Evaluation of Xpert MTB/RIF Ultra performance for pulmonary tuberculosis diagnosis on smear-negative respiratory samples in a French centre
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Tuberculosis (TB) is a worldwide public health concern, including in high-resource countries with a low prevalence of TB. Xpert MTB/RIF assay was developed to improve TB and rifampicin (RIF) resistance detection, but sensitivity remains poor on smear-negative sputum. Xpert MTB/RIF Ultra assay was designed to enhance the sensitivity of TB detection in clinical samples. Herein, we evaluated retrospectively the performance of this test on smear-negative respiratory samples. Respiratory specimens with smear-negative and a Mycobacterium tuberculosis (MTB) complex-positive culture were retrospectively selected from those taken from patients during routine care, and analysed in the Mycobacteria Laboratory of the Lyon University hospital, France. Specimens were stored at − 20 °C before testing by Xpert MTB/RIF Ultra. For each sample, growth delay and date of anti-TB treatment initiation were recorded. Forty-six samples—29 sputum, 8 bronchial aspirates, 6 broncho-alveolar lavages, and 3 gastric aspirates—were selected. Among samples collected before treatment initiation (n = 33), sensitivity was 81.8% (95% CI [64.5; 93.0]) and there was a significant correlation between the quantitative measurements (Ct) of Xpert MTB/RIF Ultra assay and the time to growth detection in culture. Among samples collected after treatment initiation (n = 12), sensitivity was 100%, without correlation with time to growth detection due to presence of afterglow DNA in samples. In high-resource settings, the Xpert MTB/RIF Ultra test represents a useful tool for pulmonary TB diagnosis, notably for the paucibacillary forms. Moreover, quantitative measurement of Xpert MTB/RIF Ultra could help to predict time to MTB culture positivity and be used as a quality indicator of MTB culture process.
KeywordsXpert MTB/RIF Ultra Pulmonary tuberculosis Diagnosis High-resource setting Smear-negative
We thank the ECCMID (European Congress of Clinical Microbiology and Infectious Diseases) 2018 Programme Committee to have accepted this work for ECCMID 2018 congress (ePoster session), and Philip Robinson (DRCI, Hospices Civils de Lyon) for help in manuscript preparation. We thank Cepheid for having provided the Xpert MTB/RIF Ultra cartridges used for this study.
EH, CG, IF, JPR, GL, and OD designed the experiments. EH, AM, LC, and CB performed the experiments. EH, GL, and OD wrote the manuscript.
Compliance with ethical standards
This study was in accordance with the ethics committee of the Lyon University hospital, France (declared sample collection: DC-2011-1306). In accordance with French legislation, written informed patient consent was not required to compare technical performance of assays with clinical specimens collected following clinical recommendation.
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