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Richard E. Chaisson

, and Jean B. Nachega

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date: 02 March 2021

Tuberculosis is caused by organisms of the Mycobacterium tuberculosis complex, including M. tuberculosis (the most important), M. bovis, and M. africanum. It has been present since antiquity and is the leading infectious cause of death ahead of HIV infection. An estimated 2 billion people worldwide carry latent infection, when M. tuberculosis persists within cells and granulomas, with the potential to reactivate to cause disease decades later. Tubercle bacilli are transmitted between people by aerosols generated when an infectious person coughs. Proximity to an infectious person determines the risk of infection. Host immunity and factors affecting it—most importantly HIV infection but also diabetes, cigarette smoking, and alcohol and drug abuse—determine the risk of active disease following infection.

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