Differentiating between infectious and non-infectious influenza A virus and coronavirus RNA levels using long-range RT-qPCR

During the Coronavirus Disease 2019 (COVID-19) pandemic, residual SARS-CoV-2 genome and subgenomic RNA fragments were observed in recovered COVID-19 patients. The presence of such RNAs in the absence of live virus leads to incorrectly positive RT-qPCR results, potentially delaying medical procedures and quarantine release. We here propose a simple modification to turn commercial COVID-19 RT-qPCR protocols into long-range RT-qPCR assays that can differentiate between infectious and non-infectious influenza and coronavirus RNA levels. We find that the long-range RT-qPCR method has a sensitivity that is indistinguishable from a commercial Taq-Path COVID-19 RT-qPCR assay when tested on clinical samples taken withing 5 days of the onset of symptoms. In clinical samples taken at least 15 days after the onset of symptoms when patients had recovered from COVID-19, the modified RT-qPCR protocol leads to significantly fewer positive diagnoses. These findings suggest that the long-range RT-qPCR method may improve test-to-release protocols and expand the tools available for clinical COVID-19 diagnosis. Importance Various molecular tests can detect viral RNA in clinical samples. However, these molecular tests cannot differentiate between RNA from infectious viruses or residual viral genome fragments that are not infectious. In several percent of COVID-19 patients, such residual viral RNAs can be detected long after recovery and the disappearance of infectious SARS-CoV-2. These “persistently-positive” RT-qPCR results are different from false-positive RT-qPCR results, which can be generated due to in vitro cross-reactivity or contaminations. However, the detection of RNA fragments leads to incorrect conclusions about the status of a COVID-19 patient and an incorrect diagnosis. We here modified the commercial Taq-Path COVID-19 RT-qPCR kit to make this test less sensitive to residual viral RNA genome fragments, reducing the likelihood that incorrect RT-qPCR results affect the treatment or quarantine status of recovered COVID-19 patients. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study was funded by joint Wellcome Trust and Royal Society grant 206579/Z/17/Z, and grant G107570 from Public Health England. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The Vilnius Regional Bioethics Committee approved this study with samples from the Vilnius Santaros Klinikos Biobank under number 2021/5-1342-818. The National Accreditation Board for testing and calibration Laboratories (NABL) approved this study under code KDPLP on 22 June 2021. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data produced in the present study are provided as supplemental tables or available upon reasonable request to the authors