PWAT-D-21-00005

Shared water facilities and risk of COVID-19 in resource-poor settings: a transmission modelling study

PLOS Water

Dear Dr. Eisenberg,

Thank you for submitting your manuscript to PLOS Water. After careful consideration, we feel that it has merit but does not fully meet PLOS Water'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 reviewers have outlined a number of issues for your consideration. Here I would highlight two main areas that need to be addressed. First, the paper requires a clearer explanation of typical water collection scenarios and how they relate to the model parameters and associated values. This may require further consideration of the patterns as to how and when people collect water (e.g. even temporal spread vs peak times; possible changes in effective area as number of people collecting water increases; how the outdoor nature of water collection is reflected in the parameter values). Second, one of the reviewers has noted a a few concerns with the modelling, including (i)  the appropriateness of assuming a linear relationship when modelling the density-dependent force of infection, (ii) lack of information about the time frame of the model, and (iii) why in some scenarios the peak is zero.

Please submit your revised manuscript by Nov 08 2021 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at water@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pwat/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

• A rebuttal letter that responds to each point raised by the editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.
• A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.
• An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

We look forward to receiving your revised manuscript.

Kind regards,

Timothy Foster

Academic Editor

PLOS Water

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3. In the online submission form, you indicated that "Data was not collected for this theoretical modeling study, rather, parameters from other published literature were used to calibrate the models and are described in Figure X. Matlab analysis scripts and functions will be made available upon request by contacting Michael Hayashi at mhayash@umich.edu."

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Does this manuscript meet PLOS Water’s publication criteria? Is the manuscript technically sound, and do the data support the conclusions? The manuscript must describe methodologically and ethically rigorous research with conclusions that are appropriately drawn 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: I don't know

Reviewer #2: Yes

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3. Have the authors made all data underlying the findings in their manuscript fully available (please refer to the Data Availability Statement at the start of the manuscript PDF file)?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception. 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 Water 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: This paper sets out to examine the role that mixing at water collection sites my play in the transmission of Covid-19 for a number of different scenarios. This could be a useful addition to the literature on WASH and Covid, which is currently consists mainly of very broad policy presciptions on the importance of WASH for infection control.

I have no expertise in disease modelling so cannot comment on that, so take as correct and for other reviewers to examine. My expertise is in the operations and performance of the sort of water supply systems that the authors are examining.

As the paper is currently written I am finding it very difficult to assess whether the scenarios proposed are representative of these situations. Table 4 described four scenarios, for which the k values are stated, but these seem to state the outcome of the modelling rather than an input scenario. Table 3 described other parameters with unit, but it is difficult to relate this to an actual water user scenario.

This paper would benefit from a narrative description of some typical water collection scenarios, with a clearer explanation of what the k (and other values) are derived from. Key factors that might describe this are:

1. Number of water users using the source each day.

2. Effective hours of operation per day (noting that water collection is not spread evenly over the hours of use so a pump that is nominally available for 24 hours per day may see 90% of its use in six hours).

3. Effective number of users per hour.

4. Effective area of site, noting that this is not independent of the number of users, who will naturally spread out.

5. Effective density of users.

For example, considering a water site surface area down to 5m^2, makes sense in theory as that is approximately the size of, say, a handpump hard standing or the point of actual water collection at a kiosk, but the effective area of that site is much large as only two or three people would ever be in that space at a given time, and that would be for a few minutes at the most.

Notwithstanding assumptions about wind/ventilation/transmission given most water collection sites are outside, such proximity may lead to a high likelihood of transmission between the two or three people who shared it for the short period of time, but that does not equate to a high overall attack rate the the site as a whole. None of this is to question the modelling itself. But it is difficult for the reader to see how the findings of this modelling may inform management decisions. An analagous situation might be a supermarket: shoppers may spend 40 mins in the supermarket but only a short time at the checkout, and while all shoppers pass through the checkout at some point during those 40 mins not all shoppers are exposed to each other.

To be able to understand where typical scenarios fall within the various Figures presented would be very useful. It may be that the social distancing required to reduce transmission is already the normal in many instances. Making this paper more accessible to those making operational decisions about water supply services and infrastucture could make this a useful contribution to the WASH/Covid literature.

