ABSTRACT
The COVID-19 pandemic highlights the need for fast and simple assays for nucleic acid detection. As an isothermal alternative to RT-qPCR, we outline the development of a detection scheme for SARS-CoV-2 RNA based on reverse transcription recombinase polymerase amplification (RT-RPA) technology. RPA uses recombination proteins in combination with a DNA polymerase for rapid amplification of target DNA at a constant temperature (39-42 °C) within 10 to 20 minutes and can be monitored in real-time with fluorescent probes.
ABSTRACT
BACKGROUND: The current outbreak of SARS-CoV-2 has spread to almost every country with more than 5 million confirmed cases and over 300,000 deaths as of May 26, 2020. Rapid first-line testing protocols are needed for outbreak control and surveillance. METHODS: We used computational and manual designs to generate a suitable set of reverse transcription recombinase polymerase amplification (RT-RPA) primer and exonuclease probe, internally quenched (exo-IQ), sequences targeting the SARS-CoV-2 N gene. RT-RPA sensitivity was determined by amplification of in vitro transcribed RNA standards. Assay selectivity was demonstrated with a selectivity panel of 32 nucleic acid samples derived from common respiratory viruses. To validate the assay against full-length SARS-CoV-2 RNA, total viral RNA derived from cell culture supernatant and 19 nasopharyngeal swab samples (8 positive and 11 negative for SARS-CoV-2) were screened. All results were compared to established RT-qPCR assays. RESULTS: The 95% detection probability of the RT-RPA assay was determined to be 7.74 (95% CI: 2.87-27.39) RNA copies per reaction. The assay showed no cross-reactivity to any other screened coronaviruses or respiratory viruses of clinical significance. The developed RT-RPA assay produced 100% diagnostic sensitivity and specificity when compared to RT-qPCR (n = 20). CONCLUSIONS: With a run time of 15 to 20 minutes and first results being available in under 7 minutes for high RNA concentrations, the reported assay constitutes one of the fastest nucleic acid based detection methods for SARS-CoV-2 to date and may provide a simple-to-use alternative to RT-qPCR for first-line screening at the point of need.