There is currently a lot of discussion about face masks for medical and community use.
According to the World Health Organisation, respiratory droplets from infected individuals are a major mode of transmission (2020). Droplets come from coughing or sneezing and in asymptomatic and pre-symptomatic individuals, droplets are generated via talking and breathing (Anfinrud et al 2020). There is growing evidence that aerosols are a significant vector for transmission of SARS-CoV-2. Guo et al (2020), Liu et al (2020), Ong et al (2020), van Doremalen etal (2020), Anfinrud et al (2020).
For this reason masks are recommended in medical settings especially in high-risk medical areas where aerosols are generated via procedures like intubation. They are also crucial in the community and for personnel like GPs to slow or stop the spread of the virus especially in known “hotspots” where there are a significant number of cases and community transmission is occurring.
The protection against dissemination of infectious organisms is achieved by two methods: (1) those meant to prevent inhalation by the user (i.e., respirator) and (2) those meant to protect people who are not infected by limiting exhaled particles from people who are infected (i.e., mask).
The Institute of Medicine. 2006 Consensus study report on Reusability of Facemasks During an Influenza Pandemic (2006) describes the modes of particle capture of infectious organisms.
Firstly, Inertial impaction. This model postulates that aerosols approximately 1µm and larger have enough inertia in the airstream that they cannot easily flow around the respirator fibers. Instead of flowing through the mask material, the large particles deviate from the air streamlines and collide with the fibers and may stick to or be caught in them.
“For much smaller particles—those that are 0.1 µm and smaller—diffusion is regarded as an effective filtration mechanism. Brownian motion—the process by which the constant motion of oxygen/nitrogen molecules causes collisions between particles—results in a “wandering” pathway. The complex path that is followed by the small particles increases the chance that they will collide with the filter fiber and remain there.
Another efficient method of capturing both large and small particles from the airstream is said to be electrostatic attraction, in which electrically charged fibers or granules are embedded in the filter to attract oppositely charged particles from the airstream. The attraction between the oppositely charged fibers and particles is strong enough to effectively remove the particles from the air. The first electrostatic filters used resins.”
These principles apply to manufactured N95/P2 and surgical and also cloth masks to varying degrees.
These masks will be familiar to the community in bushfire-affected areas who used them to protect themselves against the fine particles in smoke. Medically they are very important masks for the protection of medical staff from infection.
“Media used for the filtration of airborne particles do not work by the same principles as those used for the filtration of liquids. Filters used in respirators and medical masks must allow the user to breathe and thus cannot clog when particles adhere to their fibers. Respirator and medical mask filters are typically composed of mats of nonwoven fibrous materials, such as wool felt, fiberglass paper, or polypropylene. The material creates a tortuous path, and various mechanisms result in the adhesion of particles to the fibers without necessarily blocking the open spaces, still allowing air to flow easily across the filter (Revoir and Bien, 1997).”
These masks are crucial protection for medical personnel when they are treating patients with SARS-CoV-2, the virus that causes Covid-19. They reduce the wearer’s exposure to particles including small aerosol particles and large droplets, are tight fitting, filter out at least 95% of airborne particles including large and small particles and ideally should be discarded after each use or between patients.
The N95/P2 masks MUST be kept available for medical staff. They are crucial when medical personnel are intubating Covid-19 patients because this procedure produces aerosols containing the virus that can be breathed in. Staff working in Covid-19 wards also need this higher level of protection.
Safe Work Australia (2020) says these masks are recommended for medical procedures that generate aerosols and are not suitable for non-healthcare settings. Because they are so necessary for high risk medical environments, the community should not be buying and using them at this time unless specifically advised to use them by a medical professional.
Surgical Face Masks
These are single-use, disposable masks that provide a physical barrier but do not contain a filter like the N95/P2 respirators. They are looser fitting and there are gaps at the edges so they do not provide the 95% exclusion of infectious particles such as bacteria and viruses that the N95/P2 do. They are fluid resistant and provide the wearer with protection against large droplets, splashes, or sprays of bodily or other hazardous fluids. They protect others from the wearer’s respiratory emissions which could contain bacteria or viruses.
Safe Work Australia (2020) recommends that these masks are worn by suspected or confirmed COVID-19 patients, healthcare workers undertaking routine care of patients or those who have close or frequent contact with sick or vulnerable people.
