Soft drinks can be misused to give false “false positive” SARS-CoV-2 lateral flow device results

  1. L Oni
  2. DB Hawcutt
  3. IE Buchan
  4. MG Semple

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Abstract

The COVID-19 pandemic created the need for very large scale, rapid testing to prevent and contain transmission of the SARS-CoV-2 virus. Lateral flow device (LFD) immunoassays meet this need by indicating the presence of SARS-CoV-2 antigen from nose/throat swab washings in 30 minutes without laboratory processing, and can be manufactured quickly at low cost. Since March 2021, UK schools have asked pupils without symptoms to test twice weekly. Pupils have posted on social media about using soft drinks to create positive results. The aim of this study was to systematically test a variety soft drinks to determine whether they can cause false “false positive” LFD results.

Methods

This study used 14 soft drinks and 4 artificial sweeteners to determine the outcome of misusing them as analyte for the Innova SARS-CoV-2 antigen rapid qualitative LFD. The pH value, sugar content and ingredients of each sample are described. The LFD results were double read and a subset was repeated using the same devices and fake analytes but differently sourced.

Findings

One sample (1/14; 7%), spring water, produced a negative result. Ten drinks (10/14; 71%) produced a positive or weakly positive result. Three samples (3/14; 21%) produced void results, mostly the fruit concentrate drinks. There was no apparent correlation between the pH value (pH 5.0 in 13/14, 93%; pH 6.5 in 1/14; 7%) or the sugar content (range 0-10.7 grams per 100mls) of the drinks and their LFD result. The 4 artificial sweeteners all produced negative results. A subset of the results was fully replicated with differently sourced materials.

Interpretation

Several soft drinks can be misused to give false positive SARS-CoV-2 LFD results. Daily LFD testing should be performed first thing in the morning, prior to the consumption of any food or drinks, and supervised where feasible.

Funding

This work was self-funded by author LO and the LFD were gifted for use in this study.

Research in context

Evidence before this study

  • Lateral flow devices (LFD) for SARS-CoV-2 antigen testing have been used extensively in the UK and internationally in COVID-19 pandemic responses, providing rapid testing at low cost

  • Recent reports from young people on social media suggested soft drinks might be misused as LFD analyte and produce a seemingly positive result

Added value of this study

  • Various common soft drinks used as fake analyte can produce false positive SARS-CoV-2 LFD results

  • Artificial sweeteners alone in fake analyte solution did not produce false positive results

Implications of all the available evidence

  • Soft drinks misused as analyte can produce false “false positive” SARS-CoV-2 LFD results

  • Daily testing is best done first thing in the morning, prior to any food or drink, and under supervision where possible

Article activity feed

  1. Rapid Reviews Infectious Diseases

    Lorenzo Azzi

    Review 1: "Soft drinks can be misused to give false “false positive” SARS-CoV-2 lateral flow device results"

    This preprint claims that soft drinks can be misused to generate false-positive results on SARS CoV-2 lateral flow assays. Since the study was done on only one type of test kit, the reviewer raised concerns about its generalizability as this may not be the case in other kits.

  3. ScreenIT

    SciScore for 10.1101/2021.07.05.21260003: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    Ethicsnot detected.
    Sex as a biological variablenot detected.
    Randomizationnot detected.
    BlindingDH was blinded to the sample type.
    Power Analysisnot detected.

    Table 2: Resources

    No key resources detected.

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: An explicit section about the limitations of the techniques employed in this study was not found. We encourage authors to address study limitations.

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

    Results from scite Reference Check: We found no unreliable references.

    About SciScore

    SciScore is an automated tool that is designed to assist expert reviewers by finding and presenting formulaic information scattered throughout a paper in a standard, easy to digest format. SciScore checks for the presence and correctness of RRIDs (research resource identifiers), and for rigor criteria such as sex and investigator blinding. For details on the theoretical underpinning of rigor criteria and the tools shown here, including references cited, please follow this link.

  4. Version published to 10.1101/2021.07.05.21260003v1 on medRxiv