Minimize Risk as We Emerge from Lockdown

Date: 5/14/20

As many states and counties begin to slowly emerge from lockdown, it’s important for all of us to understand how to minimize the risks of COVID-19.

Dr. Erin Bromage, an Associate Professor of Biology at the University of Massachusetts Dartmouth, has written a useful guide on what the recent research has shown in this area. I recommend reading his full post for all of the details, but I’ll summarize it here.

The risk of acquiring SARS-Cov-2 can be expressed in this simple formula:

Successful Infection = Exposure to Virus x Time

The greater your exposure to the virus, and the longer you are exposed, the higher your risk of infection.

Let’s look at each part of that formula more specifically, starting with exposure to the virus.

The two primary drivers of exposure to the virus are airborne and surface contact.

According to Dr. Bromage:

“In order to get infected you need to get exposed to an infectious dose of the virus; based on infectious dose studies with other coronaviruses, some estimate that as few as 1000 SARS-CoV2 viral particles are needed for an infection to take hold.”

To minimize our risk of exposure, we need to understand both the airborne (coughing, sneezing, breathing) and surface vectors of the virus.

  • Sneezing is the worst. A sneeze releases about 30,000 droplets traveling at 200 miles per hour! The droplets from a sneeze are small, can travel across a room, and are more likely to linger in the air.
  • Coughing is next. A cough releases 3,000 droplets traveling at 50 miles per hour. Most droplets from a cough fall to the ground quickly, but some can linger in the air.

Bromage points out that if a person is infected, a single cough or sneeze can expel as many as 200,000,000 viral particles—far more than the 1,000 needed to cause an infection.

Even talking can be problematic—especially loud talking. A brand new study, not mentioned in Bromage’s report, found that talking can release 1,000 droplets, and these droplets can linger in the air for an average of 8–14 minutes.

A breath can release 50–5,000 droplets. Most fall to the ground quickly, so although a breath may still contain enough droplets to infect someone, the risk is lower because the droplets fall to the ground quickly.

What about surfaces? Most studies suggest that coming into contact with the virus on surfaces only accounts for about 10 percent of infections. Bathrooms—especially public ones—likely present the greatest risk.

Here are the key takeaways:

  • The risk of infection in outdoor environments is very low. (Only a single outbreak has been traced to an outdoor setting.) This means that taking walks or doing other outdoor exercise, and even spending time with others in small groups outside—while maintaining appropriate social distance—is likely to be safe.
  • The highest risk of infection occurs when spending long periods of time with groups of people in enclosed spaces. This is particularly true when ventilation is poor. Indoor birthdays, parties, funerals, weddings, restaurants, offices and other indoor workplaces, in-person conferences, churches, choirs, and theaters have all been sources of significant outbreaks.
  • Brief trips to the grocery store or other retail locations are fairly low risk. Remember, infection is a product of exposure + time. In a grocery store, the volume of air is large, and if the staff and other shoppers are wearing masks, the likelihood of being exposed to a high number of respiratory droplets (and thus viral particles) is low. And since you’re only there for a relatively short time, that also reduces the risk.
  • Returning to an indoor workplace can be high or low risk. If the space is well-ventilated, adequate social distancing is maintained, masks are worn, and there are relatively few employees present, then the risk is likely low. But if ventilation is poor, employees are numerous and close together, and/or masks are not required work (e.g. in the recent outbreaks in meatpacking plants), the risk is likely high. Rest assured, we have excellent ventilation in our clinic, with opening windows and HEPA filters. We are wearing masks and gloves and require our patients to wear masks too. You can read our new policies and procedures here.
  • The risk of the gym and other indoor exercise venues also varies. If the gym is strictly limiting the number of members present, the ventilation is good, and you are vigilant about wiping down surfaces, the risk is fairly low—though higher than it is with outdoor exercise. But other indoor activities and sports may pose a higher risk. A curling event in Canada with 72 attendees led to 24 of them becoming infected.

I hope this helps keep you and your loved ones safe as we begin to venture back out into the world.

Warmest wishes for staying healthy and safe~