How Talking Spreads COVID-19

One of the three main ways COVID-19 spreads is via respiratory droplets—tiny emissions produced by infected people when they cough, sneeze, talk, sing, and even breathe. The link to coughing and sneezing was obvious (those who are ill often cough and sneeze) to researchers, but speech and singing seemed much less suspicious—that is, until May 2020, when it was at the forefront of a report by the Centers for Disease Control and Prevention (CDC).

In a Morbidity and Mortality Weekly Report published on May 15, 2020, 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 that same year in Skagit 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 went 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." That March night was one of the first pieces of evidence that made researchers realize that airborne transmission of COVID-19 was possible.

Can Talking Spread COVID-19?

In the simplest of terms, yes. In a correspondence published May 21, 2020, 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," said the authors.

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 it 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 suggested 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."

What About Talking Loudly? Does That Increase the Spread of COVID-19?

That's also a yes—even back in their May 2020 choir practice report, the CDC specifically called out loud talking as a possible vector for COVID-19. "Aerosol emission during speech has been correlated with loudness of vocalization," wrote the CDC in their choir practice report.

More studies confirming this followed. In March 2022, a study published in Journal of Exposure Science & Environmental Epidemiology discussed the results of an experiment that had people sustain the sound /a/. The study showed that both loudness and pitch contributed to the emission of more aerosol particles.

These particles are small enough to stay in the air as an aerosol for minutes and even hours, and they can travel long distances.

The combination of speech emission of small droplets and their ability to stay suspended in the air in an enclosed space for a certain amount of time can explain how COVID-19 can quickly spread in confined spaces with people who are infected, symptomatic or not.

Is There Anything Else I Need To Know About How Talking Can Spread COVID-19?

Yes: In the CDC's May 15, 2020, report, the agency also called out the role a "superemitter" may have played in the transmission of COVID-19 among choir members.

Superemitters, who are (fortunately) statistical outliers, may have a higher possibility of transmitting viruses to anyone they come into contact with. When superemitters are infected with a virus, they unknowingly become superspreaders.

"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," said the CDC.

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, said Dr. Englud. "A superemitter would be somebody who is able to produce more particles per second of [the] virus," said Dr. Englund.

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," said Dr. Englund.

The May 2020 CDC report was compelling evidence as to why it was important to stop gathering in large groups, physically distance, and wear masks.

"If everybody's wearing a mask, it reduces that transmission between people," Purvi Parikh, MD, pediatric allergist and immunologist at NYU Langone Health, told Health. And that reduction is no small thing: For example, a January 2022 study from Johnson County, Iowa, published in Emerging Infectious Diseases, showed that if both people wear masks and one is infected, the risk of infection for the other is reduced by a half.

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.