By Dr Tan Poh Tin
“MY mask protects you. Your mask protects me. Our masks protect others.”
We have a few weeks before our children return to school and kindy, and all to work. Should we and our children still wear masks in public places? Surgical masks at RM1 to RM1.50 each may be burdensome for the average family to sustain long term. Are DIY cloth masks good alternatives? Which material works best?
As a public health specialist and paediatrician, I have summarised the current scientific findings to help you decide. As Covid-19 is a new virus and much research is ongoing, recommended good practice may change with new publications and as the epidemic curve flattens or gets worse. Speak to your doctor or Google to keep up to date with the latest guidelines.
Be reminded that masks must be used in conjunction with other preventative measures — good respiratory etiquette, regular and frequent hand hygiene, self-isolation when unwell, and avoiding crowded and noisy places (with people talking or shouting).
Both the American Academy of Pediatrics and CDC strongly advise against masks for children below two years, especially babies, because of the high risk of suffocation.
Universal wearing of masks in public areas have reduced Covid-19 spread in countries like Taiwan. Taiwan did not lock down but efficiently implemented all the strategies — test, trace, isolate, treat (early), social distancing, hand washing, and compulsory face masks. To date they have only over 440 cases and seven deaths, after testing almost 70,000 (population 24 million).
‘Mouth and nose lockdown’ to minimise community transmission is more sustainable than ‘full body lockdown’ from economic, social and mental health standpoints.
Your mask protects me and my mask protects you from the germ-loaded mucous and saliva droplets expelled as we talk, laugh, sing, or sneeze. During surgery, a surgeon wears a surgical mask so that his droplets/aerosol will not contaminate the wound. The mask also reduces the risk of the patient’s body fluids, saliva, or blood from splashing onto his mouth and nose (and if he wears eye protection, eyes).
Masks, even homemade cloth ones, have been shown to trap exhaled droplets and help reduce contamination of the environment and fomites where these droplets settle.
Studies of healthy volunteers wearing homemade masks, surgical masks, or no masks showed that both masks significantly reduced the number of microorganisms expelled when they coughed. Compared to homemade masks, surgical masks were three times more effective in blocking outward transmission to others and two times better in preventing inward passage of germs to wearer. To prevent droplet transmission from infected individuals, home-made mask should only be a last resort, but it would be better than no protection.
Surgical masks are made from non-woven polypropylene melted and blown onto a conveyor in a web. As the strands cool, they bond with each other. This material is able to block microorganisms smaller than 25nm (coronavirus is three times bigger and can be filtered out).
Surgical masks are less efficient for inward protection because of the leak around the edges.
Hence, healthcare workers handling Covid-19 cases must wear N95 respirators. This must be test fitted for each wearer. To protect from inhaling infectious particles, the seal should be so tight that one can still breathe through it but cannot smell anything. The USA standard N95 mask blocks 95 per cent of aerosols or viruses if properly fitted. Protection drops when this seal is not tight, as with people with facial hair or when the correct size mask is unavailable.
Keep N95 for front-liners
N95 should be reserved for healthcare workers and front-line Covid-19 responders.
Two of the three high school students who collapsed and died during intense running or physical exercise in China in April 2020 were noted to be wearing N95 equivalent masks.
Although autopsy reports for the sudden deaths were not available, the current advice is against wearing high-grade medical ones (N95) during strenuous exercise or in the gym as these tightly fitted masks may impede the oxygen supply and carbon dioxide removal.
Wearing a mask while driving alone in the car is also not recommended. A US man, who lost consciousness while driving and ran into a pole, was noted by police to have been wearing an N95 mask. He was not under the influence of alcohol or drugs. Although his preexisting medical condition was not known, it was thought that the wearing of a N95 mask over a prolonged period could have contributed to his loss of consciousness.
How well do household materials block bacterial or viral aerosols?
