Identification of nsp1 gene as the target of SARS-CoV-2 real-time RT-PCR using nanopore whole-genome sequencing

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused the coronavirus disease 2019 (COVID-19) pandemic. Accurate detection of SARS-CoV-2 using molecular assays is critical for patient management and the control of the COVID-19 pandemic. However, there is an increasing number of SARS-CoV-2 viruses with mutations at the primer or probe binding sites, and these mutations may affect the sensitivity of currently available real-time reverse transcription-polymerase chain reaction (RT-PCR) assays targeting the nucleocapsid (N), envelope (E), and open reading frame 1a or 1b genes. Using sequence-independent single-primer amplification and nanopore whole-genome sequencing, we have found that the nonstructural protein 1 (nsp1) gene, located at the 5′ end of the SARS-CoV-2 genome, was highly expressed in the nasopharyngeal or saliva specimens of 9 COVID-19 patients of different clinical severity. Based on this finding, we have developed a novel nsp1 real-time RT-PCR assay. The primers and probes are highly specific for SARS-CoV-2. Validation with 101 clinical specimens showed that our nsp1 RT-PCR assay has a sensitivity of 93.1% (95% confidence interval [CI]: 86.2%-97.2%), which was similar to those of N and E gene RT-PCR assays. The diagnostic specificity was 100% (95% CI: 92.9%-100%). The addition of nsp1 for multitarget detection of SARS-CoV-2 can avoid false-negative results due to mutations at the primers/probes binding sites of currently available RT-PCR assays.