I walk four to five miles per day, rain or shine, in virus-saturated air or not. I've felt relaxed about it, so long as no one gets within six feet of me. Which raises today's issue.
I'm getting tired of runners and bikers who seem oblivious to the need for distancing. Even on the very wide walkways of the University, they seem to enjoy crowding me as I cringe along the pavement edge. Are they malicious? I doubt it. I think their minds are in an oblivious zone, no more concerned with my presence -- a lowly walker -- than they would be with an intrepid cockroach crossing the sidewalk.
Finally -- after dodging speeding bikes coming up behind me on the narrow sidewalks of the Montlake Bridge -- I prepared to let off steam in my accustomed fashion -- a harangue on my Facebook page. Just before I began haranguing, however, I read an interesting post by a professor of biology offered on a friend's page.
The post -- "The Risks -- Know Them -- Avoid Them"* -- was essentially a long protest about the haste to "open up" the economy while the rates of Covid-19 infections and deaths still continue upward. I was interested in all aspects of his discussion -- especially the ease with which a single, asymptomatic carrier of the virus can infect and kill a large number of patrons in a restaurant. It makes me think very carefully about my enthusiasm for returning to my practice of eating breakfast out while lingering over my newspaper.
But the article was encouraging about the risks incurred out of doors. And causes my hackles to flatten out to some degree when confronted with incursions by runners and bikers into my invisible safety zone.
The author points out that no one is infected by a single virus. Infection requires a minimum load of viruses, probably something like a thousand, based on other viral infections, although a number has not been yet determined for the Covid-19 virus. And the number probably differs from one individual to another.
If you are outside and someone sneezes in your face, you have a problem. But, he reminds us of the formula for infection:
(Successful Infection) = (Exposure to virus) x (Time of exposure)
You can reach a one thousand viral particle threshold by breathing in 500 viral particles per minute for two minutes, or 20 viral particles per minute for 50 minutes.
The time that a walker is exposed to a passing runner -- or even more, a passing biker -- is very slight. Even though the passer is breathing heavily, and blowing out hypothetically infected aerosol, my exposure will be for a very short period of time, and even slight breezes will disperse the cloud. Moreover, viruses decay and lose their ability to infect more quickly out of doors, in sunlight and dryness of air. He summarizes:
If I am outside, and I walk past someone, remember it is "dose and time" needed for infection You would have to be in their airstream for 5+ minutes for a chance of infection. While joggers may be releasing more virus due to deep breathing, remember the exposure time is also less due to their speed.
No one claims that infection is impossible under these conditions -- just as no one claims that an airplane never crashes. But the risk is small enough to be, for most of us, an acceptable risk.
He reminds us to avoid distances closer than six feet, and advises us to wear masks. My problem, of course, is with rogue exercisers getting within six feet of me, but I can see now that the risk still is minimal for very short exposures. And I'm still not wearing a mask on the routes I follow, where -- for the greater part of the route by far -- I'm in no proximity to others.
WARNING -- I'm not an epidemiologist, or any other kind of physician. I'm merely summarizing an online article that I found helpful and interesting. No warranties as to its scientific or medical validity is offered to my readers.
---------------------------------------
Dr. Bromage is an Associate Professor of Biology at the University of Massachusetts at Dartmouth. His studies have focused on epidemiology and immunology. He references another post that provides additional information on the specific question of risks of contracting Covid-19 while outdoors.
Sigal Samuel, "Why You're Unlikely to Get the Coronavirus from Runners or Cyclists," https://www.vox.com/future-perfect/2020/4/24/21233226/coronavirus-runners-cyclists-airborne-infectious-dose?fbclid=IwAR1XkiJk6Tu81-QqCP6RZFWfswBzqSZson29ZcRYM_pS9xt5AjGtkXYt020
The author is a staff writer for Vox's Future Perfect. She is not a trained scientist, but writes on general science matters.
No comments:
Post a Comment