Quantification and validation of SARS-CoV-2 viral copy number in saliva using SARS-CoV-2 Droplet Digital PCR

Lisa Oberding, Noah Toppings, Omar Abdullah, Dylan Pillai

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Received date: 11th February 2021

Nasopharyngeal (NP) and throat swabs are both currently used as the standard sample types for SARS-CoV-2 testing. However, these procedures are invasive and require consumables which are in high demand. As a result, there is interest in using saliva to detect SARS-CoV-2. This study aimed to compare the performance of the Bio-Rad SARS-CoV-2 Droplet Digital PCR (ddPCR) Kit and the CDC N2 RT-PCR test for detecting SARS-CoV-2 RNA in saliva, and to assess limit of detection and potential inhibitory substances found in saliva. A good correlation between viral copy number and Ct value obtained for the CDC N2 RT-PCR test was shown in saliva. The Bio-Rad SARS-CoV-2 ddPCR showed a sensitivity of 100.00% (87.66 - 100.00) and specificity of 93.75% (79.19 - 99.23) compared to a consensus gold standard of reference RT-PCR methods. However, all positive patients had previously been diagnosed with COVID-19 and suggest that ddPCR is in fact capable of detecting low-level infections. Rather than improvement in limit of detection, interferences studies suggest that ddPCR is better able to overcome inhibitory substances in saliva.

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This is an abstract of a preprint hosted on a preprint server, which is currently undergoing peer review at Scientific Reports. The findings have yet to be thoroughly evaluated, nor has a decision on ultimate publication been made. Therefore, the results reported should not be considered conclusive, and these findings should not be used to inform clinical practice, or public health policy, or be promoted as verified information.

Scientific Reports

Nature Research, Springer Nature