Ideally, genotypic DST is indicated for all patients at the start of TB treatment, as to ensure that the most appropriate therapy for each individual can be determined23.
At the very least, the following patients should have DST performed to isoniazid and rifampicin, or rifampicin alone:
– Previously treated patients;
– Persons who develop active TB after exposure to a patient with documented MDR-TB;
– Patients who remain smear-positive after two months of therapy;
– New patients in countries with high prevalence of MDR-TB.
The following groups are targeted for DST for second-line drugs:
– Patients with a DST showing a resistance to at least rifampicin;
– Patients with a DST showing a resistance to at least isoniazid and another Group 1 drug;
– Patients who remain culture positive on or after Month 4 of an MDR-TB treatment or who reconvert to a positive culture after Month 4;
– Persons who develop active TB after exposure to a patient with documented MDR-TB.