Added Value of Xpert MTB/RIF Ultra for Diagnosis of Pulmonary Tuberculosis in a Low-Prevalence Setting

• Published in: Journal of clinical microbiology 2019-02, Vol.57 (2)
• Main Authors: Opota, Onya, Zakham, Fathiah, Mazza-Stalder, Jesica, Nicod, Laurent, Greub, Gilbert, Jaton, Katia
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Aged, 80 and over; Antitubercular Agents - pharmacology; Drug Resistance, Bacterial; Female; Humans; Male; Microbial Sensitivity Tests - methods; Middle Aged; Molecular Diagnostic Techniques - methods; Mycobacteriology and Aerobic Actinomycetes; Mycobacterium tuberculosis - drug effects; Mycobacterium tuberculosis - genetics; Mycobacterium tuberculosis - isolation & purification; Rifampin - pharmacology; Sensitivity and Specificity; Switzerland; Tuberculosis, Pulmonary - diagnosis; Young Adult
• ISSN: 0095-1137; 1098-660X
• DOI: 10.1128/JCM.01717-18

Xpert MTB/RIF (Xpert) for direct molecular detection of and rifampin resistance from clinical specimens has dramatically improved the diagnosis of tuberculosis (TB). Xpert MTB/RIF Ultra (Ultra) is proposed as a substitute of Xpert with increased sensitivity and improved rifampin resistance detection. We evaluated the diagnostic performance of Ultra and Xpert for pulmonary TB diagnosis in a low-TB-burden setting. Performance of Ultra and Xpert were compared to culture on respiratory specimens from patients with suspected pulmonary TB (November 2016 to August 2018; = 196) in Lausanne (Switzerland). Clinical data were used to investigate discrepant results. Correlation between semiquantitative result of Ultra and smear microscopy status for the detection of acid-fast bacilli (AFB) was established. The sensitivities of Xpert and Ultra were 82.9% (39/47) and 95.8% (45/47), respectively, when considering all culture-positive specimens, 100% (23/23) for both assays on smear-positive specimens, and 66.7% (16/24) and 91.7% (22/24) on smear-negative specimens. Using culture as gold standard, the specificities of Xpert and Ultra were 97.3% (145/149) and 96.64% (144/149), respectively. All the patients with Ultra-positive results with the new category "trace" were diagnosed with active TB based on clinical findings and microbiological culture. The semiquantitative results of both Xpert and of Ultra positively correlated with the semiquantitative result of AFB detection. Our data support an increased sensitivity of Ultra compared to Xpert in a low-prevalence setting. Correlation between the Ultra semiquantitative result and AFB burden can help in evaluating a patient's transmission potential.