The emergence and transmission of these strains of M. tuberculosis highlight the urgency of strengthening national TB and HIV/acquired immunodeficiency syndrome control programs worldwide, particularly in settings with high HIV prevalence. CDC is collaborating with national and international health agencies to provide leadership, technical support, and capacity building to ensure proper action is taken to limit the development and spread of XDR TB. An initial consultation was convened by the South Africa Medical Research Council in Johannesburg, South Africa, during September 6-7, 2006. A seven-point emergency action plan to combat XDR TB was issued by agencies represented at this meeting (additional information is available
at http://www.mrc.ac.za/pressreleases/8pres2006.htm). Subsequently, WHO organized the first meeting of the Global XDR TB Task Force, held in Geneva, Switzerland, during October 8-9, 2006. This meeting was called by WHO to develop a rapid response to the emerging problem of XDR TB. As a result of the meeting, participants agreed upon a revised case definition of XDR TB. According to laboratory professionals in attendance, drug-susceptibility testing to fluoroquinolones and second-line injectable drugs (i.e., amikacin [aminoglycoside], kanamycin [aminoglycoside], or capreomycin [polypeptide]) yields reproducible and reliable results, whereas drug-susceptibility testing to other second-line drugs is less reliable. Additionally, investigators have observed that resistance to these drugs (fluoroquinolones and second-line injectable drugs) has been associated with poor treatment outcomes. Accordingly, the new agreed-upon definition of XDR TB is the occurrence of TB in persons whose M. tuberculosis isolates are resistant to isoniazid and rifampin plus resistant to any fluoroquinolone and at least one of three injectable second-line drugs (i.e., amikacin, kanamycin, or capreomycin).