CNN  — 

Stop worrying about those runners and cyclists without a mask, whom you scoff at as you walk outside. Worry instead about the loud talkers in crowded indoor spaces.

That’s according to Erin Bromage, a University of Massachusetts Dartmouth associate professor of biology, who started a blog about the ways in which coronavirus spreads to keep his family and friends informed.

It turns out other people liked his smart, practical way of explaining the virus and risky behavior. His latest post, “The Risks — Know Them — Avoid Them,” went viral and gained more than 13 million views in about a week.

The explainer illustrated how breathing versus talking loudly versus sneezing can put out different amounts of respiratory droplets in the air.

“A big part of me writing these posts is just to give some tangible advice to friends, family, about what risks they should really be worrying about and wasting mental energy on,” he told CNN’s John Berman on “New Day.”

“Not a lot of my friends know what we should be doing now in this brave new world,” Bromage said.

“I was trying to give them the tools they need to know if you end up indoors — which we’re going to — in an environment where there seems like there’s a lot of people, and it just doesn’t feel right, then that’s a situation that you should avoid. Use your feet, find somewhere else that feels more comfortable for you.”

Bromage, who also showed how an outbreak can occur even while social distancing in workplaces and other enclosed areas, answered more questions for CNN. His responses are lightly edited for clarity.

CNN: Why are grocery stores, bike riders and inconsiderate runners less of a concern when compared to sharing enclosed spaces like an office or restaurant?

Bromage: It comes down to the concentration of the virus in the air and the length of exposure. In larger spaces with better ventilation or outdoors, the concentration of the virus can be diluted in the larger volume of the air. The lower the virus burden in the air, the longer you can be in that environment before receiving an infectious dose.

CNN: What is the difference between sneezing, talking loudly and singing in terms of virus transmission?

Bromage: Respiratory droplet emission follows this sequence. Talking loudly emits a lesser amount of droplets than singing. Sneezing emits the most. The more force by which a sound leaves your mouth, the more respiratory particles are emitted, and they travel a further distance.

CNN: If people have a cold or other virus, should they stay away from everyone as if they had Covid-19?

Bromage: If Covid-19 is prevalent in your area and you have symptoms in the Covid-19 spectrum, you need to treat your sickness as Covid-19. If you are sick, you should stay home and you should limit interactions with household members.

CNN: As states reopen, where can people go and where should they reconsider going?

Bromage: People should go to any outdoor space with ample room for social distancing, such as beaches, parks and trails. However, they should limit their time in outdoor spaces where social distancing can’t be maintained most of the time — any crowded spot, such as the protests we have been seeing lately.

People should also limit how much time they spend in any indoor spaces with poor air exchange and lots of people with no effective ability to social distance. I hope when we reopen, none of these places will exist, and guidelines would have been put in place to stop it from occurring. I believe that almost every business can engineer their space to ensure that they limit numbers of people at one time to a number that is determined by air exchange and size of their facility.

CNN: What steps are you taking to keep safe in your home and community?

Bromage: We repeatedly remind ourselves to wash our hands and not to touch our faces! If we go grocery shopping or hiking on a local trail, we wash our hands immediately after coming back to the house. We open packages in the garage and leave packaging outside.

For the groceries that come in plastic packaging that will be refrigerated or frozen, we wipe down the packaging using disinfectant wipes. We allow the packaging to dry before we put those items into the fridge or freezer. All pantry items are just put away as usual.

We wear masks in public where we can’t socially distance all the time. We have higher-quality masks for environments where we linger, like the grocery store or work. And we have lower-quality masks for short interaction. We use a neck sleeve or T-shirt mask to pull up in places like a forest trail where we might have to pass within 6 feet of other people.

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CNN: What do you wish people would take away from your post?

Bromage: With knowledge, you can limit your risk of infection and so you can take power away from the fear of the virus. People should know that enclosed spaces with lots of people and poor airflow are problematic. So avoid them when possible. And finally, feel comfortable in indoor or outdoor environments when you have plenty of space and good airflow.