Evaluation of clinical utility of novel coronavirus antigen detection reagent, Espline® SARS-CoV-2

Abstract

Background: To prevent the novel coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), it is necessary to perform early identification and isolation of people shedding the infectious virus in biological materials with high viral loads several days prior to symptom onset. Rapid antigen tests for infectious diseases are useful to prevent the pandemic spread in clinical settings.

Methods: We evaluated a SARS-CoV-2 antigen test, Espline® SARS-CoV-2 reagent, with reverse transcription polymerase chain reaction (RT-PCR) as reference test, using 129 nasopharyngeal swab specimens collected from COVID-19 hospitalized patients or from patients suspected having COVID-19-like symptoms. Out of these, 63 RT-PCR positive and 66 RT-PCR negative specimens were identified.

Results: Among 63 RT-PCR positive specimens, 25 were positive in the Espline test. Test sensitivity was estimated based on the 532.4 copies/reaction of SARS-CoV-2 RNA obtained through receiver operating characteristic analysis. When the specimens were classified based on time since symptom onset, Espline test sensitivity were 73.3% and 29.2% in specimens collected before day 9 and after day 10, respectively.

Conclusion: Although the overall sensitivity of the Espline® SARS-CoV-2 reagent compared with RT-PCR is less, this antigen test can be useful in identifying people with high risk of virus transmission with high viral loads in order to prevent the pandemic and is useful for diagnosing COVID-19 within 30 min.

Keywords: Antigen detection; COVID-19; Diagnosis; Immunochromatography; SARS-CoV-2.

Fig. 1

Characterization of SARS-CoV-2 antigen-positive and negative specimens. (A) Box-plot of SARS-CoV-2 viral loads in nasopharyngeal swabs: the specimens of Espline positive (Ag+)/RT-PCR positive (PCR+) and Espline negative (Ag-)/RT-PCR positive (PCR+) were plotted. Mean and median values of the RNA titers are indicated at the bottom of the panel. The p-value of the t-test between RNA titers of the specimens is indicated at the top of the panel. (B) ROC curve of the concordance of SARS-CoV-2 antigen-positive result with the SARS-CoV-2 RNA positive specimens.

Fig. 2

Characterization of SARS-CoV-2 RNA positive specimens. (A) The cumulative agreement rates for positive, and positive or negative judgment between the antigen test and RT-PCR test along days since symptom onset were plotted as open circles and crosses, respectively. (B) Box-plot of SARS-CoV-2 RNA titers in Ag+/RNA+ and Ag−/RNA+ specimens. Mean and median values of RNA titers are indicated at the bottom of the panel. The p-value of the t-test between the RNA titers in Ag+/RNA+ and Ag−/RNA+ specimens is indicated at the top of the panel. (C) SARS-CoV-2 viral loads in nasopharyngeal swabs were plotted against the days of collection after symptom onset. Specimens of Ag+/RNA+ and Ag−/RNA+ were indicated by closed circles and open circles, respectively. The vertical dash-line indicates the viral load of 532 copies/reaction.