Tiny airborne particles may pose a big coronavirus problem

At a University of Maryland lab, people infected with new coronavirus take turns sitting in a chair and putting ir faces into big end of a large cone. y recite alphabet and sing or just sit quietly for a half hour. Sometimes y cough.

cone sucks up everything that comes out of ir mouths and ses. It's part of a device called “Gesundheit II” that is helping scientists study a big question: Just how does virus that causes COVID-19 spre from one person to ar?

It clearly hitchhikes on small liquid particles sprayed out by an infected person. People expel particles while coughing, sneezing, singing, shouting, talking and even breathing. But drops come in a wide range of sizes, and scientists are trying to pin down how risky various kinds are.

answer affects what we should all be doing to avoid getting sick. That's why it was thrust into helines a few days ago when a U.S. health ncy appeared to have shifted its position on issue, but later said it h published new langu in error.

recommendation to stay at least 6 feet (2 meters) apart — some authorities cite about half that distance — is based on idea that larger particles fall to ground before y can travel very far. y are like droplets in a spritz of a window cleaner, and y can infect somebody by landing on ir se, mouth or eyes, or maybe being inhaled.

But some scientists are w focusing on tinier particles, ones that spre more like cigarette smoke. Those are carried by wisps of air and even urd drafts caused by warmth of our bodies. y can linger in air for minutes to hours, spreing throughout a room and build up if ventilation is poor.

potential risk comes from inhaling m. Measles can spre this way, but new coronavirus is far less contagious than that.

For se particles, called aerosols, “6 feet is t a magic distance,’’ says Linsey Marr, a leing researcher who is studying m at Virginia Tech in Blacksburg. But she says it's still important to keep one's distance from ors, “ farr better,” because aerosols are most concentrated near a source and pose a bigger risk at close range.

Public health ncies have generally focused on larger particles for coronavirus. That prompted more than 200 or scientists to publish a plea in July to pay attention to potential risk from aerosols. World Health Organization, which h long dismissed a danger from aerosols except in case of certain medical procedures, later said that aerosol transmission of coronavirus can’t be ruled out in cases of infection within crowded and poorly ventilated indoor s.

issue drew attention recently when U.S. Centers for Disease Control and Prevention posted and n deleted statements on its website that highlighted idea of aerosol spre. ncy said posting was an error, and that statements were just a draft of proposed changes to its recommendations.

Dr. Jay Butler, CDC's deputy director for infectious disease, told Associated Press that ncy continues to believe larger and heavier droplets that come from coughing or sneezing are primary means of transmission.

Last month Butler told a scientific meeting that current research suggests aerosol spreing of coronavirus is possible but it doesn’t seem to be main way that people get infected. Furr research may change that conclusion, he ded, and he urged scientists to study how often aerosol spre of coronavirus occurs, what situations make it more likely and what reasonable steps might prevent it.

Marr said she thinks infection by aerosols is “happening a lot more than people initially were willing to think.”

As a key piece of evidence, Marr and ors point to so-called “superspreer” events where one infected person evidently passed virus to many ors in a single setting.

In March, for example, after a choir member with coronavirus symptoms attended a rehearsal in Washington state, 52 ors who h been seated throughout room were found to be infected and two died. In a crowded and poorly ventilated restaurant in China in January, virus evidently spre from a lunchtime patron to five people at two joining tables in a pattern suggesting aerosols were spre by air conditioner. Also in January, a passenger on a Chinese bus apparently infected 23 ors, many of whom were scattered around vehicle.

Butler said such events raise concern about aerosol spre but don’t prove it happens.

re could be ar way for tiny particles to spre. y may t necessarily come directly from somebody's mouth or se, says William Ristenpart of University of California, Davis. His research found that if paper tissues are seeded with influenza virus and n crumpled, y give off particles that bear virus. So people emptying a wastebasket with tissues discarded by somebody with COVID-19 should be sure to wear a mask, he said.

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

Wearing a mask is still important, and make sure it fits snugly. Keep washing those hands diligently. And again, staying farr apart is better than being closer toger. Avoid crowds, especially indoors.

ir main dition to recommendations is ventilation to avoid a buildup of aerosol concentration. So, researchers say, stay out of poorly ventilated rooms. Open windows and doors. One can also use air-purifying devices or virus-inactivating ultraviolet light.

Best of all: Just do as much as you can outdoors, where dilution and sun's ultraviolet light work in your favor.

“We kw outdoors is most spectacularly effective measure, by far,’’ says Jose-Luis Jimenez of University of Coloro-Boulder. “Outdoors it is t impossible to get infected, but it is difficult.”

various precautions should be used in combination rar than just one at a time, researchers say. In a well ventilated environment, “6 feet (of separation) is pretty good if everybody’s got a mask on” and body stays directly downwind of an infected person for very long, says Dr. Donald Milton of University of Maryland School of Public Health, whose lab houses Gesundheit II machine.

Duration of exposure is important, so re's probably t much risk from a short elevator ride while masked or being passed by a jogger on sidewalk, experts say.

Scientists have published online tools for calculating risk of airborne spre in various settings.

At a recent meeting on aerosols, however, Dr. Georges Benjamin, executive director of American Public Health Association, ted that preventive steps can be a challenge in real world. Keeping apart from or people can be difficult in homes that house multiple generations. Some old buildings have windows that were “nailed shut years ago,” he said. And “we have far too many communities where y simply don’t have access to clean water to wash ir hands."

It might seem strange that for all scientific frenzy to study new coronavirus, details of how it spres can still be in doubt nine months later. But history suggests patience.

“We've been studying influenza for 102 years," says Milton, referring to 1918 flu epidemic. “We still don't kw how it's transmitted and what role of aerosols is."