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CDC Officially Acknowledges Airborne Transmission of Coronavirus

Health + Wellness
CDC Officially Acknowledges Airborne Transmission of Coronavirus
The CDC has acknowledged that the coronavirus can spread via airborne transmission, especially in poorly ventilated spaces. avdeev007 / E+ / Getty Images

The Centers for Disease Control and Prevention (CDC) has officially acknowledged that the new coronavirus can be spread via airborne transmission.


"Today, CDC issued updated guidance to its How COVID-19 Spreads website, which includes information about the potential for airborne spread of the virus that causes COVID-19," the agency wrote Monday in a press release.

By doing so, the CDC is finally catching up with what many health experts have been warning for months, NPR pointed out. The World Health Organization acknowledged airborne transmission in July after 239 scientists wrote a letter urging the organization to take airborne spread seriously. The U.S. agency seemed ready to accept airborne transmission last month, when it posted guidance saying that COVID-19 was most commonly spread "through respiratory droplets or small particles, such as those in aerosols," as CBS News reported at the time. However, it quickly removed the update, saying it was draft language posted in error.

Monday's updated guidance admits to airborne transmission once again, but says it is not the most common way the coronavirus spreads.

"CDC continues to believe, based on current science, that people are more likely to become infected the longer and closer they are to a person with COVID-19," the agency wrote in the press release announcing the change. "Today's update acknowledges the existence of some published reports showing limited, uncommon circumstances where people with COVID-19 infected others who were more than 6 feet away or shortly after the COVID-19-positive person left an area. In these instances, transmission occurred in poorly ventilated and enclosed spaces that often involved activities that caused heavier breathing, like singing or exercise. Such environments and activities may contribute to the buildup of virus-carrying particles."

In the updated guidance, the CDC compared the airborne transmission of COVID-19 to the spread of other diseases like tuberculosis and chicken pox.

Outside scientists were pleased with the change.

"It's gratifying to see CDC acknowledge that there's a role for airborne transmission with this virus," University of Maryland aerobiologist Donald Milton told NPR.

Milton co-wrote a letter in Science Monday urging clearer public health communication around airborne transmission of the new coronavirus. Unlike the CDC, Milton and his colleagues think that COVID-19 is primarily airborne, even when spread between people in close contact with one another.

In the letter, they differentiate between virus spread via droplets, which are larger and tend to fall to the ground, and virus spread via aerosols, which are smaller and remain aloft.

"Individuals with COVID-19, many of whom have no symptoms, release thousands of virus-laden aerosols and far fewer droplets when breathing and talking. Thus, one is far more likely to inhale aerosols than be sprayed by a droplet, and so the balance of attention must be shifted to protecting against airborne transmission," they wrote. "In addition to existing mandates of mask-wearing, social distancing, and hygiene efforts, we urge public health officials to add clear guidance about the importance of moving activities outdoors, improving indoor air using ventilation and filtration, and improving protection for high-risk workers."

In its list of preventative measures, the CDC does call for avoiding crowded indoor spaces and making sure indoor spaces are properly ventilated, as well as for spending time outdoors or in well-ventilated spaces as much as possible.

The CDC also recommends staying six feet apart from others, wearing masks, washing hands and surfaces frequently and self-isolating if sick.

A net-casting ogre-faced spider. CBG Photography Group, Centre for Biodiversity Genomics / CC BY-SA 3.0

Just in time for Halloween, scientists at Cornell University have published some frightening research, especially if you're an insect!

The ghoulishly named ogre-faced spider can "hear" with its legs and use that ability to catch insects flying behind it, the study published in Current Biology Thursday concluded.

"Spiders are sensitive to airborne sound," Cornell professor emeritus Dr. Charles Walcott, who was not involved with the study, told the Cornell Chronicle. "That's the big message really."

The net-casting, ogre-faced spider (Deinopis spinosa) has a unique hunting strategy, as study coauthor Cornell University postdoctoral researcher Jay Stafstrom explained in a video.

They hunt only at night using a special kind of web: an A-shaped frame made from non-sticky silk that supports a fuzzy rectangle that they hold with their front forelegs and use to trap prey.

They do this in two ways. In a maneuver called a "forward strike," they pounce down on prey moving beneath them on the ground. This is enabled by their large eyes — the biggest of any spider. These eyes give them 2,000 times the night vision that we have, Science explained.

But the spiders can also perform a move called the "backward strike," Stafstrom explained, in which they reach their legs behind them and catch insects flying through the air.

"So here comes a flying bug and somehow the spider gets information on the sound direction and its distance. The spiders time the 200-millisecond leap if the fly is within its capture zone – much like an over-the-shoulder catch. The spider gets its prey. They're accurate," coauthor Ronald Hoy, the D & D Joslovitz Merksamer Professor in the Department of Neurobiology and Behavior in the College of Arts and Sciences, told the Cornell Chronicle.

What the researchers wanted to understand was how the spiders could tell what was moving behind them when they have no ears.

It isn't a question of peripheral vision. In a 2016 study, the same team blindfolded the spiders and sent them out to hunt, Science explained. This prevented the spiders from making their forward strikes, but they were still able to catch prey using the backwards strike. The researchers thought the spiders were "hearing" their prey with the sensors on the tips of their legs. All spiders have these sensors, but scientists had previously thought they were only able to detect vibrations through surfaces, not sounds in the air.

To test how well the ogre-faced spiders could actually hear, the researchers conducted a two-part experiment.

First, they inserted electrodes into removed spider legs and into the brains of intact spiders. They put the spiders and the legs into a vibration-proof booth and played sounds from two meters (approximately 6.5 feet) away. The spiders and the legs responded to sounds from 100 hertz to 10,000 hertz.

Next, they played the five sounds that had triggered the biggest response to 25 spiders in the wild and 51 spiders in the lab. More than half the spiders did the "backward strike" move when they heard sounds that have a lower frequency similar to insect wing beats. When the higher frequency sounds were played, the spiders did not move. This suggests the higher frequencies may mimic the sounds of predators like birds.

University of Cincinnati spider behavioral ecologist George Uetz told Science that the results were a "surprise" that indicated science has much to learn about spiders as a whole. Because all spiders have these receptors on their legs, it is possible that all spiders can hear. This theory was first put forward by Walcott 60 years ago, but was dismissed at the time, according to the Cornell Chronicle. But studies of other spiders have turned up further evidence since. A 2016 study found that a kind of jumping spider can pick up sonic vibrations in the air.

"We don't know diddly about spiders," Uetz told Science. "They are much more complex than people ever thought they were."

Learning more provides scientists with an opportunity to study their sensory abilities in order to improve technology like bio-sensors, directional microphones and visual processing algorithms, Stafstrom told CNN.

Hoy agreed.

"The point is any understudied, underappreciated group has fascinating lives, even a yucky spider, and we can learn something from it," he told CNN.

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