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Small airborne particles can be a big coronavirus problem

Small airborne particles can be a big coronavirus problem

This February 2018 photo provided by the University of Maryland School of Public Health shows the Gesundheit II machine in Dr. Donald Milton’s Laboratory of Aerobiology, Virology, and Exhaled Biomarkers of Public Health of the University of College Park, Md. The device is helping scientists study a big question: How does the virus that causes COVID-19 spread from one person to another? (University of Maryland School of Public Health via AP)

In a University of Maryland laboratory, people infected with the new coronavirus take turns sitting in a chair and putting their faces into the large end of a large cone. They recite the alphabet and sing or just sit in silence for half an hour. Sometimes they cough.

The cone sucks in everything that comes out of the mouth and nose. It’s part of a device called “Gesundheit II” that is helping scientists study a big question: How does the virus that causes COVID-19 spread from one person to another?

Clearly hitchhiking on small liquid particles sprayed by an infected person. People expel the particles as they cough, sneeze, sing, scream, speak, and even breathe. But the drops come in a wide range of sizes, and scientists are trying to define just how risky the various types are.

The answer affects what we should all do to avoid getting sick. That’s why it was made in the headlines a few days ago when an American health agency appeared to have changed stance on the issue, but later claimed to have published a new language by mistake.

The recommendation to stay at a distance of at least 6 feet (2 meters) – some authorities cite about half that distance – is based on the idea that larger particles fall to the ground before they can travel very far. They are like droplets in a window cleaner spritz and can infect someone by landing on their nose, mouth or eyes, or perhaps by being inhaled.

But some scientists are now focusing on smaller particles, ones that spread more like cigarette smoke. Those are carried by puffs of air and even upward air currents caused by our body’s heat. They can stay in the air for minutes or hours, spreading around a room and building up if ventilation is poor.

The potential risk comes from inhaling them. Measles can spread this way, but the new coronavirus is far less contagious than that.

For these particles, called aerosols, “6 feet is no magic distance,” says Linsey Marr, a lead researcher studying them at Virginia Tech in Blacksburg. But he says it’s still important to keep your distance from others, “the farther the better,” because aerosols are more concentrated near a source and pose a greater risk at close range.

Public health agencies have generally focused on the larger particles for the coronavirus. This prompted more than 200 other scientists to issue an appeal in July to pay attention to the potential risk of aerosols. The World Health Organization, which had long ruled out a hazard from aerosols except in the case of certain medical procedures, later said that aerosol transmission of the coronavirus cannot be ruled out in cases of infection within indoor spaces. crowded and poorly ventilated.

The matter attracted attention recently when the US Centers for Disease Control and Prevention posted and then deleted statements on their website highlighting the idea of ​​aerosol spread. The agency said the posting was a mistake and that the statements were just a draft of the proposed changes to its recommendations.

Dr Jay Butler, the CDC’s deputy director of infectious diseases, told The Associated Press that the agency continues to believe that larger, heavier droplets that come from coughing or sneezing are the primary means of transmission.

Butler told a scientific meeting last month that current research suggests aerosol spread of the coronavirus is possible but does not appear to be the primary way people get infected. Further research could change that conclusion, he added, and urged scientists to study how often the coronavirus aerosol spread occurs, what situations make it more likely, and what reasonable measures could prevent it.

Marr said he thinks the aerosol infection “is happening a lot more than people were initially willing to think.”

As a key piece of evidence, Marr et al point to so-called “superspreader” events in which one infected person evidently passed the virus to many others in a single context.

In March, for example, after a choir member with coronavirus symptoms attended a rehearsal in Washington state, 52 others who had sat across the room were found infected and two died. In a crowded, poorly ventilated restaurant in China in January, the virus evidently spread from a lunchtime customer to five people at two adjacent tables in a pattern that suggests that the aerosols had been spread by the air conditioner. Also in January, a passenger on a Chinese bus reportedly infected 23 others, many of whom were scattered around the vehicle.

Butler said such events raise concern about aerosol spread but do not prove that this is happening.

There may be another way to spread the tiny particles. They may not necessarily come directly from someone’s mouth or nose, says William Ristenpart of the University of California, Davis. His research found that if paper towels are sown with the flu virus and then crumpled, they emit particles that carry the virus. So people who empty a trash can with handkerchiefs discarded by someone with COVID-19 should make sure they are wearing a mask, he said.

Scientists who warn about aerosols say the current recommendations still make sense.

Wearing a mask is still important and make sure it fits well. Keep washing your hands diligently. And again, being further away is better than being closer. Avoid crowds, especially indoors.

Their main addition to the recommendations is ventilation to avoid an accumulation of aerosol concentration. So, the researchers say, stay away from poorly ventilated rooms. Open windows and doors. Devices for air purification or ultraviolet light which inactivates viruses can also be used.

Best of all: do everything you can outdoors, where dilution and ultraviolet light from the sun work in your favor.

“We know that outdoors is by far the most spectacular measure,” says Jose-Luis Jimenez of the University of Colorado-Boulder. “On the outside it’s not impossible to get infected, but it’s difficult.”

The various precautions should be used in combination rather than just one at a time, the researchers say. In a well-ventilated environment, “6 feet (of separation) is good enough if everyone is wearing a mask” and no one stands directly downwind of an infected person for long, says Dr. Donald Milton of the University of Maryland School of Public Health, the whose laboratory houses the Gesundheit II machine.

Exposure duration matters, so there’s probably not much risk from a short elevator ride while masked or being overtaken by a jogger on the sidewalk, experts say.

Scientists have published online tools to calculate the risk of airborne spread in various contexts.

In a recent meeting on aerosols, however, Dr. Georges Benjamin, executive director of the American Public Health Association, noted that preventative measures can be a challenge in the real world. Keeping separate from others can be difficult in homes that host multiple generations. Some older buildings have windows that were “nailed shut years ago,” he said. And “we have too many communities where they simply don’t have access to clean water to wash their hands.”

It might seem odd that despite all the scientific frenzy to study the novel coronavirus, the details of how it spreads may still be in doubt nine months later. But history suggests patience.

“We have been studying influenza for 102 years,” says Milton, referring to the 1918 flu epidemic. “We still don’t know how it is transmitted and what the role of aerosols is.”

CDC changes, then withdraws, posting on the web how the virus spreads

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Small Airborne Particles May Be a Big Coronavirus Problem (2020, September 26)
recovered September 27, 2020
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