title: Added value of molecular assay Xpert MTB/RIF compared to sputum smear microscopy to assess the risk of tuberculosis transmission in a low-prevalence country.
abstract: Airborne precautions are required at hospital admission for patients with suspected pulmonary tuberculosis. The isolation is maintained until 3 serially collected sputum smears are acid-fast bacilli negative, a time- and labor-intensive method with limited sensitivity and specificity, which has a great impact on patient flow management. We evaluated the possibility of replacing the result of microscopy by the semiquantitative result of the molecular point-of-care test Xpert MTB/RIF to assess patients' transmission risk to quickly guide airborne isolation decisions in low-endemic countries. The performance of the Xpert MTB/RIF, used as a first-line test, was compared to the results of microscopy for specimens (n=242) collected from May 2010 to December 2014 in Lausanne, Switzerland. The sensitivity and specificity of Xpert MTB/RIF were 91.5% (65/71) and 99.6% (170/171), respectively, vs. 64.8% (46/71) and 94.2% (161/171) for microscopy. Samples with negative Xpert MTB/RIF were all smear negative for Mycobacterium tuberculosis (negative predictive value, 100%). The semiquantitative results of Xpert MTB/RIF-high, medium, low or very low-were found to correlate with acid-fast bacilli detection: positive predictive value of 100% (6/6), 96.5% (27/28), 52.2% (12/23) and 11.1% (1/9) respectively. Finally, when including clinical criteria, we identified 11 smear-negative but Xpert MTB/RIF-positive patients with a significant transmission potential. In conclusion, our data support the introduction of an Xpert MTB/RIF-based strategy as a replacement of smear microscopy for a faster and more accurate management of tuberculosis patients' transmission risk in a low-prevalence country.
authors.affiliation: Institute of Microbiology, University of Lausanne, University Hospital of Lausanne, Lausanne, Switzerland.
authors.forename: O
authors.initials: O
authors.lastname: Opota
authors.affiliation: Hospital Preventive Medicine and Infectious Diseases Service, University of Lausanne, University Hospital of Lausanne, Lausanne, Switzerland.
authors.forename: L
authors.initials: L
authors.lastname: Senn
authors.affiliation: Institute of Microbiology, University of Lausanne, University Hospital of Lausanne, Lausanne, Switzerland.
authors.forename: G
authors.initials: G
authors.lastname: Prod'hom
authors.affiliation: Pneumology Service, University Hospital of Lausanne, Lausanne, Switzerland.
authors.forename: J
authors.initials: J
authors.lastname: Mazza-Stalder
authors.affiliation: Infectious Diseases Service, University Hospital of Lausanne, Lausanne, Switzerland.
authors.forename: F
authors.initials: F
authors.lastname: Tissot
authors.affiliation: Institute of Microbiology, University of Lausanne, University Hospital of Lausanne, Lausanne, Switzerland; Infectious Diseases Service, University Hospital of Lausanne, Lausanne, Switzerland. Electronic address: gilbert.greub@chuv.ch.
authors.forename: G
authors.initials: G
authors.lastname: Greub
authors.affiliation: Institute of Microbiology, University of Lausanne, University Hospital of Lausanne, Lausanne, Switzerland.
authors.forename: K
authors.initials: K
authors.lastname: Jaton
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008853:Microscopy / Q000379:methods*; D008875:Middle Aged; D025202:Molecular Diagnostic Techniques / Q000379:methods*; D009169:Mycobacterium tuberculosis / Q000166:cytology / Q000235:genetics / Q000302:isolation & purification*; D019095:Point-of-Care Systems; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity; D013183:Sputum / Q000382:microbiology*; D013557:Switzerland; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis*; D055815:Young Adult
keywords: Acid-fast bacilli staining; Molecular POCT; Molecular diagnostic; Real-time PCR; Transmissibility; Tuberculosis diagnosis; Xpert MTB/RIF