PONE-D-21-20494Comparison of longitudinal trends in self-reported symptoms and COVID-19 case activity in Ontario, CanadaPLOS ONE

Dear Dr. Maharaj,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

The Authors are expected to address all the criticisms by all Reviewers. In particular, please reconsider the use of symptoms only approach for the surveillance of COVID-19, and the conclusion on the use of participatory surveillance or specifically the adopted CLI definition (Reviewer #1) and strengthen the discussion (Reviewer #2). In additional to the above comments, please address,

1. To fully assess the use of participatory surveillance using a symptom only approach, the authors may consider other combinations symptom which may be less affected by other respiratory infections (e.g. rhinoviruses or enteroviruses). Such alternative definitions have been considered in Reses et al. (BMC Public Health, 2021).

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Eric HY Lau, Ph.D.

Academic Editor

PLOS ONE

Additional Editor Comments (if provided):

The Authors are expected to address all the criticisms by all Reviewers. In particular, please reconsider the use of symptoms only approach for the surveillance of COVID-19, and the conclusion on the use of participatory surveillance or specifically the adopted CLI definition (Reviewer #1) and strengthen the discussion (Reviewer #2). In additional to the above comments, please address,

1. To fully assess the use of participatory surveillance using a symptom only approach, the authors may consider other combinations symptom which may be less affected by other respiratory infections (e.g. rhinoviruses or enteroviruses). Such alternative definitions have been considered in Reses et al. (BMC Public Health, 2021).

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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: No

Reviewer #2: Partly

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

Reviewer #1: Yes

Reviewer #2: Yes

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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: No

Reviewer #2: No

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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 authors compared longitudinal trends in self-reported symptoms and COVID-19 case activity in Ontario, Canada, and concluded that a participatory surveillance tool showed poor longitudinal correspondence with COVID-19 case counts. The conclusion doesn’t seem reliable with current data analysis.

Major comments:

1. The major issue comes from definition of COVID-like illness (CLI), defined by

“the presence of at least two of: fever (measured or subjective), chills, ... or new taste disorder. “ Though they cited these symptoms from CDC website (https://ndc.services.cdc.gov/case-definitions/coronavirus-disease-2019-2021/), the CDC has never defined these symptoms as CLI. Indeed, on the same webpage, under the section of “Case Classification > Probable”, the CDC requires a case to be probable, under the condition when no confirmatory or presumptive laboratory evidence for SARS-CoV-2 is available, to have at least “epidemiologic linkage” which is not reported in current study BUT can surely be obtained using a participatory approach, as shown in other published studies. Thus, the conclusion can only be that using the symptom-only survey cannot help surveil COVID-19. By no mean can it be concluded that the participatory surveillance tool does not work. In fact, the participatory surveillance works very well with the large amount of data collected in a short period of time, as shown by the authors.

Reviewer #2: The manuscript is well written. I believe it is worth to be published in Plos One. I however suggest that the authors move the historical COVID 19 trends in Ontario to the background section. The authors also refer to a 2016 census in the methodology section but do not provide a citation for it. The authors have rigorously presented the findings but sort of gross over them in the discussion section. Strengthening of the discussion section would further enrich the manuscript. Lastly, the conclusion in the main document is a bit light weight considering the amount of findings presented.

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Reviewer #1: No

Reviewer #2: No

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Comparison of longitudinal trends in self-reported symptoms and COVID-19 case activity in Ontario, Canada

PONE-D-21-20494R1

Dear Dr. Maharaj,

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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If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Eric HY Lau, Ph.D.

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

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 #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 #2: Yes

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

Reviewer #2: Yes

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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 #2: No

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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 #2: Yes

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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 #2: Thank you for addressing my comments. Minor comment: please insert links to the web pages referred to in the document.

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7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #2: No