PONE-D-23-10986

Airborne virus shedding by patients in health care units: Removal mechanisms affecting virus transmission

PLOS ONE

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2. We noticed you have some minor occurrence of overlapping text with the following previous publication(s), which needs to be addressed:

Detection of influenza virus in air samples of patient rooms - https://doi.org/10.1016/j.jhin.2020.10.020

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Additional Editor Comments:

Both reviewers are of the impression that the title of the manuscript be changed to avoid any ambiguity and remove the RSV part. One of the reviewers has given a very detailed suggestions to improve the manuscript quality and I suggest the authors to give good attention to the critical comments when modifying the manuscript..If possible give patients demographic information for  better understanding of the data presented.

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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: 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?

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 paper reports data on airborne influenza concentrations and other parameters collected in a hospital, and presents a model of the effects of different parameters on airborne influenza concentrations. Although previous studies have examined airborne influenza in healthcare facilities and other locations, the data in the paper is useful. However, I have concerns about the reliability of the model.

The title says “airborne virus” and the first sentence of the abstract says, “In this study, we characterize the distribution of airborne viruses (respiratory syncytial virus (RSV) and influenza A/B) in hospital rooms of patients with confirmed infections.” However, none of the patients in the study has RSV, and the only viruses that were studied were influenza A and B. The title should be changed to something like “airborne influenza virus” and the abstract rewritten to just say “airborne influenza A and B viruses”. This also needs to be corrected in the last paragraph of the Introduction and elsewhere throughout the paper.

In the Introduction, the authors say, “the avian influenza virus”. This should be avian influenza viruses, since there are numerous strains. Later in the same sentence the authors say, “COVID-19 pandemic [32-34] caused by the severe acute respiratory syndrome coronavirus (SARS-CoV1 or SARS-CoV2).” COVID-19 is caused by SARS-CoV-2, not SARS-CoV-1. Note also that the virus is written as SARS-CoV-2, not SARS-CoV2.

Introduction, second paragraph: The authors are correct that, historically, droplets have been defined as particles > 5 µm in diameter that fall rapidly to the ground, while droplet nuclei (aerosols) were defined as particles < 5 µm that can remain airborne for an extended period. In the past, these definitions were used to distinguish between airborne transmission by aerosols and droplet transmission by droplets. However, these definitions are not based on aerosol science, and in reality particles much larger than 5 µm can remain airborne for a significant time and be inhaled. Unfortunately, during the early part of the COVID-19 pandemic, these definitions were used to justify the erroneous assumption that COVID-19 was not spread by aerosols. Humans continuously emit aerosols of respiratory fluids as they breathe, talk, cough, sneeze, and sing. These respiratory aerosols can have a very broad size range, from tens of nanometers in diameter to visible droplets of a millimeter or more (Morawska et al. 2009; Gralton et al. 2011; Bourouiba et al. 2014; Fennelly 2020). Airborne particles larger than 100 µm are ballistic; that is, they are affected primarily by gravity and fall quickly to the ground. Respiratory aerosol particles in this size range tend to deposit within a few meters of the source (Prather et al. 2020). As the aerosol particle diameter decreases from 100 µm, a gradual transition occurs where the settling velocity rapidly decreases and the particles remain airborne for longer times. For example, a 100 µm aerosol particle takes 4 seconds to fall 1 meter in still air, while a 10 µm aerosol particle takes 5.4 minutes, a 5 µm aerosol particle takes 21 minutes, and a 1 µm aerosol particle takes 8 hours to settle the same distance (Hinds 1999). Because of this, there is a growing consensus in the aerosol science community that the term aerosols and aerosol transmission should be used for particles less than 100 µm rather than 5 µm, and that droplet transmission be used only for particles larger than 100 µm that truly do settle rapidly. See these references: (Fennelly 2020; Prather et al. 2020; Marr and Tang 2021; Randall et al. 2021; Tang et al. 2021; Jimenez et al. 2022)

Introduction, second paragraph: The authors say, “Variations in temperature (T) and relative humidity (RH) play an important role in the activation or deactivation of viruses [39-41]”. Viruses are expelled from the body and become deactivated over time; they are not activated by the environment.

Introduction, third paragraph: The authors say, “Despite earlier efforts and until recently, many of these studies fell short of defining clear statistical relationships between the concentrations of the influenza virus (or other microorganisms) in patient rooms and the physical determinants (such as T, RH, AER) and the location of the patient in the room [48].” I would expect that the most fundamental factor determining the concentration of airborne influenza virus would be the rate of airborne virus shedding by the patient.

