Professor looks at dangerous aerosols spreading during Thanksgiving

Posted at 4:22 PM, Nov 25, 2020

This week, experts are sending warnings to those considering seeing people outside their household without quarantining first. One aerosol expert weighs in on just how dangerous the holiday could be.

"My simplest advice is it is not a good idea to meet with people outside of your household for a holiday meal. That’s the most important message that can be underscored, and the reason for that is there are multiple ways this virus can be transferred,” said Alex Huffman, an aerosol expert and associate professor at the University of Denver. “The closer you are increases the chances of that, but aerosols can come out of your mouth and mix into the room. The longer you're in that room, the more chance you have of getting sick.”

Huffman says time, ventilation and proximity have a big impact on whether coronavirus droplets can spread and infect others.

"When you breathe and talk, the louder you talk, droplets and aerosols come out of your mouth. So, traditionally, droplets are on the bigger side, aerosols are on the smaller side," said Huffman.

With no mask on, these droplets can land on the faces of people around you or on their plates.

"And so, the biggest danger with the Thanksgiving meal or holiday meal or any meal specifically, restaurants included, are that you have to take off your mask to eat and that is why eating together indoors is so dangerous," said Huffman.

Huffman demonstrated how fast droplets can spread in the air by showing how quickly food coloring can spread in water. He also analyzed the risks of eating a Thanksgiving meal in person, taking commonly-used models and applying varying factors that come into play when eating with people outside of your household.

"And then, I used the same model to say, ‘What happens if we meet for holiday meals?’ Let's say we have 10 people. We all eat for two hours. We all don't have masks on, and then, we ran different scenarios. If it was a small room, a large room, a medium-sized room and then estimate the amount of risk that would be from aerosol," said Huffman.

Matching with community transmission rates, Huffman estimated that the probability of each person at the table having COVID-19 was about 5 percent.

"If it's a small room, everybody has something like a 15 percent chance of getting infected, even if we had no idea if anybody was infected or not. If it's a big room, it's a little bit less than that," explained Huffman.

Ventilation also comes into play, which is why experts are advising that if you really are planning to meet with family this holiday, do it outside. Opening windows and doors also helps. Huffman also has some tools people can use, such as a carbon dioxide monitor or you can create your own box fan air filter.

"On the back, this is a furnace filter that’s also 20 inches and so you tape them together so they're well-sealed. You turn it on high and you blow the air through this filter and that removes the particles in the room that could potentially contain virus in it," said Huffman.

Still, Huffman and other medical experts agree this won't completely eliminate the risk of spreading COVID-19. The safest thing to do is stay home and avoid celebrating Thanksgiving with people who are not part of your household.