The main way people without COVID-19 symptoms spread the virus

Mike Moffitt, SFGATE

These days hearing someone cough or sneeze in public can cause instant anxiety if you’re nearby, especially in closed spaces.

But how often do you think of the other major route for COVID-19 — the simple act of talking to another person?

Droplets spewed during speech are believed to be the key transmission vector for COVID-19 for asymptomatic and presymptomatic patients, says research scientist Jeremy P. Howard, co-founder of fast.ai, which promotes deep learning via artificial intelligence.

Asymptomatic infections may account for 40-45 percent of all COVID-19 cases, according to a new Scripps Research Institute analysis published this month in the Annals of Internal Medicine. An additional percentage of cases, yet unknown, involve presymptomatic patients.

“Our estimate of 40 to 45 percent asymptomatic means that, if you’re unlucky enough to get infected, the probability is almost a flip of a coin on whether you’re going to have symptoms. So to protect others, we think that wearing a mask makes a lot of sense,” Scripps Research behavioral scientist Daniel Oran told Science News.

COVID-19 results in viral shedding in the upper respiratory tract, where droplets can form.

The picture above shows speech droplets, which are believed to be the key transmission vector for COVID-19, with vs without a paper towel face cover. As you see, nearly all droplets are blocked.

Here’s a video with a cloth covering, from this NEJM paper: https://t.co/QoGBBZpQEa pic.twitter.com/HGqz3U7NQU

— Jeremy #Masks4All Howard (@jeremyphoward) June 19, 2020

Every time people speak, they spray a cloud of droplets that vary widely in size. Large droplets fall quickly to the ground, but small ones can dehydrate and linger as “droplet nuclei” in the air, behaving like an aerosol, according to a National Institutes of Health and University of Pennsylvania study published last month in the New England Journal of Medicine.

The researchers measured droplets generated on a laser light sheet by a person speaking into a cardboard box. Video clips (see the tweet) showed a dramatic difference between speech with and without a cloth cover over the mouth. 
 
Young people infected at bars, clubs, parties and other indoor gatherings may not get seriously ill, but they can spread the virus to parents, grandparents and other vulnerable people.

Systems biologist Dr. David States noted on Twitter that deaths of older family members infected by young people in the recent spike of cases in Texas, Arizona, Florida, California and other, mostly Southern, states won’t show up in statistics for a month or more.

At a press conference Monday in Columbus, Ohio, Republican Gov. Mike DeWine — who has rejected the anti-mask arguments of the right — held up a face covering for viewers to see.

“If we want to be able to go out and live our lives, this mask is a symbol of freedom,” he said. “It’s a symbol of freedom because if you wear these, if we get 75-80 percent of the people who are out in public who are wearing this mask, we are going to see these numbers get better.”

Studies back him up. Modeling presented by Cambridge and Greenwich university scientists in Proceedings of the Royal Society indicated that 100% face mask use seriously diminishes disease spread.

Wearing masks could also shore up the struggling economy, research shows.

A new study from Goldman Sachs suggests a national mask mandate would slow the growth rate of new coronavirus infections and prevent a 5% GDP loss caused by additional lockdown measures, Forbes reported Monday.

Hong Kong, a metropolitan area and special administrative region of 7.5 million, has had just six confirmed COVID-19 deaths since the beginning of the pandemic.

The key to the Hong Kong’s success is nearly universal mask compliance (97%) in the early morning rush hour, according to Hong Kong University Prof. Yuen Kwok-yung, one of the world’s top coronavirus experts. Yuen said the 3% of people who don’t wear masks are mainly Americans and Europeans.

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Mike Moffitt is an SFGATE Reporter. Email: moffitt@sfgate.com. Twitter: @Mike_at_SFGate




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