"The airborne lifetime of small speech droplets and their potential importance in SARS-CoV-2 transmission" report by The University of Pennsylvania and the National Institutes of Health was published this week in the journal 'Proceedings of the National Academy of Sciences.'
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While the experiment did not specifically involve COVID-19 or any other virus, researchers used a laser light to examine the number of small respiratory droplets produced from human speech.
The Centers for Disease Control and Prevention has said a person can get coronavirus from respiratory droplets when an infected person coughs, sneezes, or talks. Or as the study said, "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."
Researchers found that talking loudly for one minute in a confined space could generate at least 1,000 speech droplets. And if someone were to inhale them, it could potentially trigger new infections.
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The experiment involved a person repeating the phrase "stay healthy" in a closed environment for 25 seconds.
This specific phrase was chosen because "the 'th' phonation in the word 'healthy' was found to be an efficient generator of oral fluid speech droplets," researchers said.
The report found, "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."
Researchers also released video of the droplets showing the results of their experiment.
The report concluded, "This direct visualization 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 CDC has recommended wearing cloth face coverings where other social distancing measures are difficult to maintain.