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A12 science
Monday 28 SepteMber 2020
Tiny airborne particles may pose a big coronavirus problem

By MALCOLM RITTER together. Avoid crowds, es-
AP Science Writer pecially indoors.
NEW YORK (AP) — At a Their main addition to rec-
University of Maryland lab, ommendations is ventila-
people infected with the tion to avoid a buildup of
new coronavirus take turns aerosol concentration. So,
sitting in a chair and put- the researchers say, stay
ting their faces into the big out of poorly ventilated
end of a large cone. They rooms. Open windows and
recite the alphabet and doors. One can also use
sing or just sit quietly for a air-purifying devices or vi-
half hour. Sometimes they rus-inactivating ultraviolet
cough. light.
The cone sucks up every- Best of all: Just do as much
thing that comes out of as you can outdoors, where
their mouths and noses. dilution and the sun’s ultra-
It’s part of a device called violet light work in your fa-
“Gesundheit II” that is help- vor.
ing scientists study a big “We know outdoors is the
question: Just how does the most spectacularly effec-
virus that causes COVID-19 tive measure, by far,’’ says
spread from one person to Jose-Luis Jimenez of the
another? University of Colorado-
It clearly hitchhikes on small This February 2018 photo provided by the University of Maryland School of Public Health shows The Boulder. “Outdoors it is not
liquid particles sprayed Gesundheit II machine in Dr. Donald Milton's Public Health Aerobiology, Virology, and Exhaled impossible to get infected,
out by an infected per- Biomarker Laboratory of the university in College Park, Md. Associated Press but it is difficult.”
son. People expel particles The various precautions
while coughing, sneezing, from inhaling them. Mea- The agency said the post- a rehearsal in Washington should be used in combi-
singing, shouting, talking sles can spread this way, ing was an error, and that state, 52 others who had nation rather than just one
and even breathing. But but the new coronavirus the statements were just a been seated throughout at a time, researchers say.
the drops come in a wide is far less contagious than draft of proposed changes the room were found to be In a well ventilated envi-
range of sizes, and scien- that. to its recommendations. infected and two died. In a ronment, “6 feet (of sepa-
tists are trying to pin down For these particles, called Dr. Jay Butler, CDC’s depu- crowded and poorly venti- ration) is pretty good if ev-
how risky the various kinds aerosols, “6 feet is not a ty director for infectious dis- lated restaurant in China in erybody’s got a mask on”
are. magic distance,’’ says ease, told The Associated January, the virus evidently and nobody stays directly
The answer affects what Linsey Marr, a leading re- Press that the agency con- spread from a lunchtime downwind of an infected
we should all be doing to searcher who is studying tinues to believe larger and patron to five people at person for very long, says
avoid getting sick. That’s them at Virginia Tech in heavier droplets that come two adjoining tables in a Dr. Donald Milton of the Uni-
why it was thrust into head- Blacksburg. But she says from coughing or sneezing pattern suggesting aerosols versity of Maryland School
lines a few days ago when it’s still important to keep are the primary means of were spread by the air con- of Public Health, whose lab
a U.S. health agency ap- one’s distance from oth- transmission. ditioner. Also in January, a houses the Gesundheit II
peared to have shifted its ers, “the farther the bet- Last month Butler told a sci- passenger on a Chinese machine.
position on the issue, but ter,” because aerosols are entific meeting that current bus apparently infected Duration of exposure is im-
later said it had published most concentrated near a research suggests aerosol 23 others, many of whom portant, so there’s prob-
new language in error. source and pose a bigger spreading of the coronavi- were scattered around the ably not much risk from a
The recommendation to risk at close range. rus is possible but it doesn’t vehicle. Butler said such short elevator ride while
stay at least 6 feet (2 me- Public health agencies seem to be the main way events raise concern about masked or being passed by
ters) apart — some authori- have generally focused that people get infect- aerosol spread but don’t a jogger on the sidewalk,
ties cite about half that dis- on the larger particles for ed. Further research may prove it happens. experts say.
tance — is based on the coronavirus. That prompt- change that conclusion, There could be another Scientists have published
idea that larger particles ed more than 200 other he added, and he urged way for tiny particles to online tools for calculating
fall to the ground before scientists to publish a plea scientists to study how of- spread. They may not nec- risk of airborne spread in
they can travel very far. in July to pay attention to ten aerosol spread of the essarily come directly from various settings.
They are like the droplets in the potential risk from aero- coronavirus occurs, what somebody’s mouth or nose, At a recent meeting on
a spritz of a window clean- sols. The World Health Or- situations make it more says William Ristenpart of aerosols, however, Dr.
er, and they can infect ganization, which had long likely and what reasonable the University of California, Georges Benjamin, execu-
somebody by landing on dismissed a danger from steps might prevent it. Davis. His research found tive director of the Ameri-
their nose, mouth or eyes, aerosols except in the case Marr said she thinks infec- that if paper tissues are can Public Health Associa-
or maybe being inhaled. of certain medical proce- tion by aerosols is “hap- seeded with influenza virus tion, noted that preventive
But some scientists are now dures, later said that aero- pening a lot more than and then crumpled, they steps can be a challenge
focusing on tinier particles, sol transmission of the coro- people initially were willing give off particles that bear in the real world. Keeping
the ones that spread more navirus can’t be ruled out to think.” the virus. So people emp- apart from other people
like cigarette smoke. Those in cases of infection within As a key piece of evidence, tying a wastebasket with can be difficult in homes
are carried by wisps of air crowded and poorly venti- Marr and others point to tissues discarded by some- that house multiple gener-
and even upward drafts lated indoor spaces. so-called “superspreader” body with COVID-19 should ations. Some old buildings
caused by the warmth of The issue drew attention re- events where one infected be sure to wear a mask, he have windows that were
our bodies. They can lin- cently when the U.S. Cen- person evidently passed said. Wearing a mask is still “nailed shut years ago,” he
ger in the air for minutes to ters for Disease Control and the virus to many others in important, and make sure said. And “we have far too
hours, spreading through- Prevention posted and a single setting. it fits snugly. Keep washing many communities where
out a room and build up if then deleted statements on In March, for example, after those hands diligently. And they simply don’t have ac-
ventilation is poor. its website that highlighted a choir member with coro- again, staying farther apart cess to clean water to wash
The potential risk comes the idea of aerosol spread. navirus symptoms attended is better than being closer their hands.”q