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Coronavirus might spread much farther than 6 feet in the air. CDC says wear a mask in public.

USA TODAY logo USA TODAY 4/4/2020 Ramon Padilla and Javier Zarracina, USA TODAY
Promo image for aerosol transmission. © Ramon Padilla/ Javier Zarracina, USA TODAY Promo image for aerosol transmission.

Air contaminated with the COVID-19 virus might travel four times farther than the 6 feet the CDC asks we distance ourselves, according to a recent study. 

The study published in the Journal of the American Medical Association found that under the right conditions, liquid droplets from sneezes, coughs and just exhaling can travel more than 26 feet and linger in the air for minutes.

Findings such as these may have some bearing on the CDC's recommendation on Friday that Americans wear non-surgical face masks in public — especially in places "where other social distancing measures are difficult to maintain."

“There is no virtual wall at this 3- to 6-feet distance” says Lydia Bourouiba, the study's author, who specializes in fluid dynamics and is an associate professor at the Massachusetts Institute of Technology. These findings suggest the greatest risk is for health care workers working with infected patients, she says.

As seen in this video, shot from different views and posted with Bourouiba's report, the invisible cloud can travel up to 26 feet:

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The study focuses on a turbulent gas, the cloud emitted when someone coughs, sneezes or exhales. Liquid droplets of various sizes drop onto surfaces, while others can be trapped in a cloud that can swirl around a room with a payload, in theory, of pathogen-bearing droplets.

How cough and sneeze droplets travel

A lot goes into how far the cloud and its droplets travel: a person's physiology, the environment, humidity and temperature. “The cloud can reach up to 26 feet for sneezes and less than that for coughs — about 16 to 19 feet,” Bourouiba says.

According to a 2009 World Health Organization report, when someone coughs, they can spray up to 3,000 droplets. A sneeze could yield 40,000.

Virus-filled droplets smaller than a human hair

Bourouiba’s study did not look at gas clouds of patients infected with the SARS-CoV-2 virus but it hypothesized:  "The rapid international spread of COVID-19 suggests that using arbitrary droplet size cutoffs may not accurately reflect what actually occurs with respiratory emissions" and lead to inadequate recommendations and more sick people.

These droplets can be very small — “ as small and invisible as the micron size to the ones that you can see that are on the order of the millimeter” says Bourouiba. A human hair is 60 to 120 microns thick. 

Aerosols: The smallest droplets may carry COVID-19

Researchers don’t know how many virus-laden particles people infected with COVID-19 might expel in the average droplet, including the micron-size droplets — called aerosols — that linger in the air.

"Aerosols are different," says Dr. Stanley Deresinski, clinical professor of medicine and infectious diseases at Stanford University. "Very small particles may be suspended in the air for a long time, sometimes for hours. They're suspended by air currents."

Those floating airborne droplets — some shielded by turbulent gas clouds — can stay suspended long enough for someone to walk through and inhale the virus. Inside the gas cloud “the lifetime of a droplet could be considerably extended by a factor of up to 1000, from a fraction of a second to minutes,” Bourouiba's study says.

Droplets containing virus reach air circulation systems

Pathogens in the cloud could potentially reach air circulation systems inside buildings, says Bourouiba. “There was sampling done in air vents with positive detection of the virus.”

A separate JAMA Network study found that exhaust outlets tested positive for SARS-CoV-2: “small virus-laden droplets may be displaced by airflows and deposited on equipment such as vents,” the study says. 

“Now, there are other questions about whether the detected virus particles are still live," says Bourouiba. "However, finding the virus in air vents is more compatible with that longer distance range that can be reached through the cloud.” 

Fresh air can help rid coronavirus droplets

These findings heighten the dangers for those caring for COVID-19 patients. Without sufficient air circulation to disperse the cloud, its concentrated payload of droplets can linger in hospitals and homes. 

“Drops are trapped in the cloud for quite some time and they can remain locally concentrated,” says Bourouiba. 

The best defenses are the outdoors and open windows which dissipate the clouds or droplets.

“When one is outside, with air circulation or wind, the cloud and its payload is easily dispersed and less concentrated. Making sure that indoor spaces are aired frequently also reduces the concentration,” Bourouiba says.

Masks protect against floating droplets

Surgical masks are helpful at blocking large droplets, but unlike respirators they do not provide a reliable level of protection from inhaling smaller airborne particles, according to the CDC.

N95 respirators are tight-fitting and filter out at least 95% of airborne particles as small as 0.3 microns. They have a protection factor (APF) of 10, according to the CDC. That means the N95 reduces the aerosol concentration to 1/10 of that in the room — or blocking 90% of airborne particles.

An elastomeric respirator is a reusable device with exchangeable cartridge filters. It fits tight against the user's face and also has a APF of 10. Before reusing the mask, all its surfaces need to be wiped down with a disinfectant.

In addition to respirators, health care workers should wear personal protective equipment (PPE) to help limit exposure to the virus through their eyes or contaminated clothing.

Should you make a homemade face mask?

The CDC now recommends Americans wear cloth face coverings in public settings where its difficult to stay at least 6 feet apart  such as grocery stores and pharmacies — especially in areas with high levels of community transmission.

When asked about the CDC recommendations of the general public wearing masks or other improvised devices, Bourouiba offered a qualified response:

 “The efficacy of those homemade solutions need to be quantified. Exhalations or violent exhalations such as coughs or sneezes would be deflected to the sides of these masks — as they are not perfectly sealed. Flow follows the path of least resistance. The benefit of these masks is that the cloud deflection and impact against the mask dissipate energy and thus can reduce the range of  propagation of the cloud. It is important therefore to understand that such masks are not necessarily protective for the wearer in terms of preventing inhalation of the residual droplets in the air, which enter from the sides unfiltered, but they can provide a way to reduce the range of contamination from the droplets-laden cloud. ”

The CDC  press release says that cloth face coverings fashioned from household items or made at home from common materials at low cost can be used as an additional, voluntary public health measure. They recommend that critical supplies such as surgical masks or N-95 respirators, continue to be reserved for healthcare workers and other medical first responders. Top trends on Google Friday were face mask patterns and bandanas.

The start of allergy season could also hasten new infections. Bourouiba warned  that asymptomatic carriers could spread COVID-19 through any sneezing and coughing triggered by allergies.

Contributing: George Petras and Jim Sergent

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