Last week, scientists expressed their concern about World Health Organization-commissioned-study on physical distancing after Prime Minister Boris Johnson announced to ease social distancing regulations. The government decision was followed by another study on how SARS-CoV-2 droplets can be exchanged between two people who are three feet apart while wearing a surgical-grade face mask.
The University of Nicosia in Cyprus conducted a study on respiratory droplets and face masks, also discovering that masks became less efficient if people are coughing into them. Professor Dimitris Drikakis said that wearing a mask alone cannot prevent saliva droplets from spreading completely. 'Many droplets penetrate the mask shield and some saliva droplet disease-carrier particles can travel more than 1.2 meters (4ft),' he said.
The WHO guidelines revised the former two-meter rule (six feet) to saying that one meter apart won't significantly increase the chances of infection. Drikakis and his team are on the side of senior scientists who disagree with these social distancing rules. Since the pandemic broke out, a general guideline had been to wear face masks in public to reduce the possibilities of spreading coronavirus. However, not enough research determines how effective they really are or which conditions they fail at.
Droplet Travel
The study adds insight into the reduced transmission of airborne droplets even though they cannot be completely eliminated. Not wearing a mask allows droplets to travel double its distance than wearing one, increasing the risk of infection.
However, coughing repeatedly into the mask reduces its as more droplets pass through. In a previous study, the team demonstrated that when a person coughs saliva droplets can travel 18 feet (five meters) in just five seconds when the individual is not wearing a mask.
In their current study, a precise computer model was used to map out the expected flow patterns of a person coughing with a mask on. They also took into account the possible weather conditions, air turbulence, and even the skin and mouth temperature of an individual.
Since surgical masks have a porous filter, they calculated the number of droplet interactions with numerical simulations. The authors wrote, 'the results are alarming. Even when a mask is worn, some droplets can travel a considerable distance during periods of mild coughing.'
Using a standard surgical mask results showed a 91% efficiency of preventing droplets from escaping. As a visual guide, they up-scaled the droplets to a factor of 600 for easier tracking. 'The droplet sizes change and fluctuate continuously during cough cycles as a result of several interactions with the mask and face,' said Drikakis.
Complex Saliva
Dr. Talib Dbouk, the co-author, said that face masks can decrease the droplet accumulation with mild coughing, a coronavirus symptom while stopping droplets escaping less effectively. 'However, it remains unclear whether large droplets or small ones are more infectious,' said Dbouk.
Their advice for health care workers is to always wear to wear complete personal protective equipment (PPE) when handling patients. This includes 'helmets with built-in air filters, face shields, disposable gowns, and double sets of gloves' which should be changed regularly.
Their previous study on airborne droplet transmission analyzed the complexities of saliva, which suspends in the air when an individual coughs. The scientists are urging 'manufacturers and regulatory authorities to consider new criteria for assessing mask performance' that accounts for flow physics and cough dynamics.
