PONE-D-21-21141Clinical evaluation of the SD Biosensor saliva antigen rapid test with symptomatic and asymptomatic, non-hospitalized patients.PLOS ONE

Dear Dr. Iglói,

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The author(s) received no specific funding for this work.

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3. Thank you for stating the following in the Acknowledgments/ Funding Section of your manuscript: 

The SARS-CoV-2 Rapid Antigen Test-Standard Q COVID-19 Ag Saliva- Research use only (Lot number QCO9021001; expiry date 04-01-2023) was provided by SD Biosensor 

No other funding was received.

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Partly

Reviewer #2: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: No

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3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

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4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The manuscript is clearly written and presents public health relevant findings. It will benefit from minor revision in relation to the data presentation and interpretation in the public health context.

Title: it would be helpful to specify in the title that this saliva test is for SARS-CoV2 antigen.

Abstract: clear and appropriate

Introduction: It would be valuable to introduce an applied epidemiology perspective here; such as

a) The manuscript discusses PPV, yet in public health, the NPV can be equally valuable. Especially in the context of self-tests being used by citizens prior to engaging in increased social interaction. Please elaborate on this perspective (useful reference: European Centre for Disease Prevention and Control. Considerations on the use of self-tests for COVID-19 in the EU/EEA – 17 March 2021. ECDC: Stockholm; 2021)

b) the dependency of population prevalence. In the manuscript, only the prevalence among the tested population is used, though it would be insightful to understand what was the population COVID19 prevalence at the time of this study;

c) Please describe what is known about access to testing in the described population of Rotterdam: how large is the estimated group that is unable to come to these XL-locations? This is relevant context in the discussion on the value of self tests.

Methods: Clearly written. It would be helpful to clarify why only 789 of the 816 included persons had a PCR result.

Results:

- Define 'recent onset' (P4-L89) (from table 1, we deduce this must be <8 days, but this could be made explicit)

- table 1:

Every time when "CT<=30" is printed in the table, this should be "CT<30"

The numbers of CT>=30 and CT<30 among the NP AgRDT group should add up, yet they don't: 9+39=48, yet 49 (of 52) should have a positive PCR. Please check the data

- Table 2: (page 7)

It is not clear why the N is larger than 556 in the columns of "0-3 days post onset" and "0-7 days post onset". It is my understanding that only 556 participants indicated an onset of symptoms.

The row <ct30 91.2="" a="" among="" bit="" can="" clinical="" confusing:="" explain="" group="" how="" is="" overall="" sensitivity="" symptomatic="" that="" the="" we="">

- Table 2 (page 8)

Here too: It is not clear why the N is larger than 556 in the columns of "0-3 days post onset" and "0-7 days post onset". It is my understanding that only 556 participants indicated an onset of symptoms.

Same on page 9

Discussion:

Clear focus chosen on the discussion topics. What is missing, is a perspective on public health consequences of the PPV and the NPV found in this study: it would not be inappropriate to indulge in a 'what if' scenario, exploring how the saliva test would perform if used widely in the given population of Rotterdam, given the estimated COVID19 prevalence at that time.

Lastly, it would be of interest to elaborate a bit on the risk of aerosolisation while taking the saliva samples, and discuss how that would compare to the other tests used in this study.

The numbers of CT>=30 and CT<30 among the saliva AgRDT group should add up, yet they don't: 2+38=40, yet 41 (of 44) should have a positive PCR. Please check the data</ct30>

Reviewer #2: Review of “Clinical evaluation of the SD Biosensor saliva antigen rapid test with symptomatic andasymptomatic, non-hospitalized patients”. Short article with promising results. Methods section is very clear. The results could be better displayed as far as I am concerned. Also, the statistical comparison that is made to compare sensitivity estimates by time since symptom onset needs to be looked at more closely. Furthermore, I found it very encouraging that the saliva antigen test was able to detect 97% of the positive viral cultures. This is in my opinion a very convincing result to implement this easy-to-use test as a public health tool for in particular health care workers and for the general public for SARS-CoV-2 and potentially beyond for other infectious diseases as well for example influenza.

Major points:

I find the results section too brief. I would like to see clearer sentences where it is made explicit which two tests are being compared and show how the sensitivity was estimated. For example, "of the XX samples that tested positive with PCR saliva, XX tested positive with the saliva antigen test (XX/ XX = XX sensitivity)." I find it difficult at this point to determine from the text which tests were compared and how sensitivity was estimated.

To me the main finding of this study is that the saliva RDT detected all but one positive virus cultures. Assuming virus culture is the best indicator of infectiousness, the saliva RDT is in this study the best test to detect infectious persons, and would therefore be very suitable for at home use, and therefore be an excellent public health tool to stop transmission. I think this finding deserves a better location in the results and discussion section.

Line 100: Overall performance of saliva was inferior to these other two tests. But comparing one test to another will always result in an inferior test, right? There is always going to be one sample, which was tested positive in the bench mark test, that will be negative in the evaluated test? Also, inferior in finding what? RNA or samples with infectious potential? The saliva test found more of the samples that tested positive in viral culture than the nasopharyngeal test, right? In that sense, the saliva test is superior over the nasopharyngeal test finding samples that positive with positive culture.

Table 2: I am confused about the N-values. In total, there were 789 samples tested. Of these, 62 were PCR-positive, 52 with the NP Ag RDT, and 44 with the saliva Ag RDT. The sensitivity estimates can therefore never be estimated with the numbers I am seeing in this table. I would provide the actual numbers from which the sensitivity estimates were estimates in the parentheses instead of one N number, for example: 79.2% (XX/XX)

“Analysis by days post onset did not result in higher sensitivities”. How was this concluded? Looking at table 2, I see percentages for the group 0-3 days post onset and the group 0-7 post onset. For a proper comparison, one would have to make two different groups, for example comparing samples taken 0-3 days after symptom onset, and samples taken 4-7 days post symptom onset.

Minor points:

Line 47: People were either tested because of respiratory symptoms or because of being a contact of an individual with a confirmed SARS-CoV-2 infection as mentioned in line 47/48. Could you provide information on the number of samples that were from contact persons, perhaps in Table 1?

Line 62: This sentence requires rewriting.

Line 98: To me, this summary statistic is redundant and without meaning.

Line 99: Sensitivity increased to 88.6, but where is it increasing from?

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Reviewer #1: Yes: Arnold Bosman

Reviewer #2: Yes: Tom Woudenberg

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Clinical evaluation of the SD Biosensor SARS-CoV-2 saliva antigen rapid test with symptomatic and asymptomatic, non-hospitalized patients.

PONE-D-21-21141R1

Dear Dr. Iglói,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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Kind regards,

Etsuro Ito

Academic Editor

PLOS ONE

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

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3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The edited manuscript successfully addresses all points in the review. I would consider this manuscript appropriately suitable for publication.

Reviewer #2: Excellent revision. Results are very clear.

One final comment from my side, and I leave this up to the authors whether they'd like to change this. I'd change the first sentence of the discussion. I think it should be made in clear what the performance refers to. Is its poorer performance in detecting PCR+ve samples or positive cell cultures?

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Reviewer #1: Yes: Arnoldus Bosman

Reviewer #2: Yes: Tom Woudenberg