P40
Evaluation of Xpert MTB/XDR testing in a low tuberculosis incidence setting.
M T Tórtola Fernández(1,2) M C Vivas(1) M Mena(1) A Rando Segura(1) A Rando Segura()
1:Hospital Universitario Vall d'Hebron; 2:Universidad Autónoma de Barcelona (UAB)
Introduction
Xpert MTB/XDR detects resistance to isoniazid, fluoroquinolones, ethionamide and second line injectable drugs. The objective was to evaluate Xpert in a clinical laboratory with a low incidence of tuberculosis.
Methods
We performed Xpert/MTB on all those samples that had a previous positive result with Xpert/MTB ultra. GenoType MTBDRplus and the first-line and second-line drug susceptibility testing (DST) were performed. When any discrepancy was detected between the genotypic and phenotypic results for rifampin, sequencing of the rpob gene was performed.
Results
Between October 2021 and April 2022 we enrolled 13 patients. The samples studied were 8 respiratory samples and 5 extrapulmonary samples. MDR-TB was detected in four samples, monoresistance to isoniazid was detected in 2 samples, and resistance to fluoroquinolones (FQ) was detected in 1 sample. Concordance of Xperts with GenoType MTBDRplus was 100%. DST could only be performed on 10 isolates since 3 cultures are pending growth. Nine DST coincided with the results obtained with Xpert MTB/RIF ultra and Xpert MTB/XDR, one isolate was resistant to rifampicin with Xpert MTB/RIF ultra and sensitive with DST. When sequencing of the rpob gene, L533P mutation was detected, which is a low-level resistance mutation.
Conclusions
Xpert MTB/XDR is a fast and very useful technique since it allows the detection of monoresistance to isoniazid and resistance to fluoroquinolones. FQ is recommended for the treatment of MDR-TB and is also widely used in daily clinical practice. Xpert MTB/XDR is also very useful in those patients who present toxicity to the standard treatment of tuberculosis.