Coughs or sneezes may not be the only way people transmit infectious pathogens like the coronavirus to one another. Talking can also propel thousands of droplets so small they can remain suspended in the air for eight to 14 minutes, according to a new study.
The research, published Wednesday in the Proceedings of the National Academy of Sciences, could help 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.
The study’s experimental conditions would need to be replicated in more real-world circumstances, and researchers still don’t know how much virus has to be transmitted from one person to another to cause infection. But its findings strengthen the case for wearing masks and taking other precautions to reduce the spread of the virus.
To see how many droplets were 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.
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 viral 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.