An infectious disease, commonly called TB, caused in humans by the bacterium. TB is usually transmitted in airborne droplets expelled when an infected person coughs or sneezes. An inhaled droplet enters the lungs and the bacteria begin multiplying. The immune system usually seals off the infection at this point, but in about 5 per cent of cases the infection spreads to the lymph nodes. It may also spread to other organs through the bloodstream, which may lead to miliary tuberculosis, a potentially fatal form of the disease. In about another 5 per cent of cases, bacteria held in a dormant state by the immune system become reactivated months, or even years, later. The infection may then progressively damage the lungs, forming cavities. The primary infection is usually without symptoms. Progressive infection in the lungs causes coughing (sometimes bringing up blood), chest pain, shortness of breath, fever and sweating, poor appetite, and weight loss. Pleural effusion or pneumothorax may develop. The lung damage may be fatal. A diagnosis is made from the symptoms and signs, from a chest X-ray, and from tests on the sputum. Alternatively, a bronchoscopy may also be carried out to obtain samples for culture. Treatment is usually with a course of 3 or 4 drugs, taken daily for 2 months, followed by daily doses of isoniazid and rifampicin for 4–6 months. However, TB bacteria are increasingly resistant to the drugs used in treatment, and others may have to be used and treatment carried out for a longer period. If the full course of drugs is taken, most patients recover. TB can be prevented by BCG vaccination, which is offered routinely at birth or age 10–14. Any contacts of an infected person are traced and examined, and, if infected, are treated early to reduce the risk of the infection spreading.


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