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Extensively drug-resistant TB (XDR-TB), first described in 2006, has now been reported in 49 countries. Researchers recently conducted a retrospective study of patients who had received individualized TB treatment at a referral center in Lima, Peru, between February 1, 1999, and July 31, 2002. Among the 810 patients, 651 patients had multidrug-resistant TB (MDR-TB), and 48 had XDR-TB, which was defined as resistance to at least isoniazid, rifampin, a fluoroquinolone, and a second-line injectable agent. None of the patients with XDR-TB had HIV infection.
The patients with XDR-TB had undergone, on average, 4.2 treatment regimens before the study and had isolates that were resistant to a mean of 8.4 of the 12 agents or classes of drugs for whic…