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Transmission of the virus by air occurs through droplets formed during respiratory events associated with the flow of air through a network of nasal and buccal passages. The airflow interacts with the saliva / mucus films where droplets form and disperse, creating a path for transmitting SARS-CoV-2.
A new study from the University of Central Florida aimed to understand the “why” behind the distance traveled by sneezing. This is the first study that has identified physiological characteristics that could make people super virus spreaders.
Using computer-generated models, the scientists numerically simulated sneezing in different types of people. They later determined associations between people’s physiological characteristics and how far sneezing droplets travel and remain in the air.
They found that people’s characteristics, similar to a stuffy nose or a full set of teeth, could increase their potential to spread viruses by influencing the distance the droplets travel when they sneeze.
Michael Kinzel, assistant professor in the UCF Department of Mechanical Engineering and co-author of the study, said: “Knowing more about the factors that influence the distance these droplets travel can inform efforts to control their spread.”
“We show that the human body has influencers, such as a complex system of ducts associated with the nasal flow that interrupts the jet from the mouth and prevents it from dispersing droplets over great distances.”
The study suggests that when people have a clean nose, like blowing it into a handkerchief, the speed and distance traveled by the sneezing droplets decrease. This is because a clear nose offers a path beyond the mouth for the sneeze to exit. However, when individuals’ noses are congested, the area from which the sneeze can exit is limited, thus causing an increase in the speed of the sneeze droplets expelled from the mouth.
Likewise, the teeth also narrow the sneeze exit area and increase the speed of the droplets.
Kinzel says, “The teeth create a shrinking effect in the casting which makes it stronger and more turbulent. They seem to drive the transmission. So, if you see someone with no teeth, you can expect a weaker sneeze jet from them. “
When they simulated sneezing in the different models, they found that the spray distance of the droplets expelled when a person has a congested nose and a full set of teeth is about 60 percent greater than when they don’t.
It means that when someone keeps their nose clean, for example by blowing it into a handkerchief, it could reduce the distance their germs travel.
Scientists also simulated three types of saliva: thin, medium and thick.
They found that thinner saliva resulted in sneezing consisting of smaller droplets, which created a spray and stayed in the air longer than average, thick saliva.
For example, three seconds after a sneeze, when thick saliva reached the ground and thereby lessened its threat, the thinner saliva still floated in the air as a potential transmitter of disease.
Kareem Ahmed, associate professor in the UCF Department of Mechanical and Aerospace Engineering and co-author of the study, said: “The results provide new insights into the variability of exposure distance and indicate how physiological factors influence transmissibility rates. “
“The results show that exposure levels are highly dependent on fluid dynamics which can vary according to different human characteristics. Such characteristics may be factors behind super-diffusion events in the COVID-19 pandemic. “
In future studies, the scientists intend to investigate the interactions between gas flow, mucus film, and tissue structures within the upper respiratory tract during respiratory events.
Journal reference:
- D. Fontes et al., A study of fluid dynamics and human physiology factors that drive droplet dispersion from a human sneeze, Physics of Fluids (2020). DOI: 10.1063 / 5.0032006
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