are more likely to affect children. TB usually affects the lungs, but it can affect almost any part of the body including bones and the nervous system. It can be treated by a long course of antibiotics, but TB that is resistant to antibiotics is becoming more common.
Worldwide, TB is the main cause of death among infectious diseases that can be cured and prevented. It is a leading killer of people living with HIV and causes one in five of all deaths in this group. The World Health Organization (WHO) estimates that, in 2013, 9 million people fell ill with TB and 1.5 million of these people died. WHO also estimates that about a third of the world’s population has latent TB (where the TB bacteria remain in the body but the disease is not active). In 1993 WHO declared TB a global emergency.
When TB affects the lungs (pulmonary TB), the main symptoms are a persistent cough lasting more than three weeks, and coughing up phlegm that may contain blood.
Other symptoms include a high temperature, loss of appetite, weight loss, night sweats, and tiredness or weakness. TB can sometimes lead to meningitis. This is most common in children aged 0-4 years in areas with high rates of TB, and most common in adults in areas with low rates of TB.
Many people who are infected with TB develop a latent TB infection. This means that the TB bacteria remain in the body, but the disease is not active. People with latent TB do not show any symptoms, and cannot pass the disease on to anyone else. However, they are at risk of developing active TB at a later stage, especially if their immune system becomes weakened (for example, because of chemotherapy treatment, HIV infection, or old age). Latent TB develops into active TB in around 10% of cases.
TB can be very difficult to diagnose, especially in children.
TB is almost always passed on by tiny droplets coughed or sneezed into the air by an infected person. Infection usually happens after prolonged close contact with someone who has TB; for example, TB can pass between people living in the same house. Less commonly, TB is passed on outside the home.
A vaccine against TB (the BCG vaccine) is available to protect groups who are particularly at risk of developing the disease. The vaccine is not currently offered to all children as part of the routine schedule in the UK except in areas with very high rates of disease.