Reverse transcription PCR and sequencing
The suspension was used for real-time reverse transcription polymerase chain reaction (RT-PCR) assay of SARS-CoV-2 RNA. The real-time RT-PCR assay was performed using a SARS-CoV-2 nucleic acid detection kit according to the manufacturer's protocol (Shanghai ZJ Bio-Tech Co., Ltd.). Two different targets on the SARS-CoV-2 genome, namely, the RNA-dependent RNA polymerase (RdRp) and nucleocapsid (N) genes, were employed, and a third target, the envelope (E) gene, was used for real-time quantitative PCR.10 A sample was considered positive when the qPCR Ct value was ≤43.