Usefulness of Xpert Mycobacterium tuberculosis/Rifampicin (MTB/RIF) to Guide Respiratory Isolation Precautions in a Tuberculosis Low Prevalence Setting

Abstract

Background. The Xpert MTB/RIF is a point-of-care molecular test that allows rapid detection of tuberculosis (TB) and rifampicin resistance. Early diagnosis of pulmonary (PTB) and extrapulmonary (EPTB) tuberculosis is critical, especially in terms of indications for patient treatment and infection prevention in a low prevalence setting. Methods. A retrospective study in individuals aged >=18 years undergoing evaluation for TB was done from August 2011 to May 2013 in two large hospitals in Belgium (Ghent University and Sint-Lucas Hospital). Xpert MTB/RIF (Cepheid, Sunnyvale, CA) testing was performed in routine laboratory conditions, offering continuous test access. One single analysis was performed during diagnostic evaluation of high-risk patients driven by clinicians' demand. Laboratory and clinical data were collected from patient records and processed using descriptive analysis. Results. In total, 107 patients were included: 66 PTB and 41 EPTB suspects. In the PTB and the EPTB group, 80% and 39% from the patients had 1 or more clinical symptom suggesting possible TB. Radiographic findings were abnormal in 91% and 78% of the PTB and EPTB group, respectively. Twenty-seven percent of all patients had culture-confirmed TB (16% PTB and 11% EPTB). Xpert MTB/RIF demonstrated a sensitivity of 88% in the PTB group and 75% in the EPTB group, while microscopy of auramine-stained smears detected 71% and 50%, respectively. Xpert MTB/RIF predicted the absence of culture-positive TB with an overall NPV of 94% and predicted absence of smear-positive TB with an NPV of 100% for both PTB and EPTB. Xpert MTB/RIF detected M. tuberculosis in 18% of PTB and 25% of EPTB specimens that were missed by microscopy. For two samples M. tuberculosis was detected by Xpert MTB/RIF, but was missed by both culture and microscopy, with the two patients responding clinically on TB therapy. Conclusion. In comparison to microscopy, the sensitivity of one-specimen Xpert MTB/RIF was higher in this low prevalence setting. The excellent NPV of the assay makes it a fast and reliable tool for the clinician to exclude tuberculosis. These data indicate the usefulness of Xpert MTB/RIF in algorithms assessing the need for respiratory isolation in a population of high-risk patients in a low prevalence setting.