Extensively drug-resistant tuberculosis:

To describe the origin, epidemiology, diagnosis, treatment, prevention, and control of extensively drug-resistant tuberculosis (XDR TB). XDR TB is defined as the occurrence of TB in persons whose Mycobacterium tuberculosis isolates are resistant to isoniazid and rifampin and to any fluoroquinolone and at least one of three injectable second-line drugs (i.e., amikacin, kanamycin, or capreomycin). As of June 2008, XDR TB has been found in 49 countries including the United States. It generally takes several weeks to detect XDR TB using conventional culture-based methods, although some progress is being made in developing rapid molecular tests. Treatment for XDR TB is difficult, usually requiring at least 18–24 months of four to six second-line anti-TB drugs. Treatment success rates are generally 30–50%, with very poor outcomes in HIV-infected patients. Management of contacts to infectious XDR TB patients is complicated by the lack of a proven effective treatment for XDR latent tuberculosis infection. XDR TB is an emerging global health threat. The disease is difficult and expensive to diagnose and treat, and outcomes are frequently poor. New rapid diagnostic tests and new classes of anti-TB drugs are needed to successfully combat this global problem