Improved Molecular Diagnosis of COVID-19 by the Novel, Highly Sensitive and Specific COVID-19-RdRp/Hel Real-Time Reverse Transcription-PCR Assay Validated In Vitro and with Clinical Specimens

J Clin Microbiol. 2020 Apr 23;58(5):e00310-20. doi: 10.1128/JCM.00310-20. Print 2020 Apr 23.


On 31 December 2019, the World Health Organization was informed of a cluster of cases of pneumonia of unknown etiology in Wuhan, China. Subsequent investigations identified a novel coronavirus, now named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), from the affected patients. Highly sensitive and specific laboratory diagnostics are important for controlling the rapidly evolving SARS-CoV-2-associated coronavirus disease 2019 (COVID-19) epidemic. In this study, we developed and compared the performance of three novel real-time reverse transcription-PCR (RT-PCR) assays targeting the RNA-dependent RNA polymerase (RdRp)/helicase (Hel), spike (S), and nucleocapsid (N) genes of SARS-CoV-2 with that of the reported RdRp-P2 assay, which is used in >30 European laboratories. Among the three novel assays, the COVID-19-RdRp/Hel assay had the lowest limit of detection in vitro (1.8 50% tissue culture infective doses [TCID50]/ml with genomic RNA and 11.2 RNA copies/reaction with in vitro RNA transcripts). Among 273 specimens from 15 patients with laboratory-confirmed COVID-19 in Hong Kong, 77 (28.2%) were positive by both the COVID-19-RdRp/Hel and RdRp-P2 assays. The COVID-19-RdRp/Hel assay was positive for an additional 42 RdRp-P2-negative specimens (119/273 [43.6%] versus 77/273 [28.2%]; P < 0.001), including 29/120 (24.2%) respiratory tract specimens and 13/153 (8.5%) non-respiratory tract specimens. The mean viral load of these specimens was 3.21 × 104 RNA copies/ml (range, 2.21 × 102 to 4.71 × 105 RNA copies/ml). The COVID-19-RdRp/Hel assay did not cross-react with other human-pathogenic coronaviruses and respiratory pathogens in cell culture and clinical specimens, whereas the RdRp-P2 assay cross-reacted with SARS-CoV in cell culture. The highly sensitive and specific COVID-19-RdRp/Hel assay may help to improve the laboratory diagnosis of COVID-19.

Keywords: COVID-19; PCR; SARS; Wuhan; coronavirus; diagnostic; emerging; virus.

Publication types

  • Research Support, Non-U.S. Gov't
  • Validation Study

MeSH terms

  • Adult
  • Aged
  • Animals
  • Betacoronavirus / isolation & purification*
  • COVID-19
  • COVID-19 Testing
  • COVID-19 Vaccines
  • China
  • Chlorocebus aethiops
  • Clinical Laboratory Techniques*
  • Coronavirus Infections / diagnosis*
  • Coronavirus Infections / virology
  • Female
  • Humans
  • In Vitro Techniques
  • Male
  • Middle Aged
  • Molecular Diagnostic Techniques / standards
  • Pandemics
  • Pneumonia, Viral / diagnosis*
  • Pneumonia, Viral / virology
  • Reverse Transcriptase Polymerase Chain Reaction / standards*
  • SARS-CoV-2
  • Sensitivity and Specificity
  • Vero Cells
  • Viral Proteins / genetics*


  • COVID-19 Vaccines
  • Covid-19 aAPC vaccine
  • Viral Proteins