Coronavirus-carrying air droplets may survive in a confined space more than eight minutes after an infected person has stopped talking in it, a US study has found.
The researchers from Stanford University warned their findings may suggest COVID-19 could spread more easily when people talk to each other in confined spaces, like inside a small room or a car.
Their study was conducted in a very small space and did not demonstrate transmission of the virus, only that air droplets emitted when speaking could remain in the air for eight minutes or longer.
When people speak, we unknowingly produce thousands of oral fluid droplets per second.
Given the coronavirus is a respiratory disease, it is possible some of these little droplets could be carrying pathogens such as SARS-CoV-2, which causes the coronavirus.
The World Health Organisation has been urging everyone to wash their hands frequently, and to practise ‘cough etiquette’ by coughing into elbows rather than hands to try to limit the virus’s spread.
But it’s not just coughing or sneezing we need to worry about, according to the American study.
It’s talking in a small space, too.
The study also suggests we could unknowingly be breathing in coronavirus-carrying air droplets if we enter a confined space minutes after an infected person has left it.
As part of the study, the researchers used laser light scattering to examine the tiny droplets that can linger in the air for minutes after exiting someone’s mouth.
They reported that one minute of loud speaking could generate more than 1000 virus-containing droplets that would remain airborne for eight minutes or longer.
“Our laser light scattering method not only provides real-time visual evidence for speech droplet emission, but also assesses their airborne lifetime,” the researchers said.
“This direct visualisation demonstrates how normal speech generates airborne droplets that can remain suspended for tens of minutes or longer and are eminently capable of transmitting disease in confined spaces.”
The results suggested that speaking normally in enclosed environments may carry a significant risk of COVID-19 transmission.
The researchers also noted that temperature, humidity and air flows all influenced how long droplets could remain airborne.