Comparison of Xpert MTB/RIF Ultra with Xpert MTB/RIF for the detection of Mycobacterium tuberculosis and rifampicin resistance in a primary-level clinic in rural China

The Xpert MTB/RIF Ultra (Ultra) is not yet used for the diagnosis of tuberculosis (TB) in China. We compared the performance of the Xpert and Ultra for detecting Mycobacterium tuberculosis and rifampicin resistance in a primary-level clinic in rural China. Sputum samples from suspected pulmonary TB patients were collected and subjected to smear microscopy, liquid culture, Xpert and Ultra tests. We then compared the sensitivity and specificity of Xpert and Ultra for diagnosing TB against liquid culture. Whole-genome sequencing was performed to predict rifampicin resistance and the results were compared with the Xpert and Ultra tests. The sensitivities of Xpert and Ultra were 88.1% and 95.1%, and the specificities were 91.9% and 84.4%, respectively. Among the 61 smear-negative culture-positive patients, the sensitivities of Xpert and Ultra were 80.3% and 91.8%. All Xpertpositive patients were Ultra-positive. Among culture-negative Xpert or Ultra-positive patients, 69.6% were taking anti-TB drugs or had a previous history of TB. Of the samples that Ultra classified as trace, nearly 25% were probably false-positives. Both Xpert and Ultra accurately detected all rifampicin-resistant patients. In conclusion, Ultra was more sensitive than Xpert, especially for smear-negative patients but had decreased specificity with more false-positives, especially with Ultra trace results.