A recent study spearheaded by scientists from the University of Texas at San Antonio has found staying 6 feet apart outdoors might not be enough on its own to protect against the coronavirus.
The study, published in September, was led by UTSA associate professor of mechanical engineering Kiran Bhaganagar. Bhaganagar’s research found that in low-wind conditions coronavirus aerosol particles can spread from 1 to 2 kilometers, or a little over a mile, and can survive up to 30 minutes.
Focusing on New York City, the study took into account March and April weather conditions and how the virus could have potentially spread during its earliest months within the U.S. Using computer modeling, Bhaganagar and her team of students created a real-time, high-fidelity simulation of a virus-filled cough as it was released into the atmosphere from an infected person.
“We have confidence that we have enough background information, which was good enough to go ahead and introduce these particles and then predict their dispersion,” Bhaganagar told the San Antonio Report.
Depending on the time of the day and the wind direction, the direction of spread was either toward Massachusetts, toward New Jersey, or toward southern New York, UTSA said in a press release.
When someone with COVID-19 coughs or sneezes, respiratory droplets that contain infectious particles are released into the air, UTSA said. The simulations found that combinations of warmer or wetter weather conditions favor the spread of the virus.
A person spreading COVID-19 disperses thousands of viral particles in a cough or sneeze, at a much higher concentration than the common cold or flu, Bhaganagar said.
The rate at which the virus spread proves aerosol transmission definitely took place, she added, noting it spread too fast to just be from non-aerosol transmission like touching. This is why indoor events like football games at the Alamodome, or other indoor events are still not safe yet despite the 6-feet-apart rule, she said.
Hypothetically, there could be risk of infection if someone walks through aerosol particles within 30 minutes of a cough or sneeze, for example. Bhaganagar said that would help explain the wildfire-like spread of the coronavirus in the New York City metropolitan area during the spring.
Dr. Fred Campbell, an internal medicine physician in the Long School of Medicine at UT Health San Antonio, said while infection is technically possible at such a distance, it’s highly unlikely.
“It appears that the greater distance away from the source, the lower number of viral particles [a person is exposed to],” Campbell said.
Campbell explained the more viral particles a person is exposed to, the more likely they are to actually become sick or to suffer more severely from infection.
Both Bhaganagar and Campbell said wearing a mask and being outdoors decreases the risk of a carrier spreading the virus to an uninfected person. Campbell added wearing a mask can also somewhat protect an uninfected person from getting more viral particles in his or her system.
The best way to prevent the spread of the virus is to combine different deterrents such as mask wearing, social distancing, and being in a ventilated or outdoor environment, Campbell said.
“It’s a combo,” he said. “That’s really what I’m trying to get across.”
Another UTSA researcher, Juan Gutiérrez, seconded Bhaganagar in that it is too early to let down any sort of restrictions. During a San Antonio CityFest panel Tuesday, Gutiérrez told San Antonio Report’s Senior Environmental Reporter Brendan Gibbons that as winter approaches, the United States will likely see an exponential increase in cases if precautions aren’t taken soon.
“Once people started receiving a directive from the government, that ‘You have to be careful, you have to wear face masks,’ then the curve started to flatten,” he said. “If you have to go in public, go to restaurants, try to minimize interaction, try to work your face masks as much as possible.”