Dose of Coronavirus, Timing Matters for Infection

By Cara Murez
HealthDay reporter

THURSDAY, November 5, 2020 (HealthDay News) – The likelihood of you getting infected with coronavirus may depend on how much virus you inhale, where these particles land in your airways and even the weather, researchers report .

Researchers from many institutions are working on a project funded by the National Science Foundation to develop a mask with a reusable respirator that captures and kills the COVID-19 virus.

As part of this effort, Saikat Basu, assistant professor in the Department of Mechanical Engineering at South Dakota State University, developed a model that uses respiratory frequencies to track the sizes of droplets likely to reach areas vulnerable respiratory tract.

“To get infected you have to inhale the virus first, so inhalation patterns are important,” Basu explained in a college press release.

Wearing masks is also important. A cell culture study from the University of North Carolina found that the upper part of the throat behind the nasal passages and above the esophagus and voice box – an area known as the nasopharynx – is the most accessible seeding area for the virus.

In his study, Basu used numerical models to simulate inhalation rates in healthy adults. He reported that the droplet sizes most likely to reach this area were larger than expected.

“Most masks would block these droplet sizes, so wearing a mask is very helpful,” Basu said. “These are also the droplet sizes we need to make sure our new respirator design captures.”

The data could also be useful in developing inhaled antivirals and intranasal vaccines that reach this initial site of infection.

One negative finding is that virus-carrying droplets can dehydrate in the air, increasing the concentration of virus particles and their potential to cause disease. This could impact the transmission of COVID-19 this winter, when humidity drops and triggers a faster rate of droplet dehydration.

“The droplets inhaled after dehydration in the outside air carry a higher viral load,” noted Basu.

To estimate the infection threshold, Basu looked at reports of a super-diffusion event in May among a choral group of 61 people in Skagit Valley, Wash., Where a symptomatic person transmitted COVID-19 to 52 other members.


To estimate the likelihood of a droplet containing at least one viral particle, Basu used a study on the amount of virus in the sputum and mucus of patients with COVID-19 and explained dehydration. He conservatively estimated about 300 virus particles as the infection threshold. Typically, an inhaled viral infection requires 1,950 to 3,000 virus particles.

“The fact that the number of viral particles needed to initiate infection is in the hundreds is very remarkable and shows how contagious this virus is,” Basu said.

The results of the droplet inhalation modeling have been reviewed by the medRxiv science team. The corresponding research manuscript is currently being peer reviewed in the journal PLOS One.

More information

Visit the World Health Organization to learn more about the global COVID-19 pandemic.

SOURCE: South Dakota State University, press release, September 28, 2020

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