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A community-deployable SARS-CoV-2 screening test using raw saliva with 45 minutes sample-to-results turnaround

Our take —

This study, available as a preprint and thus not yet peer reviewed, shows the development of a sensitive and specific, rapid SARS-CoV-2 test that uses self-collected saliva samples and produces results in 45 minutes. The test requires minimal laboratory equipment, eliminates contact between lab personnel and infectious samples. The main limitations are the lack of assessment of the approach using samples collected from infected individuals, and the potential for difficulty interpreting borderline samples.

Study design

Other

Study population and setting

The authors developed a rapid, screening test for SARS-CoV-2 using Reverse transcription loop-mediated isothermal amplification (RT-LAMP) technology, which amplifies viral nucleic acid without the need for thermal cycling required by RT-PCR. Authors assessed the assay’s limit of detection and test characteristics using saliva samples spiked with SARS-CoV-2 in the absence of true clinical samples.

Summary of Main Findings

The study describes the development and assessment of a rapid test to detect SARS-CoV-2 infection using self-collected saliva samples, with minimal laboratory equipment (pipettes, microfuge tubes, and a heating source) with results in 45 minutes. The study shows high sensitivity (97%) and specificity (100%) and a limit of detection of 100 viral copies using lab-derived SARS-CoV-2. The authors assessed 3 different viral gene regions (ORF1e, N2, and As1e), each with six primer sets, and showed through replicate testing that their primers targeting the As1e and N2 regions performed the best. The final method required both gene primer sets to produce a positive reaction to be considered a positive test, increasing the potential specificity of the test.

Study Strengths

Authors assessed different viral gene regions and combinations thereof. The approach was tested across multiple ranges of viral concentration and with multiple replications.

Limitations

The major limitation is the lack of in vivo testing. The authors assessed the characteristics of the test by spiking lab-derived SARS-CoV-2 virions into saliva samples. Test characteristics and limits of detection should be assessed in actual clinical samples from individuals with known SARS-CoV-2 infection, particularly among a population of pre-symptomatic and asymptomatic individuals, and compared to the gold-standard RT-PCR results. Additionally, borderline positive samples may be difficult to interpret by visual inspection.

Value added

This study shows the potential for a sensitive and specific rapid and easily deployable saliva-based SARS-CoV-2 test, requiring minimal laboratory equipment and expertise, that could be used outside of clinical laboratories for mass-screening and surveillance.

This review was posted on: 23 September 2020