Evaluating a novel, highly sensitive, and quantitative reagent for detecting SARS-CoV-2 antigen

Abstract

Introduction: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is rapidly spreading all over the world. A new quantifying reagent for detecting SARS-CoV-2 antigen was developed for early and accurate detection. We evaluated the novel quantitative reagent for detecting SARS-CoV-2 antigen using an automated laboratory device.

Methods: One-hundred nasopharyngeal samples were collected from 47 SARS-CoV-2-infected patients, and 200 samples were collected from healthy donners. We measured the SARS-CoV-2 antigen and nucleic acid using Lumipulse Presto SARS-CoV-2 Ag and the 2019 Novel Coronavirus Detection Kit, respectively.

Results: The sensitivity and specificity of the SARS-CoV-2 antigen test were 75.7% (56/74) and 96.0% (192/200), respectively. The concordance rate in the positive group between the antigen and nucleic acid tests was 66% (66/100). In addition, the correlation coefficient between the concentration of SARS-CoV-2 antigen and the level of SARS-CoV-2 RNA was 0.74. There were 19 discrepant samples in which SARS-CoV-2 RNA was detected without SARS-CoV-2 antigen. There was significant difference between the discrepant and matched samples in terms of the time since symptom onset: the 19 discrepant samples were collected a median of 33 days after onset, while the 55 matched samples were collected a median of 19 days after onset. In addition, the 19 discrepant samples were collected from patients who were immune against SARS-CoV-2.

Conclusions: This novel SARS-CoV-2 antigen detection assay is highly sensitive, rapid, accurate, easily diagnostic. It may be useful in both clinical diagnosis and in screening because it does not require special methods such as PCR.

Keywords: Antigen; Detection; Lumipulse; SARS-CoV-2.

Fig. 1

Correlation between SARS-CoV-2 antigen concentration and level of RNA.

Fig. 2

Predicting the level of RNA in the cut-off range of the antigen test. The level of RNA was estimated based on the intersection of the horizontal arrow at an antigen concentration of 1.0 pg/mL and the regression equation, as well as on the intersection of the down arrow and the X-axis.

Fig. 3

Comparing universal transport medium (UTM) with viral transport medium (VTM) in terms of the SARS-CoV-2 antigen and RNA levels. The number of samples in UTM and VTM were 41 and 17, respectively. The median levels of RNA in UTM and VTM were 4.21 copies/μL and 22.25 copies/μL, respectively (a). The median SARS-CoV-2 concentrations in UTM and VTM were 1.9 pg/mL and 0.42 pg/mL, respectively (b). All p-values were calculated using the Wilcoxon rank-sum test.

Fig. 4

Measurement distribution in the negative group.

Fig. 5

Receiver operating characteristic curve analysis.

Fig. 6

Comparing days after onset at the time of sample collection between the positive matched and antigen-only positive groups. The median number of days after onset was 33 days in the 19 samples that only tested positive in the antigen test. The median number of days after onset was 19 days in the 55 samples that tested positive in both the antigen and nucleic acid tests. All p-values were calculated using the Wilcoxon rank-sum test.

Fig. 7

Changes over time in the antigen concentration and Ct value in two cases. Open circle (〇): SARS-CoV-2 antigen negative, closed circle (●): SARS-CoV-2 antigen positive, opened square (□): PCR negative, closed square (■): PCR positive, open square with asterisk (□^∗): not detected, closed circle with asterisk (●^∗): out of Y-axis range.