In November 2020, the WHO Global TB Programme (WHO/GTB) convened an online consultation and released new definitions of TB treatment outcomes, which were the same for DS-TB and DR-TB (97-99).
The principles guiding the update of the definitions were as follows:
- applicability to treatment regimens of different duration;
- a lessening of the traditional division between the intensive and continuation phases;
- identification of appropriate criteria for bacteriological conversion (or reversion) in relation to the definitions of “treatment failed”, “cured” and “treatment completed” that are grounded in knowledge from microbiology;
- consideration of the use of appropriate diagnostics for treatment monitoring;
- setting of clear parameters for defining treatment failure, based on reliable evidence of nonresponse or other reasons that lead to a decision to change or stop treatment; and
- aiming for practical clinical and programmatic monitoring, and feasible implementation.
A new optional definition, “sustained treatment success”, was also proposed for use in operational research only. Post-treatment follow-up may be useful, when or if it is feasible, for patients suffering from post-treatment sequelae, for example (100).
The new treatment outcome definitions are summarized in Table 10.1.
The 2020 treatment outcome definitions allow all patients with either DS-TB or DR-TB to have a treatment outcome assigned when completing treatment (cure or treatment success) or when unfavourable events occur (e.g. loss to follow-up, failure or death).
Although the definitions of treatment outcomes have been harmonized, minor differences remain between those for DS-TB and DR-TB (e.g. treatment monitoring by sputum culture for DR-TB and by sputum smear microscopy for DS-TB).
Despite some distinct treatment phases remaining in current regimens, the overall trend is towards monophasic regimens. Thus, it is best to avoid linking definitions to treatment phases; hence, the time thresholds for declaring cure or treatment failure have been revised.
Although the role of new bacteriological tests was considered, treatment monitoring will continue to rely on the available tools (i.e. sputum culture for DR-TB and sputum microscopy for DS-TB), despite their limitations.