The World Health Organization (WHO)’s Global TB Program has revised the definition of extensively drug-resistant tuberculosis (XDR-TB). The program also defined pre-XDR-TB for the first time, highlighting the seriousness of these forms of TB, the WHO said.
New definitions for pre-XDR and XDR-TB will help to define more precisely groups of TB patients who require complex treatment regimens. These new definitions are also expected to lead to better reporting, surveillance and monitoring of drug-resistant TB. They may also stimulate the development of better treatment regimens for these dangerous forms of TB disease, the WHO said.
The new definition of pre-XDR-TB is: TB caused by Mycobacterium tuberculosis (M. tuberculosis) strains that meet the definition of multi-drug resistant and rifampicin-resistant TB (MDR/RR-TB) and which are also resistant to any fluoroquinolone. The definition of MDR-TB remains unchanged.
The updated definition of XDR-TB is: TB caused by Mycobacterium tuberculosis (M. tuberculosis) strains that meet the definition of MDR/RR-TB and that are also resistant to any fluoroquinolone and at least one additional Group A drug (Group A drugs are the most potent group of drugs in the ranking of second-line medicines for the treatment of drug-resistant forms of TB using longer treatment regimens and comprise levofloxacin, moxifloxacin, bedaquiline and linezolid).
About 470,000 people fall ill with MDR/RR-TB and about 180,000 die from this form of TB each year, according to WHO estimates. Globally, in 105 countries with representative data, 20 percent of the people with MDR/RR-TB also have resistance to another potent drug for the treatment of drug-resistant TB – a fluoroquinolone. Extensively drug resistant TB is a more serious form of MDR-TB, with poorer treatment outcomes reported for those affected by this condition.
