Sneezing from people who have congested noses and a complete set of teeth travels about 60% longer than from people who do not, according to a new study.
New research from the University of Central Florida has identified physiological features that could make people super-spreaders of viruses such as COVID-19.
In a study published this month in the journal Liquid physics, researchers at UCF’s Department of Mechanical and Aerospace Engineering used computer-generated models to numerically simulate sneezing in different types of people and determine relationships between people’s physiological traits and how far their sneezing droplets move and linger in the air.
They found that people’s properties, such as a stuffy nose or a complete set of teeth, could increase their potential for spreading viruses by influencing how far droplets travel when they sneeze.
According to the U.S. Centers for Disease Control and Prevention, the most important way people become infected with the virus that causes COVID-19 is through exposure to respiratory droplets, such as from sneezes and coughs that carry infectious viruses.
Knowing more about factors that affect how far these droplets travel can inform efforts to control their spread, says Michael Kinzel, an assistant professor at UCF’s Department of Mechanical Engineering and study author.
“This is the first study aimed at understanding the underlying ‘why’ of how far sneezing travels,” says Kinzel. “We show that the human body has influencers, such as a complex duct system connected to the nasal stream, that actually interferes with the beam from the mouth and prevents it from dispersing droplets far away.”
For example, when people have a clear nose, such as from blowing it into a tissue, speed and distance sneezing drops fall, according to the study.
This is because a clear nose provides a path beyond the mouth so that sneezing can come out. However, when people’s nose is congested, the area from which sneezing can come out is limited, causing sneezing droplets expelled from the mouth to increase in speed.
Similarly, teeth also limit the exit area of the sneeze and cause droplets to increase in speed.
“Teeth create a constriction effect in the beam that makes it stronger and more turbulent,” says Kinzel. “It simply came to our notice then. So if you see someone without teeth, you can actually expect a weaker ray of sneezing from them. ”
To conduct the study, the researchers used 3D modeling and numerical simulations to recreate four types of mouth and nose: a person with teeth and a clear nose; a person without teeth and a clear nose a person without teeth and congested nose and a person with teeth and an congested nose.
When they simulated sneezing in the different models, they found that the spray distance for drops that are expelled when a person has an overloaded nose and a complete set of teeth is approx. 60 percent larger than when they do not.
The results indicate that when someone keeps their nose free, e.g. By blowing it into a tissue, they can reduce the distance their bacteria move.
The researchers 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 medium and thick saliva.
For example, three seconds after a sneeze, when thick saliva reached the ground and thus reduced the threat, the thinner saliva still swam in the air like a potential disease transmitter.
The work is linked to the researchers’ project to create a COVID-19 cough drop that would give people thicker saliva to reduce the distance that drops from a sneeze or cough would travel and thus reduce the likelihood of disease transmission.
The results provide new insight into the variation in exposure distance and indicate how physiological factors affect the transfer rates, says Kareem Ahmed, associate professor in UCF’s department of mechanical and aerospace technology and study co-author.
“The results show that exposure levels are highly dependent on fluid dynamics, which can vary depending on multiple human traits,” says Ahmed. “Such features may be underlying factors driving super-dispersive events in the COVID-19 pandemic.”
The researchers say they hope to move the work towards clinical trials to compare their simulation results with those of real people with different backgrounds.
Study co-authors were Douglas Fontes, a postdoctoral researcher at the Florida Space Institute and lead author of the study, and Jonathan Reyes, a postdoctoral researcher in the UCF’s Department of Mechanical and Space Engineering.
Fontes says the research team wants to investigate the interactions between gas flow, mucus film and tissue structures in the upper airways during airway events to further the results of the study.
“Numerical models and experimental techniques must work side by side to provide accurate predictions of the primary upper respiratory tract resolution during these events,” he says.
“This research will potentially provide information on more accurate safety measures and solutions to reduce pathogen transmission, providing better conditions for dealing with the usual diseases or with pandemics in the future,” he says.
Reference: “A Study of Fluid Dynamics and Human Physiological Factors That Drive the Dispersion of Drops from a Human Sneeze” by D. Fontes, J. Reyes, K. Ahmed, & M. Kinzel Liquid physics.
DOI: 10.1063 / 5.0032006
The work was funded by the National Science Foundation.
Kinzel received his doctorate in aeronautical technology from Pennsylvania State University and joined UCF in 2018. In addition to being a member of UCF’s Department of Mechanical and Aerospace 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 UCF’s Department of Mechanical and Space Technology, a faculty member in the Center for Advanced Turbomachinery and Energy Research and the Florida Center for Advanced Aero-Propulsion. He served more than three years as a senior aero / thermo engineer at Pratt & Whitney Military Engines, working on advanced engine programs and technologies. He also served as a faculty member at Old Dominion University and Florida State University. At UCF, he leads research in propulsion and energy with applications for electricity generation and gas turbine engines, propulsion jet engines, hypersonics and fire safety, as well as research related to supernova science and COVID-19 transmission control. He received his doctorate in mechanical engineering from the State University of New York in Buffalo. He is an American Institute of Aeronautics and Astronautics associate fellow and a U.S. Air Force Research Laboratory and Office of Naval Research faculty fellow.