Shira Feder Apr 8, 2020, 6:02 AM
In March, 60 members of a choir group in Washington, by then already an epicenter of coronavirus in the US, tentatively went ahead with a rehearsal. They kept their distance and used hand sanitizer.
Three weeks later, the LA Times reported, 45 members were diagnosed with COVID-19, three were hospitalized, and two died.
That one case adds weight to evidence that droplets can travel further than six feet if they are ejected by people speaking loudly or singing.
A not-yet-peer-reviewed study by the National Institutes of Health, released on Monday and first reported by the Guardian, used laser imagery and video to show that, when people speak, thousands of fine droplets can be spewed into the air — up to 360 droplets in 17 milliseconds — a finding, they said, which could hold lessons for the public during the novel coronavirus pandemic.
It's something scientists have been warning about for weeks.
"While the current specific research is limited, the results of available studies are consistent with aerosolization of virus from normal breathing," Dr. Harvey Fineberg, chairman of the National Academy of Sciences Standing Committee on Emerging Infectious Diseases and 21st Century Health Threats, wrote in a letter to the White House.
The coronavirus is heavier than other viruses, so it typically falls to the ground
Some viruses move in droplets, and some in aerosols. Droplets are heavier, so they tend not to linger in the air, falling instead on surfaces or coughed-on hands. Aerosols are tiny particles, smaller than five micrometers, that can float in the air.
The World Health Organization has taken pains to emphasize that the coronavirus is primarily spread through respiratory droplets, unlike, for example, measles, which is transmitted in aerosols and can linger for hours in the air.
We know that the virus can be aerosolized in certain hospital settings — the most common example being when a patient is intubated, and oxygen from the machine converts infectious cough droplets into a fine spray.
In most settings, droplets cannot travel further than a three to six feet. Though some studies of the coronavirus have found it could linger in the air in a lab, they were not representative of real-world conditions, and experts say it's unlikely the coronavirus could linger like measles or chickenpox.
Projecting your voice could send droplets further — but it's unclear how infectious they are at the end of their journey
William Schaffner, professor of infectious diseases at Vanderbilt University Medical Center, told Business Insider that, no matter how far coronavirus droplets travel, they are not, technically, "airborne," an academic term that is causing some controversy in medical circles.
"By airborne, we mean that the virus can linger in the air for substantial periods of time, and might even infect someone who walks into the room an hour later," Schaffner said. "Could it happen occasionally? Sure. It happens occasionally with influenza, too, but it's pretty darn unusual for the most part."
Still, projecting your voice could send droplets further afield.
"These droplets are usually transmitted within three to six feet, but these droplets can be pushed farther out, sometimes even beyond six feet, if you give the exhalation more energy, with a cough or a sneeze or even singing," Schaffner said.
Lydia Bourouiba, an associate professor at MIT whose lab explores the effects of exhalations like coughs or sneezes, is another scientist who believes the virus can travel far further than previously appreciated. In an article for JAMA, Bourouiba wrote that "peak exhalation speeds can reach up to 33 to 100 feet per second, creating a cloud that can span approximately 23 to 27 feet," and called for revised CDC and WHO guidelines.
What should you do if you're a loud talker or you like to sing in public?
After analyzing all of the aerosol studies on coronavirus so far published, the WHO concluded on March 20 that its recommendations remain unchanged: medics need personal protective equipment and to use airborne precautions when intubating patients, and the general public should stay home.
"From the available studies that we have seen, we are confident that the guidance we have is appropriate," WHO representative Maria Van Kerkhove said in a press conference. The general consensus among virologists is that's right: the coronavirus probably won't travel further than six feet.
The authors of the newly-released NIH study on loud speech said that a damp homemade cloth mask could help to catch the amount of droplets produced when talking, adding their findings to the growing pile of evidence declaring homemade masks a necessary part of fighting off a virus.
But masks do not make up for what the WHO and the CDC and all the public health experts agree is the gold standard of virus-fighting; social distancing, which they maintain remains the best approach.
Schaffner agrees with the WHO: Stay home and skip any in-person group singing.
"And at this juncture, we don't want people doing voice lessons, even standing eight-and-a-half feet apart," Schaffner said.