Tuberculosis (TB) is an infectious disease usually caused by the bacterium Mycobacterium tuberculosis (MTB).[1] Tuberculosis generally affects the lungs, but can also affect other parts of the body.[1] Most infections do not have symptoms, in which case it is known as latent tuberculosis.[1] About 10% of latent infections progress to active disease which, if left untreated, kills about half of those infected.[1] The classic symptoms of active TB are a chronic cough with blood-containing sputum, fever, night sweats, and weight loss.[1] The historical term "consumption" came about due to the weight loss.[4] Infection of other organs can cause a wide range of symptoms.[5]

Tuberculosis is spread through the air when people who have active TB in their lungs cough, spit, speak, or sneeze.[1][6] People with latent TB do not spread the disease.[1] Active infection occurs more often in people with HIV/AIDS and in those who smoke.[1] Diagnosis of active TB is based on chest X-rays, as well as microscopic examination and culture of body fluids.[7] Diagnosis of latent TB relies on the tuberculin skin test (TST) or blood tests.[7]

Prevention of TB involves screening those at high risk, early detection and treatment of cases, and vaccination with the bacillus Calmette-Guérin (BCG) vaccine.[8][9][10] Those at high risk include household, workplace, and social contacts of people with active TB.[10] Treatment requires the use of multiple antibiotics over a long period of time.[1] Antibiotic resistance is a growing problem with increasing rates of multiple drug-resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB).[1]

Presently, one-third of the world's population is thought to be infected with TB.[1] New infections occur in about 1% of the population each year.[11] In 2016, there were more than 10 million cases of active TB which resulted in 1.3 million deaths.[3] This makes it the number one cause of death from an infectious disease.[3] More than 95% of deaths occurred in developing countries, and more than 50% in India, China, Indonesia, Pakistan, and the Philippines.[3] The number of new cases each year has decreased since 2000.[1] About 80% of people in many Asian and African countries test positive while 5–10% of people in the United States population test positive by the tuberculin test.[12] Tuberculosis has been present in humans since ancient times.[13]

Tuberculosis may infect any part of the body, but most commonly occurs in the lungs (known as pulmonary tuberculosis).[5] Extrapulmonary TB occurs when tuberculosis develops outside of the lungs, although extrapulmonary TB may coexist with pulmonary TB.[5]

General signs and symptoms include fever, chills, night sweats, loss of appetite, weight loss, and fatigue.[5] Significant nail clubbing may also occur.[15]

If a tuberculosis infection does become active, it most commonly involves the lungs (in about 90% of cases).[13][16] Symptoms may include chest pain and a prolonged cough producing sputum. About 25% of people may not have any symptoms (i.e. they remain "asymptomatic").[13] Occasionally, people may cough up blood in small amounts, and in very rare cases, the infection may erode into the pulmonary artery or a Rasmussen's aneurysm, resulting in massive bleeding.[5][17] Tuberculosis may become a chronic illness and cause extensive scarring in the upper lobes of the lungs. The upper lung lobes are more frequently affected by tuberculosis than the lower ones.[5] The reason for this difference is not clear.[12] It may be due to either better air flow,[12] or poor lymph drainage within the upper lungs.[5]

This page was last edited on 2 July 2018, at 14:53 (UTC).
Reference: under CC BY-SA license.

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