ABSTRACT
Background: Molecular testing for SARS-CoV-2 continues to suffer from delays and shortages. Antigen tests have recently emerged as a viable alternative to detect patients with high viral loads, associated with elevated risk of transmission. While rapid lateral flow tests greatly improved accessibility of SARS-CoV-2 detection in critical areas, their manual nature limits scalability and suitability for large-scale testing schemes. The Elecsys(R) SARS-CoV-2 Antigen assay allows antigen immunoassays to be carried out on fully automated high-throughput serology platforms. Methods: A total of 3139 nasopharyngeal and oropharyngeal swabs were collected at 3 different testing sites in Germany. Swab samples were pre-characterized by RT-qPCR and consecutively subjected to the antigen immunoassay on either the cobas e411 or cobas e801 analyzers. Results: Of the tested respiratory samples, 392 were PCR positive for SARS-CoV-2 RNA. Median concentration was 2.95x104 (interquartile range [IQR] 5.1x102-3.5x106) copies/mL. Overall sensitivity and specificity of the antigen immunoassay were 60.5% (95% confidence interval [CI] 55.5-65.4) and 99.9% (95% CI 99.6-100), respectively. A 93.7% (95% CI 89.7-96.5) sensitivity was achieved at a viral RNA concentration [≥]104 copies/mL (cycle threshold (Ct) value <29.9). Conclusion: The Elecsys SARS-CoV-2 Antigen assay reliably detected patient samples with viral loads of 10,000 copies/mL and higher. It thus represents a viable high-throughput alternative for pre-screening of patients, or in situations where PCR testing is not readily available.
ABSTRACT
The true prevalence and population seropositivity of SARS-CoV-2 infection remains unknown, due to the number of asymptomatic infections and limited access to high-performance antibody tests. To control the COVID-19 pandemic it is crucial to understand the true seroprevalence, but not every region has access to extensive centralized PCR and serology testing. Currently available rapid antibody tests lack the accuracy needed for recommendation by health authorities. To fill this gap, we analyzed and validated the clinical performance of a new point-of-care SARS-CoV-2 Rapid Antibody Assay, a chromatographic immunoassay for qualitative detection of IgM/IgG antibodies for use in near-patient settings. Analysis was performed using 42 Anti-SARS-Cov-2 positive (CoV+) and 92 Anti-SARS-Covid-2 negative (CoV-) leftover samples from before December 2019, using the Elecsys(R) Anti-SARS-CoV-2 as the reference assay. Analytical specificity was tested using leftover samples from individuals with symptoms of common cold collected before December 2019. The SARS-CoV-2 Rapid Antibody Test was 100.0% (95% CI 91.59-100.00) sensitive and 96.74% (95% CI 90.77-99.32) specific with an assay failure rate of 0.00%. No cross-reactivity was observed against the common cold panel. Method comparison was additionally conducted by two external laboratories, using 100 CoV+/275 CoV-samples, also comparing whole blood versus plasma matrix. The comparison demonstrated for plasma 96.00% positive/96.36% negative percent agreement with the Elecsys Anti-SARS-CoV-2 and overall 99.20% percent agreement between whole blood and EDTA plasma. The SARS-CoV-2 Rapid Antibody Test demonstrated similar clinical performance to the manufacturer's data and to a centralized automated immunoassay, with no cross-reactivity to common cold panels.