Study Identifies Two Features That Could Make People Covid-19 Superspreaders

Computer model of sneeze velocity for a person with teeth and an unblocked nasal passage. Fontes et al., Physics of Fluids 32, 111904 (2020) CC BY 4.0

Mounting evidence is showing that superspreaders are a key hallmark of the Covid-19 pandemic. A number of studies have shown that the majority of people with the virus don't transmit the infection to many other people, while a small number of people potentially spread the virus to a large number of their contacts. In extreme cases, a single sick person can spread Covid-19 to dozens of people in a single superspreading event. 

However, it has remained unclear what makes certain people a superspreader. In a new study, researchers from the University of Central Florida (UCF) have identified a few features that appear to make people more likely to be a superspreader of viral infections, such as Covid-19.

As reported in the journal Physics of Fluids, the researchers used 3D modeling and computer simulations to show that sneezes from people who have a blocked nose and a full set of teeth travel about 60 percent farther than those who don’t. The researchers argue this could be an important insight into why some people seem to transmit respiratory infections more than others. 

“We show that the human body has influencers, such as a complex duct system associated with the nasal flow that actually disrupts the jet from your mouth and prevents it from dispersing droplets far distances," said Michael Kinzel, study co-author and an assistant professor with UCF’s Department of Mechanical Engineering, in a statement

“Teeth create a narrowing effect in the jet that makes it stronger and more turbulent,” Kinzel explained. "They actually appear to drive transmission. So, if you see someone without teeth, you can actually expect a weaker jet from the sneeze from them.”

Sneeze velocity for four different nose and mouth types. A is open nasal passage with teeth, B is open nasal passage without teeth, C is blocked nasal passage without teeth, and D is blocked nasal passage with teeth. Fontes et al., Physics of Fluids 32, 111904 (2020) CC BY 4.0

Other pieces of research — some carried out before Covid-19 sprang into existence — have weighed in on this question of what makes certain people more infectious than others. Back in early 2019, a study in Scientific Reports suggested that speaking loudly might be a factor. Their experiments showed that the louder a person speaks, the more spit, mucus, and aerosols they spray from their mouth, However, they also found that some people simply produced more aerosols than others, even when speaking at the same volume.

Other research has suggested that some infected people might have a higher viral load in their bodies and shed more of the virus. This means that their saliva and aerosols likely contain a higher concentration of viral particles, making that person more infectious to others. While some scientists have suggested this is an important key, it remains relatively unstudied and there’s still a lot of uncertainty.

Crucially, the surrounding environment is also an important factor in the creation of a superspreading event. Simply put, it’s clear that a stuffy, badly ventilated room full of people in close proximity is notably riskier than an outdoor gathering where everyone keeps a distance of at least 2 meters (over 6 feet) and wears a face mask. Environments with brighter UV light, higher temperatures, and higher levels of humidity are also known to slash the survival rate of the Covid-19 virus in the air and on the surfaces, lowering the risk of people spreading the infection. 

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