Abstract
Using saliva samples would facilitate sample collection, diagnostic feasibility, and mass screening of SARS-CoV-2. We tested two rapid antigen (RAD) immunochromatographic tests designed for detection of SARS-CoV-2 in saliva: Rapid Response™ COVID-19 Antigen Rapid Test Cassette for oral fluids and DIAGNOS™ COVID-19 Antigen Saliva Test. Evaluation of detection limit was performed with purified SARS-CoV-2 nucleocapsid protein and live SARS-CoV-2 virus. Sensitivity and specificity were further evaluated with reverse transcription quantitative PCR (RT-qPCR) positive and negative saliva samples from hospitalized individuals with COVID-19 (n = 39) and healthcare workers (n = 20). DIAGNOS showed higher sensitivity than Rapid Response for both nucleocapsid protein and live virus. The limit of detection of the saliva test from DIAGNOS was further comparable with the Abbott Panbio™ COVID-19 Ag Rapid Test designed for nasopharyngeal samples. DIAGNOS and Rapid Response detected nine (50.0%) and seven (38.9%), respectively, of the 18 RT-qPCR positive saliva samples. All RT-qPCR negative saliva (n = 41) were negative with both tests. Only one of the RT-qPCR positive saliva samples contained infectious virus as determined by cell culture and was also positive using the saliva RADs. The results show that the DIAGNOS may be an important and easy-to-use saliva RAD complement to detect SARS-CoV-2 positive individuals, but validation with a larger sample set is warranted.
Highlights
There is an urgent need for rapid and easy to use diagnostics for SARSCoV-2 to limit disease transmission during the ongoing pandemic
In this study we have evaluated two SARS-CoV-2 rapid antigen (RAD) designed for use of saliva samples, enabling noninvasive and easy sampling
We investigated the detection limit of the assays comparing to PanbioTM COVID-19 Ag Rapid Test (Panbio), a widely used RAD for nasopharyngeal samples, using the SARS-CoV-2 nucleocapsid protein (NCp) protein in a 10-fold concentration range from 500 ng to 5 pg of NCp
Summary
There is an urgent need for rapid and easy to use diagnostics for SARSCoV-2 to limit disease transmission during the ongoing pandemic. We have evaluated saliva RADs from two suppliers: Rapid ResponseTM COVID-19 Antigen Rapid Test Cassette for oral fluids (Rapid Response, BTNX, Markham, Canada) and DIAGNOSTM COVID-19 Antigen Saliva Test (DIAGNOS, Nantong Diagnos Biotechnology, Rugao, China). Both RADs are immunochromatographic assays detecting the SARS-CoV-2 nucleocapsid protein in saliva without any specialized instruments. The tests were first evaluated using SARS-CoV-2 nucleocapsid protein (NCp) and live SARS-CoV-2 virus titrated in saliva or test kit buffer and compared to Abbott PanbioTM COVID-19 Ag Rapid Test (Panbio) designed for nasopharyngeal samples. We further correlated the sensitivity of the RADs with regards RT-qPCR Ct-values and infectivity in cell culture
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