Evaluation of Xpert MTB/RIF Ultra for Diagnosis of Extrapulmonary Tuberculosis: A Retrospective Analysis in a Low-Tuberculosis Prevalence Setting

Abstract

Background: Extrapulmonary tuberculosis (EPTB) remains difficult to diagnose because the clinical specimens to be examined are often paucibacillary and obtained with difficulty from inaccessible sites. An updated Xpert® MTB/RIF Ultra (Ultra) test has been designed and licensed to improve sensitivity in the detection of Mycobacterium tuberculosis complex. The aim of the present study is to evaluate the performance of Ultra assay for the clinical diagnosis of EPTB in a low tuberculosis prevalence country. Methods: A retrospective analysis was performed at “A. O dei Colli” of Naples on consecutive extrapulmonary specimens for EPTB across a three-year period. All different types of extrapulmonary specimens were tested for EPTB by smear microscopy, culture and Ultra assay in accordance with relevant guidelines. Results: A total of 606 EPTB samples, 561 culture negative EPTB and 45 culture positive EPTB were included. Using culture as reference standard, the overall sensitivities and specificities of Ultra assay were 95.6% (95% CI 84.8 - 99.5) and 97.5% (95% CI 95.8 - 98.6) respectively. Sensitivity and specificity of Ultra for individual category of specimens were also performed. Conclusion: In a low-tuberculosis prevalence setting, Ultra assay confirms to have a good performance in the diagnosis of EPTB for all different extrapulmonary samples.