Comparison of the Xpert Flu/RSV XC and Xpress Flu/RSV assays

Molecular diagnostics for influenza and respiratory syncytial virus (RSV) have become commonplace, and various tests and systems have been cleared by the FDA for use in the United States. We performed a retrospective study to compare the Cepheid Xpress Flu/RSV assay with the Xpert Flu/RSV XC assay, using laboratory-developed tests (LDTs) as the reference method. The Xpress assay was 100% accurate compared to LDTs, whereas the Xpert Flu/RSV XC assay was 96.0% accurate. The Xpress test was determined to be faster and more sensitive than the XC assay

Multicenter evaluation of the Xpert Norovirus assay for detection of norovirus genogroups I and II in fecal specimens

Norovirus is the most common cause of sporadic gastroenteritis and outbreaks worldwide. The rapid identification of norovirus has important implications for infection prevention measures and may reduce the need for additional diagnostic testing. The Xpert Norovirus assay recently received FDA clearance for the detection and differentiation of norovirus genogroups I and II (GI and GII), which account for the vast majority of infections. In this study, we evaluated the performance of the Xpert Norovirus assay with both fresh, prospectively collected ( n = 914) and frozen, archived ( n = 489) fecal specimens. A Centers for Disease Control and Prevention (CDC) composite reference method was used as the gold standard for comparison. For both prospective and frozen specimens, the Xpert Norovirus assay showed positive percent agreement (PPA) and negative percent agreement (NPA) values of 98.3% and 98.1% for GI and of 99.4% and 98.2% for GII, respectively. Norovirus prevalence in the prospective specimens (collected from March to May of 2014) was 9.9% ( n = 90), with the majority of positives caused by genogroup II (82%, n = 74). The positive predictive value (PPV) of the Xpert Norovirus assay was 75% for GI-positive specimens, whereas it was 86.5% for GII-positive specimens. The negative predictive values (NPV) for GI and GII were 100% and 99.9%, respectively

Evaluation of a novel multiplex PCR panel compared to quantitative bacterial culture for diagnosis of lower respiratory tract infections

Quantitative bacterial culture of bronchoalveolar lavage fluids (BALF) is labor-intensive, and the delay involved in performing culture, definitive identification, and susceptibility testing often results in prolonged use of broad-spectrum antibiotics. The Unyvero lower respiratory tract (LRT) panel (Curetis, Holzgerlingen, Germany) allows the multiplexed rapid detection and identification of 20 potential etiologic agents of pneumonia within 5 h of collection. In addition, the assay includes detection of gene sequences that confer antimicrobial resistance. We retrospectively compared the performance of the molecular panel to routine quantitative bacterial culture methods on remnant BALF. Upon testing 175 BALF, we were able to analyze positive agreement of 181 targets from 129 samples, and 46 samples were negative. The positive percent agreement (PPA) among the microbial targets was 96.5%, and the negative percent agreement (NPA) was 99.6%. The targets with a PPA of <100% were Staphylococcus aureus (34/37 [91.9%]), Streptococcus pneumoniae (10/11 [90.9%]), and Enterobacter cloacae complex (2/4 [50%]). For the analyzable resistance targets, concordance with phenotypic susceptibility testing was 79% (14/18). This study found the Unyvero LRT panel largely concordant with culture results; however, no outcome or clinical impact studies were performed

Performance Characteristics of Xpert Flu/RSV XC Assay

The Xpert Flu/RSV XC assay was compared to laboratory-developed tests (LDTs) ( n = 207) and the Xpert Flu assay ( n = 147) using archived nasopharyngeal swabs. The percentages of positive agreements with LDTs were 97.8% for influenza A, 97.2% for influenza B, and 89.3% for RSV. The sensitivity of influenza detection was improved with the Xpert Flu/RSV XC assay compared to the Xpert Flu assay

Comparison of the Biofire FilmArray RP, Genmark eSensor RVP, Luminex xTAG RVPv1, and Luminex xTAG RVP Fast Multiplex Assays for Detection of Respiratory Viruses

There are several U.S. FDA-cleared molecular respiratory virus panels available today, each with advantages and disadvantages. This study compares four multiplex panels, the BioFire Diagnostics FilmArray RP (respiratory panel), the GenMark Dx eSensor RVP (respiratory viral panel), the Luminex xTAG RVPv1, and the Luminex xTAG RVP fast. Three hundred specimens (200 retrospective and 100 consecutive) were tested using all four platforms to determine performance characteristics. The overall sensitivity and specificity, respectively, and 95% confidence interval (CI; in parentheses) for each panel were as follows: FilmArray RP, 84.5% (79.2, 88.6) and 100% (96.2, 100); eSensor RVP, 98.3% (95.5, 99.5) and 99.2% (95.4, 100); xTAG RVPv1, 92.7% (88.5, 95.4) and 99.8% (96.0, 100); and xTAG RVP fast, 84.4% (78.5, 88.9) and 99.9% (96.1, 100). The sensitivity of each assay fluctuated by viral target, with the greatest discrepancies noted for adenovirus and influenza virus B detection. Hands-on time and time to result were recorded and ease of use was assessed to generate a complete profile of each assay

Comparative Evaluation of the Nanosphere Verigene RV+ Assay and the Simplexa Flu A/B & RSV Kit for Detection of Influenza and Respiratory Syncytial Viruses