Introduction, third paragraph: The authors say, “In this study, we monitor the viral load (RSV and influenza A/B), particulate matter (PM2.5 & PM10,), and physical parameters (AER, T, RH) within patient rooms for the purpose of assessing airborne virus shedding by patients in health care units using an integrated approach of coupling field measurements with statistical and numerical analyses.” Why would you expect there to be a relationship between PM and airborne virus? These would seem to be independent to me, unless PM is an indirect indicator of room ventilation and filtration or something similar.

Materials and Methods, second paragraph: The Coriolis sampler only collects aerosol particles from about 0.5 to 20 µm. The authors should note this.

Figure 1: More information is needed here. Where was the ventilation system inlet into the room and outlet from the room relative to the patient and aerosol samplers? The amount of virus collected could be greatly affected if the samples were collected directly downwind or upwind from the patient.

Materials and Methods, equations 2-5: This seem like a very complex model with a large number of assumptions that are being applied to a very limited data set. I question how reliable the results are here. Note, for example, that the authors have assumed that the surface tension of the droplets is 0.072 N/m because that is the surface tension of pure water. In fact, however, this is not true: respiratory fluids contain a large amount of surfactant and the surface tension of these fluids is much lower than water.

Materials and Methods, page 9: The recitation of variables here in paragraph form is very difficult to read. The variable should be given as a list with one line for each variable.

Materials and Methods, page 10: The authors say, “The AER was estimated to be 7.2 AER and was validated by the hospital’s physical plant engineers.” Was the AER of the study rooms actually measured during the study? The nominal setting for the AER can vary from the actual AER, and the AER can vary from room to room. How confident are the authors that this value was correct for all the rooms?

Materials and Methods, page 11: The authors say, “Normalization was conducted by dividing the total concentration measures in the sample by the number of coughs recorded over the sampling period.” Patients with influenza shed virus during tidal breathing as well as coughing, and some researchers believe that tidal breathing is actually a greater source of virus than coughing for most patients. See, for example, (Milton et al. 2013; Yan et al. 2018; Bueno de Mesquita et al. 2021)

Results and Discussion, page 18: The authors say, “Moreover, the role of AER on removal was found to be marginal with a reduction rate of 1%”. I see several problems with this statement. The authors did not vary the AER during their study, so their data does not support this conclusion. The authors’ model assumes a value for the combined effects of settling and ventilation; it is not based on their experimental results. Numerous studies have shown that increased ventilation is an effective way to reduce exposure to airborne particles. In fact, the Yang and Marr paper that the authors cite as the basis for the assumed decay rate in their model (Yang and Marr 2011) says, “We have demonstrated the relative importance of the three removal mechanisms. Settling can remove over 80% of droplets emitted from a cough within 10 min; however, it is effective only for larger droplets and allows the smaller ones (<5 µm) to remain suspended. In contrast, ventilation is able to remove all droplets regardless of size simply by air exchange. Therefore, higher AERs will facilitate the elimination of virus-containing droplets from indoor environments, especially to compensate for the inefficacy of settling in removing the small ones. This observation also justifies the requirement to maintain a high AER in public places (e.g., 12 ACH in hospital waiting areas).”

References

Bourouiba, L, E Dehandschoewercker and John WM Bush (2014). Violent expiratory events: on coughing and sneezing. J Fluid Mech 745: 537-563. https://doi.org/10.1017/jfm.2014.88

Bueno de Mesquita, PJ, J Nguyen-Van-Tam, B Killingley, J Enstone, R Lambkin-Williams, AS Gilbert, A Mann, J Forni, J Yan, J Pantelic, ML Grantham and DK Milton (2021). Influenza A (H3) illness and viral aerosol shedding from symptomatic naturally infected and experimentally infected cases. Influenza Other Respir Viruses 15(1): 154-163. https://doi.org/10.1111/irv.12790

Fennelly, KP (2020). Particle sizes of infectious aerosols: implications for infection control. Lancet Respir Med 8(9): 914-924. https://doi.org/10.1016/S2213-2600(20)30323-4

Gralton, J, E Tovey, ML McLaws and WD Rawlinson (2011). The role of particle size in aerosolised pathogen transmission: a review. J Infect 62(1): 1-13. https://doi.org/10.1016/j.jinf.2010.11.010

Hinds, WC (1999). Aerosol Technology. Properties, Behavior, and Measurement of Airborne Particles. New York, John Wiley & Sons.

