Limit your stay in enclosed places to one hour

By all accounts, we have to proceed with life while the pandemic rages on.

Four months should have made us experts by now on the prescribed safety protocols — wear a mask as soon as you are out of your doorstep, wash or sanitize your hands often, keep a safe distance of at least one meter from others and keep gatherings to a minimum and do it outdoors.

Recently, additional information caught the media’s attention as a blog post of Dr. Erin Bromage reached 18,988,771 views (www.erinbromage.com). Dr. Bromage is the associate professor of Biology at the University of Massachusetts Darthmouth since 2007. He teaches courses in Immunology and Infectious disease, as well as Ecology of Infectious Disease. The latter focused on the current pandemic.

The specific post centered on the topic that COVID-19 infection is related to prolonged time exposure to the virus. Simply stated, the longer you stay in an enclosed space that contains the virus, the higher the risk of getting sick. Dr. Bromage illustrated this reality through the equation “Successful Infection = Exposure to Virus x Time.”

"The longer time you spend in that environment — so minutes or hours in there — the more virus you breathe in, the more it can build up and then establish infection. So it's always a balance of exposure and time,” Dr. Bromage said.

He compared the difference in risk to grocery store staff who stay for eight-hour shifts versus customers who just shop briefly.

"Even if there is virus in that environment, you hopefully haven't had that extended time needed to get to that infectious dose. The employees, though, are in that environment all day. So what wouldn't infect you and I because it didn't get to that infectious dose number, has a much stronger effect or larger effect on an employee that gets that low dose all day."

Dr. Bromage reported that the main sources for infection are the home, office, public transport, social gatherings, and restaurants. “This accounts for 90 percent of all transmission events. In contrast, outbreaks spread from shopping appear to be responsible for a small percentage of traced infections,” he added.

“Indoor spaces, with limited air exchange or recycled air and lots of people, are concerning from a transmission standpoint. We know that 60 people in a volleyball court-sized room (say, a choir) results in massive infections. Same situation with the restaurant and the call center.  Social distancing guidelines don't hold in indoor spaces where you spend a lot of time, as people on the opposite side of the room were infected,” he elaborated.

“The principle is viral exposure over an extended period of time. In all these cases, people were exposed to the virus in the air for a prolonged period (hours). Even if they were 50 feet away (choir or call center), even a low dose of the virus in the air reaching them, over a sustained period, was enough to cause infection and, in some cases, death,” Dr. Bromage added.

“When assessing the risk of infection (via respiration) at the grocery store or mall, you need to consider the volume of the air space (very large), the number of people (restricted), how long people are spending in the store (workers = all day; customers = an hour). Taken together, for a person shopping: the low-density, high air volume of the store, along with the restricted time you spend in the store, means that the opportunity to receive an infectious dose is low,” he clarified.

“Basically, as the work closures are loosened, and we start to venture out more, possibly even resuming in-office activities, you need to look at your environment and make judgments. How many people are here, how much airflow is there around me, and how long will I be in this environment? If you are in an open floor plan office, you really need to critically assess the risk (volume, people, and airflow). If you are in a job that requires face-to-face talking, or even worse, yelling, you need to assess the risk. If you are sitting in a well-ventilated space, with few people, the risk is low,” he added.

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