A recent study by researchers at the National Institutes of Health has found that particles of the coronavirus released by talking can remain in the air for 8 to 14 minutes, a warning sign that airborne transmission may be even more widespread than previously thought.
While it's been long accepted that coughing and sneezing can transmit respiratory viruses through droplets, it's less known that just regular talking produces thousands of oral fluid droplets, the scientists behind the study said.
"There is a substantial probability that normal speaking causes airborne virus transmission in confined environments," the research, published in last week's edition of the peer-reviewed Proceedings of the National Academy of Sciences, concluded.
"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," the study, entitled "The airborne lifetime of small speech droplets and their potential importance in SARS-CoV-2 transmission," found.
And loud talkers present a bigger risk: "Highly sensitive laser light scattering observations have revealed that loud speech can emit thousands of oral fluid droplets per second," it said.
While Covid-19 is less deadly than SARS, it is far more easily transmitted, and scientists are still working to understand the extent to which it can be spread and how long it can survive. That data has huge ramifications for how we interact with one another and what kinds of spaces and activities are considered safe.
The researchers used a closed, stagnant-air environment, and found that the droplets stop being visible after 8 minutes to 14 minutes, which they say "corresponds to droplet nuclei of ca. 4um (micrometers) diameter, or 12um to 21um droplets prior to dehydration." One um, or micrometer, equals one millionth of a meter. The coronavirus is even tinier than that — a mind-bendingly small 0.125 um.
The velocity and length of time droplets stay in the air are also dependent on a range of factors, including the volume at which the speaker is talking, their age, and how dry their mouth is.
"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," the study found. "Highly sensitive laser light scattering observations have revealed that loud speech can emit thousands of oral fluid droplets per second."
Public transport and rooms with poor ventilation are considered high-risk areas for this kind of transmission. Scientific studies continue to produce new and sometimes varying findings on the fast-spreading coronavirus — scientists at Princeton University, UCLA and the National Institutes of Health reported in the New England Journal of Medicine that the virus could survive for up to three hours in the air "post aerosolization."
And a team of researchers at the Academy of Military Medical Sciences in Beijing found that droplets can travel as far as 13 feet, meaning that many governments' social-distancing recommendations of six feet may not be enough. Numerous variables can affect this, including air temperature and humidity.
States are grappling with this information as they try to balance reopening their economies after months of lockdown with ensuring the safety of their populations. The respiratory virus has infected more than 4.8 million people worldwide and killed more than 300,000.
Funding for the National Institutes of Health is primarily provided by the the annual Departments of Labor, Health and Human Services, and Education, and Related Agencies Appropriations Act.