Performance evaluation of an automated SARS-CoV-2 Ag test for the diagnosis of COVID-19 infection on nasopharyngeal swabs

Objectives: The detection of SARS-CoV-2 in infected people is a key tool to help in controlling COVID-19 pandemic. Like rapid antigenic tests, automated antigen tests, that present the advantage of a higher throughput flow, may be of interest. The LIAISON (R) SARS-CoV-2 Ag test was evaluated for the quantification of SARS-CoV-2 nucleocapsid antigen in nasopharyngeal swabs by comparison to RT-PCR. Methods: The study involved 378 nasopharyngeal samples (UTM (R) and FLOQSwab (TM), Copan Diagnostics), including 46 swabs positive for SARS-CoV-2 by RT-PCR. These samples came from asymptomatic (n=99, 26.2%) or symptomatic people (n=279, 73.8%), at different times from symptom onset. The samples were analyzed on LIAISON (R) XL. Results: The overall specificity was 99.4% (CI95% [98.6-100]). The negative predictive value reached 100% in asymptomatic people. Among the 46 positive samples, the overall sensitivity was 84.8% (CI95% [74.4-95.2]), reached 91.9% (CI95% [83.1-100]) in the first fourth days after symptoms onset and was 100% for Cq values <= 25. Antigen was not detected in samples with Cq values >25. Similar results were observed on nasopharyngeal swabs coming from patients infected with the 20I/501Y.V1 variant or the 20H/501Y.V2 variant. Conclusions: According to technical performances, the LIAISON (R) SARS-CoV-2 Ag test may be a useful tool for COVID-19 diagnosis, especially during the first four days of symptoms.

Automated summary

The LIAISON(R) SARS-CoV-2 Ag test showed a specificity of 99.4% and a negative predictive value of 100% in asymptomatic individuals. It demonstrated an overall sensitivity of 84.8%, reaching 91.9% in the first four days after symptom onset. The test may be particularly useful for COVID-19 diagnosis, especially within the early symptom onset period.