Performance of Xpert MTB/RIF Ultra assay on respiratory and extra-respiratory samples in a high-resource setting with a low tuberculosis prevalence

The Xpert MTB/RIF assay is a molecular assay that has improved the detection of tuberculosis and rifampicin resistance. However, its sensitivity is limited in patients with paucibacillary disease. Xpert MTB/RIF Ultra has been developed to resolve this limitation. We compared the performance of Xpert Ultra with that of culture for detection of Mycobacterium tuberculosis and rifampicin resistance. We reviewed laboratory records for 848 respiratory and 419 extrarespiratory samples that were processed between April 2018 and October 2019. The sensitivity, specificity, negative predictive value, and positive predictive value of Xpert Ultra were 94.8%, 98%, 98.8%, and 91.3% for respiratory samples and 83.8%, 96.9%, 98.4% and 72.1% for nonrespiratory ones. We found 26 culture-negative/Ultra-positive samples. Most of them have low bacillary burden and more than half belonged to patients with history of tuberculosis. Xpert Ultra demonstrates excellent diagnostic accuracy for tuberculosis detection, including paucibacillary specimens. In patients with history of tuberculosis, PCR results should be interpreted carefully.