A combined oro-nasopharyngeal swab is more sensitive than mouthwash in detecting SARS-CoV-2 by a high-throughput PCR assay

  1. Wiebke Michel
  2. Jacqueline Färber
  3. Milica Dilas
  4. Hans-Gert Heuft
  5. Ina Tammer
  6. Jannik Baar
  7. Achim J. Kaasch

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Abstract

Objectives

The optimal diagnostic specimen to detect SARS-CoV-2 by PCR in the upper respiratory tract is unclear. Mouthwash fluid has been reported as an alternative to nasopharyngeal and oropharyngeal swabs. We compared mouthwash fluid with a combined oro-nasopharyngeal swab regarding test performance.

Methods

In a large refugee facility, we retested individuals with a previous positive test for SARS-CoV-2 and their quarantined close contacts. All individuals were asymptomatic at the time of testing. First, a mouthwash (gargling for at least 5 s) with sterile water was performed. Then, with a single flocked swab the back of the throat and subsequently the nasopharynx were sampled. Samples were inactivated and analysed on a Roche cobas 6800 ® system with the Roche SARS-CoV-2 test.

Results

Of 76 individuals, 39 (51%) tested positive for SARS-CoV-2 by oro-nasopharyngeal swab. Mouthwash detected 13 of 76 (17%) infections, but did not detect any additional infection. Samples that were positive in both tests, had lower cycle threshold ( Ct )-values for oro-nasopharyngeal samples, indicating a higher virus concentration, compared to samples only positive in oro-nasopharyngeal swabs.

Conclusion

Mouthwash is not as sensitive as combined oro-nasopharyngeal swab in detecting upper respiratory tract infection.

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  1. Version published to 10.1007/s15010-021-01600-1
  2. ScreenIT

    SciScore for 10.1101/2020.09.25.20201541: (What is this?)

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

    Table 1: Rigor

    Institutional Review Board StatementIRB: Approval was obtained from the ethics committee of the Medical Faculty of the Otto-von-Guericke University Magdeburg.
    Consent: Written informed consent was obtained by all participants or their guardians.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.
    Sex as a biological variablenot 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: We detected the following sentences addressing limitations in the study:
    Our study has also limitations. Mouthwash with gargling was performed as a self-administered procedure and we observed some variation in adherence to the protocol regarding the duration and intensity of gargling, which may have influenced the results. Furthermore, we did not compare different RNA extraction methods, which may show a better performance with mouthwash specimens. There is a high likelihood of aerosol formation during gargling. Thus, mouthwash should be performed alone in a well-ventilated area. This may limit its use in patients to minimize exposure of health-care personel.In conclusion, SARS-CoV2 detection with mouthwash showed a low sensitivity compared to oro-nasopharyngeal swabs. Thus, we do not recommend mouthwash performing combined oro-nasopharyngeal swabs, especially in patients with no or mild symptoms.

    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.

    About SciScore

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  3. Version published to 10.1101/2020.09.25.20201541v1 on medRxiv