It divides every 16 to 20 hours, which is an extremely slow rate compared with other bacteria, which usually divide in less than an hour. The high lipid content of this pathogen accounts for many of its unique clinical characteristics. The main cause of TB is Mycobacterium tuberculosis (MTB), a small, aerobic, nonmotile bacillus. It may be due to either better air flow, or poor lymph drainage within the upper lungs. The reason for this difference is not clear. The upper lung lobes are more frequently affected by tuberculosis than the lower ones. Tuberculosis may become a chronic illness and cause extensive scarring in the upper lobes of the lungs. 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. About 25% of people may not have any symptoms (i.e. Symptoms may include chest pain and a prolonged cough producing sputum. If a tuberculosis infection does become active, it most commonly involves the lungs (in about 90% of cases). Significant nail clubbing may also occur. General signs and symptoms include fever, chills, night sweats, loss of appetite, weight loss, and fatigue. Extrapulmonary TB occurs when tuberculosis develops outside of the lungs, although extrapulmonary TB may coexist with pulmonary TB. Tuberculosis may infect any part of the body, but most commonly occurs in the lungs (known as pulmonary tuberculosis). Multiple variants may be present simultaneously. The main symptoms of variants and stages of tuberculosis are given, with many symptoms overlapping with other variants, while others are more (but not entirely) specific for certain variants. Tuberculosis has been present in humans since ancient times. About 80% of people in many Asian and African countries test positive while 5–10% of people in the United States population test positive via the tuberculin test. By 2021 the number of new cases each year was decreasing by around 2% annually. As of 2018, most TB cases occurred in the regions of South-East Asia (44%), Africa (24%), and the Western Pacific (18%), with more than 50% of cases being diagnosed in seven countries: India (27%), China (9%), Indonesia (8%), the Philippines (6%), Pakistan (6%), Nigeria (4%), and Bangladesh (4%). In 2020, an estimated 10 million people developed active TB, resulting in 1.5 million deaths, making it the second leading cause of death from an infectious disease after COVID-19. New infections occur in about 1% of the population each year. In 2018, one quarter of the world's population was thought to have a latent infection of TB. Antibiotic resistance is a growing problem with increasing rates of multiple drug-resistant tuberculosis (MDR-TB). Treatment requires the use of multiple antibiotics over a long period of time. Those at high risk include household, workplace, and social contacts of people with active TB. Prevention of TB involves screening those at high risk, early detection and treatment of cases, and vaccination with the bacillus Calmette-Guérin (BCG) vaccine. Diagnosis of Latent TB relies on the tuberculin skin test (TST) or blood tests. Diagnosis of active TB is based on chest X-rays, as well as microscopic examination and culture of body fluids. Active infection occurs more often in people with HIV/AIDS and in those who smoke. People with Latent TB do not spread the disease. Tuberculosis is spread from one person to the next through the air when people who have active TB in their lungs cough, spit, speak, or sneeze. Infection of other organs can cause a wide range of symptoms. It was historically referred to as consumption due to the weight loss associated with the disease. Typical symptoms of active TB are chronic cough with blood-containing mucus, fever, night sweats, and weight loss. Around 10% of latent infections progress to active disease which, if left untreated, kill about half of those affected. Most infections show no symptoms, in which case it is known as latent tuberculosis. Tuberculosis generally affects the lungs, but it can also affect other parts of the body. Tuberculosis ( TB) is an infectious disease usually caused by Mycobacterium tuberculosis (MTB) bacteria.
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