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

Link to article at PubMed

Infection. 2021 Mar 18. doi: 10.1007/s15010-021-01600-1. Online ahead of print.


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.

PMID:33738680 | DOI:10.1007/s15010-021-01600-1

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