Evaluating an extraction-free sample preparation method for multiplex detection of SARS-Cov-2, influenza A/B, and RSV with implementation on a microfluidic chip.

Following the relaxation of COVID-19 restrictions, other respiratory viruses such as influenza and respiratory syncytial virus (RSV), whose transmission were decreased due to COVID-19 precautions, are rising again. Because of similar clinical features and reported co-infections, multiplex detection of SARS-CoV-2, influenza A/B, and RSV is required to use specific treatments. This study assessed an extraction-free sample preparation (heat treatment at 95°C for 3 minutes) for multiplex detection using rRT-PCR. Despite an observed Ct-delay (∆Ct) averageing 1.26 compared to the standard method, an acceptable total sensitivity of 92 % and a negative predictive value (NPV) of 96 % were obtained. Moreover, Implementation on a microfluidic chip demonstrated efficiency, maintaining an excellent correlation (R2 =0.983) with the standard method. Combining this extraction-free procedure with rRT-PCR on a microfluidic chip seems promising, because it simplifies the design and reduces the cost and complexity of the integrated assay for multiplex detection of SARS-CoV-2, influenza A/B, and RSV.