- On whether masks can help filter the virus, she says they can reduce the spread from an infected person and for protection of the wearer.
A US professor has dismissed the two-metre distance rule as not enough to give protection from Covid-19, saying it is based on old science.
The Massachusetts Institute of Technology researcher, Prof Lydia Bouroiba, said the two-metre “social distancing” recommendation is too close – and that to avoid the virus, people have to keep much farther – possibly eight metres.
“Although such social distancing strategies are critical in the current time of pandemic, it may seem surprising that the current understanding of the routes of host-to-host transmission in respiratory infectious diseases are predicated on a model of disease transmission developed in the 1930s that, by modern standards, seems overly simplified,” Prof Bouroiba says in her paper published in the Journal of the American Medical Association.
She also warns that besides the cough and sneeze droplets, people have to be wary of “turbulent gas cloud” that traps and carries within it the virus.
“The locally moist and warm atmosphere within the turbulent gas cloud allows the contained droplets to evade evaporation for much longer than occurs with isolated droplets. Under these conditions, the lifetime of a droplet could be considerably extended by a factor of up to 1,000 from a fraction of a second to minutes,” says the professor, who studies the fluid dynamics of disease transmission.
While her research had previously focused on flu, she says the current six-feet guideline is based on an assumption that viruses are transmitted only through droplets from coughs or sneezes.
The researcher says that there is not enough data on how the virus is spreading.
At the moment, transmission is classified into large droplets, which fall closer to the affected person, and smaller droplets, which evaporate before settling on a surface and which can be carried farther by the wind.
The scholar says a powerful sneeze can send droplets flying more than the recommended two metres and that a gas cloud with the droplets can travel seven to eight metres.
“Moreover, throughout the trajectory, droplets of all sizes settle out or evaporate at rates that depend not only on their size but also on the degree of turbulence and speed of the gas cloud, coupled with the properties of the environment (temperature, humidity and airflow).”
She says that “droplets that settle along the trajectory can contaminate surfaces, while the rest remain trapped and clustered in the moving cloud.”
“Eventually the cloud and its droplet payload lose momentum and coherence, and the remaining droplets within the cloud evaporate, producing residues or droplet nuclei that may stay suspended in the air for hours, following airflow patterns imposed by ventilation or climate-control systems,” she says.
Whether ventilation systems are also helping spread the virus is not known, but she says that a 2020 report from China “demonstrated that SARS-CoV-2 particles could be found in the ventilation systems in hospital rooms of patients with Covid-19”.
While the World Health Organisation (WHO) is currently recommending that healthcare workers should stay one metre from a person exhibiting coronavirus symptoms, the researcher says that “these distances are based on estimates of range that have not considered the possible presence of a high-momentum cloud carrying the droplets long distances”.
“For these and other reasons, wearing of appropriate personal protection equipment is vitally important for healthcare workers caring for patients who may be infected, even if they are farther than six feet away from a patient,” Prof Bouroiba says.
WHITE HOUSE SLATE
On whether masks can help filter the virus, she says they can reduce the spread from an infected person and for protection of the wearer.
But White House has dismissed her findings: “I’m sorry, but I was disturbed by that report because that’s misleading,” said Dr Anthony Fauci, a member of the White House task force.
“Mask efficacy as source control depends on the ability of the mask to trap or alter the high-momentum gas cloud emission with its pathogenic payload,” she says.
“There’s an urgency in revising the guidelines currently being given by the WHO and the CDC on the needs for protective equipment, particularly for the frontline healthcare workers,” Prof Bourouiba told USA Today in a separate interview.