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Tuberculosis (TB) is an infectious disease caused by bacteria belonging to the Mycobacterium tuberculosis complex.
Over nine million new cases of TB, and nearly two million deaths from TB, are estimated to occur around the world every year, and new infections occur at a rate of about one per second. TB is the leading cause of death among curable infectious diseases. The World Health Organization declared TB a global emergency in 1993. In addition, more people in the developed world contract tuberculosis because their immune systems are more likely to be compromised due to higher exposure to immunosuppressive drugs, substance abuse, or AIDS. The distribution of tuberculosis is not uniform across the globe; about 80% of the population in many Asian and African countries test positive in tuberculin tests, while only 5-10% of the US population test positive
TB usually causes disease in the lungs (pulmonary), but can also affect other parts of the body (extra-pulmonary). Only the pulmonary form of TB disease is infectious. Transmission occurs through coughing of infectious droplets, and usually requires prolonged close contact with an infectious case. TB is curable with a combination of specific antibiotics, but treatment must be continued for at least six months. Most infections in humans result in an asymptomatic, latent infection, and about one in ten latent infections eventually progresses to active disease, which, if left untreated, kills more than 50% of its victims.
The classic symptoms are a chronic cough with blood-tinged sputum, fever, night sweats, and weight loss (the last giving rise to the formerly prevalent colloquial term "consumption"). Infection of other organs causes a wide range of symptoms. Diagnosis relies on radiology (commonly chest X-rays), a tuberculin skin test, blood tests, as well as microscopic examination and microbiological culture of bodily fluids. Treatment is difficult and requires long courses of multiple antibiotics. Contacts are also screened and treated if necessary. Antibiotic resistance is a growing problem in (extensively) multi-drug-resistant tuberculosis. Prevention relies on screening programs and vaccination, usually with Bacillus Calmette-Guérin vaccine.