The novel coronavirus has new developments every day. It seems like Covid-19 spreading through coughing and sneezing is passé. A new study reveals that the virus can also apparently spread through merely talking and breathing.
According to a new study, talking can also launch thousands of droplets so small they can remain suspended in the air for eight to 14 minutes. The scientists said the virus can stay suspended in air in the ultrafine mist that is produced when people exhale.
The research, published in The Proceedings of the National Academy of Sciences, helps explain how people with mild or no symptoms may infect others in close quarters such as offices, nursing homes, cruise ships and other confined spaces.
Speech droplets generated by asymptomatic carriers of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are increasingly considered to be a likely mode of disease transmission. Highly sensitive laser light scattering observations have revealed that loud speech can emit thousands of oral fluid droplets per second.
In a closed, stagnant air environment, they disappear from the window of view with time constants in the range of 8 to 14 min, which corresponds to droplet nuclei of ca. 4 mm diameter, or 12- to 21-mm droplets prior to dehydration.
These observations confirm that there is a substantial probability that normal speaking causes airborne virus transmission in confined environments.
Scientists agree that the coronavirus jumps from person to person most often by hitching a ride inside tiny respiratory droplets. These droplets tend to fall to the ground within a few feet of the person who emits them.
They may land on surfaces like doorknobs, where people can touch lingering virus particles and transfer them to their face. But some droplets can remain aloft, and be inhaled by others.
To see how many droplets are produced during normal conversation, researchers at the National Institute of Diabetes and Digestive and Kidney Diseases and the University of Pennsylvania, who study the kinetics of biological molecules inside the human body, asked volunteers to repeat the words “stay healthy” several times.
While the participants spoke into the open end of a cardboard box, the researchers illuminated its inside with green lasers, and tracked bursts of droplets produced by the speaker.
The laser scans showed that about 2,600 small droplets were produced per second while talking. When researchers projected the amount and size of droplets produced at different volumes based on previous studies, they found that speaking louder could generate larger droplets, as well as greater quantities of them.
Although the scientists did not record speech droplets produced by people who were sick, previous studies have calculated exactly how much coronavirus genetic material can be found in oral fluids in the average patient.
Based on this knowledge, the researchers estimated that a single minute of loud speaking could generate at least 1,000 virus-containing droplets.
What researchers don’t yet know is whether all speech, cough and sneeze droplets carrying virus particles are equally infectious, or if a specific amount of virus needs to be transmitted for a person to get sick by breathing it in.