Salivary SARS-CoV-2 antigen rapid detection: A prospective cohort study.

ABSTRACT

BACKGROUND AND AIM: SARS-CoV-2 quick testing is relevant for the containment of new pandemic waves. Antigen testing in self-collected saliva might be useful. We compared salivary and naso-pharyngeal swab (NPS) SARS-CoV-2 antigen detection by a rapid chemiluminescent assay (CLEIA) and two different point-of-care (POC) immunochromatographic assays, with results of molecular testing. METHODS: 234 patients were prospectively enrolled. Paired self-collected saliva (Salivette) and NPS were obtained to perform rRT-PCR, chemiluminescent (Lumipulse G) and POC (NPS Fujirebio and Abbott; saliva Fujirebio) for SARS-CoV-2 antigen detection. RESULTS: The overall agreement between NPS and saliva rRT-PCR was 78.7%, reaching 91.7% at the first week from symptoms. SARS-CoV-2 CLEIA antigen was highly accurate in distinguishing positive and negative NPS (ROC-AUC = 0.939, 95%CI0.903-0.977), with 81.6% sensitivity and 93.8% specificity. This assay on saliva reached the optimal value within 7 days from symptoms onset (Sensitivity 72%; Specificity 97%). Saliva POC antigen was limited in sensitivity (13%), performing better in NPS (Sensitivity 48% and 66%; Specificity 100% and 99% for Espline and Abbott respectively), depending on viral loads. CONCLUSIONS: Self-collected saliva is a valid alternative to NPS for SARS-CoV-2 detection by molecular, but also by CLEIA antigen testing, which is therefore potentially useful for large scale screening.