INTRODUCTION: After the implementation of the Xpert® Xpress Flu/RSV assay for rapid respiratory molecular testing, we investigated the significance of reported endpoint values for influenza A, influenza B and RSV. METHODS: This study prospectively analyzed nasopharyngeal swabs submitted to our virology laboratory in the 2018/19 influenza season. Initial testing was performed on the Xpress Flu/RSV assay. Samples were further tested on a laboratory-developed multiplex PCR (LDT) if the sample was reported as negative by the Xpress Flu/RSV but had an elevated endpoint value ≥5 for any respiratory virus target. RESULTS: There were 1040 negative results on the Xpress Flu/RSV; thirty-one had at least one endpoint value ≥5 [influenza A(25), influenza B(1), RSV(2), influenza A/RSV(1) and influenza A/B/RSV(2)]. Five samples (5/31, 16.1%) were positive on the LDT for influenza A or RSV. In contrast, the positivity rate on the LDT for negative Xpress Flu/RSV samples with endpoint values <5 was 0.35% (p<0.0001). A threshold for endpoint values could not reliably be established to differentiate a potential influenza A positive result from a negative result on the LDT. CONCLUSION: Routine evaluation of endpoint values should be a consideration for laboratories implementing Xpress Flu/RSV, in addition to supplementary respiratory virus testing for clinically relevant situations. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
INTRODUCTION: After the implementation of the Xpert® Xpress Flu/RSV assay for rapid respiratory molecular testing, we investigated the significance of reported endpoint values for influenza A, influenza B and RSV. METHODS: This study prospectively analyzed nasopharyngeal swabs submitted to our virology laboratory in the 2018/19 influenza season. Initial testing was performed on the Xpress Flu/RSV assay. Samples were further tested on a laboratory-developed multiplex PCR (LDT) if the sample was reported as negative by the Xpress Flu/RSV but had an elevated endpoint value ≥5 for any respiratory virus target. RESULTS: There were 1040 negative results on the Xpress Flu/RSV; thirty-one had at least one endpoint value ≥5 [influenza A(25), influenza B(1), RSV(2), influenza A/RSV(1) and influenza A/B/RSV(2)]. Five samples (5/31, 16.1%) were positive on the LDT for influenza A or RSV. In contrast, the positivity rate on the LDT for negative Xpress Flu/RSV samples with endpoint values <5 was 0.35% (p<0.0001). A threshold for endpoint values could not reliably be established to differentiate a potential influenza A positive result from a negative result on the LDT. CONCLUSION: Routine evaluation of endpoint values should be a consideration for laboratories implementing Xpress Flu/RSV, in addition to supplementary respiratory virus testing for clinically relevant situations. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
Authors: Christopher F Lowe; Nancy Matic; Gordon Ritchie; Tanya Lawson; Aleksandra Stefanovic; Sylvie Champagne; Victor Leung; Marc G Romney Journal: J Clin Virol Date: 2020-04-28 Impact factor: 3.168