Ahead of a prospective second wave of COVID-19 outbreaks, Ladders decided to review the risk assessments published thus far by medical experts.
Given the majority of new cases are driven by pre-symptomatic carriers, it stands to reason that speech would be a viable means of person-to-person transmission. Recently, a new paper published in the New England Journal of Medicine determined the severity of this estimation. It found that droplets produced during only one minute of loud speech by an individual infected with SARS-CoV-2 virus could contain more than 1000 virus particles.
“The act of speaking generates oral fluid droplets that vary widely in size, and these droplets can harbor infectious virus particles,” the authors wrote. “Whereas large droplets fall quickly to the ground, small droplets can dehydrate and linger as droplet nuclei in the air, where they behave like an aerosol and thereby expand the spatial extent of emitted infectious particles. We report the results of a laser light-scattering experiment in which speech-generated droplets and their trajectories were visualized.”
Participants involved in the paper were directed to say the phrase “stay healthy” into a large cardboard box, painted black inside. With the help of a green laser, the authors were able to analyze the size and trajectories of speech-generated droplets emitted from this piece of dialogue alone.
According to the research, numerous aerosol droplets were detected by the laser-light scattering technology. Particularly loud speech appears to emit thousands of oral fluid droplets per second.
“We found that the number of flashes increased with the loudness of speech; this finding was consistent with previous observations by other investigators. In one study, droplets emitted during the speech were smaller than those emitted during coughing or sneezing. Some studies have shown that the number of droplets produced by speaking is similar to the number produced by coughing.”
Speech-Generated Coronavirus droplets
“Wearing a suitable mask whenever it is thought that infected persons may be nearby and of providing adequate ventilation of enclosed spaces where such persons are known to be or may recently have been,” the report continued.
Independently conducted research defines coronavirus super emitters as individuals who produce 10 times as many virions compared to the average infected individual via speech.
Although the study neither measured the length of time infected speech droplets remain active or the length of time that they’re able to travel from their host, we can rely on a collection of papers published in the last few months to animate a hypothesis.
We know that the average SARS-CoV-2 virion is small—with an average diameter of 0.1 micrometers.
“Long ago it was established that ordinary breathing and speech both emit large quantities of aerosol particles. These expiratory particles are typically about one micron in diameter, and thus invisible to the naked eye; most people unfamiliar with aerosols are completely unaware that they exist,” researchers wrote in a recent study published in the journal Aerosol Science and Technology. “The particles are sufficiently large, however, to carry viruses such as SARS-CoV-2, and they are also in the correct size range to be readily inhaled deep into the respiratory tract of a susceptible individual.”
We also know that vIral debris can they remain active for at least three hours while airborne
A series of papers released around the same time as the report above determined that coronavirus-bearing droplets of all sizes can actually travel 23 to 27 feet from their host after emission.
Still, more research needs to be conducted to rank speech among the known person-to-person routes of transmission.
“Although we argue here that speech plausibly serves as an important and under-recognized transmission mechanism for COVID-19, it is up to aerosol scientists to provide the technology and hard data to either corroborate or reject that hypothesis. In terms of technology, improved bioaerosol sampling technology is necessary; the authors of a recent study concluded.”The stakes for the world are enormous. The aerosol science community needs to step up and tackle the current challenge presented by COVID-19, and also help better prepare us for inevitable future pandemics.”
CW Headley is a reporter for the Ladders and can be reached at firstname.lastname@example.org.