Men and people who speak at louder volumes more easily spread COVID-19, according to researchers at Colorado State University (CSU).
In a November study published in the journal Environmental Science and Technology Letters, a multidisciplinary team at the school examined respiratory aerosol emissions from a panel of healthy individuals of varying age and gender while talking and singing in a controlled laboratory setting.
The group measured particle number concentrations between 0.25 and 33 micrometers from 63 participants ages 12-61 years old, and voice volume and exhaled CO2 (carbon dioxide) levels were monitored.
Measurements were taken while subjects were both masked and unmasked inside the lab of professor and study co-author John Volckens.
Researchers concluded that singing produced 77% more aerosol than talking, adults produced 62% more aerosol than minors and males produced 34% more aerosol than females.
However, after accounting for participant voice volume and exhaled CO2 measurements in linear models, the age and sex differences were "attenuated and no longer statistically significant."
Results from wind instrument-playing experiments are pending further data analysis and peer review. The study was originally developed early on during the COVID-19 pandemic in an effort to determine what people in performing arts can do to safely return to the stage.
"Is singing worse than talking when it comes to how many particles are being emitted? Yes, according to the study. And, the louder one talks or sings, the worse the emissions," the university said in a news post on its website, detailing the study.
"If there were significant differences after accounting for CO2 between males and females and kids, then you’d have to know how many males, females, and minors were in a room to estimate transmission risks," Volckens said in a statement. "Our data suggest that you don’t need to know that if you just measure CO2 and noise levels, because those measures are an equalizer for these demographic differences."
Limitations include that controlled study designs – including the laboratory environment – may "lack generalizability" to real-world situations, other types of vocal activities were not considered, the group did not quantify respiratory disease transmission risk and that additional observation and research is necessary to characterize respiratory aerosol emissions during early childhood development.
Dan Goble, director of the CSU School of Music, Theatre and Dance, and colleagues raised nearly $100,000 in support of the study.
Goble said that working with the CSU engineers helped his team to better understand how visual and performing arts could reimplement their programming.
After going virtual in spring 2020, current performing arts protocols at CSU include the use of masks, restrictions on occupancy venue times, physical distancing of at least six feet for voice lessons and extra time between classes for performance rooms to undergo sufficient air exchanges between rehearsals.
The availability of COVID-19 vaccines – CSU has a 90% vaccination rate – has "changed the game," according to Goble.
"We are so fortunate to have experts like (Volckens) who gave us some really wonderful information to help us make decisions about what we can and can’t do in the (University Center for the Arts)," he said.
These results, study authors noted, support further investigation of voice volume and CO2 as indicators of infection risk indoors.