Impact of the revised definition of extensively drug-resistant tuberculosis

Recently, the World Health Organization (WHO) has released a revised definition of extensively drug-resistant (XDR) tuberculosis (TB) that should be used for clinical and surveillance purposes starting from 1 January, 2021 [1, 2]. The previous definition of XDR-TB was TB that is resistant to any fluoroquinolone (levofloxacin and/or moxifloxacin) and to at least one of three second-line injectable drugs (SLIs: capreomycin, kanamycin and amikacin), in addition to multidrug resistance. The revised definition is: TB caused by Mycobacterium 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. WHO group A drugs currently include fluoroquinolones (levofloxacin or moxifloxacin), linezolid and bedaquiline. In addition, pre-XDR-TB is now a WHO-endorsed definition, identified as MDR/RR-TB with any fluoroquinolone resistance. Although the previous definition of XDR-TB has proved to be predictive of poor treatment outcome [3], the 2020 update appears in line with recent changes of treatment regimens given, i.e. less frequent use of SLI in favour of the potent oral drugs, bedaquiline and linezolid. Moreover, a large meta-analysis failed to show an association between mortality reduction and SLI use, whereas this association was shown for bedaquiline and linezolid [4]. In this study, we aimed to measure retrospectively the impact of the revised definition on the epidemiology of XDR-TB in France. The revised WHO definition of XDR-TB decreases the number of TB cases classified as such, and allows better focus on the most difficult to treat cases of TB <https://bit.ly/3tgaXQA> We thank all technicians working at the CNR-MyRMA for their dedication to their work.