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XDR-TB in the U.S.

Cases of extensively drug-resistant TB have been reported in this country every year since 1993.

Recent attention has focused on outbreaks of extensively drug-resistant TB (XDR-TB) — i.e., infection with Mycobacterium tuberculosis strains resistant to isoniazid, a rifamycin, a fluoroquinolone, and a second-line injectable agent (JW Infect Dis Aug 6 2008). Treatment options are limited, and the mortality rate is high. CDC investigators analyzed national surveillance data for 1993 through 2007 to define the scope of XDR-TB in the U.S.

During this 15-year period, 212,896 culture-confirmed TB cases were reported in the U.S. Drug-susceptibility results for isoniazid and rifamycin were available for 201,399 of them. A total of 183,536 cases were caused by drug-susceptible (DS) strains; 3379 cases were caused by strains resistant to at least isoniazid and a rifamycin (i.e., multidrug-resistant [MDR]), and 83 such cases met criteria for XDR-TB. Fifty-five of the XDR-TB cases were identified based on the initial positive culture, and 28 were identified based on a follow-up culture.

XDR-TB cases were reported each year, ranging from 18 cases in 1993 to 1 case each in 2001 and 2003. The majority of XDR-TB patients were male (64%), U.S.-born (54%), unemployed (53%), and aged 25 to 44 (58%). Compared with DS-TB patients, XDR-TB patients were more likely to be Hispanic and to reside in a correctional facility. Sputum-culture conversion to negative occurred in only 66% of the XDR-TB patients (median time to conversion, 183 days). Thirty-five percent of the XDR-TB patients died, compared with 24% of the MDR-TB patients and 10% of the DS-TB patients.

Comment: These data affirm the concern regarding XDR-TB. Unfortunately, information on treatment history, exposure history, and genotyping are not included in case reporting. Such data could provide insight into case clusters and the relative transmissibility of XDR-TB.

— Richard T. Ellison III, MD

Published in Journal Watch Infectious Diseases November 26, 2008

Citation(s):

Shah NS et al. Extensively drug-resistant tuberculosis in the United States, 1993-2007. JAMA 2008 Nov 12; 300:2153.

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