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. 2021 Feb 23:8:621160.
doi: 10.3389/fmed.2021.621160. eCollection 2021.

Prospective Comparison of Saliva and Nasopharyngeal Swab Sampling for Mass Screening for COVID-19

Mathieu Nacher  1   2 , Mayka Mergeay-Fabre  1 , Denis Blanchet  3 , Orelie Benoit  4 , Tristan Pozl  4 , Pauline Mesphoule  4 , Vincent Sainte-Rose  3 , Véronique Vialette  3 , Bruno Toulet  3 , Aurélie Moua  3 , Mona Saout  5 , Stéphane Simon  3 , Manon Guidarelli  1 , Muriel Galindo  1 , Barbara Biche  1 , William Faurous  1 , Laurie Chaizemartin  6 , Aniza Fahrasmane  1 , Devi Rochemont  1 , Nicolas Vignier  1 , Astrid Vabret  7 , Magalie Demar  3   5
Affiliations

Prospective Comparison of Saliva and Nasopharyngeal Swab Sampling for Mass Screening for COVID-19

Mathieu Nacher et al. Front Med (Lausanne). .

Abstract

Current testing for COVID-19 relies on reverse-transcriptase polymerase chain reaction from a nasopharyngeal swab specimen. Saliva samples have advantages regarding ease and painlessness of collection, which does not require trained staff and may allow self-sampling. We enrolled 776 persons at various field-testing sites and collected nasopharyngeal and pooled saliva samples. One hundred sixty two had a positive COVID-19 RT-PCR, 61% were mildly symptomatic and 39% asymptomatic. The sensitivity of RT-PCR on saliva samples vs. nasopharygeal swabs varied depending on the patient groups considered or on Ct thresholds. There were 10 (6.2%) patients with a positive saliva sample and a negative nasopharyngeal swab, all of whom had Ct values <25 for three genes. For symptomatic patients for whom the interval between symptoms onset and sampling was <10 days sensitivity was 77% but when excluding persons with isolated N gene positivity (54/162), sensitivity was 90%. In asymptomatic patients, the sensitivity was only 24%. When we looked at patients with Cts <30, sensitivity was 83 or 88.9% when considering two genes. The relatively good performance for patients with low Cts suggests that Saliva testing could be a useful and acceptable tool to identify infectious persons in mass screening contexts, a strategically important task for contact tracing and isolation in the community.

Keywords: COVID-19; PCR; nasopharyngeal; saliva; sensitivity.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Flow chart of the Covisal study.
Figure 2
Figure 2
Sensitivity of saliva testing vs. nasopharyngeal swabs for RT-PCR for different groups in a community screening context.
Figure 3
Figure 3
Sensitivity of saliva testing vs. nasopharyngeal swabs for different RT-PCR Cts in a community screening context.
Figure 4
Figure 4
Scatterplot matrix for the Ct of different genes in the nasopharyngeal and saliva samples. There was a “fanning” pattern with greater dispersion at higher Ct values for different genes in the nasopharyngeal and saliva samples.
See this image and copyright information in PMC

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