Using retrospective (n = 200) and prospective (n = 150) nasopharyngeal specimens, we evaluated the Nanosphere Verigene RV+ and the Focus Diagnostics Simplexa Flu A/B & RSV tests. Overall, RV+ demonstrated sensitivities and specificities of 96.6% and 100% for influenza A virus, 100% and 99.7% for influenza B virus, and 100% and 100% for respiratory syncytial virus (RSV), while the Simplexa test sensitivities and specificities were 82.8 and 99.7%, 76.2 and 100%, and 94.6 and 100%, respectively

Multiplexed identification, quantification and genotyping of infectious agents using a semiconductor biochip

The emergence of pathogens resistant to existing antimicrobial drugs is a growing worldwide health crisis that threatens a return to the pre-antibiotic era. To decrease the overuse of antibiotics, molecular diagnostics systems are needed that can rapidly identify pathogens in a clinical sample and determine the presence of mutations that confer drug resistance at the point of care. We developed a fully integrated, miniaturized semiconductor biochip and closed-tube detection chemistry that performs multiplex nucleic acid amplification and sequence analysis. The approach had a high dynamic range of quantification of microbial load and was able to perform comprehensive mutation analysis on up to 1,000 sequences or strands simultaneously in <2 h. We detected and quantified multiple DNA and RNA respiratory viruses in clinical samples with complete concordance to a commercially available test. We also identified 54 drug-resistance-associated mutations that were present in six genes of Mycobacterium tuberculosis, all of which were confirmed by next-generation sequencing

Diagnostic accuracy of the Xpert ® MTB/RIF cycle threshold level to predict smear positivity: a meta-analysis

SETTING: Xpert® MTB/RIF is the most widely used molecular assay for rapid diagnosis of tuberculosis (TB). The number of polymerase chain reaction cycles after which detectable product is generated (cycle threshold value, CT) correlates with the bacillary burden.OBJECTIVE To investigate the association between Xpert CT values and smear status through a systematic review and individual-level data meta-analysis. DESIGN: Studies on the association between CT values and smear status were included in a descriptive systematic review. Authors of studies including smear, culture and Xpert results were asked for individual-level data, and receiver operating characteristic curves were calculated. RESULTS: Of 918 citations, 10 were included in the descriptive systematic review. Fifteen data sets from studies potentially relevant for individual-level data meta-analysis provided individual-level data (7511 samples from 4447 patients); 1212 patients had positive Xpert results for at least one respiratory sample (1859 samples overall). ROC analysis revealed an area under the curve (AUC) of 0.85 (95%CI 0.82-0.87). Cut-off CT values of 27.7 and 31.8 yielded sensitivities of 85% (95%CI 83-87) and 95% (95%CI 94-96) and specificities of 67% (95%CI 66-77) and 35% (95%CI 30-41) for smear-positive samples. CONCLUSION: Xpert CT values and smear status were strongly associated. However, diagnostic accuracy at set cut-off CT values of 27.7 or 31.8 would not replace smear microscopy. How CT values compare with smear microscopy in predicting infectiousness remains to be seen

Xpert MTB/RIF Assay Shortens Airborne Isolation for Hospitalized Patients With Presumptive Tuberculosis in the United States

Background. In the United States, individuals with presumptive pulmonary tuberculosis are placed in airborne infection isolation (AII) and assessed by smear microscopy on 3 respiratory specimens collected 8–24 hours apart. Xpert MTB/RIF assay (Xpert) on 1, 2, or 3 specimens may be more efficient for determining AII discontinuation

Quantitative thresholds enable accurate identification of clostridium difficile infection by the luminex xTAG gastrointestinal pathogen panel

Clostridium difficile colonizes the gastrointestinal (GI) tract, resulting in either asymptomatic carriage or a spectrum of diarrheal illness. If clinical suspicion for C. difficile is low, stool samples are often submitted for analysis by multiplex molecular assays capable of detecting multiple GI pathogens, and some institutions do not report this organism due to concerns for high false-positive rates. Since clinical disease correlates with organism burden and molecular assays yield quantitative data, we hypothesized that numerical cutoffs could be utilized to improve the specificity of the Luminex xTAG GI pathogen panel (GPP) for C. difficile infection. Analysis of cotested liquid stool samples (n 1,105) identified a GPP median fluorescence intensity (MFI) value cutoff of 1,200 to be predictive of two-step algorithm (2-SA; 96.4% concordance) and toxin enzyme immunoassay (EIA) positivity. Application of this cutoff to a second cotested data set (n 1,428) yielded 96.5% concordance. To determine test performance characteristics, concordant results were deemed positive or negative, and discordant results were adjudicated via chart review. Test performance characteristics for the MFI cutoff of 150 (standard), MFI cutoff of 1,200, and 2-SA were as follows (respectively): concordance, 95, 96, and 97%; sensitivity, 93, 78, and 90%; specificity, 95, 98, and 98%; positive predictive value, 67, 82, and 81%;, and negative predictive value, 99, 98, and 99%. To capture the high sensitivity for organism detection (MFI of 150) and high specificity for active infection (MFI of 1,200), we developed and applied a reporting algorithm to interpret GPP data from patients (n 563) with clinician orders only for syndromic panel testing, thus enabling accurate reporting of C. difficile for 95% of samples (514 negative and 5 true positives) irrespective of initial clinical suspicion and without the need for additional testing