During the 1990s, multidrug-resistant (MDR) tuberculosis (TB), defined as resistance to at least isoniazid and rifampin, emerged as a threat to TB control worldwide. MDR TB treatment requires the use of second-line drugs (SLDs) that are less effective, more toxic, and costlier than first-line isoniazid- and rifampin-based regimens. In 2000, a committee was created to increase access to SLDs worldwide while ensuring their proper use to prevent increased drug resistance. While assisting MDR TB treatment programs worldwide, the committee en-countered reports of multiple cases of TB with resistance to virtually all SLDs. An international survey was conducted to assess the frequency and distribution of extensively drug-resistant (XDR) TB cases. The survey found that during 2000 to 2004, of 17,690 TB isolates, 20% were MDR and 2% were XDR. In addition, population-based data on drug susceptibility of TB isolates were obtained from the United States for 1993 to 2004, where 4% of MDR TB cases were XDR. XDR TB has emerged worldwide as a threat to public health and TB control, raising concerns of a future epidemic of virtually untreatable TB. New anti-TB drug regimens, better diagnostic tests, and international standards for SLD-susceptibility testing are needed for effective detection and treatment of drug-resistant TB.
(Source: Morbidity and Mortality Weekly Report, Centers for Disease Control and Prevention, March 24, 2006)
