Effects of distancing and pattern of breathing on the filtering capability of commercial and custom-made facial masks: An in-vitro study

Lorenzo Ball; Stefano Alberti; Claudio Belfortini; Chiara Almondo; Chiara Robba; Denise Battaglini; Carlo Cravero; Paolo Pelosi; Valentina Caratto; Maurizio Ferretti

doi:10.1371/journal.pone.0250432

Peer Review History

Original SubmissionDecember 21, 2020
8 Mar 2021 Decision Letter - Francesco Di Gennaro, Editor PONE-D-20-40104 Effects of distancing and pattern of breathing on the filtering capability of commercial and custom-made facial masks: an “in-vitro” study. PLOS ONE Dear Dr. Alberti, 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. We also had some further concerns, which should be addressed in the revised manuscript. PLOS specifies that experiments, statistics, and other analyses are performed to a high technical standard; sample sizes are large enough to produce robust results; and methods are described in sufficient detail to allow another researcher to reproduce the experiment (http://journals.plos.org/plosone/s/criteria-for-publication#loc-3). We are concerned that you have not provided sufficiently detailed methodology for the study to be reproducible. Nor is the rationale clear for some of their methodological choices -- i.e., why do you choose a 40-minute spray time, and is this realistic in terms of real-world scenarios? We also note that you do not specify the amount of time that you pause to refill, nor why you designed the experiment where a refill is necessary. We are also concerned that the conclusions of your study are overstated, and that they are not directly supported by the results of the experiments. PLOS ONE's fourth publication criterion (http://journals.plos.org/plosone/s/criteria-for-publication#loc-4) states that the data presented in PLOS ONE manuscripts must support the conclusions drawn. We would like you to clarify that you are not claiming this method reduces infection rates, just the amount of aerosol particulates inhaled. As such, we ask you to revise the language used in your Discussion and Conclusions sections, to ensure that all statements are supported by the results of the study. Please submit your revised manuscript by 24 March 2021. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ 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 academic 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'. 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If the PLOS editorial team finds any language issues in text that either AJE or Editage has edited, the service provider will re-edit the text for free. Upon resubmission, please provide the following: The name of the colleague or the details of the professional service that edited your manuscript A copy of your manuscript showing your changes by either highlighting them or using track changes (uploaded as a supporting information file) A clean copy of the edited manuscript (uploaded as the new manuscript file) Additional Editor Comments: dear authors follow reviewer suggestions to improve your paper [Note: HTML markup is below. Please do not edit.] 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: Yes Reviewer #2: Yes ******** 2. Has the statistical analysis been performed appropriately and rigorously? Reviewer #1: Yes Reviewer #2: Yes ****** 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 ****** 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 ****** 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: It is a scientifically and methodologically well-articulated study. I found it very relevant to the current global pandemic situation. I recommend acceptance for publication after a minor revision is done. I hope the following clarity concerns will help the authors to improve their manuscript. Specific comments 1. I suggest ‘physical or social distancing or just simply distance’ to include as a keyword. 2. Page6, 2nd Paragraph • The nebulizer was operated for 40 minutes and a refill was possible. But it is not clear how long was the exposure time for each test? The test was replicated three times? Was any difference recorded among each test? • Does exposure time(Length of exposure influenced the percentage of inhalation fraction? 3. Page9, the 1st paragraph of discussion the phrase “ 1) all investigated variables resulted significant (p < 0.001)” need to be clarified. Does it mean all investigated materials resulted in a significant reduction of an inhaled fraction? The result showed that Cotton masks at a 40cm distance with polypneic pattern only reduce to 41.1% ± 0.3%. Can we say this is significant as compared to certified FFP3 or FFP2 + surgical mask which reduce to lower than 1%? 4. Page12, as a limitation, it is mentioned that the sensitivity of the technique for this study is 1%. Can we say this technique is valid or acceptable with this very low sensitivity rate? If I am not mistaken how sensitivity is used in this case, a 1% sensitivity rare makes your methodology unacceptable. Please revised or clarify how the sensitivity of the technique was measured and used in your methodology. Reviewer #2: First of all it was interesting area of study and I would like to thank the authors. Then I have minor comments regarding your manuscript; Generally it is better to see your English, some re-arrangements of your reporting and clarity of your statements for every reader. Please change INTERPRETATION to Discussion in your abstract section. In result section please start with Report from figure 3 shows… The pattern of breathing had a negative impact on the filtering capacity: compared to normal breathing... Also, incorrect positioning of the mask decreased the mask’s performances. “Statements that are discussing should be taken to discussion section °Significant difference compared to distance of 40 cm, § what are the signs at first and end of statements? “The main findings of this study are that: 1) all investigated variables resulted significant (p < 0.001); 2) all tested masks reduced the inhaled fraction compared to distancing alone; 3) distance decreased the inhaled fraction; 4) the differences between devices were more pronounced at shorter distances; 5) polypneic breathing pattern led to a decrease in most masks’ efficacy; 6) findings clarified the limitations/advantages of using masks both for individual and other protection.” Take this statement to finding section. [17], [18] your citation should better like this [17, 18]. Some of your statements are not easy to understand for all readers please revise all of your write up…“Distance alone markedly reduced the inhaled fraction also without masks, thus underlining how physical distancing policies intrinsically increase the protective effect of all other measures.” “Worst experimental condition” what does this mean? Is there such experiment? ****** 6. 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 #1: Yes: Serebe Gebrie Reviewer #2: Yes:** THOMAS AYALEW ABEBE [NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.] While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step. Attachments Attachment Submitted filename: PONE-D-20-40104_reviewerTA.pdf https://doi.org/10.1371/journal.pone.0250432.r001
