After Drug-resistant Tuberculosis, Now XDR

Studies of extensively drug-resistant (XDR) tuberculosis in an HIV-positive population in Kwazulu-Natal in South Africa have shown alarmingly high mortality rates. If this were to become a durable phenomenon, the progress made year after year against tuberculosis could be jeopardized, not only as regards tuberculosis control, but also HIV/AIDS, as together they form a fearsome enemy.

What is XDR-TB?MDR-TB (Multidrug Resistant TB) describes strains of tuberculosis that are resistant to at least the two main first-line TB drugs - isoniazid and rifampicin. XDR-TB, or Extensive Drug Resistant TB (also referred to as Extreme Drug Resistance) is MDR-TB that is also resistant to three or more of the six classes of second-line drugs.The description of XDR-TB was first used earlier in 2006, following a joint survey by WHO and the US Centres for Disease Control and Prevention (CDC).Resistance to anti-TB drugs in populations is a phenomenon that occurs primarily due to poorly managed TB care. Problems include incorrect drug prescribing practices by providers, poor quality drugs or erratic supply of drugs, and also patient non-adherence.What is the current evidence of XDR-TB?Recent findings from a survey conducted by WHO and CDC on data from 2000-2004 found that XDR-TB has been identified in all regions of the world but is most frequent in the countries of the former Soviet Union and in Asia.In the United States, 4% of MDR-TB cases met the criteria for XDR-TB.In Latvia, a country with one of the highest rates of MDR-TB, 19% of MDR-TB cases met the XDR-TB criteria.Separate data on a recent outbreak of XDR-TB in an HIV-positive population in Kwazulu-Natal in South Africa was characterized by alarmingly high mortality rates.Of the 544 patients studied, 221 had MDR-TB. Of the 221 MDR-TB cases, 53 were defined as XDR-TB. Of the 53 patients, 44 had been tested for HIV and all were HIV-positive.52 of 53 patients died, on average, within 25 days including those benefiting from antiretroviral drugs.Scarce drug resistance data available from Africa indicate that while population prevalence of drug resistant TB appears to be low compared to Eastern Europe and Asia, drug resistance in the region is on the rise. Given the underlying HIV epidemic, drug-resistant TB could have a severe impact on mortality in Africa and requires urgent preventative action.What action is required to prevent XDR-TB?XDR-TB poses a grave public health threat, especially in populations with high rates of HIV and where there are few health care resources. Recommendations outlined in the WHO Guidelines for the Programmatic Management of Drug Resistant Tuberculosis include:

strengthen basic TB care to prevent the emergence of drug-resistance
ensure prompt diagnosis and treatment of drug resistant cases to cure existing cases and prevent further transmission
increase collaboration between HIV and TB control programmes to provide necessary prevention and care to co-infected patients
increase investment in laboratory infrastructures to enable better detection and management of resistant cases.

(Source: World Health Organisation : January 2007.)