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Air Conditioning May Be Spreading COVID
By Brenda
Goodman, MA
As COVID-19 cases rise rapidly
throughout the South, some scientists believe there could be an important, but
overlooked factor in the spread of the virus in the region -- air conditioning.
Just as chilly winter temps create the
perfect conditions for passing colds and
flu — driving people indoors and into closer proximity for more hours of the
day where it’s easy to swap germs, researchers believe broiling heat in the
southern U.S. could be having the same effect, sending people indoors where
whirring air conditioners are running full blast.
“You go indoors for
the cool, just as in the northeast and other cool places you go in for the
warmth in winter, so you’re less socially distanced,” says Edward Nardell,
MD, professor of environmental health and immunology and infectious diseases at
Harvard’s T.H. Chan School of Public Health.
“You’re more likely
to be touching the same surfaces that have been contaminated by people speaking
and coughing etc.,”
he says.
And that’s not the only problem.
Air conditioning is also risky because
of the way air handlers work. When outdoor temperatures are extreme, HVAC
systems adjust the mix of fresh air they pull in to save energy.
That means the hotter
it is outside, the more indoor air recirculates, which means, “You’re
breathing a higher percentage of the same air that other people are exhaling,” Nardell
says.
If someone in the building is
shedding the new coronavirus, it can build up in the
recirculated air.
And this may seem obvious, but air
conditioners have fans that blow the air around.
That gives the smallest viral particles
— aerosols -- extra lift to say suspended in the air for longer.
“The air currents
that are produced by air conditioners and also fans and other air moving
devices can carry particles further than they might otherwise go,” he says.
Air conditioners also
remove moisture from the air, “and we know viruses prefer dry air,” he
says.
In certain situations, that combination
of factors may create the perfect conditions for contagion.
Emerging
Evidence Points To Airborne Transmission
Studies of air conditioning come as
more evidence emerges about airborne spread of COVID-19.
In a commentary published this week in the journal
Clinical Infectious Diseases, an international group of 239 scientists have
appealed to “national and international bodies” including the World Health
Organization, to recognize this potential for airborne spread.
“We’re pushing
because we need very clear, consistent messaging to the world,” said Shelly Miller,
PhD, a professor of mechanical engineering who studies indoor air quality at
the University of Colorado at Boulder.
Miller was one of the chief proponents
of the commentary.
“This virus is
opportunistically airborne, you can get it by inhaling it,” she says.
Miller and others believe that WHO and
other public health agencies have a blind spot when it comes to airborne
transmission.
“Based on our
assessments of outbreaks, air sampling, and animal studies and we have just as
much evidence to show that airborne transmission is happening as is surface
transmission, so we need clear guidance for how to address this,” Miller says.
In its latest press briefing, WHO
experts responded to the communication, and said the agency would be publishing
a scientific brief summarizing their view of the science shortly.
“We acknowledge that
there is emerging evidence in this field,” said Benedetta Allegranzi, MD, WHO’s
technical lead for infection prevention and control.
“We believe we have to be open to this
evidence and understand its implications regarding the modes of transmission
and the precautions that need to be taken,” she said.
The
Role of Air Conditioning
So far, there are just a few studies
pointing to the role of air conditioning in the spread of COVID-19. They
indicate more research in the area is needed.
In July, Chinese scientists published
a short study detailing the results of
their investigation of a cluster of COVID-19 cases linked to the same
restaurant.
The 10 diners who fell ill were all
sitting at tables on the same side of the room.
The tables were spaced more than 3 feet
apart, though, indicating that the virus probably wasn’t being passed through
larger droplets, which fall out of the air pretty quickly.
Instead, they think “strong airflow” from
a wall mounted air conditioner probably spread aerosols, or “micro-droplets”,
from a single infected, but asymptomatic person over the tables, infecting
three different families.
In another study, which hasn’t yet been
peer reviewed, researchers swabbed three different HVAC units at the Oregon
Health and Science University Hospital in Portland.
Then they checked their samples for the
presence of genetic material from the SARS-CoV-2
virus. The swabs were positive in 1 out of every 4 samples taken.
“We found it in
multiple locations within the air handler,” says study author Kevin Van Den
Wymelenberg, PhD, a professor of architecture and director of the Institute for
Health in the Built Environment at the University of Oregon in Eugene.
A similar study, from the University of Nebraska
Medical Center, detected genetic material from the virus in air samples
collected from rooms of COVID-19 patients, even air samples collected from more
than six feet away.
Van Den Wymelenberg says their study
can’t prove that the remnants of the virus they picked up could have actually
infected anyone.
To know that, they would have had to
try to grow their samples alongside cells in a petri dish and watch to see if
those cells were infected.
Those are expensive studies to perform
and they require a specialized lab certified to handle highly contagious germs —
called a biosafety level 3 lab.
Those are less common, and they’re all
currently slammed with projects.
But he says his study does show
that genetic material from the virus is making it into the machinery
of massive air handlers in hospitals, even ones that are using good filters,
and he thinks that should make public health experts closely consider air
conditioning as a vehicle for virus spread.
Steps
for Safer Indoor Air
Miller says that the easiest thing to
keep the virus from building up inside is to bring in more outdoor air.
In homes, that means opening windows
and doors regularly to let fresh air in.
That’s harder to do in commercial
buildings.
“What we’ve been
recommending to minimize risk indoors is to provide 100% outside air, which you
can’t do if you’re trying to heat or cool because it just costs way too much
money,”
she said.
Another strategy to reduce the risk of
being indoors is to kill airborne viruses with special wall or ceiling mounted
boxes that emit short-range UV radiation.
This kind of UV light doesn’t damage
skin the way sunlight does, but still zaps harmful germs.
These so-called upper-room germicidal
systems have successfully controlled outbreaks of other airborne pathogens,
like tuberculosis, Nardell says.
Finally, you can invest in an air cleaner.
Miller cautions that if you go this
route, you need to do a fair amount of homework first, learning about things
like a machine’s clean air delivery rate, or CADR.
“I purchased an air
cleaner strictly to operate when and if somebody in my household gets sick so
we can reduce the viral load in my house air,” she says.
Ionizing cleaners don’t work, she says.
Miller recommends checking the website
of the Association of Home Appliance Manufacturers, or AHAM to find a good air
cleaner.
“They have a whole website set
up to do your research and buy a good air cleaner that will work in your home
or office,”
she says.
Brenda
Goodman,
MA, is a staff writer for WebMD. Her work has appeared in The New
York Times, Scientific American, Psychology Today, The Boston Globe, Self,
Shape, Parade, U.S. News and World Report, and Atlanta Magazine. She has a
master’s degree in science and environmental reporting from New York
University.
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