Maybe 6 feet is not enough!
Keep your distance
Over the last decade, Lydia Bourouiba, an associate professor directing the Fluid Dynamics of Disease Transmission Laboratory at MIT, has focused on characterizing and modeling infectious disease dynamics and transmission at various scales. Through experiments in the lab and clinical environment, she has reported that when a person coughs or sneezes, they do not emit a spray of individual droplets that quickly fall to the ground and evaporate, as scientists had once thought. Instead, they produce a complex cloud of hot and moist air that traps droplets of all sizes together, propelling them much further through the air than any individual droplet would travel on its own.
On average, her experiments have revealed that a cough can transmit droplets up to 13 to 16 feet, while a sneeze can eject them up to 26 feet away. Surrounding air conditions can act to further disperse the residual droplets in upper levels of rooms.
Bourouiba notes that the presence of the high-speed gas cloud is independent of the type of organism or pathogen that the cloud may contain. The droplets within it depend on pathogenesis coupled with a patient’s physiology — a combination which her laboratory has focused on deciphering in the context of influenza. She is now expanding her studies and modeling to translate the work to Covid-19, and says now is a critical time to invest in research.
“This virus is going to stay with us for a while — and certainly data suggest that it is not going to suddenly disappear when the weather changes,” she says. “There’s a fine and important balance between safety, precautions and action that is important to strike to enable and dramatically accelerate research to be done now so we can be better prepared and informed for actions in the weeks and months to come when the worst of the pandemic will unfold.”
She is also working with others to evaluate ways to limit a cloud’s dispersal and slow Covid-19 transmission to health care workers and others in shared spaces. “A surgical mask is not protective against inhalation of a pathogen from the cloud,” she says. “For an infected patient wearing it, it can contain some of the forward ejecta from coughs or sneezes, but these are very violent ejections and masks are completely open on all sides, and fluid flows through the path of least resistance.”
Based on the data, she recommends that health care workers consider wearing a respirator, whenever possible. And, for the general public, Bourouiba emphasizes that the risk of contracting COVID-19 remains relatively low locally, and that risk should be thought of in the context of the community. |
