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XDR TB: A Growing Public Health Concern
Global increases in multidrug-resistant and extensively drug-resistant TB are threatening both TB and HIV treatment programs worldwide and raise concerns about a future epidemic of virtually untreatable TB.
Extensively drug-resistant tuberculosis (XDR TB) is not a new public health problem, but it rose to the forefront in 2006, when several reports detailed its prevalence and severity, particularly among HIV-coinfected patients.
In an international, retrospective survey of nearly 18,000 TB isolates collected from 2000 through 2004, 20% of samples were multidrug-resistant (MDR) TB, and 10% of these (or 2% overall) were XDR TB (MMWR Morb Mortal Wkly Rep 2006; 55:301). A smaller survey in Iran yielded similar results, with 11% of MDR TB strains identified as XDR TB (Clin Infect Dis 2006; 43:841). Although XDR TB is present throughout the world, the international survey suggests that it is most common in Asia and Eastern Europe. However, because of poor surveillance and lack of resistance testing, the frequency in Africa is probably higher than was reported.
Emerging evidence from sub-Saharan Africa indicates an alarming rise in the prevalence of both MDR TB and XDR TB. Between 2000 and 2004, only 347 cases of XDR TB were identified worldwide. However, in 2006, more than 300 cases were detected in KwaZulu-Natal, South Africa, alone. In a study conducted in a rural subdistrict of this province between January 2005 and March 2006, MDR TB was present in 221 (41%) of 542 patients with positive cultures for Mycobacterium tuberculosis; 53 of these patients had XDR TB. Of the 44 with known HIV status, all were HIV-infected. XDR TB was rapidly — and almost uniformly — fatal, with 98% of patients dying a median 16 days after specimen collection. Notably, 55% of patients with XDR TB had never been treated for TB, and 30% had documented cure or completion of their previous TB treatment course (ACC Nov 13 2006).
The association between HIV and XDR TB has also been documented in other regions of the world. In Latvia, for example, 10% of patients with XDR TB were HIV-coinfected, compared with 3% of patients with MDR TB (Leimane V. 37th Union World Conference on Lung Health, Paris, 2006).
The convergence of the HIV and TB epidemics is placing great strain on healthcare services in resource-poor settings and threatens to overturn the survival gains achieved by DOTS (Directly Observed Treatment, Short Course) programs for TB and by antiretroviral therapy for HIV infection. The findings of 2006 highlight the urgent need for active surveillance of MDR TB and XDR TB, as well as improved TB-treatment adherence, better diagnostic tools, and new therapeutic drugs for TB. The South African Medical Research Council, the CDC, and the WHO have put forward a seven-point emergency plan to combat XDR TB.
— Salim S. Abdool Karim, MD, PhD
Published in AIDS Clinical Care December 29, 2006