OpiniãoDrug-susceptible TB (DS-TB): A bacteriologically confirmed or clinically diagnosed case of TB without evidence of infection with strains resistant to rifampicin and isoniazid.
Drug susceptibility testing (DST): In vitro testing using either: 1) molecular, genotypic techniques to detect resistance-conferring mutations; or 2) phenotypic methods to determine susceptibility to a medicine.¹
Extensive (or advanced) pulmonary tuberculosis (TB) disease: Presence of bilateral cavitary disease or extensive parenchymal damage on chest radiography. In children aged under 15 years, advanced disease is usually defined by the presence of cavities or bilateral disease on chest radiography.²
New case: a newly registered episode of TB in a patient who has never been treated for TB or who has taken anti-TB medicines for less than 1 month.
Rifampicin-susceptible, isoniazid-resistant TB (Hr-TB): TB caused by M. tuberculosis strains resistant to isoniazid and susceptible to rifampicin.
A bacteriologically confirmed TB case is one from whom a biological specimen is positive by smear microscopy, culture or a WHO-recommended rapid diagnostic (such as Xpert MTB/RIF). All such cases should be notified, regardless of whether TB treatment has started.
A clinically diagnosed TB case is a person who does not fulfil the criteria for bacteriological confirmation but has been diagnosed with active TB by a clinician or other medical practitioner who has decided to give the patient a full course of TB treatment. This definition includes cases diagnosed on the basis of X-ray abnormalities or suggestive histology and extrapulmonary cases without laboratory confirmation.
Pulmonary tuberculosis (PTB) refers to any bacteriologically confirmed or clinically diagnosed case of TB involving the lung parenchyma or the tracheobronchial tree.
Extrapulmonary tuberculosis (EPTB) refers to any bacteriologically confirmed or clinically diagnosed case of TB involving organs other than the lungs (e.g. pleura, lymph nodes, abdomen, genitourinary tract, skin, joints and bones, meninges).
Rifampicin-resistant TB (RR-TB): TB caused by M. tuberculosis strains resistant to rifampicin. These strains may be susceptible or resistant to isoniazid (i.e. MDR-TB), or resistant to other first-line or second-line TB medicines. In these guidelines and elsewhere, MDR-TB and RR-TB cases are often grouped together as MDR/RR-TB and are eligible for treatment with MDR-TB regimens.
Pre-XDR-TB:³ TB caused by Mycobacterium tuberculosis (M. tuberculosis) strains that fulfil the definition of MDR/RR-TB and that are also resistant to any fluoroquinolone.⁴
XDR-TB: TB caused by Mycobacterium tuberculosis (M. tuberculosis) strains that fulfil the definition of MDR/RR-TB and that are also resistant to any fluoroquinolone and at least one additional Group A drug.⁵
Treatment support terminology in this document is used to describe an approach to supporting patients who are taking prescribed doses of TB medicines in order to help ensure adherence to treatment and maximize its efficacy. Treatment support needs to be provided in the context of people-centred care and should be based on the individual patient’s needs, acceptability and preferences. It includes aspects of support, motivation and understanding of patients without coercion. Historically, this group of interventions were labelled as “directly observed treatment” or DOT.
¹ Implementing tuberculosis diagnostics: a policy framework. Geneva: World Health Organization; 2015. (http://apps.who.int/iris/ bitstream/10665/162712/1/9789241508612_eng.pdf, accessed 27 September 2021).
² WHO consolidated guidelines on tuberculosis. Module 4: treatment – drug-resistant tuberculosis treatment. (https://apps.who.int/iris/ rest/bitstreams/1280998/retrieve, accessed 27 September 2021).
³ 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-consultationon-the-definition-of-extensively-drug-resistant-tuberculosis, accessed 27 September 2021).
⁴ The fluoroquinolones include levofloxacin and moxifloxacin because these are the fluoroquinolones currently recommended by WHO for inclusion in shorter and longer regimens.
⁵ The Group A drugs are currently levofloxacin or moxifloxacin, bedaquiline and linezolid; therefore, XDR-TB is MDR/RR-TB that is resistant to a fluoroquinolone and either bedaquiline or linezolid (or both). The Group A drugs may change in the future. Consequently, the terminology “Group A” is appropriate here and will apply to any Group A drugs in the future.