medical and N95 respirator masks

The spread of respiratory viruses, such as the novel coronavirus (SARS-CoV-2), can occur via droplets that are dispersed by infected individuals through coughing and sneezing. There is also evidence to suggest that these droplets can be dispersed by talking or even normal breathing.1-2 The use of medical masks and N95 respirator masks might be useful in preventing this dispersal.

Personal protective equipment, such as a protective face mask, is necessary for healthcare workers who require adequate protection when treating infected patients. In addition to healthcare workers, there is evidence to suggest that masks may be a useful tool that can be used in the fight against the spread of respiratory diseases, such as COVID-19.

Who should wear face masks?

The current recommendation on who should wear face masks, and which types of facemasks should be worn, take into account multiple factors including the risk of exposure, risk of severe COVID-19 disease, and the preservation of specific medical supplies during this current crisis.

Medical professionals

There is no question that healthcare professionals are currently at greatest risk of contracting COVID-19 and are therefore required to wear personal protective equipment, including face masks.1,3

N95 respirator masks should be worn by healthcare professionals who are on the front lines, taking care of patients with COVID-19. Under these circumstances, respirator masks should be worn to protect the healthcare professionals from respiratory droplets or fine airborne particles that may contain the SARS-CoV-2 virus.2 While the SARS-CoV-2 virus is believed to spread most commonly via respiratory droplets, there are some medical procedures that can cause the aerosolization of the virus and therefore result in airborne transmission.4 Some of these medical procedures include intubation, endotracheal aspiration, induction of sputum, face mask ventilation, and mechanical ventilation. This means that healthcare workers taking care of patients with COVID-19 should take airborne transmission precautions, which includes the use of N95 respirator masks.5

However, N95 respirator masks may only be necessary for those medical personnel who are in close contact with infected patients or performing medical procedures.6 Medical masks may be sufficient for the remainder of healthcare providers who are not at such a high risk of coming into contact with aerosolized particles.

Patients who have tested positive for COVID-19 and those caring for them

Patients who have tested positive for COVID-19 should wear medical masks to prevent virus particles from spreading due to coughing, sneezing, or talking. This can protect those who might come into close contact with these patients, including those who are caring for them. In addition, this prevents the unintended spread of virus particles that can fall from the droplets and settle onto surfaces that others my inadvertently come into contact with.

A recent study found that in households where one person was infected with a respiratory virus, implementing the use of face masks reduced the transmission of the virus by up to 80%.7 The results of this study did not differ between the use of medical masks or N95 respirators.

Vulnerable populations

Those who are at greater risk of severe COVID-19 disease should protect themselves by wearing masks. According to the World Health Organization, those who are at significantly greater risk for COVID-19 complications have been identified as people who are over the age of 60, although the risk begins to increase at approximately 40 years of age. People who have underlying medical conditions, including cardiovascular disease, diabetes, chronic respiratory disease, and cancer are also at greater risk of serious COVID-19 infection.8

The general public

In the case of the current pandemic, while it is widely accepted that healthcare workers, those caring for the sick, and those with COVID-19 infection should be wearing masks, significant controversy exists surrounding the use of masks as protection for the general population.9

Some studies have, in fact, demonstrated that wearing masks in the community can provide effective protection, particularly in crowded areas.10 Respiratory droplets have been found to spread in some instances further than the estimated two meters, and sometimes more than eight.1 The SARS-CoV-2 virus spreads primarily via respiratory droplets from infected patients. However, critically, there issignif icant evidence to suggest that patients begin to spread the virus asymptomatically, either prior to symptoms appearing, or in the absence of symptoms altogether.11-12 The spread of the virus may therefore be reduced if masks were worn as a public health intervention, particularly in crowded places, or areas where it is difficult to maintain an appropriate amount of physical distancing.13-15 Taken together, evidence from these studies suggests that combining mask-wearing with current hand hygiene and physical distancing recommendations may provide added benefit in reducing transmission.

The CDC and Health Canada recommend that the general public wear non-medical or cloth masks but not wear medical or N95 masks, in an effort to conserve those for medical professionals who require them.16-17

Types of masks

There are different types of masks that differ in their ability to prevent the transmission of microorganisms, and are therefore typically used for different purposes.

Medical masks (surgical masks)

Medical masks, also known as surgical masks, are typically worn in healthcare settings to prevent infection via droplets that occur due to coughing or sneezing. These loose-fitting masks can prevent, for example, the spread of pathogens during surgical procedures, protecting both the patient and healthcare provider.

In terms of protection against SARS-CoV-2, medical masks can protect the wearer from larger respiratory droplets (> 5μm), however, smaller particles such as airborne particles (generally < 5 μm), or single virus particles (60-140nm) would still be able to pass through the pores in these masks.3,18-19

N95 respirator masks

N95 respirator masks are tighter fitting than medical masks and provide a higher degree of protection. This type of mask requires specific fit testing, and can be easily mis-used by the general public. Standard N95 respirators that are approved by the National Institute of Occupational Safety and Health (NIOSH) are tested to make sure that these masks filter at least 95% of airborne particles. The NIOSH standards are accepted by Health Canada as a quality standard.20

N95 masks are the US standard respirator mask, however, other international equivalents include KN95 (China), FFP2 (Europe), and P2 (Australia).21 Although there are some differences between the N95 and KN95, they are both rated to be able to capture 95% of tiny particles (0.3 microns), and have been authorized by the FDA.22

Non-medical masks

Although there is limited research to demonstrate the effectiveness of non-medical or cloth masks,23 the CDC does recommend wearing a cloth mask in while in public – such as while grocery shopping – particularly in areas where there has been a significant amount of community spread.16 Health Canada suggests that although cloth masks can be a useful protective measure, they should not replace physical distancing and hand hygiene practices.17

Can masks be disinfected and re-used?