Revision 1
26 Mar 2021 Author Response PONE-D-20-40104 Effects of distancing and pattern of breathing on the filtering capability of commercial and custom-made facial masks: an “in-vitro” study. PLOS ONE Dear Dr. Alberti, 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. Reply: We are thankful to the Editor for giving us the opportunity to revise our manuscript. We have modified the manuscript according to the reviewers’ and Editor’s additional comments and we hope you will find the revised manuscript suitable for publication on PLOS ONE. We also had some further concerns, which should be addressed in the revised manuscript. PLOS specifies that experiments, statistics, and other analyses are performed to a high technical standard; sample sizes are large enough to produce robust results; and methods are described in sufficient detail to allow another researcher to reproduce the experiment (http://journals.plos.org/plosone/s/criteria-for-publication#loc-3). We are concerned that you have not provided sufficiently detailed methodology for the study to be reproducible. Nor is the rationale clear for some of their methodological choices -- i.e., why do you choose a 40-minute spray time, and is this realistic in terms of real-world scenarios? We also note that you do not specify the amount of time that you pause to refill, nor why you designed the experiment where a refill is necessary. Reply: We agree that part of the methods was unclear and poorly described. We better clarified the experimental setting in the revised version of the manuscript. The choice of 40 minutes of nebulization was to simulate a prolonged person-to-person exposure and also conditioned by the necessity of achieving a sufficient sensitivity to detect inhaled fractions below 1%. The chosen study design required two brief stops of nebulization (<10 seconds) over 40 minutes, we judged these suspensions of nebulization irrelevant to the findings of our study. We hope that these aspects are now better clarified in the revised manuscript. We are also concerned that the conclusions of your study are overstated, and that they are not directly supported by the results of the experiments. PLOS ONE's fourth publication criterion (http://journals.plos.org/plosone/s/criteria-for-publication#loc-4) states that the data presented in PLOS ONE manuscripts must support the conclusions drawn. We would like you to clarify that you are not claiming this method reduces infection rates, just the amount of aerosol particulates inhaled. As such, we ask you to revise the language used in your Discussion and Conclusions sections, to ensure that all statements are supported by the results of the study. Reply: Thank you for pointing this out. We recognize that the original submitted manuscript contained parts that tended to over-interpret our findings. We have extensively revised the abstract and the discussion in order to avoid such over-interpretation. Reply to Reviewer #1 comments Reviewer #1: It is a scientifically and methodologically well-articulated study. I found it very relevant to the current global pandemic situation. I recommend acceptance for publication after a minor revision is done. I hope the following clarity concerns will help the authors to improve their manuscript. Reply: we thank the reviewer for their positive and constructive comments. Specific comments 1. I suggest ‘physical or social distancing or just simply distance’ to include as a keyword. Reply: thank you for your suggestion, we added the suggested keyword. 2. Page6, 2nd Paragraph • The nebulizer was operated for 40 minutes and a refill was possible. But it is not clear how long was the exposure time for each test? The test was replicated three times? Was any difference recorded among each test? Reply: Thank you for pointing out this lack of clarity. As also requested by the Editor, we better clarified the experimental design in particular concerning the nebulization time. As better stressed in the revised manuscript, each measurement was performed in triplicate. Reproducibility was good, as highlighted by the standard deviations illustrated in the figures. • Does exposure time(Length of exposure influenced the percentage of inhalation fraction? Reply: as now better clarified in the revised manuscript, the exposure time was constantly kept at 40 minutes, therefore no effect of time could be investigated. 3. Page9, the 1st paragraph of discussion the phrase “ 1) all investigated variables resulted significant (p < 0.001)” need to be clarified. Does it mean all investigated materials resulted in a significant reduction of an inhaled fraction? The result showed that Cotton masks at a 40cm distance with polypneic pattern only reduce to 41.1% ± 0.3%. Can we say this is significant as compared to certified FFP3 or FFP2 + surgical mask which reduce to lower than 1%? Reply. We recognize that the reporting of statistic was unclear. We now better clarify that the first p-values refer to the linear model using device, distance and pattern of breathing as co-factors. The following analyses refer to the Dunn post-hoc tests. We also agree that the clinical relevance of 41% protection compared to FFP3 with inhaled fraction <1% deserves better discussion. We restructured the discussion and results to better reflect this reasoning. 