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Notice to Readers: Revised Definition of Extensively
Drug-Resistant Tuberculosis
In a report published on March 24, 2006, MMWR
reported that CDC, in collaboration with the World
Health Organization (WHO) and participating supranational reference laboratories, had agreed to define extensively
drug-resistant tuberculosis (XDR TB) as cases of TB disease in persons whose
Mycobacterium tuberculosis isolates were resistant to
isoniazid and rifampin and at least three of the six main classes of
second-line drugs (aminoglycosides, polypeptides,
fluoroquinolones, thioamides, cycloserine, and para-aminosalicyclic acid)
(1). Since that original publication, additional reports
have documented the presence of XDR TB in Iran and South Africa with high mortality among persons infected with
human immunodeficiency virus (HIV) who are benefiting from antiretroviral therapy
(2,3).
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/2006/8pres2006.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).
Health-care providers and local health departments in
the United States should collect all second-line
drug-susceptibility results obtained at diagnosis and during treatment of persons with TB disease and report these results to
their local and state health department TB programs. Complete capture of these results will allow health departments and CDC
to accurately identify XDR TB cases and monitor trends. Additional information about XDR TB is available at
http://www.who.int/tb/en.
Masjedi MR, Farnia P, Sorooch S, et al. Extensively drug-resistant tuberculosis: 2 years of surveillance in Iran. Clin Infect Dis 2006;43:841--7.
Gandhi NR, Moll A, Sturm AW, et al. Extensively drug-resistant tuberculosis as a cause of death in patients co-infected with tuberculosis and HIV
in a rural area of South Africa. Lancet [Online]; October 26, 2006. Available at
http://www.thelancet.com/journals/lancet/article/PIIS0140673606695731.
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