Evaluation of SARS-CoV-2 rapid antigen diagnostic tests for saliva samples

Abstract

Background: The COVID-19 pandemic has highlighted the need for rapid, cost effective and easy-to-use diagnostic tools for SARS-CoV-2 rapid antigen detection (RAD) for use in point of care settings or as self-tests, to limit disease transmission. Using saliva samples would further greatly facilitate sample collection, diagnostic feasibility, and mass screening. Objective: We tested two rapid antigen immunochromatographic tests designed for detection of SARS-CoV-2 in saliva: Rapid Response COVID-19 Antigen Rapid Test Cassette for oral fluids (Rapid Response) and DIAGNOS COVID-19 Antigen Saliva Test (DIAGNOS). Evaluation of detection limit was performed with purified SARS-CoV-2 nucleocapsid protein and titrated live SARS-CoV-2 virus and compared to Abbott Panbio COVID-19 Ag Rapid Test (Panbio) designed for nasopharyngeal samples. Sensitivity and specificity were further evaluated on RT-qPCR positive and negative saliva samples from individuals hospitalized with COVID-19 (n=34); and asymptomatic health care personnel (n=20). Results: The limit of detection of the saliva test from DIAGNOS was comparable with the Panbio test and showed higher sensitivity than Rapid Response for both nucleocapsid protein and diluted live viruses. DIAGNOS and Rapid Response further detected seven (47%) and five (33%), respectively, of the 15 RT-qPCR positive saliva samples in individuals hospitalized with COVID-19. Of the 39 RT-qPCR negative samples, all were negative with both tests (specificity 100%; 95% c.i. 0.91-1.00). Only one of the RT-qPCR positive saliva samples (Ct 21.6) contained infectious virus as determined by cell culture and was also positive using the saliva RADs. Conclusion: The results show that the DIAGNOS test exhibit a similar limit of detection as the Panbio RAD and may be an important and easy-to-use saliva RAD complement to detect infectious individuals.