Jimenez, JL, LC Marr, K Randall, ET Ewing, Z Tufekci, T Greenhalgh, R Tellier, JW Tang, Y Li, L Morawska, J Mesiano-Crookston, D Fisman, O Hegarty, SJ Dancer, PM Bluyssen, G Buonanno, M Loomans, WP Bahnfleth, M Yao, C Sekhar, P Wargocki, AK Melikov and KA Prather (2022). What were the historical reasons for the resistance to recognizing airborne transmission during the COVID-19 pandemic? Indoor Air 32(8): e13070. https://doi.org/10.1111/ina.13070

Marr, LC and JW Tang (2021). A Paradigm Shift to Align Transmission Routes With Mechanisms. Clin Infect Dis 73(10): 1747-1749. https://doi.org/10.1093/cid/ciab722

Milton, DK, MP Fabian, BJ Cowling, ML Grantham and JJ McDevitt (2013). Influenza virus aerosols in human exhaled breath: particle size, culturability, and effect of surgical masks. PLoS Pathog 9(3): e1003205. https://doi.org/10.1371/journal.ppat.1003205

Morawska, L, GR Johnson, ZD Ristovski, M Hargreaves, K Mengersen, S Corbett, CYH Chao, Y Li and D Katoshevski (2009). Size distribution and sites of origin of droplets expelled from the human respiratory tract during expiratory activities. J Aerosol Sci 40(3): 256-269. https://doi.org/10.1016/j.jaerosci.2008.11.002

Prather, KA, LC Marr, RT Schooley, MA McDiarmid, ME Wilson and DK Milton (2020). Airborne transmission of SARS-CoV-2. Science 370(6514): 303-304. https://doi.org/10.1126/science.abf0521

Randall, K, ET Ewing, LC Marr, JL Jimenez and L Bourouiba (2021). How did we get here: what are droplets and aerosols and how far do they go? A historical perspective on the transmission of respiratory infectious diseases. Interface Focus 11(6): 20210049. https://doi.org/10.1098/rsfs.2021.0049

Tang, JW, WP Bahnfleth, PM Bluyssen, G Buonanno, JL Jimenez, J Kurnitski, Y Li, S Miller, C Sekhar, L Morawska, LC Marr, AK Melikov, WW Nazaroff, PV Nielsen, R Tellier, P Wargocki and SJ Dancer (2021). Dismantling myths on the airborne transmission of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). J Hosp Infect 110: 89-96. https://doi.org/10.1016/j.jhin.2020.12.022

Yan, J, M Grantham, J Pantelic, PJ Bueno de Mesquita, B Albert, F Liu, S Ehrman, DK Milton and E Consortium (2018). Infectious virus in exhaled breath of symptomatic seasonal influenza cases from a college community. Proc Natl Acad Sci USA 115(5): 1081-1086. https://doi.org/10.1073/pnas.1716561115

Yang, W and LC Marr (2011). Dynamics of airborne influenza A viruses indoors and dependence on humidity. PLoS ONE 6(6): e21481. https://doi.org/10.1371/journal.pone.0021481

Reviewer #2: This is a very well written paper with a sound scientific approach and appropriate conclusions. The technical and mathematical descriptions may be difficult for non-specialized readers but this is forgivable. The conclusions are of wide impact and should be transmitted to different disciplines including infection control programs, hospital engineers, and infectious diseases experts. Following are some comments and suggestions:

• The patient population is not described. Were all the subjects enrolled adult patients? Any pediatric patients? Were there any elderly patients who may have a weakened cough? Did any patients receive nebulized medications or saline as part of their treatment? If this information was not available, it should be stated as a limitation

• Since all the patients enrolled had influenza virus and none had RSV, I wonder why the authors refer to “RSV” in their abstract and use the title as “airborne virus” instead of “influenza”. I think the latter would be more appropriate.

• A brief description of the Coriolis µ Biological Air Sampler should be provided. How it works, volume collected, filters, etc.

• Lines 79-83: It is not clear how written informed consent was obtained (where by definition the patient has to sign their name), yet the patients’ identities were kept confidential. This is a bit confusing.

• Line 172: the unit for AER is 1/hour or L/hour?

• Lines 187-188: “The AER was estimated to be 7.2 AER…”. Is there a unit missing or a period after “7.2”?

• Figure 2: The labeling of the pie-charts should be corrected

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Reviewer #1: No

Reviewer #2: No

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Airborne influenza virus shedding by patients in health care units: Removal mechanisms affecting virus transmission

PONE-D-23-10986R1

Dear Dr. El-Fadel,

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.

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Sreekumar Othumpangat, PhD

Academic Editor

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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 #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

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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 #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

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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 #1: All of my comments have been addressed. I don't have anything further to add, but your editorial manager software won't let me submit my review until this box contains at least 100 characters, which is annoying.

Reviewer #2: All comments have been answered. The paper is ready for publication from my end.

I don't have anything more to add

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Reviewer #1: No

Reviewer #2: No

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