4. Page12, as a limitation, it is mentioned that the sensitivity of the technique for this study is 1%. Can we say this technique is valid or acceptable with this very low sensitivity rate? If I am not mistaken how sensitivity is used in this case, a 1% sensitivity rare makes your methodology unacceptable. Please revised or clarify how the sensitivity of the technique was measured and used in your methodology. Reply: Thank you for raising this point. Sensitivity of 0.92% (rounded to 1%) is defined as the smallest amount of nebulized particles that we were able to detect, defined as percent of what was detected with zero distance between receiver and emitter and no mask. While we understand the concerns of the reviewer, we believe that 1% is sufficient for the purposes of this study. In fact, this resolution allowed us to describe a wide range of values (from above 60% to the sensitivity limit) according to the type of mask used. We agree that we could not claim that a device with <1% inhaled fraction would be as protective as a certified FFP3 mask, but this would be out of the scopes of the study, and no such claims are made throughout the manuscript. We better discuss this limitation in the revised manuscript, also de-emphasizing the translation from our in vitro findings and possible implications for masking policies, which was an error of over-interpretation we acknowledge and we worked on in this revision process. Reply to Reviewer #2 comments Reviewer #2: First of all it was interesting area of study and I would like to thank the authors. Then I have minor comments regarding your manuscript; Generally it is better to see your English, some re-arrangements of your reporting and clarity of your statements for every reader. Reply: We thank the reviewer for their positive and constructive comments. We edited extensively the manuscript including revision of wording and phrasing of certain parts. Please change INTERPRETATION to Discussion in your abstract section. Reply: Thank you. We changed accordingly. In result section please start with Report from figure 3 shows… Reply: Thank you. We changed accordingly. The pattern of breathing had a negative impact on the filtering capacity: compared to normal breathing... Also, incorrect positioning of the mask decreased the mask’s performances. “Statements that are discussing should be taken to discussion section Reply: We thank the reviewer for underlining this important point. We extensively revised the results section, removing these statements and presenting data in a more straightforward way. °Significant difference compared to distance of 40 cm, § what are the signs at first and end of statements? Reply: We apologize for this lack of clarity. As per PLOS ONE editorial guidelines, figure legends are in-line with the main text. Symbols should be interpreted as legends of the corresponding figure (Figure 3). “The main findings of this study are that: 1) all investigated variables resulted significant (p < 0.001); 2) all tested masks reduced the inhaled fraction compared to distancing alone; 3) distance decreased the inhaled fraction; 4) the differences between devices were more pronounced at shorter distances; 5) polypneic breathing pattern led to a decrease in most masks’ efficacy; 6) findings clarified the limitations/advantages of using masks both for individual and other protection.” Take this statement to finding section. Reply: We have extensively revised the discussion, and this introductory part was shortened and now serves as introduction of the discussion section. [17], [18] your citation should better like this [17, 18]. Reply: Thank you. We changed accordingly. Some of your statements are not easy to understand for all readers please revise all of your write up…“Distance alone markedly reduced the inhaled fraction also without masks, thus underlining how physical distancing policies intrinsically increase the protective effect of all other measures.” “Worst experimental condition” what does this mean? Is there such experiment? Reply: We apologize for the lack of clarity. All the sections mentioned by the reviewer have been extensively revised and clarified according to the reviewer’s suggestions. We hope you will find the revised manuscript clearer to follow. Attachments Attachment Submitted filename: Response to reviewers.docx https://doi.org/10.1371/journal.pone.0250432.r002
7 Apr 2021 Decision Letter - Francesco Di Gennaro, Editor Effects of distancing and pattern of breathing on the filtering capability of commercial and custom-made facial masks: an “in-vitro” study. PONE-D-20-40104R1 Dear Dr. Alberti 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. An invoice for payment will follow shortly after the formal acceptance. To ensure an efficient process, please log into Editorial Manager at http://www.editorialmanager.com/pone/, click the 'Update My Information' link at the top of the page, and double check that your user information is up-to-date. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org. 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, Francesco Di Gennaro Academic Editor PLOS ONE Additional Editor Comments (optional): congratulations 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 ******** 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: (No Response) Reviewer #2: Yes ****** 3. Has the statistical analysis been performed appropriately and rigorously? Reviewer #1: (No Response) 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: (No Response) Reviewer #2: Yes ****** 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: (No Response) 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: All my comments and concerns are addressed. I see the authors have done lots of improvement on the method, results, and discussion. Now, I feel it is scientifically acceptable for publication. Reviewer #2: Thank you for considering my comments and improved your manuscript apropriately. I found Authors revision sound for publication. ****** 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 #1: Yes: Serebe Gebrie Reviewer #2: Yes:** Thomas Ayalew Abebe https://doi.org/10.1371/journal.pone.0250432.r003
Formally Accepted
13 Apr 2021 Acceptance Letter - Francesco Di Gennaro, Editor PONE-D-20-40104R1 Effects of distancing and pattern of breathing on the filtering capability of commercial and custom-made facial masks: an “in-vitro” study. Dear Dr. Alberti: I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department. If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. 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. If we can help with anything else, please email us at plosone@plos.org. Thank you for submitting your work to PLOS ONE and supporting open access. Kind regards, PLOS ONE Editorial Office Staff on behalf of Dr. Francesco Di Gennaro Academic Editor PLOS ONE https://doi.org/10.1371/journal.pone.0250432.r004

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