A bacterial infection that most often affects the lungs but may also affect many other parts of the body
Tuberculosis (TB) is a slow-developing bacterial infection that usually begins in the lungs but can spread to many other parts of the body. TB can now be treated very effectively using oral antibiotics (see Antituberculous drugs), but, left untreated, it may cause long-term ill health and can be fatal.
Worldwide, TB causes more deaths among adults than any other bacterial infection. The disease is still common in developing countries, especially in Asia. In developed countries, the number of cases steadily decreased during most of the 20th century due to improved health care, diet, and housing. However, since 1985 there has been a worldwide increase in the number of cases of TB. In the UK, TB is a notifiable disease, and about 8,400 cases were reported in 2007. This rise in TB is associated with an increase in travel and with the spread of strains of TB bacteria that are resistant to antibiotic treatment. Another factor is the emergence of HIV infection and AIDS, which lowers immunity, making people more susceptible to infection.
The bacterium Mycobacterium tuberculosis causes most cases of TB and is usually transmitted in airborne droplets that are produced when an infected person coughs. Although many people are infected with the bacterium at some point in their lives, only a small proportion of these people develop TB.
When the bacteria are inhaled, an initial minor infection develops in the lungs. The outcome of this initial lung infection will depend on the strength of a person’s immune system. In many healthy people, the infection does not progress. However, some TB bacteria lie dormant in the lungs, and the disease may be reactivated years later if a person’s immunity is reduced.
In some cases, the bacteria enter the bloodstream and spread to other sites in the body. Rarely, the infection does not begin in the lungs but in another part of the body. For example, TB may affect the gastrointestinal tract if a person drinks unpasteurized milk from a cow infected with TB.
People with reduced immunity are more likely to develop TB. This includes people who are infected with HIV, those who have diabetes mellitus, and those who are taking immunosuppressant drugs. Others at risk of TB include people with long-term lung disease and those living in overcrowded conditions with poor sanitation or who have a poor diet. Generally, elderly people and children are more susceptible.
During the initial stages of the infection, many people have no symptoms. However, some people may experience:
Cough, which may be dry.
Generally feeling unwell.
Enlarged lymph nodes, especially in the neck.
If the disease progresses, further symptoms usually appear over 2–6 weeks, but progression may be more rapid. Later symptoms may include:
Persistent cough, which may produce greenish or yellowish sputum that is sometimes blood-streaked.
Chest pain when inhaling deeply.
Shortness of breath.
Poor appetite and weight loss.
Excessive sweating at night.
Untreated TB that begins in the lungs can spread directly to the tissue covering the heart (see Pericarditis). The infection may also be carried in the blood to the brain (see Meningitis), the bones, the kidneys, and many other parts of the body.
The onset of TB in areas of the body other than the lungs is very slow, and symptoms are not specific, making the condition difficult to diagnose.
If you are coughing up sputum, a sample will be sent to the laboratory so that it can be examined for bacteria and tested for sensitivity to particular drugs. In the meantime, you will be treated with a combination of antituberculous drugs.
Sometimes, a bronchoscopy may be necessary to obtain lung tissue samples for examination. In addition, if your doctor suspects that you may have infection in a part of the body other than the lungs, such as in the lymph nodes, a sample of tissue may be taken from the area to look for TB.
If you have recently been in close contact with someone with TB bacteria in his or her sputum, you need to be screened. A chest X-ray may be carried out to look for signs of infection, along with a TB skin test, in which a substance extracted from TB bacteria is injected under the skin. The injection site is checked for a reaction 2 or 3 days later. A positive reaction indicates that you have previously been exposed to TB, have active TB, or have been immunized against it.
If you have TB, you will probably be treated at home unless you are very ill. You will be prescribed a combination of antituberculous drugs, which should be taken for at least 6 months. Using a combination of drugs helps to prevent the development of bacterial resistance to antibiotics. The drugs that are used depend on the antibiotic sensitivity of the bacteria and whether the infection has spread to other areas of the body. TB affecting areas that drugs do not penetrate easily, such as the bones, generally needs treatment for a longer period.
It is important to complete the full course of antituberculous drugs to help prevent the development of drug resistance. Since it is very easy to forget to take the drugs, some people need help with their treatment using directly observed therapy, in which they attend a health centre regularly to be given the drugs under medical supervision. While you are undergoing treatment for TB, you will probably need to have chest X-rays and blood tests repeated on a regular basis to make sure that the infection is responding to treatment and to detect side effects of the drugs.
The BCG vaccine against TB is recommended for particular at-risk groups, including newborns and infants in areas where there is a high rate of TB; new immigrants from countries where there is a high rate of TB; health-care workers who are likely to have contact with TB patients; and those intending to live in a country with a high rate of TB. Those who are recommended for immunization will generally first be given a skin test to check whether they have been previously immunized, have had previous contact with TB, or have active TB infection. If the test is positive, BCG immunization is not given.
Most people make a full recovery from TB if antituberculous medication is taken regularly as directed. However, in people who have a type of TB that is resistant to two or more drugs, in those whose immunity is severely weakened, or in people with widespread TB, the disease may be fatal.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.