WHO announces updated definitions of extensively drug-resistant TB

02 February 2021

Article: 55/0505

The World Health Organization’s (WHO) Global Tuberculosis (TB) Programme has revised the definition of extensively drug-resistant TB (XDR-TB), and also defined pre-XDR-TB for the first time.

The new definition of pre-XDR-TB is: 

  • TB caused by Mycobacterium tuberculosis (M. tuberculosis) strains that fulfil the definition of multidrug resistant and rifampicin-resistant TB (MDR/RR-TB), and which are also resistant to any fluoroquinolone.

The updated definition of XDR-TB is: 

  • TB caused by M. tuberculosis strains that fulfil the definition of MDR/RR-TB and which 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.

The new definitions for pre-XDR and XDR-TB aim to help define more precisely groups of TB patients who require complex treatment regimens. The WHO hope that these new definitions will also lead to better reporting, surveillance and monitoring of drug-resistant TB.

Source: WHO, 27 January 2021