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Penn Medicine researchers found that normal speaking in confined environments may lead to airborne transmission of the coronavirus. Credit: Sukhmani Kaur

A recent study conducted by Penn researchers found that respiratory droplets from human speech can remain in the air for over eight minutes. Researchers say this may explain why coronavirus outbreaks occur in confined spaces.

In conjunction with the National Institute of Diabetes and Digestive and Kidney Diseases, the researchers studied how people generate respiratory droplets through various sound levels of human speech, The Philadelphia Inquirer reported. The study concluded that there is a “substantial probability” normal speaking causes airborne virus transmission in confined environments. 

The experiment used highly sensitive laser light in a closed-air environment, and focused on small droplets that linger in the air longer than larger droplets, The Inquirer reported. The researchers found that respiratory speech droplets only began to disappear from the air after a range of eight to 14 minutes. 

Researchers also found the speaker’s volume affects the number of droplets. The study found louder speech produces more droplets, estimating that one minute of "loud speaking" emits thousands of droplets, The Inquirer reported. 

Other factors, such as dehydration and age, also affect the velocity of the droplets and how long the droplets stay in the air, according to The Inquirer.

The new findings may explain why coronavirus infections often occur in enclosed spaces with little air circulation, such as in nursing homes, which have been sites of outbreaks in the larger Philadelphia area. 

In a study conducted at the Hospital of the University of Pennsylvania last month, Penn researchers developed a coronavirus antibody test to determine the infection rate among healthcare workers. This week, the Wistar Institute's coronavirus vaccine showed signs of eliciting an immune response in animals.