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Extensively drug-resistant TB (XDR-TB)

Extensively drug-resistant TB (XDR-TB), also known as Extremely Drug-Resistant TB, is emerging as an even more ominous threat. XDR-TB is defined as TB that is resistant to any fluoroquinolone, and at least one of three injectable second-line drugs (capreomycin, kanamycin, and amikacin), in addition to isoniazid and rifampin. This makes XDR-TB treatment extremely complicated, if not impossible, in resource-limited settings.

In a 2006 XDR-TB outbreak in KwaZulu-Natal, South Africa, 52 of 53 people who contracted the disease died within months. It is estimated that 70% of XDR-TB patients die within a month of diagnosis.

The most recent drug-resistance surveillance data issued by the WHO estimates that an average of roughly 5 percent of MDR-TB cases are XDR-TB. Estimating the incidence of XDR-TB is extremely difficult because most laboratories are ill-equipped to detect and diagnose it; it is thought that the majority of XDR-TB cases go undocumented.

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Multidrug-Resistant Tuberculosis (MDR-TB)

Multidrug-resistant (MDR) tuberculosis is defined as disease caused by strains of Mycobacterium tuberculosis that are at least resistant to treatment with isoniazid and rifampicin; extensively drug-resistant (XDR) tuberculosis refers to disease caused by multidrug-resistant strains that are also resistant to treatment with any fluoroquinolone and any of the injectable drugs used in treatment with second-line anti-tuberculosis drugs (amikacin, capreomycin, and kanamycin). MDR tuberculosis and XDR tuberculosis are serious threats to the progress that has been made in the control of tuberculosis worldwide over the past decade.

The emergence and spread of multidrug-resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB) are major medical and public problem, threatening the global health.