New definitions of extensively drug resistant tuberculosis: update from the World Health Organization

<b>Background:</b> Extensively drug resistant tuberculosis (XDR-TB) is a severe form of multidrug-resistant (MDR)-TB. Prior to 2021 it was defined as: TB that is resistant to any fluoroquinolone and to at least one of three second-line injectable drugs, in addition to multidrug resistance (WHO, 2006). <b>Aims and objectives:</b> The objectives of a WHO convened online expert consultation meeting held in October 2020 were to determine how recent changes in treatment regimens and diagnostics for drug-resistant TB might affect the definition of XDR-TB and discuss options for changing it. <b>Methods:</b> The latest WHO policy recommendations on treatment regimens and diagnostics for drug resistant TB were presented as well as independent research. <b>Results:</b> The WHO has proposed a definition of pre-XDR-TB as well as a revised definition of XDR-TB, which apply from January 2021 (Table 1) (WHO, 2021).