In an effort to conserve masks, healthcare workers are currently extending the use of masks to more than one patient encounter even though these are ‘single-use’ items.24 This practice may significantly increase risk of infection due to the continuous touching of the mask, which may become contaminated after extended use.23 Repeated use increases the chances that the surfaces of the mask could be contaminated with virus particles, which can cause infection if the wearer touches these surfaces and then touches their face.

The possibility of decontaminating and reusing masks as a method of prolonging their use has recently been explored. Systematic scientific research will be necessary to clearly define the best possible methods that have sufficiently decontaminate, while maintaining the integrity of the masks to ensure they remain effective.

Research studies have found that washing masks in water, disinfecting with alcohol, UV light, or cleaning chemicals can significantly damage the masks and impair their effectiveness.25-31

A recent study reported that wrapping N95 masks in protective peel pouches and then steam sterilizing them may be a successful method of decontamination.25 Another study tested a relatively simple method of sterilizing masks, where medical masks and N95 respirator masks were placed in plastic bags and steamed on a pot of boiling water for five minutes. In this way, the masks remained dry, ensuring they remained effective, while the researchers found a complete inactivation of avian coronaviruses that were used to simulate contamination.32 Similarly, researchers investigated whether a rice cooker could be used to steam-sterilize masks, comparing this with dry-heat decontamination.33 The steam treatment took a maximum of 15 minutes, which included 5 minutes of active steaming. Dry heat contamination was performed in an oven, which consisted of exposing the masks to 100-degree heat for 15 minutes. The researchers found the steam treatment to be a superior method of decontaminating the masks compared to the dry heat; they also reported that the steaming method was more effective than UV light decontamination. This study did not, however, assess the effectiveness of the masks following decontamination.

How to choose a face mask

Choosing a face mask might seem like a simple task, and the more time goes on, the more variety of face coverings are available in various designs and styles; but should you choose your face mask based on looks alone? What are the things you should look out for, and how can you be sure you are choosing the right mask for you?

It is a current recommendation that medical-grade masks (surgical masks, medical masks, and N95 respirator masks) are only used by healthcare workers or those providing care for patients with COVID-19. Keeping healthcare workers safe is a top priority, as they are at greatest risk of coming into contact with infected patients and being infected with the virus.

Non-medical masks or cloth face coverings should be worn by the general public. According to recommendations by Health Canada and the CDC, when choosing a face mask, you should look for:

–  a mask that fits securely either with ties or ear loops – covers comfortably and securely over your nose and mouth without gaping

–  a mask that can be washed and dried without loosing shape or fit

–  a mask that is comfortable so that you don’t always need to adjust it

–  a mask that is made from two layers (at least) of a tightly woven, breathable fabric (for example cotton or linen)

If you wear glasses, choosing a mask that has a nose wire to help it fit more snugly over your nose may help to prevent fogging of your glasses.

What type of fabric is best for a cloth mask?

It is important that any mask you chose should not be made of a material that is non-breathable – such as plastic.

Although cloth masks can’t block single virus particles, the transmission of viruses usually happens by larger ‘droplets’ that contain many particles. These droplets can be spread into the air when people speak, eat, cough, or sneeze. It is these larger particles that are more likely to be blocked by cloth masks. In addition to being spread into the air, the droplets can also then fall onto objects – such as tables – which are then touched by others, potentially allowing the transmission of the virus. Wearing masks can potentially prevent the transmission of droplets suspended in the air as well as those that come to rest on objects in the surrounding environment.

Although the filtration efficiency of cloth masks is less than that of surgical or N95 masks, they still provide significant protection against the spread of droplets containing viral particles. According to one study, when applying “the principles of evidence-based medicine to public policy, there is high-quality, consistent evidence that many (but not all) cloth masks reduce droplet and aerosol transmission and may be effective in reducing contamination of the environment by any virus, including SARS-CoV-2”. 34  However, since the filtration is not 100 percent, it is important to remember to maintain physical distancing and continue with handwashing procedures.

A research study35 that compared filtration efficiency of different fabrics that are typically used to make cloth masks reported that cotton, natural silk, and chiffon provided good protection, as long as the weave was tight. They reported that higher threads per inch (thread count) were better at filtering particles. In addition, they reported that silk and chiffon were also effective and that combining cotton with either silk or chiffon could provide better protection. This study also reported that the fit of the mask was very important.

Other things to consider

Other safety issues should be considered when choosing a face mask. You should not share your mask with anyone else and your mask should in no way impair your vision or interfere with other important tasks.

Masks should never be placed on anyone who cannot remove them without help, anyone who has breathing problems, or children under the age of two.

Keeping more than one mask on hand might be helpful – especially for young children – who might be likely to need to have a clean mask during the day.

Having enough masks to ensure they are always available to you – for example spare masks while others are in the process of being washed – is also a good idea. Washing masks after each use is recommended, so this might mean you need a few spare ones on hand at any particular time.

References:

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  2. Gralton J, Tovey E, McLaws ML, Rawlinson WD. The role of particle size in aerosolised pathogen transmission: a review. Journal of Infection 2011; 62: 1–13.
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Image by Andrey_Lesya from Pixabay 

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