PONE-D-23-26467N95 Respirator Hybrid Decontamination Method Using Ultraviolet Germicidal Irradiation (UVGI) Coupled with Microwave-Generated Steam (MGS)PLOS ONE

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: I Don't Know

Reviewer #2: I Don't Know

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Reviewer #1: No

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Thank you for the opportunity to review this interesting paper on decontamination of N95 respirators. Below are my recommendations for areas that should be addressed before publication.

When introducing the term UVGI in the abstract, specify the type of UV eg UVC

The use of the word ‘mask’ is confusing. If referring to an N95 respirator, the term ‘respirator’ would be more appropriate and accurate.

Remember to define acronyms eg. COVID

On Pg.4 – the term pathogens are denatured is used. Feels. Proteins are denatured and pathogens are typically described as inactivated, killed, lysed, etc.

Interesting mention of the drawbacks on page 4. I would recommend moving these to the discussion.

Viral Kill Time Assay methods – please describe how the masks were ‘infected’. Eg 100 ul was pipetted over the entire surface of the mask piece?

There needs to be a description in the methods of how the dual exposure to MGS and UVGI happened. Was it sequential? Which treatment occurred first?

How is the hybrid method is a significant time or cost savings as purported by the authors? Hybrid method: 3 logs was 36 seconds, 4 logs 39 seconds. MGS: 4 logs was 45 seconds; UVGI 3 logs after 9 seconds and 4 logs after 100 seconds. Without a thorough explanation of the hybrid method procedure, it is hard to imagine the total operating time would be less using the hybrid method, including operator time to operate two different decon machines. Please provide an explanation.

Reviewer #2: Title

- The title of the manuscript is suitable and clear.

Abstract

- Abstract is an adequate summary of the work presented.

Introduction

- The word sterilization should be changed in disinfection when you use UVC

- “3M indicates that reducing”: I think it is useful to write 3M company

- “HPV” : an acronym should be written out in full the first time it is used.

- “By causing damage to their DNA, UV-C radiation either kills or inactivates microorganisms (5).” : On this subject, I believe there are more effective citations, for example Kciuk M, Marciniak B, Mojzych M, Kontek R. Focus on UV-Induced DNA Damage and Repair-Disease Relevance and Protective Strategies. Int J Mol Sci. 2020 Oct 1;21(19):7264. doi: 10.3390/ijms21197264. PMID: 33019598; PMCID: PMC7582305 or Rastogi RP, Richa, Kumar A, Tyagi MB, Sinha RP. Molecular mechanisms of ultraviolet radiation-induced DNA damage and repair. J Nucleic Acids. 2010 Dec 16;2010:592980. doi: 10.4061/2010/592980. PMID: 21209706; PMCID: PMC3010660.

- “In addition, the limited space of the microwave oven constricts the number of masks that can be decontaminated in one cycle (1).” : Is the number in brackets a citation or is it the number of masks that can be decontaminated in one cycle?

Method

- The timing of the study (start, run and end) should be described.

- The design/type of the study is missing

- “5 UVC bulbs (TUV PL-S 9W; Phillips)” : I think it is useful to specify the wavelength. The manufacturer states a peak of 253.7 nm in the data sheet, does the value in the prototype correspond to this?

- “This 1200W-rated microwave oven is capable of producing an output power of 600 - 650 W.” : It is useful to specify the power used for the experiment, as the product data sheet states a maximum output power of 800 Watts with 6 different levels.

- There is no description of how the three tests are carried out, particularly in relation to the combined test. Which decontamination method is used first in the combined test? Was there any downtime between methods? In my opinion, a step-by-step description of the procedure for the three tests is necessary.

- Repetitions of the tests are not present

- Provide a more detailed description of the decontamination techniques used. Adding explanatory figures about the techniques employed and the execution protocols could make the reading more understandable for the readers.

- Include the brand names of the culture media and solutions used, along with the legal headquarters of the manufacturing company.

Results

- Table 1 is not consistent with the log reduction. The results are inaccurate. How many times were repeated the tests?

Discussion

- “FFR” : An acronym should be written out in full the first time it is used.

- it should be verified what would happen, using microwaves, to the masks on a mechanical level. I believe that heating could have a negative impact. It is plausible that there could be an alteration in the fiber structure. This aspect should be investigated.

- The analyzed sample is relatively small. Is it conceivable that the distribution of microwaves inside the chamber is uniform? If not, there could be a different level of disinfection on the mask.

- Another aspect that should be investigated is the energy distribution of UVC light inside the chamber when a mask is inserted. Would the energies at play per unit of surface area change? These aspects should be commented on.

- The research is solely based on testing one virus. The resistance to other pathogens could be at least estimated based on the literature and the presented results. The hypothesis of the technique used is that it may be effective with other microbial species as well.

- With regard to the limitations of the work, more data would have given the study greater significance and, in addition, repeating the tests on several samples for each exposure time would have avoided the ambiguity of the data found in the UVGI-only decontamination test.

Conclusion

- It should be noted: UVGI reaches 3 logs (minimum required pathogen reduction to

completely disinfect a contaminated) in about a quarter of the time compared to UVGI + MGS.

References

- Cited References are relevant and sufficient to place the work in context. (Have a look at the suggested work in the Introduction section.)

Tables and Figures

- The tables and graph are clear. Graph needs better quality

- For the sake of clarity, the legend should be reproduced below the relevant figure.

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Reviewer #1: Yes: Jesse Cooper

Reviewer #2: Yes: Gabriele Messina

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N95 Respirator Hybrid Decontamination Method Using Ultraviolet Germicidal Irradiation (UVGI) Coupled with Microwave-Generated Steam (MGS)

PONE-D-23-26467R1

Dear Dr. Gopalan,

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Kind regards,

Vittorio Sambri, M.D., Ph.D.

Academic Editor

PLOS ONE

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