Application of digital PCR to determine the reliability of Xpert Xpress SARS-CoV-2 assay with envelope (E) gene negative and nucleocapsid (N2) gene positive results

River Chun-Wai Wong; Ann Han Wong; Yolanda Iok-Ieng Ho; Gilman Kit-Hang Siu; Lam-Kwong Lee; Eddie Chi-Man Leung; Raymond Wai-Man Lai

doi:10.1016/j.diagmicrobio.2022.115726

Application of digital PCR to determine the reliability of Xpert Xpress SARS-CoV-2 assay with envelope (E) gene negative and nucleocapsid (N2) gene positive results

Diagn Microbiol Infect Dis. 2022 Aug;103(4):115726. doi: 10.1016/j.diagmicrobio.2022.115726. Epub 2022 May 20.

Authors

River Chun-Wai Wong¹, Ann Han Wong², Yolanda Iok-Ieng Ho², Gilman Kit-Hang Siu³, Lam-Kwong Lee³, Eddie Chi-Man Leung², Raymond Wai-Man Lai²

Affiliations

¹ Department of Microbiology, Prince of Wales Hospital, Hong Kong. Electronic address: [email protected].
² Department of Microbiology, Prince of Wales Hospital, Hong Kong.
³ Department of Health Technology and Informatics, The Hong Kong Polytechnic University, Hung Hom, Hong Kong.

Abstract

This study used digital polymerase chain reaction (dPCR) to determine whether envelope (E) gene-negative and nucleocapsid (N2) gene-positive (E-N+) results obtained with the Cepheid Xpert Xpress SARS-CoV-2 assay are reliable. Using droplet digital PCR results as a reference, 18 of 22 E-N+ samples with a low viral load (81.8%) were identified as true positives.

Keywords: Cepheid Xpert Xpress SARS-CoV-2 assay; E gene negative; N2 gene positive; SARS-CoV-2; digital PCR; low viral load.

MeSH terms

COVID-19 Testing
COVID-19* / diagnosis
Clinical Laboratory Techniques / methods
Humans
Nasopharynx
Nucleocapsid / genetics
Polymerase Chain Reaction
Reproducibility of Results
SARS-CoV-2* / genetics
Sensitivity and Specificity