Covid-19 Airborne Transmission and Its Prevention: Waiting for Evidence or Applying the Precautionary Principle?

Round 1

Reviewer 1 Report

The manuscript by Carducci and colleagues review the published litterature with regards to risk associated to aerosol transmission of SARS-CoV-2 virus and concludes on the need to apply precautionary principle by promoting respiratory protection. 

First minor comment: throughout the manuscript, please use the term "infectivity or infectious" instead of "viability or viable" when refering to viral particles. 

It is not clear why some retreived studies showed up with the search keywords altough they are presenting data with viral surrogates only (refs 46, 50, 55). If such manuscripts were included, other studies using phages as surrogates or other airborne viruses could have been included as well (e.g.Nathalie Turgeonet al. (2014). Comparison of Five Bacteriophages as Models for Viral Aerosols Studies. Applied and Environmental Microbiology 80(14):4242-50; Daniel Verreault et al. (2011). Detection of Airborne Lactococcal Bacteriophages in Cheese Plants. Applied and Environmental Microbiology 77(2):491-7; Daniel Verreault et al.  (2010). Comparison of polycarbonate and polytetrafluoroethylene filters for sampling of airborne bacteriophages. Aerosol Science and Technology, 44: 197-201; Daniel Verreault et al.(2010). Airborne Porcine Circovirus in Canadian Swine) Confinement Buildings. Veterinary Microbiology, 141(3-4):224-30

 

Interpretation of available literature is sound and efficient. Categories of reports are well designed to include laboratory (in vitro), environmental monitoring and epidemiological data. The review raises the need to develop and validate more efficient detection and quantification methods, namely for infective viruses. I think adding to the discussion that most reports do not present the theoretical Limit of detection or detection treshold (sampling volume, genome extraction sensitivity, RTqPCR sensitivity and specificity). Very interesting point raised that, although aerosols role in transmission is recognized (SARS), its attribuable risk is not estimated. 

It would be important to discuss the role of face mask in the prevention not only of aerosol emission by infected persons but also fomite contamination from larger droplets. 

In the research needs, it would be important to specify :

Viral load of infected clinical materials (upper and lower air ways, saliva, feces, urines, etc.) in symptomatic and asymptomatic persons and determination of infectious rate in those samples; Given the low infectivity rate described so fat in fecal samples, for examples, wastewater or fecal exposure should be introduced in models with appropriate weight. 

To my opinion, this review manuscript is a great piece of work and highlights wholes and interesting findings in the science of bioaerosols and COVID-19 virus transmission. 

Finally, I would suggest to review this very important part of the manuscript, the statement is unclear. GIven this is the main message of the manuscript, it deserves to be expressed in a clear manner.

Nevertheless, the prevention, although preferably evidence-based, should be inspired also to the precautionary principle that imply the need of acting even on the basis of a well-founded suspicion, waiting for more proofs: this means that a preventive measure should be not recommended is the evidence of inefficacy exists, but 600 not if the complete evidence of efficacy does not exist. 

 

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

Specific comments:

1. Keyword “air survival” is suggested to be revised as “survival in air”.
2. Please check whether the death number in L33 is correct.
3. While searching literature, did authors constrain the range of published year? (L94–95)
4. Please make sure that the full name of an abbreviation is provided when it is referred at the first time.
5. Why the authors classified the virus into animal coronavirus, human coronavirus, SARS-CoV, MERS-CoV, and SARS-CoV-2? Are not SARS-CoV, MERS-CoV, and SARS-CoV-2 belong to human coronavirus? Please specify.
6. The case of sub-number of figure should be unified in the text and figure.
7. It is suggested that literature regarding the benefit of precaution could be added into Discussion to support author’s viewpoint.
8. There are some grammatical errors in the manuscript (L522, 538). Please give an overall check and revise them.

 

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

Brief summary

The authors use the standardized PRISMA guidelines for conducting a systematic literature review, aimed to collect and summarize findings from relevant research studies related to the airborne transmission possibility of coronaviruses infecting animals and humans. In particular the manuscript is focused to evaluate the role of the above mentioned transmission route in the SARS-CoV-2 transmission dynamics. In the context of the current pandemic, the precautionary principle application is recommended by the authors.

 

Broad comments

The manuscript presents interesting results obtained from a systematic literature review, mainly carried out to describe the state of the art about research findings on the airborne transmission route of SARS-CoV-2, but also including other human and animal coronaviruses. On the whole 64 papers were selected and classified in three main groups: laboratory experiments (12 papers), air monitoring (22) and epidemiological and airflow models studies (30). Although the airborne transmission of SARS-CoV-2 is suggested by studies from the three groups, complete evidence is missing. However, in the context of the current pandemic, the authors emphasize the precautionary principle based on preventive measures (such as use of masks, safety distance and air ventilation) that could improve the SARS-CoV-2 transmission dynamics control.

In general, I suggest to define abbreviations in parentheses, the first time they appear in the abstract, main text, and in figure or table captions, as well as in the Tables S1, S2 and S3 captions, and used consistently thereafter.

Specific comments:

Abstract:

• 1_13: I suggest to replace “coronavirus” with “coronaviruses”.

