Tuberculosis (TB) - Causes, treatment and prevention
Active tuberculosis (TB) disease is a serious infection that usually affects the lungs. Anyone can develop active TB, but you are more likely to develop it if you are already in poor health or have a poor immune system. With treatment, most cases are cured. Without treatment, TB can be fatal. You need to take treatment for at least six months.
What is tuberculosis?
Tuberculosis (TB) is an infection caused by a bacterium (germ) called Mycobacterium Tuberculosis. TB usually affects the lungs but any part of the body can be affected.
How does tuberculosis infection occur?
Most cases affect the lungs at first. TB bacteria are coughed or sneezed into the air by people with active TB disease. The bacteria are carried in the air in tiny water droplets. If you breathe in some TB bacteria they may then multiply in your lung. There are then three ways the infection may progress.
1. Minor infection with no symptoms - occurs in most cases
Most people in good health who breathe in TB bacteria do not develop active TB disease. The bacteria that you breathe in begin to multiply in the lung. This stimulates your immune system into action. The TB bacteria are killed or made inactive by the immune system (white blood cells, etc). There may be some mild symptoms for a short time, or no symptoms, and the infection is halted.
This is the end of the matter for most infected people. You are not usually aware that you have had this mild infection. A small scar on the lung may be seen on a chest X-ray. This shows that a 'battle' had occurred between the TB bacteria and the immune system.
2. Infection progressing into active TB disease - occurs in some cases
Active TB disease with symptoms occurs in about 1 in 20 people who breathe in some TB bacteria. In these people the immune system does not win the battle and halt the invading bacteria. The TB bacteria multiply further and spread to other parts of the lung and body. Symptoms of active TB then develop about 6-8 weeks after first breathing in some bacteria. TB infection which progresses to active disease can occur in anybody who is infected with TB bacteria. However, it is more likely if you are already in poor health. For example, it is common in malnourished children in developing countries.
3. Re-activated (secondary) infection causing active disease
Some people develop active TB months or years after a minor TB infection had been halted. The body's immune system at first stops the bacteria from multiplying (described above). However, not all the bacteria may be killed. Some bacteria may be 'walled off' in the scar tissue of the initial minor infection. They are stopped from multiplying by the immune system. They do no harm but can remain dormant (inactive) for many years. Dormant TB bacteria may start to multiply and cause active TB if the body's immune system begins to fail later in life. A failing immune system and re-activated TB is more likely to occur if you:
are elderly or frail.
take steroids or immunosuppressant medication.
have kidney failure.
are alcohol dependent ('alcoholic').
How infectious is tuberculosis?
If you have been infected with TB but have no symptoms (see above), you cannot pass on the infection. If you have active TB disease, you will cough and sneeze TB bacteria into the air which can infect others.
To catch TB you normally need close contact and 'heavy exposure' from a person who has active TB. TB is commonly caught by people who live with a person who has active TB and who coughs a lot into a badly ventilated home. The spread of TB is more common in poorer areas of the world. Overcrowding, poor sanitation and poor housing increase the risk. It is thought that the most important way to prevent the spread of TB in poorer areas of the world is to provide better living conditions with good ventilation.
How common is tuberculosis?
TB is common in developing countries. It causes more deaths world-wide than any other infectious disease (about three million per year). Poor nutrition, poor housing, poor general health and the AIDS epidemic are main reasons why TB is common. In the UK, active TB was common in the nineteenth century (the old 'consumption'). Better living conditions, better nutrition, immunisation and effective treatments in the twentieth century all combined to make TB uncommon.
The number of people with active TB was at an all time low in the UK in the early 1980s. Since then the number of cases has increased. This is probably due to a combination of factors. These include: an increase in poverty, the ageing population, immigration from areas where TB is common, more people travelling to areas in the world where TB is common, and AIDS (TB is common in people with AIDS).
What are the symptoms of active tuberculosis?
Cough is usually the first and most marked symptom. The cough often starts as a dry irritating cough. It tends to continue for months and get worse. In time the cough usually becomes 'productive' and you tend to cough up a lot of sputum (phlegm) which may be bloodstained.
Other symptoms include: fever, sweats, feeling unwell, weight loss, pains in the chest, and poor appetite. You may become breathless as the infection progresses and damages the lungs. If left untreated, complications often develop such as fluid collecting between the lung and the chest wall (pleural effusion). This can make you very breathless.
The infection may spread in the bloodstream and lymphatic system to cause swollen lymph glands, and infection in other parts of the body. Various other symptoms may then occur.
How is tuberculosis diagnosed?
Typical symptoms and changes on the chest X-ray suggest active TB. However, tests are usually done to prove the diagnosis.
Tuberculin skin testing (Mantoux, Heaf or Tine test)
This is a useful test which shows if you have been in contact with TB bacteria at some point in your life. However, it cannot prove you have a current active infection. Tuberculin is a part of the TB bacterium. It is injected into the skin. The injection site is examined a few days later.
A negative skin reaction tends to rule out TB. A negative test means you have never been infected with TB and have not had a BCG immunisation. (BCG is the vaccine used to prevent TB.) Rarely, a negative result occurs if you are very ill with severe active TB.
