7.3 Drug susceptibility pattern

Drug-susceptible tuberculosis (DS-TB) case

Patient with TB caused by a strain susceptible to first-line TB drugs.
In practice, patients with a strain not resistant to rifampicin and isoniazid are recorded (and treated) as patients with DS-TB.

Drug-resistant tuberculosis (DR-TB) case

Patients with DR-TB should be classified into one of the following categories [1] Citation 1. World Health Organization. Definitions and reporting framework for tuberculosis – 2013 revision (updated December 2014 and January 2020). Geneva: World Health Organization; 2020.
https://apps.who.int/iris/bitstream/handle/10665/79199/9789241505345_eng.pdf [2] Citation 2. World Health Organization. WHO consolidated guidelines on tuberculosis. Module 4: treatment - drug-resistant tuberculosis treatment. Geneva: World Health Organization; 2020.
https://www.who.int/publications/i/item/9789240007048 [3] Citation 3. World Health Organization. Meeting report of the WHO expert consultation on the definition of extensively drug-resistant tuberculosis, 27-29 October 2020. Geneva: World Health Organization; 2021.
https://www.who.int/publications/i/item/meeting-report-of-the-who-expert-consultation-on-the-definition-of-extensively-drug-resistant-tuberculosis :

• Isoniazid-resistant TB (Hr-TB): susceptibility to rifampicin and resistance to isoniazid
• Multidrug-resistant TB (MDR-TB) a Citation a. Patients with MDR-TB and those with RR-TB are grouped as patients with "MDR/RR-TB". : resistance to at least rifampicin and isoniazid
• Rifampicin-resistant TB (RR-TB) a Citation a. Patients with MDR-TB and those with RR-TB are grouped as patients with "MDR/RR-TB". : resistance to rifampicin, with or without resistance to other TB drugs
• Pre-extensively drug-resistant TB (pre-XDR-TB): MDR/RR-TB with additional resistance to any fluoroquinolone b Citation b. This definition applies to patients for whom DST for bedaquiline and linezolid has not been performed, and to patients for whom the DST result shows susceptibility to bedaquiline and linezolid.
• Extensively drug-resistant TB (XDR-TB): MDR/RR-TB with additional resistance to any fluoroquinolone, and at least either bedaquiline or linezolid.

Note: once the result of the full drug susceptibility test (DST) performed on a specimen collected prior to treatment initiation is obtained, patients should be reclassified if the DST shows resistance that could not be detected initially.

Unconfirmed drug-resistant tuberculosis case

Patient who is prescribed a treatment for DR-TB without DST result c Citation c. For example: contact with a known DR-TB case or failure of DS-TB treatment while waiting for DST result, or when a specimen cannot be obtained (e.g. EPTB). . These patients should be recorded in the register corresponding to their presumed resistance (i.e. to their prescribed treatment).

Note: if a DST result performed on a specimen collected prior to treatment initiation is obtained, patients should be reclassified in the appropriate category.