Tuberculosis (TB) is among the oldest recorded diseases in human history. Infection with Mycobacterium tuberculosis occurs when the bacteria are expelled—along with moisture from a diseased person's respiratory system while coughing, sneezing, speaking, singing, or exhaling—and are inhaled into another person's lungs. Transmission of TB through close human contact is common; about one third of the world is infected with TB. Only a minority of those infected will develop active TB disease, which is deadly if untreated or improperly treated. Progression from infection to active disease is much more likely among people with compromised immune systems, such as the very young, the very old, and those with HIV infection. TB has long been linked in the popular imagination with alcoholism and drug addiction, and in ...

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