Improved Sensitivity of the Novel Xpert Flu Test for Detection of Influenza B Virus

Abstract

Fully automated easy-to-use integrated molecular systems have demonstrated their capability for rapid documentation of respiratory specimens, especially in point-of-care (POC) laboratories. In our previous study (1) (1), we compared the results observed with the Xpert Flu assay with those of the real-time RT-PCR assay routinely used (Table 1) (7). As recommended by the manufacturer, 300 l of the 1-ml swab's medium was loaded into an Xpert cartridge and processed on a 4-module GeneXpert system. The specimens corresponding to discrepant results were extracted again for total nucleic acid using EZ1 Virus Minikit v2.0 and an EZ1 Advanced XL Biorobot (Qiagen, Courtaboeuf, France).In the group of 77 RT-PCR ϩ samples, the five age categories (Ͻ1 year, 1 to 4 years, 5 to 14 years, 15 to 49 years, and Ͼ50 years) were distributed in terms of numbers of patients (and sex ratios) as 11 (2.67), 22 (1.75), 10 (0.67), 12 (0.50), and 22 (1.75), respectively. A total of 73 of the 77 RT-PCR ϩ samples were found positive using the Xpert FluB test. The 4 samples that provided discrepant results were confirmed by retesting using the RT-PCR to assess that the freeze/thaw steps did not result in a drop of the viral load to an undetectable level. The remaining 13 samples were negative with the two assays. No "indeterminate" result was noticed in this study performed with the Xpert Flu assay. The Xpert FluB test exhibited 94.81% sensitivity and 100% specificity for the detection of Flu B, although the selection of samples was purposely made without the intention to address specificity, which proved satisfactory with the previous version of the Xpert Flu assay (1). From these results, it appears that the new version of the test has improved sensitivity for the detection of Flu B. ϩ /Xpert FluB Ϫ samples (P Ͻ 0.05). The samples with low viral loads were more likely to provide a false-negative result with the Flu B Xpert test. In conclusion, the sensitivity of the novel Xpert FluB test has greatly improved in reference to the previous version (1). ACKNOWLEDGMENTS

Evaluation of the Xpert Flu Rapid PCR Assay in High-Risk Emergency Department Patients

“…This is the first time that the Xpert Flu rapid diagnostic test has been evaluated in a high-acuity ED population, where undifferentiated patients are evaluated and treated. In this high-acuity target population, Xpert Flu had high overall sensitivity and specificity compared those of ProFluϩ, similar to what has been reported by several previous studies performed in more general patient populations (4,(8)(9)(10)(11)(12)(13). From a clinical viewpoint, diagnosing influenza and initiating antiviral treatment in the admitted population is most critical, as antivirals have shown substantial benefit, including a reduction in mortality rates, in this population (14-16).…”

Sample-to-result molecular infectious disease assays: clinical implications, limitations and potential

“…[6] A separate Xpert assay, the Xpert Flu/RSV XC, detects and differentiates Influenza A, Influenza B, and Respiratory syncytial virus in approximately one hour. When compared with other molecular methods, the reported sensitivity for this assay is greater than 95% [7,8] for Influenza A, 94.8% for Influenza B, [9] and 89.3% for RSV. [7] The Focus Simplexa Flu A/B & RSV Direct assay consists of a flat disk that resembles a compact disk and the 3 M Integrated Cycler instrument.…”

Integrated Polymerase Chain Reaction Technologies (Sample-to-Answer Technologies)

“…The Xpert Ò Flu/RSV XC is a different Xpert Ò assay cartridge that differentiates Influenza A, Influenza B, and Respiratory Syncytial Virus (RSV). Studies indicate that when compared with other molecular assays, the sensitivity of the Xpert Ò Flu/RSV XC assay for these viruses ranged from a low of 89% to more than 95% for Influenza A (Popowitch and Miller, 2015;Salez et al, 2013Salez et al, , 2015.…”