![]() We consider this assay acceptable for patient testing. In this study, the Xpert Flu/RSV XC showed nearly perfect agreement (99.2%) with the BioFire FilmArray respiratory panel. ![]() Another study compared the Xpert Flu/RSV XC assay with singleplex PCR tests routinely used in their laboratory and reported sensitivities/specificities of 97.8%/100% and 97.9%/100% for influenza and RSV, respectively ( 12). In one recent study ( 11), the Xpert Flu/RSV XC assay was compared to laboratory-developed tests and the older Xpert Flu assay, and the researchers reported that the sensitivity of influenza detection was improved compared to that with the Xpert Flu assay. To our knowledge, this is the only study comparing the Xpert Flu/RSV XC with the BioFire FilmArray respiratory panel. The presence of other viruses did not interfere with the assay. ![]() There was therefore a 100% positive agreement for influenza A and RSV (κ = 1) and 92.3% for influenza B (κ = 0.94 95% confidence interval, 0.88 to 1.01). All 3 initially discordant results involved the influenza B target ( Table 1). Of these, 381 (99.2%) were in initial agreement, with a Cohen's kappa coefficient (κ) of 0.98. Each of the 128 specimens provided 3 results (influenza A, influenza B, and RSV), for a total of 384 test results. Results were reported as detected or not detected. One specimen was positive for influenza A and RSV, and another was positive for influenza B and RSV. The specimens initially tested as follows: 37 positive for influenza A (including 12 samples of subtype H1 2009 and 25 samples of subtype H3), 36 positive for influenza B, 37 positive for RSV, and 20 negative for influenza A, influenza B, and RSV (8 of these were positive for other targets on the FilmArray). Testing and interpretation of results were done according to the assays' package inserts. Specimens were brought to room temperature, vortexed, and tested. Eighty-four of these specimens were stored at −80☌, and the remaining 44 specimens were stored at 4☌ for a maximum of 3 days before being tested on the Xpert. Patient ages ranged from 17 months to 93 years, with a median age of 35 years 29.7% of tested specimens were from children. We performed a verification study using a convenience sample of 128 archived NP swab specimens in viral transport medium collected from patients at The University of Chicago Medicine and previously tested for clinical purposes using the FilmArray. We sought to compare the performance of the Cepheid Xpert Flu/RSV XC with the BioFire FilmArray respiratory panel and to determine its potential utility in our laboratory, where we were routinely using the FilmArray for influenza and RSV testing. Acceptable specimens include NP swabs and nasal aspirates/washes. The assay is performed on Cepheid's GeneXpert system, an automated platform that performs extraction, amplification, and detection within 63 min using a single disposable cartridge. Unlike the FilmArray, the Xpert cannot discriminate among influenza A strains. In late 2014, Cepheid received clearance from the Food and Drug Administration for the Xpert Flu/RSV XC (Xpert) (Cepheid, Sunnyvale, CA), a molecular test for the detection and differentiation of influenza A, influenza B, and RSV. Assay targets include influenza A (including subtypes H1, H3, and H1-2009), influenza B, and respiratory syncytial virus (RSV), among other viruses and bacteria ( 10). One such assay is the BioFire FilmArray respiratory panel (FilmArray) (BioFire Diagnostics, Salt Lake City, UT), a multiplex nucleic acid amplification test for the qualitative detection and differentiation of 20 respiratory pathogens from nasopharyngeal (NP) swabs within ∼1 h. Rapid molecular assays have thus become the mainstay of testing for respiratory viruses in many clinical laboratories. Moreover, prompt initiation of antiviral therapy may shorten the duration and severity of illness, contributing to decreased transmission of disease, fewer missed work and school days, and fewer bacterial coinfections ( 3, 7).Īlthough they provide results rapidly, antigen assays can exhibit low sensitivity ( 8, 9). For example, the average duration of empirical oseltamivir was reduced by 50% when using rapid influenza testing, compared to our previous method that had a longer turnaround time for results ( 6). Rapid detection can optimize management by limiting administration of unnecessary antimicrobials and ancillary diagnostic tests ( 3, 4), while enhancing decision making on infection control practices and the allocation of health care services ( 5). Optimization of care for such patients involves accurate and rapid diagnostics ( 2). Respiratory viral infections are among the most common acute infections in patients presenting to the emergency department ( 1).
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