Sneezing from people who have stuffy noses and a full set of teeth travel about 60% farther than from people who don̵
A new study from the University of Central Florida has identified physiological characteristics that could make humans super-spreaders of viruses such as COVID-19.
In a study that appears this month in the journal Fluid physics, researchers at UCF’s Department of Mechanical and Space Engineering used computer-generated models to numerically simulate sneezing in different types of people and to determine the relationships between people’s physiological characteristics and how much their sneezing droplets travel and stay in the air.
They found that human characteristics, such as a stuffy nose or a full set of teeth, could increase their potential for the spread of viruses by affecting how far the droplets travel when they sneeze.
According to the US Centers for Disease Control and Prevention, the main way people become infected with the virus that causes COVID-19 is by exposure to respiratory droplets, such as sneezing and coughing, which carry an infectious virus.
Knowing more about the factors that affect how far these droplets travel, one can learn about efforts to control their spread, says Michael Kinzel, an assistant professor in mechanical engineering and co-author of the study.
“This is the first study that aims to understand the basic ‘why’ of how far the trip sneezes,” says Kinzel. “We show that the human body has influencers, such as a complex system of channels connected to the nasal flow that actually disrupts the flow from your mouth and prevents it from scattering droplets over long distances.”
For example, when people have a clear nose, such as blowing it into tissue, the speed and distance of sneezing droplets decrease, according to the study.
This is because a clean nose provides a pathway in addition to the mouth for sneezing. But when people’s noses are clogged, the area from which sneezing can come out is limited, leading to an increase in the speed of sneezing droplets expelled from the mouth.
In the same way, the teeth also limit the initial area of sneezing and cause an increase in the velocity of the droplets.
“Teeth create a narrowing effect in the jet, which makes it stronger and more turbulent,” says Kinzel. “They actually drive the transmission. So if you see someone without teeth, you can actually expect a weaker stream of sneezing from them. “
To conduct the study, the researchers used 3D modeling and digital simulations to recreate four types of mouth and nose: a man with teeth and a clean nose; a man without teeth and a clean nose; a man without teeth and a stuffy nose; and a man with teeth and a stuffy nose.
When they simulated sneezing in different models, they found that the spray distance of droplets ejected when a person has a stuffy nose and a full set of teeth is about 60 percent greater than when they do not.
The results show that when someone keeps their nose clean, for example by blowing into tissue, they can reduce the distance their germs travel.
The researchers also simulated three types of saliva: thin, medium and thick.
They found that thinner saliva causes sneezing made up of smaller droplets, which creates a spray and stays in the air longer than medium and thick saliva.
For example, three seconds after sneezing, when thick saliva reached the ground and thus reduced its threat, thinner saliva was still floating in the air as a potential carrier of the disease.
The work is related to the researchers’ project to create a cough drop COVID-19, which would give people thicker saliva to reduce the distance from sneezing or coughing drops and thus reduce the likelihood of transmitting the disease.
The findings give a new insight into the variability of the exposure distance and show how physiological factors affect the rate of transmission, said Karim Ahmed, an associate professor in the Department of Mechanical and Space Engineering at UCF and co-author of the study.
“The results show that exposure levels are highly dependent on fluid dynamics, which can vary depending on several human characteristics,” says Ahmed. “Such characteristics may be at the root of the factors driving the super-talking events in the COVID-19 pandemic.”
The researchers say they hope to move the work to clinical trials to compare the results of their simulation with those of real people from different backgrounds.
The study was co-authored by Douglas Fontes, a postdoctoral fellow at the Florida Space Institute and lead author of the study, and Jonathan Reyes, a postdoctoral fellow in the Department of Mechanical and Space Engineering at UCF.
Fontes says that to improve the results of the study, the research team wants to study the interactions between gas flow, mucus film and tissue structures in the upper respiratory tract during respiratory events.
“Numerical models and experimental techniques need to work side by side to provide accurate predictions of primary upper airway disintegration during these events,” he says.
“This study will potentially provide information on more accurate safety measures and solutions to reduce the transmission of pathogens, and will provide better conditions for dealing with common diseases or pandemics in the future,” he said.
Reference: “Study of the dynamics of fluids and human physiological factors driving the dispersion of droplets from sneezing in humans” by D. Fontes, J. Reyes, K. Ahmed and M. Kinzel, November 12, 2020, Fluid physics.
DOI: 10.1063 / 5.0032006
The work is funded by the National Science Foundation.
Kinzel received a doctorate in aerospace engineering from Pennsylvania State University and joined UCF in 2018. In addition to being a member of UCF’s Department of Mechanical and Space Engineering, part of UCF’s College of Engineering and Computer Science, he also works with UCF’s Center for Advanced turbomachines and energy research.
Ahmed is an associate professor in the Department of Mechanical and Space Engineering at UCF, a lecturer at the Center for Advanced Turbomachines and Energy Research, and the Florida Center for Advanced Aero propulsion. He served for more than three years as a senior aero / thermal engineer in Pratt & Whitney military engines, working on advanced engine programs and technologies. He also serves as a lecturer at the University of Old Dominion and University of Florida. At UCF, he leads research in propulsion and energy with applications for power generation and gas turbine engines, jet engines, hypersonics and fire safety, as well as research related to the science of supernova and transmission control COVID-19. He holds a PhD in mechanical engineering from New York State University in Buffalo. He is an associate of the American Institute of Aeronautics and Astronautics and a research laboratory of the United States Air Force and the Office of Naval Researchers.