mask science {part 2}

N95 masks:

12 — N95 masks explained. https://www.honeywell.com/us/en/news/2020/03/n95-masks-explained Honeywell manufactures N95 respirators. They are made with 0.3 micron filter. They are named N95 because 95% of particles having a diameter of 0.3 microns are filtered by the mask forward to the wearer by use of an electrostatic mechanism. Coronaviruses are approximately 0.125 microns in diameter. https://pubmed.ncbi.nlm.nih.gov/32342926/

 

13 — V Offeddu, C Yung, et al. Effectiveness of masks and respirators against infections in healthcare workers: A systematic review and meta-analysis. Clin Inf Dis. 65(11), 2017 Dec 1; 1934-1942.

https://academic.oup.com/cid/article/65/11/1934/4068747

Meta-analysis – found that N95 respirators did not provide superior protection to facemasks against viral infections or influenza-like infections.

 

14 — C MacIntyre, Q Wang, et al. A cluster randomized clinical trial comparing fit-tested and non-fit-tested N95 respirators to medical masks to prevent respiratory virus infection in health care workers. Influenza J. 2010 Dec 3.

https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1750-2659.2011.00198.x?fbclid=IwAR3kRYVYDKb0aR-su9_me9_vY6a8KVR4HZ17J2A_80f_fXUABRQdhQlc8Wo

Randomised clinical trial – this study did find superior protection by N95 respirators when they were properly fitted (fit-tested) compared to surgical masksLegal paperwork:

https://img1.wsimg.com/blobby/go/da49e84a-a861-4967-b23a-368fb303c14c/downloads/Mask%20Free%20Documents%20.pdf?ver=1620666816153

 

15 — M Walker. Study casts doubt on N95 masks for the public. MedPage Today. 2020 May 20.

https://www.medpagetoday.com/infectiousdisease/publichealth/86601

Original study found that 624 our to 714 people wearing N95 masks left visible gaps when putting on their own masks.

https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2766070

 

 

Surgical masks:

16 — C MacIntyre, Q Wang, et al. A cluster randomized clinical trial comparing fit-tested and non-fit-tested N95 respirators to medical masks to prevent respiratory virus infection in health care workers. Influenza J. 2010 Dec 3.

https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1750-2659.2011.00198.x?fbclid=IwAR3kRYVYDKb0aRsu9_me9_vY6a8KVR4HZ17J2A_80f_fXUABRQdhQlc8Wo

Randomized clinical trial – study found that surgical masks offered no protection at all against influenza.

 

17 — N Shimasaki, A Okaue, et al. Comparison of the filter efficiency of medical nonwoven fabrics against three different microbe aerosols. Biocontrol Sci. 2018; 23(2). 61-69.

https://www.jstage.jst.go.jp/article/bio/23/2/23_61/_pdf/-char/en

Original article – surgical masks had about 85% penetration ratio of aerosolized inactivated influenza particles and about 90% of Staphylococcus aureus bacterial although the S. aureus particles were about 6x the diameter of influenza particles.

 

18 — T Tunevall. Postoperative wound infections and surgical face masks: A controlled study. World J Surg. 1991 May; 15: 383-387.

https://link.springer.com/article/10.1007%2FBF01658736

Original article – use of masks in surgery were found to slightly INCREASE incidence of infection over not masking in a study of 3088 surgeries. The surgeons’ masks were found to give no protective effect to the patients.

 

19 — N Orr. Is a mask necessary in the operating theatre? Ann Royal Coll Surg Eng 1981: 63: 390-392.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2493952/pdf/annrcse01509-0009.pdf

Original article – no difference in wound infection rates with and without surgical masks.

 

20 — N Mitchell, S Hunt. Surgical face masks in modern operating rooms – a costly and unnecessary ritual? J Hosp Infection. 18(3); 1991 Jul 1. 239-242.

https://www.journalofhospitalinfection.com/article/0195-6701(91)90148-2/pdf

Original article – no difference in wound infection rates with and without surgical masks.

 

21 — C DaZhou, P Sivathondan, et al. Unmasking the surgeons: the evidence base behind the use of facemasks in surgery. JR Soc Med. 2015 Jun; 108(6): 223-228.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4480558/

Systematic review – “there is a lack of substantial evidence to support claims that facemasks protect either the patient or surgeon from infectious contamination.”

 

22 — L Brosseau, M Sietsema. Commentary: Masks for all for Covid-19 not based on sound data. U Minn Ctr Inf Dis Res Pol. 2020 Apr 1.

https://www.cidrap.umn.edu/news-perspective/2020/04/commentary-masks-all-covid-19-not-based

Medical masks have a wide range of filtration efficiency, with most showing a 30% to 50% efficiency.

 

23 — N Leung, D Chu, et al. Respiratory virus shedding in exhaled breath and efficacy of face masks Nature Research. 2020 Mar 7. 26,676-680 (2020).

https://www.researchsquare.com/article/rs-16836/v1

Original article – both experimental and control groups, masked and unmasked respectively, were found to “not shed detectable virus in respiratory droplets or aerosols.” The study “did not confirm the infectivity of coronavirus” as found in exhaled breath.

 

24 — S Rengasamy, B Eimer, et al. Simple respiratory protection – evaluation of the filtration performance of cloth masks and common fabric materials against 20-1000 nm size particles. Ann Occup Hyg. 2010 Oct; 54(7): 789-798.

https://academic.oup.com/annweh/article/54/7/789/202744

Original article – study of aerosol penetration showed that two of the five surgical masks studied had 51% to 89% penetration of polydisperse aerosols.

 

25 — S Bae, M Kim, et al. Effectiveness of surgical and cotton masks in blocking SARS-CoV-2: A controlled comparison in 4 patients. Ann Int Med. 2020 Apr 6.

https://www.acpjournals.org/doi/10.7326/M20-1342

Original article – observed subjects while coughing, “neither surgical nor cotton masks effectively filtered SARS-CoV-2 during coughs by infected patients.” More viral particles were found on the outside than on the inside of masks tested.

 

mask science {part 1}
mask science {part 3)

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