A study, conducted by a team from the University of Pennsylvania with the US National Institute of Health and published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS) said that speech droplets generated by asymptomatic carriers of COVID-19 are increasingly considered to be a likely mode of disease transmission.
Using the highly sensitive laser light scattering observations, they discovered that loud speech could emit thousands of droplets per second. In a closed, stagnant air environment, these droplets stay in the air with time constants between 8 minutes to 14 minutes.
These observations confirm that it is possible for normal speaking to cause airborne virus transmission in confined environments.
Visualizing Droplets Produced While Talking
It has long been recognized that respiratory viruses, such as the severe acute respiratory syndrome-2 (SARS-CoV-2), can be transmitted via droplets from coughing or sneezing. However, it is not commonly known if normal speaking also produces thousands of oral fluid droplets that can possibly infect other people.
The researchers used an intense sheet of laser light to visualize the droplets produced from a session of participants repeating phrases. This method revealed an average droplet emission rate of at least 1,000 particles with peak emission rates as high as 10,000 particles per minute, which is higher than previous reports.
The significant increase in the amount of the observed droplets is mainly accounted for by the high sensitivity of the light scattering method in observing medium-sized droplets that remain airborne for at least 30 seconds.
The researchers also suggest that it can stay in the air for longer than eight minutes and could reach up to 14 minutes. According to them, direct visualization demonstrates how normal speech generates airborne droplets that can remain suspended for minutes in the air are eminently capable of transmitting the disease in confined spaces.
The Centers for Disease Control and Prevention noted that these droplets could land on mouths or noses of people who are nearby, or it could also be inhaled to the lungs. This means that the spread is more likely to happen when people are within six feet of another person.
Can Masks Help?
The results of their observations raise serious concerns that the mere act of a COVID-19 infected person talking could dangerously transmit the coronavirus to other people. Moreover, the researchers wrote that some patients produce a more considerable amount of the virus than average, increasing the number of viruses in the droplets for up to 100,000 per minute of speech.
But the most significant implication of this study is to reinforce wearing masks under any circumstances, especially when leaving the house to avoid possible transmission.
Face masks should be perfectly fitted to your face for complete protection from germs and other contaminants because the loose fit between the mask and the face will not give you any protection, said the US FDA.
Since medical supplies are only limited, a "do-it-yourself" masks can help block large droplets, splashes or sprays that may contain germs or viruses.