The masks reduce the amount of virus from being spread when people cough, sneeze or even breathe. These masks need to be kept primarily for use by medical personnel especially in hospitals where Covid-19 is being treated. Although they are available to the public for their use, when there are a lot of cases of Covid-19 there will be a high demand for these masks in hospitals, for GPs, and for other allied health-care workers. For this reason it is recommended that people in the community use reusable cloth masks for daily use.
These are face masks made out of fabric by the community for community use. They are washable and reusable and come in various designs and thicknesses.
Cloth-based face masks reduce droplet emission by variable amounts:
- Anfinrud et al (2020) showed that viral particles are almost completely eliminated.
- Davies et al (2013) showed that cloth masks filtered viral particles during coughing at about 50 to 100% of the filtration efficiency of surgical masks, depending on fabric, with absolute filtration efficiencies of 50-70%, and about 70-80% for oral bacteria.
- van der Sande et al (2008) showed 50% filtering efficiency for airborne particles.
There are many different patterns for masks available online, however the World Health Organisation recommends a multi-layered mask with a filtration layer or pocket for a removable filter.
Cloth face masks provide a lower amount of protection to the wearer however, they provide an effective barrier between the wearer and others and therefore reduce the spread to uninfected people (between 20 and 90% protection depending on design and fabric used). Like surgical masks they can be fluid resistant (fabric recommendations coming) and provide the wearer with protection against large droplets, splashes, or sprays of bodily or other hazardous fluids. They protect other people from the wearer’s respiratory emissions which could contain bacteria or viruses. We know that people can have Covid-19 but are able to spread the virus without showing any symptoms. As many as 40-60% of infected people will not show any symptoms. Some never show symptoms (asymptomatic) and some are in the early stages of the disease and have not yet developed the symptoms (pre-symptomatic). If everyone wears cloth face masks, there is substantial evidence that this greatly reduces the risks of community transmission of the Covid-19 virus in public places.
Remember that cloth face masks are not substitutes for N95/P2 or surgical masks however cloth covers are sometimes used to protect N95/P2 masks in settings where they are in short supply or cannot be easily changed. The cloth cover protects the N95 mask from droplets and aerosols and they can be replaced frequently or between patients, washed and reused thus allowing the N95/P2 wearer to use one N95/P2 mask for a greater length of time.
Guo ZD, Wang ZY, Zhang et al. Aerosol and surface distribution of severe acute respiratory syndrome coronavirus 2 in hospital wards, Wuhan, China, 2020. Emerg Infect Dis. 2020;26:1583–91. (doi: 10.3201/eid2607.200885).
Liu Y, Ning Z, Chen et al. Aerodynamic characteristics and RNA concentration of SARS-CoV-2 aerosol in Wuhan hospitals during COVID-19 outbreak.2020;NAture 582:557–560. https://www.nature.com/articles/s41586-020-2271-3
Ong SWX, Tan YK, Chia PY et al. Air, surface environmental, and personal protective equipment contamination by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from a symptomatic patient. JAMA. 2020;323:1610. (doi: 10.1001/jama.2020.3227).
van Doremalen N, Bushmaker T, Morris DH, Holbrook MG, Gamble A, Williamson BN, et al. Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. N Engl J Med. 2020;382:1564–7. https://www.nejm.org/doi/full/10.1056/nejmc2004973
Institute of Medicine. 2006. Reusability of Facemasks During an Influenza Pandemic: Facing the Flu Washington, DC: The National Academies Press. (doi: 10.17226/11637).
World Health Organization. 2020 Modes of transmission of virus causing COVID-19: implications for IPC precaution recommendations. See https://www.who.int/news-room/commentaries/detail/modes-of-transmission-of-virus-causing-covid-19-implications-for-ipc-precaution-recommendations
Anfinrud P, Stadnytskyi V, Bax CE, Bax A. 2020 Visualizing Speech-Generated Oral Fluid Droplets with Laser Light Scattering. New England Journal of Medicine (doi: 10.1056/NEJMc2007800)
Davies A et al. 2013 Testing the efficacy of homemade masks: would they protect in an influenza pandemic?. Disaster Medicine and Public Health Preparedness (doi: 10.1017/dmp.2013.43).
van der Sande M, Teunis P, Sabel, R. 2008 Professional and home-made face masks reduce exposure to respiratory infections among the general population. PLoS One (doi: 10.1371/journal.pone.0002618