A positive reaction is a red inflamed area of the skin. This means that you either have a current infection, or have had a previous infection, or you have been immunised in the past with BCG.
Proving a current active infection
A sputum sample is usually taken to try and grow TB bacteria to prove that you currently have active TB. However, it often takes 6-8 weeks to get a result from this sputum test as the TB bacteria grow and multiply very slowly before they can be detected in the 'lab'. Newer tests are being developed which may speed up the time taken to confirm active TB infection.
Because it can take several weeks for the results to 'prove' the infection, many people with suspected active TB (with typical symptoms and x-ray changes) are started on treatment before the sputum test result is back. This is to prevent the disease from getting worse, and to prevent spread to other people.
What is the treatment for tuberculosis?
'Normal' antibiotics do not kill TB bacteria. You need to take a combination of special antibiotics for six months. Standard treatment in the UK is usually a combination of three or four antibiotics that you take for two months. These are isoniazid, rifampicin, pyrazinamide, and often ethambutol too. This is followed by continuing with rifampicin and isoniazid for a further four months. Variations on this treatment plan may be advised depending on individual circumstances.
The medicines used to treat TB have a good safety record. Sometimes side-effects occur. If one does, see a doctor rather than just stopping treatment. An alternative antibiotic may be an option. Read the leaflet which comes with the medicine packet for a list of possible side-effects.
Do family and friends need checking?
Household members and close regular contacts of a person with active TB may be advised to have tests. This may include a chest x-ray and a tuberculin skin test.
What is the outlook (prognosis) if you have active tuberculosis?
With treatment, most people make a full recovery. If left untreated, about half of people with active TB eventually die of the infection. TB bacteria multiply quite slowly compared to most other bacteria. Therefore, active TB tends to cause an illness that slowly gets worse. Some people survive without treatment and may even fully recover.
Can tuberculosis be prevented?
TB is both preventable and treatable. It is a tragedy that it remains one of the biggest killers world-wide. Relieving poverty, better nutrition, improved general health, and better housing are thought to be the most important ways of preventing TB. Immunisation also helps.
Immunisation against tuberculosis (the BCG vaccine)
The BCG vaccine (Bacillus Calmette-Guerin) is offered to the following people in the UK:
Babies living in areas of the UK where there is a high rate of TB. That is, areas where the incidence of TB is 40 cases per 100,000 people per year, or greater.
Babies whose parents or grandparents have lived in a country with a high rate of TB. That is, countries where the incidence of TB is 40 cases per 100,000 people per year, or greater.
The following groups of people who have not previously been immunised.
Immigrants to the UK from countries where TB is common.
People at risk due to their job. For example, health workers, prison staff, etc.
Close contacts of people with active TB.
People who intend to live for one month or more in countries with a high TB rate.
Note: until 2005, all schoolchildren in the UK were routinely given the BCG vaccine at about the age of 13. The policy changed in Autumn 2005 and those now immunised are in the groups listed above. The policy change was due to the changing patterns of TB in the UK. Rates of the disease are now very low in many parts of the country and children living in these areas have a very low risk of infection. However, in other areas, rates of TB are increasing. This is why the BCG vaccine is now mainly targeted at babies living in areas where there is an increasing rate of TB cases. Your doctor or midwife will be able to tell you if you live in an area with a high rate of TB.
Children who would previously have been offered BCG through the schools' programme will now be screened for risk factors, tested and immunised as appropriate.
The BCG vaccine was introduced into the UK in 1953. Over many years it has been shown to be a safe vaccine. The vaccine contains a small number of modified TB bacteria. The vaccine stimulates the immune system to be ready to fight TB bacteria.
The BCG vaccine is thought to give more than 70% protection against TB. So, although it is a good vaccine, it does not guarantee protection against TB. Some people still develop TB even if they have had the BCG vaccine.
What is atypical tuberculosis?
As mentioned above, the disease that we call 'Tuberculosis' or 'TB' is caused by a bacterium called Mycobacterium Tuberculosis. Another bacterium in the same family is called Mycobacterium Bovis. This is a rare cause of infection in the UK. It used to be more common as it is passed on from contaminated unpasteurised milk, or from infected cattle (now rare in the UK).
There are various other bacteria in the mycobacterium family which are called atypical mycobacteria. Most of these do not cause infection. However, they sometimes cause serious infection in people whose immune system is not working very well. (For example, some people who have AIDS.) Treatment is with long courses of antibiotics.
Most cases of TB are caused by a bacterium called Mycobacterium Tuberculosis.
Active tuberculosis disease is a serious infection, but can be treated.
Household members and close contacts of affected people need checking.
A six month courdr of special antibiotics cures the infection in most cases.
If you are treated, it is vital that you take antibiotics correctly for the full course.
Further help and information
British Lung Foundation
73-75 Goswell Road, London EC1V 7ER 8JR
Tel: 020 7688 5555 Web: www.lunguk.org
22 Tiverton Road, London NW10 3HL
Aims to increase awareness of the threat of TB both worldwide and at home and to raise funds to support operational work against the disease in the countries most affected.
This article is dedicated to the memory of Mr. 'Kwaku Bonto' who recently died of TB in Koforidua, Ghana. Parents are urged to ensure their children are immunised for protection against this dreadful disease. TB is preventable and treatable.