Anna Davies et al (‘Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic’ August 2013 in ‘Disaster Medicine and Pubic Health Preparedness’) showed that all materials show some capability to filter microbial aerosol.
The filtration efficiency for bacteria (0.95-1.25 micron) were linen 60 per cent, silk 58 per cent, 100 per cent cotton T-shirt 69 per cent, tea towel 83 per cent, antimicrobial pillow case 65 per cent (surgical mask 96 per cent).
Tested for bacteriophage (viral particle 23nm) the filtration efficiencies were still surprisingly high — linen 62 per cent, silk 54 per cent, 100 per cent cotton 51 per cent, tea towel 72 per cent, antimicrobial pillow 68 per cent (surgical mask 90 per cent).
Even a simple scarf can block 62 per cent of bacteria and 49 per cent virus RNA (could be useful if you are caught in a crowded closed place without a mask!).
Doubling the layer of tea towel increases filtration to 96 per cent for bacteria, or cotton 70 per cent.
Vacuum cleaner bags have been found to be as effective as surgical masks, 94 per cent and 86 per cent but are harder to breathe through, forcing air to escape around the mask.
The antimicrobial pillowcase and 100 per cent cotton T-shirt were found to be most suitable for DIY masks. T-shirt material has the added advantage of being stretchy for better fit and less leak.
Doubling the fabric improves the filtration slightly, but breathability affects long term use.
Avoid using old fabrics because washing and drying may stretch the pores and allow more particles to get through.
Paper towels have been tested and found to capture 23 per cent of particles 0.3 microns or larger if a single layer and 33 per cent if doubled.
One report claims that an extra outer lining with nylon stocking to a DIY cloth mask may improve filtration.
Face masks reduce aerosol exposure by a combination of filtration action of the fabric and the seal between the face and mask. If masks are uncomfortable, wearers may remove them to cough, sneeze, or wipe their eyes or nose. This will cause increased transmission.
Decontaminating masks for reuse
DIY cloth masks have to be washed in the washing machine or with soap and hot water, or dilute bleach and dried in the sun.
Where surgical masks are limited, they can be slipped in between the layers of DIY mask for longer reuse. The best strategy to kill the germs on these is to put the mask in a paper bag and leave it for seven days. Some healthcare workers leave the paper bag with mask in a parked car and let the heat from the sun kill the virus on the mask. Plastic bags are not used because the mask may collect moisture leading to bacterial contamination. Some have suggested washing surgical masks, but this may affect efficacy. Surgical masks are meant for single use, so in a high risk environment, all these recycling measures are not recommended.
In times of shortage, N95 respirators can be decontaminated and re-used for up to three times for UV and Vaporised Hydrogen Peroxide, and up to two times for dry heat (70 degrees Celsius).
N95 masks decontaminated with 70 per cent ethanol spray did not function effectively after decontamination. Alcohol and bleach interfere with electrostatic charges in the N95 mask, which is part of the filter so should not be used.
The take home message is 25 per cent of infected Covid-19 persons are asymptomatic throughout. Most patients may not show symptoms in the first five to six days of infection, but can infect others. By wearing masks, infected persons can trap much of the infective droplets and protect others and the environment.
Start making masks to give to those who cannot afford to buy any. Their wearing masks protects you. We can protect ourselves from breathing in aerosols, especially in crowded places, public transport, or in classrooms where we cannot stay out of range of their droplets!
The surgical mask is best, but any mask is better than none.
If four out of five wear masks, we can block the virus from leap-frogging and prevent the next Covid tsunami. Keep washing hands, frequently, for at least 20 seconds with soap and water.
Dr Tan Poh Tin is a consultant paediatrician and public health specialist who served in the Sarawak Health Department as divisional medical officer of Kapit and Sibu divisions in the 1980s and state paediatrician in the early 1990s. She retired as associate professor from the Unimas Medical School to private practice. Her passion is to simplify medical information and help people learn.
Source: Borneo Post Online, 24 May 2020