key: cord-0766916-3g0whwao
authors: Agulló, Vanesa; Fernández-González, Marta; Ortiz de la Tabla, Victoria; Gonzalo-Jiménez, Nieves; García, José A.; Masiá, Mar; Gutiérrez, Félix
title: Evaluation of the rapid antigen test Panbio COVID-19 in saliva and nasal swabs: A population-based point-of-care study
date: 2020-12-09
journal: J Infect
DOI: 10.1016/j.jinf.2020.12.007
sha: 2cc84c9bd473542270c1d721c245425773fa9340
doc_id: 766916
cord_uid: 3g0whwao

nan

Dear Editor, Recent articles in this Journal have described the usefulness of saliva to detect SARS-CoV-2 infection through real-time reverse transcription polymerase chain reaction (rRT-PCR) [1, 2] .

We analyzed the performance of antigen-detecting rapid diagnostic tests (Ag-RDT) in saliva and nasal samples.

Ag-RDT directly identify SARS-CoV-2 proteins produced by replicating virus in respiratory secretions [3] . In contrast to the reference nucleic acid amplification tests (NAAT), such as rRT-PCR, the Ag-RDT are relatively inexpensive, simple to perform, do not require infrastructure, and enable obtaining point-of-care results within a few minutes [4] .

Accordingly, despite being less sensitive than NAAT, Ag-RDT are more advantageous for guiding patient management at point-of-care, for repeat testing, and for timely large-scale public health decisions to prevent transmission [5, 6] . Panbio COVID-19 Ag-RTD (Abbott Rapid Diagnostic Jena GmbH, Jena, Germany) is a recent generation, highly sensitive and specific antigen test for the qualitative detection of SARS-CoV-2 antigen in human nasopharyngeal swab (NPS) specimens. Because obtaining a NPS requires trained healthcare professionals and a personal protective equipment (PPE), availability of a simpler and accurate alternative sample that could even be self-collected, like nasal swab (NS) or saliva, would further ease the procedure and allow large-scale testing. We evaluated the performance of Panbio COVID-19 Ag-RDT in NS and saliva specimens compared with rRT-PCR in NPS in a large prospective study conducted in three primary care centers between 15 th September and 29 th October 2020. Consecutive adults and children, either with COVID-19 signs/symptoms or asymptomatic contacts, were included. Informed consent was obtained from all the patients, and the study was approved by the Hospital General Universitario de Elche COVID-19 Institutional Advisory Board. Patients were asked to fill a questionnaire about symptoms and to collect saliva into a 100 ml sterile empty container. Then, a NS and two consecutive NPS were obtained by a qualified nurse according to the recommended standard procedure. The antigen kit was used according to the manufacturer's instructions. (Figure 1 A-C) . For symptomatic patients with Ct<25, the PPA (95% CI) was 78%

(65-88) in NS, 41% (28-56) in saliva and 85% (72-93) in NS/saliva samples. Ag-RDT performed better with duration of symptoms <7 days (Fig. 1D) Symptoms associated with higher sensitivity of the Ag-RDT in NS/saliva samples were sore throat, with PPA (95% CI) of 69% (49-84), and ageusia with 66% (12. 5-98.2) . Results from this large study show that the overall sensitivity of Panbio Ag-RDT was lower in NS and saliva than in NPS, particularly in asymptomatic patients, although the specificity was 100% in all samples. The same as with Ag-RDT in NPS, sensitivity was highly dependent on the Ct values and the presence and duration of symptoms [7] . In NS samples, the sensitivity in symptomatic patients with Ct≤30 and duration of symptoms <7 days met the minimum test performance requirements to be adequate for the diagnosis of SARS-CoV-2 infection (WHO), although the greatest performance was observed with the combination of NS and saliva samples. Therefore, although the saliva alone did not show a satisfactory performance, it added sensitivity to the NS for SARS-CoV-2 diagnosis. Infectivity risk has been associated with Ct values and duration of symptoms, with no viral growth observed in samples with PCR Ct values >25-30 [8, 9] , and with symptom duration >8 days [9, 10] . Consequently, the contagious risk of symptomatic patients not detected by the Ag-RDT in NS/saliva samples may be low. In addition to self-collection, NS and saliva samples allow performing the test without safe isolation conditions requirement to avoid propagation, thereby widening the settings where the test can be performed, and facilitating the procedure in children since it causes much less discomfort. Moreover, the same diagnostic kit could even be used to analyze both samples, through insertion of the NS in the saliva specimen. In conclusion, because of the low performance observed in asymptomatic patients, NS and saliva samples are not good options for screening or surveillance of SARS-CoV-2 with Ag-RDT. However, in settings with no availability of PPE or trained personnel, or with no safe conditions for the 

All authors: No conflict 

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