A 19-year-old Peruvian visiting the US to study English has become the first person in the country diagnosed with extremely drug-resistant tuberculosis(結核)(XXDR-TB). Though he began treatment at A.G. Holley State Hospital, the nation's last remaining TB sanitarium, in December 2007, his case had not been made public until now. The strain is highly contagious, aggressive, and incredibly resistant to existing antibiotic treatments and is so rare that only a handful of cases have been reported worldwide. Experts are particularly worried by the rapid mutation of infectious diseases like TB, malaria, and HIV, which are developing increasing resistance to drugs.