Drug-resistant tuberculosis treatment

5.3 Subgroup considerations
The recommendation would apply to any longer regimen, regardless of the number of Group A, B 
or C agents used and whether an injectable (intensive) phase was used or not. The GDG considered 
that the findings may apply to other key patient
subgroups.
Patients <15 years of age with MDR/RR-TB comprised less than 2% of the IPD-MA analysed for 
PICO question 11 (MDR/RR-TB, 2018). Younger children usually cannot produce sufficient sputum 
spontaneously to allow a bacteriological diagnosis (many are typically sputum smear-microscopy 
negative). In these patients, culture may be a more sensitive means to detect viable TB bacilli even 
if very few organisms are present in the sputum or other samples, below the detection threshold of 
direct microscopy. However, in children who are unable to expectorate, gastric aspirates or induced 
sputa may be possible but the repetition of such tests at monthly frequency may not be
acceptable.
Extrapulmonary disease is commonly paucibacillary and biological specimens may therefore contain 
few or no bacilli. In such a situation, detection of persistent disease is more likely with culture, although 
collection of samples often poses problems. Direct microscopy should still be attempted because it 
may determine positivity much faster than
culture.
HIV-negative individuals with TB typically have higher bacterial counts in the sputum and a greater 
likelihood of detection with smear microscopy. In such a situation, one may expect that the difference 
in test sensitivity between smear and culture would be less extreme, as fewer patients would have 
subthreshold bacterial counts. However, past studies on datasets from multiple sites in which HIV 

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WHO consolidated 
guidelines 
on
tuberculosis: 
drug-resistant tuberculosis treatment
57
positivity was low reported findings that led to the WHO recommendation even in 2011 for joint use 
of both microscopy and culture, preferably every
month.