Face masks allow virus-containing droplets to escape, study finds
In a study with implications for COVID-19 transmission, mild coughing can expel small saliva droplets through and around a face mask and travel as far as 1 meter (3.3 feet), according to a study published yesterday in Physics of Fluids.
Researchers from the University of Nicosia in Cyprus simulated airborne droplet transmission for a person with and without a mask using computer models and found that, while masks may reduce airborne droplet transmission and protect the wearer from other people's saliva droplets, they provide incomplete protection against the many droplets that spread around and away from them.
Mask certification standards define a surgical mask's effectiveness as a constant value and don't take into account fluid flow dynamics, droplet leakage through mask openings, or the effects of repeated coughing, which can saturate the masks and reduce their efficiency, the authors said.
The study showed that 10 cough cycles reduced mask efficiency about 8%, and severe coughing and longer mask-wearing time would reduce it even further.
The researchers found that saliva droplet sizes change constantly during cyclic coughing because of interactions between the face and the mask, which typically have gaps of 4 millimeters (0.16 inches) to 1.4 centimeters (0.55 inches).
"Masks decrease the droplet accumulation during repeated cough cycles," lead author Talib Dbouk, PhD, aid in an American Institute of Physics press release. "However, it remains unclear whether large droplets or small ones are more infectious."
The authors called for physical distancing, new criteria for assessing mask performance and assessment that consider flow physics and cough dynamics, and provision of more complete personal protective equipment to healthcare workers, such as helmets with built-in filters, face shields, disposable gowns, and double sets of gloves.
"The implications of the reduced mask efficiency and respiratory droplet transmission away from the mask are even more critical for healthcare workers," they wrote.
Jun 16 Phys Fluids study
Jun 16 American Institute of Physics press release
Study shows 5% rate of COVID-19 among symptomatic healthcare workers
Seattle emerged as the first hot spot of novel coronavirus infections in the United States in February, and new data on testing of symptomatic healthcare workers (HCWs) shows 5.3% tested positive for SARS-CoV-2, the virus that causes COVID-19. The study is published in Clinical Infectious Diseases.
To conduct the study, Seattle-area investigators tested 3,477 symptomatic healthcare workers in March and April at drive-through and walk-through sites for employees in the University of Washington Medicine system. A total of 185 employees (5.3%) tested positive for SARS-CoV-2. The prevalence was similar between frontline healthcare workers (5.2%) and medical staff (5.5%).
Symptomatic employees also filled out a survey prior to testing. Of employees who tested positive, 61.6% said they were experiencing fatigue, 59.5% had headaches, 58.4% reported a cough, and 38.4% complained of fever. Only six healthcare workers required hospitalization, and none died.
"Rapid and high throughput testing of HCWs for COVID-19 is feasible using drive-through and walk-through testing clinic models and facilitated the rapid return of SARS-CoV-2 negative HCWs to work," the authors concluded.
Jun 16 Clin Infect Dis study