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 that 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%CI:0.903-0.977), 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.

Reduced Relative Sensitivity of the Elecsys SARS-CoV-2 Antigen Assay in Saliva Compared to Nasopharyngeal Swabs

“…Our results show a clear advantage of NPS as a specimen in combination with the probed antigen test. This is in concordance with other antigen test systems which, in general, have shown lower sensitivity compared to NPS [ 35 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 ]. One of the automated antigen tests previously evaluated for saliva samples is the Lumipulse G SARS-CoV-2 Ag assay, a chemiluminescent enzyme immunoassay which received the CE marking for qualitative and quantitative detection of the SARS-CoV-2 N antigen on both saliva and NPS samples.…”

“…A recent Cochrane study reported a sensitivity of only 56.2% (95% confidence interval (CI): 29.5–79.8%) for point-of-care antigen tests [ 33 ]. Several studies have evaluated saliva as an alternative to NPS for detection of SARS-CoV-2 with antigen tests, including automated tests [ 11 , 12 , 13 , 14 , 15 , 20 , 36 , 37 , 38 , 40 , 42 , 43 , 44 ]. However, none of the current Emergency Use Authorization (EUA) tests for SARS-CoV-2 antigen detection is authorized for saliva.…”

“…Our study shows that lower sensitivity can occur in antigen tests using saliva as a medium and highlights the need for developers to establish appropriate protocols for saliva testing. It must be considered that a reduced sensitivity of SARS-CoV-2 antigen testing in saliva is likely not restricted to the assay evaluated here, as several studies noted lower sensitivity in saliva [ 11 , 12 , 13 , 14 , 15 , 20 , 22 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 ]. Alternate saliva sampling strategies that allow concentrated saliva processing may thus be of advantage in combination with antigen tests to overcome the sensitivity restrictions.…”

“…One of the automated antigen tests previously evaluated for saliva samples is the Lumipulse G SARS-CoV-2 Ag assay, a chemiluminescent enzyme immunoassay which received the CE marking for qualitative and quantitative detection of the SARS-CoV-2 N antigen on both saliva and NPS samples. Sensitivities relative to the corresponding molecular reference test ranged from 41.3% to 88.9%; specificities were reported in four of the five studies and ranged from 96.9% to 98.6% [ 42 , 43 , 44 , 46 , 51 ]. It has to be noted, however, that in the study reporting the highest sensitivity (i.e., 88.9%), only nine RT-PCR-positive saliva samples were evaluated.…”

Effective screening strategy against SARS-CoV-2 on self-collected saliva samples in primary school setting: A pilot project

“…However, this did not represent a major obstacle to achieve same day diagnostic definition, due to the timely organization and information flow. On the other hand, the disadvantage of longer process was overcome by the greater accuracy of a laboratory test compared to a POCT [2,9,10] and the ability to quickly perform the confirmation test with a system compatible with "urgent" execution.…”