Some people may even be more likely to spread the virus this way than others.

By Maggie O'Neill
May 26, 2020
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It's true: The coronavirus spreads mainly through person-to-person contact via respiratory droplets—tiny emissions produced by infected people when they cough, sneeze, or talk. The link to coughing and sneezing is obvious (those who are ill often cough and sneeze) but speech seems much less suspicious—or at least it did until it was at the forefront of a recent report by the Centers for Disease Control and Prevention.

In a Morbidity and Mortality Weekly Report published May 12, the CDC investigated a specific COVID-19 outbreak in Washington state resulting from a choir practice. The choir practice in question—a 2.5 hour event held on March 10 in Skagitt County, Washington—was attended by 61 individuals, including one symptomatic patient. In the days following, 53 more people—or 87% of the group—were identified as having COVID-19, including 33 confirmed and 20 probable cases.

The CDC report goes on to say that the transmission of COVID-19 at the choir practice was "likely facilitated by close proximity...and augmented by the act of singing." And while the evidence is clear that the act of singing can help promote the spread of COVID-19, what's less clear is how this translates to the risk of COVID-19 in the average person (read: one not involved in a choir) during a conversation.

Can talking spread COVID-19?

In the simplest of terms, yes. In a new correspondence published May 21 in the New England Journal of Medicine, researchers from the National Institutes of Health and the Perelman School of Medicine at the University of Pennsylvania wrote that the act of speaking generates droplets that vary in size. Larger droplets pose less of a risk, since they "fall quickly to the ground," according to the researchers, but smaller ones can dehydrate and linger in the air, essentially acting like an aerosol. This "expand[s] the spatial extent of emitted infectious particles," the authors said.

The authors used a "laser light-scattering experiment" to see the trajectories of speech-generated droplets after participants said the phrase "stay healthy." The volunteers spoke into a large cardboard box, painted black inside. When the person spoke, a green laser, which emitted a sheet of light about three inches from the open end of the box, "caught" the emitted droplets. The researchers were able to estimate the droplets' size as they passed through the laser, producing flashes of light.

While the study didn't specifically track droplets infected with COVID-19, nor did they track how far droplets from speech can travel in other environments, the study showed that "numerous [aerosol] droplets…were generated" via talking. In another correspondence accompanying the study, Matthew Meselson, PhD, a geneticist and molecular biologist at Harvard University, said the findings suggest the importance of "wearing a suitable mask whenever it is thought that infected persons may be nearby and of providing adequate ventilation of enclosed spaces where such persons are known to be or may recently have been."

It's important to keep in mind, too, that the six-foot social distancing requirements are also protective against any droplets emitted by talking. "If you’re six feet apart, it provides that buffer,” Waleed Javaid, MD, director of infection prevention and control at Mount Sinai Downtown in New York City, tells Health.

What about talking loudly? Does that increase the spread of COVID-19?

That's also a yes—the CDC even specifically calls out loud talking as a possible vector for COVID-19. "Aerosol emission during speech has been correlated with loudness of vocalization," the CDC wrote in their report.

But this isn't the first time loud speech has been connected to an easier spread of droplets: Research from the Proceedings of the National Academy of Sciences of the United States of America found that another experiment using laser light "revealed that loud speech can emit thousands of oral fluid droplets per second." The report, published May 13, confirms that "the total volume of droplet count increase with loudness."

But the study didn't just find the presence of droplets emitted from talking—researchers also found that those droplets were so small that they could remain suspended in the air for up to 14 minutes. The combination of speech emission of small droplets and their ability to stay suspended in the air (in a controlled environment) in an enclosed space for a certain amount of time may explain how COVID-19 can quickly spread in confined spaces with people showing no or very mild symptoms.

Is there anything else I need to know about how talking can spread COVID-19?

Yes: In the CDC's May 12 report, the agency also calls out the role a "superemitter" may have played in the transmission of COVID-19 among choir members.

Superemitters (aka super-spreaders), may have a higher possibility of transmitting viruses (in this case, the coronavirus) to anyone they come into contact with. "Certain persons, known as superemitters, who release more aerosol particles during speech than do their peers, might have contributed to this and previously reported COVID-19 superspreading events," the CDC said.

Superemitters can be dangerous anytime groups of people are meeting, no matter where they’re meeting or what they’re doing, according to Kristin Englund, MD, an infectious disease specialist at Cleveland Clinic. People can transmit from one to 50 particles of COVID-19 each second, and superemitters usually fall on the higher end of that spectrum, she says. “A superemitter would be somebody who is able to produce more particles per second of virus,” Dr. Englund says. Doctors don’t know why some people emit more particles per second and, thus, are superemitters. “It highlights the fact we can’t always tell who is able to spread the virus,” Dr. Englund says.

This is all compelling evidence as to why it’s important to continue not only social distancing but also mask wearing when you’re out in public. “If everybody’s wearing a mask, it reduces that transmission between people,” Purvi Parikh, MD, pediatric allergist and immunologist at NYU Langone Health, tells Health. And that reduction is no small thing: If everyone wears a mask we can cut transmission down by about 70 percent, she adds.

So while the chances of you spreading or contracting COVID-19 via talking are minimal, it’s certainly not worth the risk to head to the supermarket without a mask just yet.

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.

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