 

Keywords:

• 1_23-24: The following keywords could be added: “human coronaviruses” and “animal coronaviruses”.

 

1.Introduction:

• Page 1_27: I suggest to replace “SARS-CoV-2 virus is a new β-coronavirus …….” with “Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is a new β-coronavirus …….”.
• Page 1_28-30: Please define the acronyms used.
• Page 1_41: Please, replace “SARS and MERS” with “SARS-CoV and MERS-CoV”.
• Page 2_81: I suggest to replace “SARS” with “SARS-CoV”.
• Page 2_84: I suggest to replace “coronavirus and airborne transmission” with ““coronavirus airborne transmission”.

 

2.Material and Methods:

• Page 2_86: authors could define the acronym “PRISMA“ as suggested “….. following the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines …..”
• Page 3_99: Replace “(2) written in English” with “(3) written in English”.

 

3.Results

• Page 3_110-111: I suggest to modify the sentence “Their time trend shows a small increase after 2003 (when the SARS epidemic occurred) and in 2013 due to the MERS appearance, …….” as follows “Their time trend shows small increases after 2003 (when the SARS epidemic occurred) and in 2014 due to the MERS appearance, …….”. Did you mean 2014?
• Page 5_Table 1: According to the papers selected in the manuscript, it would be better to replace “Animal coronavirus” and Human coronavirus” with “Animal coronaviruses” and Common human coronaviruses”, respectively.
• Page 5_128: : Please define the acronyms used.
• Page 5_130: Please replace “is” with “are”.
• Page 7_240: “..... spry fluid .....” Did you mean “..... spray fluid .....”?
• Page 8_254: Replace “human coronaviruses” with “common human coronaviruses”.
• Page 8_257: Replace “Table 2S” with “Table S2”.
• Page 8_258: Replace “Animal coronavirus” with “Animal coronaviruses”.
• Page 8_260: “..... porcine respiratory coronavirus .....”. I suggest to add the disease acronym as follows “..... porcine respiratory coronavirus (PRCoV) .....”.
• Page 8_259-264: How many pigs were infected with the PRCoV? What kind of swabs were collected?
• Page 8_266: I suggest to delete the adjective “respiratory” in the sentence related to the PEDV (enteric virus).
• Page 8_267: “vrus” needs to be corrected
• Page 8_271: “but not for the bioassay. I suggest to complete la sentence “but not for the bioassay, consisting in ..............”.
• Page 8_278: “the same viruses”. Exactly, what are you referring to? Please, specify.
• Page 8_284: Replace “Human Coronavirus” with “Common Human Coronaviruses (Common HCoV)”. (Human coronavirus types include Common human coronaviruses and Other human coronaviruses, see https://www.cdc.gov/coronavirus/types.html).
• Page 9_304: Please complete the sentence “..... for HCoV-OC43.” as follows“..... for HCoV-OC43/HKU1.”
• Page 9_309: Replace “..... viral RNA of influenza virus .....” with “..... viral RNA of influenza viruses .....”.
• Page 9_314: “..... and cell culture for the positive ones.” Please, clarify that only PCR-positive samples were further analyzed by cell culture.
• Page 9_331: “Thirty air samples …..”. Please check this value.
• Page10_359: “..... from camel.”. You could specify “….. from dromedary camel.”
• Page 10_385 and 388: Please specify what “GC”
• Page 12_465: Amend “m” with “µm”.
• Page 12_495: I suggest to define the acronym “PPE”.
• Page 15_600-601: “….. , but not if the complete evidence of efficacy does not exist.” Could you clarify this sentence, please? Did you mean "but not excluded if ....."?
• Page 15_611: I suggest to define the acronym “QMRA”.

 

Supplementary Materials

• Page 15_634: I suggest to replace “..... by coronavirus .....” with “..... by coronaviruses .....”. Authors used chronological order to list papers in Table S1. How and by what criteria were the papers listed in Tables S2 and S3”? Please, specify this information.

 

References

Page 20_843: Ref. [83] Please check the year.

Page 21_864: Ref. [92] Please check the year.

 

Appendix 2 (Supplementary information.docx file)

Table S1

• Title: I suggest to replace “..... by coronavirus .....” with “..... by coronaviruses .....”.
• Ref [49]: Please, check viral load.

 

Table S2

• 1^st column: Please replace “Animal CoV” and Human CoV” with “Animal CoVs” and Common Human CoVs”, respectively.
• Ref [58]: Please replace “PRCV” with “PRCoV”.
• Ref [59]: Please replace [see Results column] “molecular” with “molecular test” and “genome” with “viral genome”.
• [60] and [61]: [see Sampling site and samples (type and number) column]. Are air sample numbers related to CoVs?
• [64]: Replace [see Results column] “HCoV-OC43” with “HCoV-OC43/HKU1”.
• [68]: Verify [see Sampling site and samples (type and number) column] the number of air samples.
• [75] and [73]: Verify [see Sampling site and samples (type and number) column] the numbers of surface samples.

 

Table S3

• [83] and [92] [See Ref. column] Please, check the year.

Author Response

Please see the attachment

Author Response File: Author Response.pdf