Evidence Base

WHAT IS THE EVIDENCE FOR USING CLOTH FACE MASKS?

Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1 (van Doremalen, 2020 in NEJM)

The virus can remain viable and infectious in aerosols for hours and on surfaces up to days

3M Mask Comparisons

Effectiveness of N95 respirators versus surgical masks in protecting health care workers from acute respiratory infection: A systematic review and meta-analysis (Smith, 2016, Canadian Medical Association Journal) Showed insufficient data to determine definitively whether N95 respirators are superior to surgical masks in protecting health care workers against transmissible acute respiratory infections in clinical settings.

A cluster randomised trial of cloth masks compared with medical masks in healthcare workers (Macintyre, 2015 in BMJ) This study is the first RCT of cloth masks in Vietnam, and the results caution against the use of cloth masks. This is an important finding to inform occupational health and safety. Moisture retention, reuse of cloth masks and poor filtration may result in increased risk of infection.

Professional and Home-Made Face Masks Reduce Exposure to Respiratory Infections among the General Population (van der Sande, 2008 in PLOS One)

Any type of general mask use is likely to decrease viral exposure and infection risk on a population level, in spite of imperfect fit and imperfect adherence, personal respirators providing most protection. Masks worn by patients may not offer as great a degree of protection against aerosol transmission.

Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic? (Davies, 2013, Diaster Medicine)This study examined homemade masks as an alternative to commercial face masks. Several household materials were evaluated for the capacity to block bacterial and viral aerosols. Twenty-one healthy volunteers made their own face masks from cotton t-shirts; the masks were then tested for fit. The number of microorganisms isolated from coughs of healthy volunteers wearing their homemade mask, a surgical mask, or no mask was compared using several air-sampling techniques. The median-fit factor of the homemade masks was one-half that of the surgical masks. Both masks significantly reduced the number of microorganisms expelled by volunteers, although the surgical mask was 3 times more effective in blocking transmission than the homemade mask. Our findings suggest that a homemade mask should only be considered as a last resort to prevent droplet transmission from infected individuals, but it would be better than no protection

Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus (SARS-CoV2) (Li, 2020, Science)

Estimation of the prevalence and contagiousness of undocumented novel coronavirus (SARS-CoV2) infections is critical for understanding the overall prevalence and pandemic potential of this disease. Here we use observations of reported infection within China, in conjunction with mobility data, a networked dynamic metapopulation model and Bayesian inference, to infer critical epidemiological characteristics associated with SARS-CoV2, including the fraction of undocumented infections and their contagiousness. We estimate 86% of all infections were undocumented (95% CI: [82%–90%]) prior to 23 January 2020 travel restrictions. Per person, the transmission rate of undocumented infections was 55% of documented infections ([46%–62%]), yet, due to their greater numbers, undocumented infections were the infection source for 79% of documented cases. These findings explain the rapid geographic spread of SARS-CoV2 and indicate containment of this virus will be particularly challenging.

Rational use of face masks in the COVID-19 pandemic (Feng, 2020 Lancet) recommend that people in quarantine wear face masks if they need to leave home for any reason, to prevent potential asymptomatic or presymptomatic transmission.

Can Masks Capture Coronavirus Particles? (Smart Air Filters)

Researchers in Edinburgh tested for particles 10x smaller than corona virus – surgical mask 80% (less because worn poorly) but handkerchiefs 30%

Researchers in Cambridge tested for particles 5x smaller than corona virus and found a range of 73%-57% using single layer dishcloths, t-shirts, pillowcase and linen against 89% in surgical mask. Double the layer made tea towel dishcloth go from 83% to 97%, the same as a surgical mask! But made little difference for others. However recommend pillowcase (62%) and 100% cotton T-shirt (71%) for breathability. Double vs Single-layer has a 1-2% difference. You can stick a paper towel in between 2 layers as it improves it by a further 23%.

Face masks: much more than you wanted to know.

CDC Recommendation Regarding the Use of Cloth Face Coverings, Especially in Areas of Significant Community-Based Transmission CDC

Recent Studies:

  • Rothe C, Schunk M, Sothmann P, et al. Transmission of 2019-nCoV Infection from an Asymptomatic Contact in Germany. The New England journal of medicine. 2020;382(10):970-971.
  • Zou L, Ruan F, Huang M, et al. SARS-CoV-2 Viral Load in Upper Respiratory Specimens of Infected Patients. The New England journal of medicine. 2020;382(12):1177-1179.
  • Pan X, Chen D, Xia Y, et al. Asymptomatic cases in a family cluster with SARS-CoV-2 infection. The Lancet Infectious diseases. 2020.
  • Bai Y, Yao L, Wei T, et al. Presumed Asymptomatic Carrier Transmission of COVID-19. Jama. 2020.
  • Kimball A HK, Arons M, et al. Asymptomatic and Presymptomatic SARS-CoV-2 Infections in Residents of a Long-Term Care Skilled Nursing Facility — King County, Washington, March 2020. MMWR Morbidity and mortality weekly report. 2020; ePub: 27 March 2020.
  • Wei WE LZ, Chiew CJ, Yong SE, Toh MP, Lee VJ. Presymptomatic Transmission of SARS-CoV-2 — Singapore, January 23–March 16, 2020. MMWR Morbidity and mortality weekly report. 2020;ePub: 1 April 2020.
  • Li R, Pei S, Chen B, et al. Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus (SARS-CoV2). Science (New York, NY). 2020.

How is Coronavirus Transmitted and Do Masks Work?

A video discussing the latest research on masks (cloth, surgical, N95) and how they help in various transmission modes (aerosol, droplet) for source control and as PPE

HOW COVID-19 KILLS–I’m a Surgeon–And Why We Can’t Save You

Papers about the effectiveness of basic masks #masks4all

Why we need an about-face on masks

Masks for all? The science says yes.