Reviewer #2: Summary:

The study uses mathematical models of COVID-19 transmission at shared water facilities in resource-poor countries to determine the effectiveness of social distancing and adding new water facilities. The authors develop two models where one model captures urban settings, where there are multiple water sites, and rural settings, where there is only one water site for multiple communities. The authors argue that mass gatherings at these sites pose a huge risk for COVID-19 transmission, and increasing the number of sites, i.e., reducing water sharing, is more effective at reducing transmission than social distancing alone, especially in urban settings.

Major comments:

The study is relevant to developmental policies that focus on mass gathering around shared resources in developing countries. The authors present a concise model that accurately reflects possible transmission patterns of COVID-19. Overall, I do believe this modeling study is valid and significant. However, there are a few issues and clarifications that should be addressed:

- Can the authors describe the setting of the water sharing sites? Are these sites outdoors or indoors? Is there usually a long queue to these sites?

- The density-dependent force of infection is modeled based on a linear relationship, represented by k_w and k_c. Does this linear relationship truly capture the transmission risk associated with crowding? I would expect there’s diminishing effect at a certain density level, which might be more sigmoidal or logistic, resulting in a nonlinear scaling of the transmission function (See https://doi.org/10.1016/j.mbs.2013.04.013). In other words, if you have a room packed with hundreds of people, one more person will not make much of a difference in terms of risk. Given this case, does this assumption change the effectiveness of social distancing and adding new sites? I only bring this up since the manuscript is arguing that transmission risk in highly dense areas can be mitigated by increasing water surface area, which corresponds to different mixing patterns that might not be linearly scaled, especially if there’s a queue or crowding that happens around the water reception area.

- Is there any information around the number of people gathered at each watering site? I know the model includes an explicit flow of people between community and watering sites. Are you assuming the flow rate of people that travel to the watering site is the same throughout the day, 24/7?

- What is the time frame of the model (weeks, year, days?). Is the model running until it peaks or until it levels out to an endemic level? If so, the authors should state this in the Methods.

- Figure 7: It is not obvious to me why the peak is zero in some of the scenarios. Is it implied that there is no community-level transmission of COVID-19 in the entire city if there are enough watering sites and social distancing?

Minor comments:

- Typo on Pg 17, Ln 358: “unviability” should be “unavailability.”

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Reviewer #1: No

Reviewer #2: No

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Shared water facilities and risk of COVID-19 in resource-poor settings: a transmission modelling study

PWAT-D-21-00005R1

Dear Dr. Eisenberg,

We are pleased to inform you that your manuscript 'Shared water facilities and risk of COVID-19 in resource-poor settings: a transmission modelling study' has been provisionally accepted for publication in PLOS Water.

Before your manuscript can be formally accepted you will need to complete some formatting changes, which you will receive in a follow up email. A member of our team will be in touch with a set of requests.

Please note that your manuscript will not be scheduled for publication until you have made the required changes, so a swift response is appreciated.

IMPORTANT: The editorial review process is now complete. PLOS will only permit corrections to spelling, formatting or significant scientific errors from this point onwards. Requests for major changes, or any which affect the scientific understanding of your work, will cause delays to the publication date of your manuscript.

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 water@plos.org.

Thank you again for supporting Open Access publishing; we are looking forward to publishing your work in PLOS Water.

Best regards,

Timothy Foster

Academic Editor

PLOS Water

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Reviewer Comments (if any, and for reference):

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. Does this manuscript meet PLOS Water’s publication criteria? Is the manuscript technically sound, and do the data support the conclusions? The manuscript must describe methodologically and ethically rigorous research with conclusions that are appropriately drawn based on the data presented.

Reviewer #2: Yes

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

Reviewer #2: N/A

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4. Have the authors made all data underlying the findings in their manuscript fully available (please refer to the Data Availability Statement at the start of the manuscript PDF file)?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception. 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: Yes

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

PLOS Water 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: All comments have been addressed.

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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.

Do you want your identity to be public for this peer review? If you choose “no”, your identity will remain anonymous but your review may still be made public.

For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #2: No

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