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. 2021 Apr 2;10(7):1471.
doi: 10.3390/jcm10071471.

Saliva Is a Valid Alternative to Nasopharyngeal Swab in Chemiluminescence-Based Assay for Detection of SARS-CoV-2 Antigen

Alessandra Amendola  1 , Giuseppe Sberna  1 , Eleonora Lalle  1 , Francesca Colavita  1 , Concetta Castilletti  1 , Giulia Menchinelli  2   3 , Brunella Posteraro  3   4 , Maurizio Sanguinetti  2   3 , Giuseppe Ippolito  5 , Licia Bordi  1 , Maria Rosaria Capobianchi  1 , On Behalf Of Inmi Covid-Study Group
Affiliations

Saliva Is a Valid Alternative to Nasopharyngeal Swab in Chemiluminescence-Based Assay for Detection of SARS-CoV-2 Antigen

Alessandra Amendola et al. J Clin Med. .

Abstract

Diagnostic methods based on SARS-CoV-2 antigens detection are a promising alternative to SARS-CoV-2 RNA amplification. We evaluated the automated chemiluminescence-based Lumipulse® G SARS-CoV-2 Ag assay on saliva samples, using Simplexa™ COVID-19 Direct assay as a reference test. Analytical performance was established on a pool of healthy donors' saliva samples spiked with the 2019-nCoV/Italy-INMI1 isolate, whereas clinical performance was assessed on fresh saliva specimens collected from hospitalized patients with suspect or confirmed COVID-19 diagnosis. The limit of detection (LOD) was 0.65 Log TCID50/mL, corresponding to 18,197 copies/mL of SARS-CoV-2 RNA. Antigen concentrations and SARS-CoV-2 RNA were highly correlated (r = 0.99; p < 0.0001). Substantial agreement (80.3%) and significant correlation (r = -0.675; p = 0.0006) were observed between Lumipulse® G assay results and Ct values on clinical samples, with 52.4% sensitivity and specificity 94.1%. Sensitivity exceeded 90.0% when calculated on samples with Ct < 25, and specificity was 100% when excluding samples from recovered patients with previous COVID-19 diagnosis. Overall, chemiluminescence-based antigen assay may be reliably applied to saliva samples to identify individuals with high viral loads, more likely to transmit the virus. However, the low positive predictive value in a context of low SARS-CoV-2 prevalence underscores the need for confirmatory testing in SARS-CoV-2 antigen-positive cases.

Keywords: RT-PCR; SARS-CoV-2; antigen detection; diagnosis; saliva samples.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(A) Probit regression curve (blue line) with 95% of Confidence Interval (dashed red line). (B) Correlation between the antigen concentration (Log pg/mL) and SARS-CoV-2 RNA (Log copies/mL).
Figure 2
Figure 2
Correlation between Ag concentration (Log pg/mL) and Ct values on fresh saliva samples. Linear regression with 95% of Confidence Interval (dashed line).
See this image and copyright information in PMC

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