TB is largely curable with treatment that is affordable and widely accessible. If a TB treatment regimen is not administered correctly, it may fail to deliver a relapse-free cure, thus increasing transmission and accelerating the emergence of drug resistance. Monitoring the effectiveness of TB treatment is thus critically important in both clinical practice and surveillance, to maximize the quality of individual patient care and the effectiveness of public health action. Hence, standardized TB treatment outcome definitions have been a feature of WHO policies and national TB surveillance systems for many years, as a cornerstone of effective TB strategies. This standardization has allowed the monitoring of TB treatment outcomes over time at national and global levels.
Standardized treatment outcome definitions for DS-TB have been in widespread use for more than 3 decades, and outcome definitions for DR-TB were first proposed in 2005 (148). The development of DR-TB treatment outcome definitions was based on the outcome definitions for DS-TB in use at the time. The DR-TB treatment outcome definitions were adopted by WHO soon after and remained largely unchanged until 2013, when WHO updated its TB definitions and reporting framework (149). As treatment regimens for DR-TB have significantly changed in composition and duration, an update of the treatment outcome definitions and monitoring parameters was necessary.