Aerosol microdroplets ineffective at spreading coronavirus: Study

Aerosol microdroplets, which are tiny particles that linger in the air longest after we talk, cough, or sneeze, may be ineffective at spreading the virus that leads to COVID-19, according to a new study.

The results of the modelling study, published in the journal Physics of Fluids, noted that aerosol transmission of the novel coronavirus SARS-CoV-2 in confined spaces is not very efficient.

"If someone enters a space even a few minutes after a mildly symptomatic carrier of the coronavirus has coughed in that area, the probability of infection is rather low," the researchers, including those from the University of Amsterdam in The Netherlands, noted in a statement.

It is even lower if that person was only talking, they added.

"Our study of the transmission of SARS-CoV-2 suggests that aerosol transmission is a possible but perhaps not a very efficient route, in particular from non-symptomatic or mildly symptomatic individuals that exhibit low viral loads," the study noted.

In the research, the scientists used laser technology to measure the distribution of droplets released when people speak or cough.

Test subjects spoke or coughed into a laser beam, and a jet nozzle was used to mimic tiny aerosol microdroplets, the researchers said.

Using this setup, the scientists measured how droplets spread and how likely they are to pass along SARS-CoV-2.

While the lingering microdroplets are certainly not risk-free, due to their small size they contain less virus than the larger droplets that are produced when someone coughs, speaks or sneezes directly on us, said Daniel Bonn, a co-author of the study from the University of Amsterdam.

"Based on the current insights, we actually see that aerosol-wise, it's relatively safe to go into well-ventilated modern buildings, such as airports, train stations, modern offices, etc.," Bonn said.

"Modern ventilation makes the aerosol infection risk not very large. The amount of virus in the small droplets is relatively small, meaning that it becomes dangerous if you're in a badly ventilated room for a relatively long time with an infected person or after an infected person has coughed there," he added.

According to the study, the highest probability of infection occurs when a person enters a poorly ventilated and small space where a high emitter has just coughed and inhales virus-carrying droplets.

The findings, according to the researchers, support the efficacy of wearing masks, social distancing, and other measures targeting the spread of larger droplets.

"They are so large that they fall onto the ground roughly within a metre from your mouth," Bonn said.

"If you want to minimize the risk of infection, you need to not only keep the 6 feet, or 1.5 metres, but also make sure the room you are in is well ventilated. And wash your hands," he added.

However, the scientists cautioned that highly infected people having large quantities of the virus in their saliva, and superspreaders producing lots of aerosols are likely far more dangerous.

Citing a limitation of the study, the scientists said they could not account for the viability of the virus particles inside microdroplets.

They said the infectivity of the virus particles depends on the local microenvironment of the aerosol gas clouds as produced under different circumstances.

"Our small non-ventilated room can be looked upon as a "worst-case": in better ventilated, large rooms, aerosols become diluted very rapidly," they wrote in the study.