Self-Collected Gargle Lavage Allows Reliable Detection of SARS-CoV-2 in an Outpatient Setting

ABSTRACT Current procurement of specimens for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) detection requires trained personnel and dedicated equipment. We compared standard nasopharyngeal swabs with self-collected gargle lavage fluid obtained from 80 mostly symptomatic outpatients. After RNA extraction, RT-PCR to detect SARS-CoV-2 was performed. Qualitative results obtained with the paired samples from individual outpatients were 100% congruent. Therefore, self-collected gargle lavage fluid can serve as a suitable specimen for coronavirus disease 2019 (COVID-19) testing in outpatients. IMPORTANCE The SARS-CoV-2 pandemic still strains health care systems worldwide. While COVID-19 testing is considered an essential pillar in combating this infectious disease, shortages in supplies and trained health care personnel often limit the procurement of patient samples, in particular in outpatient settings. Here, we compared the simple self-collection of gargle lavage fluid with the gold standard nasopharyngeal swab as a specimen for COVID-19 testing. By finding complete congruence of results obtained with paired samples of a sizeable patient cohort, our results strongly support the idea that the painless self-collection of gargle lavage fluid provides a suitable and uncomplicated sample for reliable SARS-CoV-2 detection.

1. Reviewer one points out that only two specimens in your study have a Ct value of >30 and suggest increasing the sample size. Your response indicated that your group feels that a sample size increase is not necessary since you have shown a statistical difference between high and low Ct specimens. I believe that the inclusion of more specimens would be difficult at this point in the pandemic and beyond the scope of the work; however, I would argue that the lack of specimens with high Ct values remains a limitation since the median value used to group high verse low Ct specimens (19.4) is very low. Please add a discussion of this limitation.
2. Line 64. Define or correct the abbreviation NLS When submitting the revised version of your paper, please provide (1) point-by-point responses to the above as file type "Response to Reviewers," not in your cover letter, and (2) a PDF file that indicates the changes from the original submission (by highlighting or underlining the changes) as file type "Marked Up Manuscript -For Review Only". Please use this link to submit your revised manuscript -we strongly recommend that you submit your paper within the next 60 days or reach out to me. Detailed information on submitting your revised paper are below.

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Editorial Comments
1. Reviewer one points out that only two specimens in your study have a Ct value of >30 and suggest increasing the sample size. Your response indicated that your group feels that a sample size increase is not necessary since you have shown a statistical difference between high and low Ct specimens. I believe that the inclusion of more specimens would be difficult at this point in the pandemic and beyond the scope of the work; however, I would argue that the lack of specimens with high Ct values remains a limitation since the median value used to group high verse low Ct specimens (19.4) is very low. Please add a discussion of this limitation.
We also agree that in some settings or patient cohorts a larger portion of samples with Ct-values >30 (meaning with low viral titers) might occur. However, we would like to point out that we investigated mostly symptomatic persons, which had been tracked by health authorities as direct contacts of verified positive cases and which visited the doctor for the first time. This means that in contrast to studies on hospitalized COVID19 patients (which are usually days to even weeks after symptom onset) our study almost exclusively focussed on a patient cohort that is just before or right at the beginning of the symptomatic infection, when virus titers are highest (hence the median Ct value of 19.4 is rather low).
Of the 26 positive cases identified in our cohort, 4 (not 2) showed a Ct-value > 30. The original data for these four were: Nasopharyngeal swab (NPS) -gargle lavage (GL) 30.1 33.0 30.2 32.9 32.4 34.6 34.6 34.5 As the four values labeled in bold are close to being identical, the data-points and also the connecting lines overlap almost completely in Fig. 1b. It is therefore almost impossible to separate these single data points by eye. We have tried to modify Fig. 1b using different symbols (open diamonds instead of rectangles), but it is still hard to resolve. Nevertheless, though this figure is not able to reveal every single data point, the main messages, that there is an overall shift to higher Ct-values, when using gargle lavage compared to nasopharyngeal swabs and that the difference is more prominent for the lower Ct-values, can be readily gained from this Figure. We also explicitly discuss this observation, that Ct-values between NPS and GL show a more pronounced difference, when the Ct-values are smaller (hence, when the viral titers are high). Furthermore, prompted by your suggestion, we now also highlight that in the few cases with Ct values >30, the delta-Ct-values between NPS and GL are even smaller: Mean delta-Ct of 8. We apologize for this mistake and replace "NLS" with "NPS", as "nasopharyngeal swab" was meant. Your manuscript has been accepted, and I am forwarding it to the ASM Journals Department for publication. You will be notified when your proofs are ready to be viewed.
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