Performance of the Simplexa^™ Flu A/B & RSV Direct Kit on respiratory samples collected in saline solution

Abstract

Background: Molecular assays for diagnosis of influenza A, influenza B, and respiratory syncytial virus (RSV) with short turnaround time are of considerable clinical importance. We have evaluated the diagnostic performance of the Simplexa^™ Flu A/B & RSV Direct Kit, which has a run time of 60 min, using different types of respiratory samples collected from patients with a suspected respiratory tract infection, including materials not previously evaluated on this kit. Methods: In total, 210 clinical respiratory samples were analyzed using both the Simplexa direct assay and a laboratory-developed assay (LDA). The 210 clinical samples included 99 nasopharyngeal aspirates collected in 0.9% saline, 91 nasopharyngeal swabs in Σ-Virocult transport medium, 9 tracheal secretions, 8 bronchoalveolar lavages (BAL), and 3 other respiratory sample materials. Results: The specificity of the Simplexa assay, using the LDA as gold standard and excluding secondary viral findings, was 100% for all three viruses, whereas the sensitivity was 94.0% for influenza A (47/50), 90.7% for influenza B (49/54), and 90.1% for RSV (46/51), respectively. Discordant results were only observed for samples with cycle threshold values (Ct) > 31 in the LDA. The Simplexa assay generated higher Ct values than the LDA for all three viruses and performed equally well on nasopharyngeal swabs and aspirates. Conclusions: The short run time of the Simplexa direct assay, in combination with high specificity and good sensitivity regarding the sample materials used in this study, make it an interesting option for rapid detection of these three important viral respiratory pathogens in a variety of clinical sample materials.

Keywords::

• Influenza
• RSV
• Simplexa
• saline
• nph aspirate

Acknowledgments

We wish to thank Mia Brytting at the Public Health Agency of Sweden for primer and probe sequences and control material for the influenza A/H1N1pdm09 assay.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.