Mycobacterium represents a family of rod-shaped Gram-positive bacteria that spreads through exposure to aerosolized respiratory secretions. While the most notable disease-causing species is Mycobacterium tuberculosis (the causative pathogen for tuberculosis [TB]), other notable pathogens include M avium (which causes a TB-like disease), and M leprae (the causative pathogen for leprosy).

Mycobacterium tuberculosis was known as the "white plague" in Europe during the 17th and 18th centuries, and continues to be a significant cause of morbidity and mortality worldwide.

TB bacterium primarily infects the lung, although extrapulmonary infections of the intestine, skin, and other organs can occur. Active TB is only seen in a small percent of infected patients; in most infected people, the TB bacterium is able to survive for decades in a quiescent or "latent disease" state. In latent infections, a complex immune response encapsulates the TB bacillus in a granulomatous structure. In immunocompromised individuals (associated with aging, concomitant HIV infection, steroids, and immunosuppressive therapy, for example), the granulatomous process can become impaired, leading to reactivation of active TB infection processes.

According to a 2004 World Health Organization estimate, TB remains endemic in much of the world, with a lower incidence of new infections in the Americas (41/100,000) to some of the highest rates in the world in Africa (356/100,000), a statistic which may be related, in part, to the increased risk of TB infections in HIV-positive individuals. []

Early antibiotics with efficacy against TB included streptomycin and isoniazid, which were introduced in the 1940s and used as single agents. In the 1960s rifampicin became available, and combination therapy was employed to overcome the resistance that emerged when single agents were used. The prevalence of TB has declined with use of combination therapy. However, outbreaks continue to plague special populations, including immigrants, HIV-positive patients, and patients treated with certain anti-TNF therapies.

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