Comparison of the Quantitative DiaSorin Liaison Antigen Test to Reverse Transcription-PCR for the Diagnosis of COVID-19 in Symptomatic and Asymptomatic Outpatients.

We evaluated the quantitative DiaSorin Liaison severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigen test in symptomatic and asymptomatic individuals consulting their general practitioners (GPs) during a period of stable intense virus circulation (213/100,000 habitants per day). Leftover reverse transcription-PCR (RT-PCR) positive (n = 204) and negative (n = 210) nasopharyngeal samples were randomly selected among fresh routine samples collected from patients consulting their GPs. Samples were tested on Liaison XL according to the manufacturer's instructions. Equivocal results were considered negative. The overall sensitivity and specificity of the Liaison antigen test compared to RT-PCR were 65.7% (95% confidence interval [CI], 58.9% to 71.9%) and 100% (CI, 97.8% to 100%). Sensitivity in samples with viral loads of ≥105, ≥104, and ≥103 copies/ml were 100% (CI, 96.3% to 100.0%), 96.5% (CI, 91.8% to 98.7%), and 87.4% (CI, 81.3% to 91.5%), respectively. All samples with ≤103 copies/ml were antigen negative. The ratio of antigen concentration to viral load in samples with ≥103 copies/ml was comparable in symptomatic and asymptomatic individuals (P = 0.58). The proportion of RT-PCR-positive participants with a high viral load (≥105 copies/ml) was not significantly higher in symptomatic than in asymptomatic participants (63.9% [CI, 54.9% to 72.0%] versus 51.9% [CI, 41.1% to 62.6%]; P = 0.11), but the proportion of participants with a low viral load (<103 copies/ml) was significantly higher in asymptomatic than in symptomatic RT-PCR-positive participants (35.4% [CI, 25.8% to 46.4%] versus 14.3% [CI, 9.0% to 21.8%]; P < 0.01). Sensitivity and specificity in samples with a viral load of ≥104 copies/ml were 96.5% and 100%. The correlation of antigen concentration with viral load was comparable in symptomatic and asymptomatic individuals.

Evaluation of Two Rapid Antigenic Tests for the Detection of SARS-CoV-2 in Nasopharyngeal Swabs.

(1) Background: In the current context of the COVID-19 crisis, there is a need for fast, easy-to-use, and sensitive diagnostic tools in addition to molecular methods. We have therefore decided to evaluate the performance of newly available antigen detection kits in "real-life" laboratory conditions. (2) Methods: The sensitivity and specificity of two rapid diagnostic tests (RDT)-the COVID-19 Ag Respi-Strip from Coris Bioconcept, Belgium (CoRDT), and the coronavirus antigen rapid test cassette from Healgen Scientific, LLC, USA (HeRDT)-were evaluated on 193 nasopharyngeal samples using RT-PCR as the gold standard. (3) Results: The sensitivity obtained for HeRDT was 88% for all collected samples and 91.1% for samples with Ct ≤ 31. For the CoRDT test, the sensitivity obtained was 62% for all collected samples and 68.9% for samples with Ct ≤ 31. (4) Conclusions: Despite the excellent specificity obtained for both kits, the poor sensitivity of the CoRDT did not allow for its use in the rapid diagnosis of COVID-19. HeRDT satisfied the World Health Organization's performance criteria for rapid antigen detection tests. Its high sensitivity, quick response, and ease of use allowed for the implementation of HeRDT at the laboratory of the University Hospital of Liège.