For months, the top health advice for avoiding coronavirus infection has remained the same: wash your hands, wear a mask in public spaces, and maintain 6 feet of separation from individuals outside your household.
While those recommendations hold true today, there is growing research to indicate 6 feet of separation isn’t enough to avoid infection, especially indoors and in areas with poor ventilation.
On Monday, the U.S. Centers for Disease Control and Prevention changed it’s COVID-19 guidance to indicate the possibility of transmission beyond 6 feet.
The reason: While the SARS-CoV-2 virus is believed to be primarily transmitted by respiratory droplets, there is growing evidence that it can also be transmitted through smaller respiratory droplets known as aerosols, which can travel further and remain in the air for multiple hours.
“CDC continues to believe, based on current science, that people are more likely to become infected the longer and closer they are to a person with COVID-19,” the agency said in a statement.
“Today’s update acknowledges the existence of some published reports showing limited, uncommon circumstances where people with COVID-19 infected others who were more than 6 feet away or shortly after the COVID-19-positive person left an area. In these instances, transmission occurred in poorly ventilated and enclosed spaces that often involved activities that caused heavier breathing, like singing or exercise. Such environments and activities may contribute to the buildup of virus-carrying particles.”
Jesse Capecelatro is an assistant professor of mechanical engineering at the University of Michigan, who studies fluid dynamics. He traces the 6-foot rule back to the late 1800s, when it was understood that the visible respiratory droplets released when you speak, cough, sneeze, sing and breathe would fall to the ground within 6 feet.
Over the last century, he said researchers have found smaller droplets known as aerosols can travel 20-30 feet when conditions are right. They can also remain in the air for minutes to hours, depending on the airflow in a given space.
It’s not clear how many coronavirus cases are caused by the virus traveling by the larger droplets, which can be up to millimeters in size, versus the smaller aerosols, which can be as small as 1 micron. But Capecelatro said a significant number of the virus can travel on both, “so it’s best not to worry about what’s an aerosol and what’s a droplet.”
“The main factor is how many contagious particles are you breathing in,” he said. “The most important thing you can do is wear a mask because it reduces the number of particles you expel and it reduces the momentum of how far they travel.”
Dr. Liam Sullivan, an infectious disease specialist at Spectrum Health, noted the evidence suggesting the virus can travel by respiratory droplets of all sizes. But he said the virus is more commonly transmitted through the larger droplets.
If aerosol were the primary means of infection, he said medical professionals and those living with infected individuals would be getting infected at higher rates.
“It’s not an absolutely steadfast rule but the amount of the virus that dissipates within the first 6 feet is substantial,” Sullivan said. “So the amount of viral load you take in will be much much lower.
“Therefore the 6 foot rule will protect you the vast majority of the time, but when it comes to a confined space indoors, you should avoid it all together.”
In addition to maintaining separation from others in public, Capecelatro said it’s critical that indoor facilities have good ventilation and air-purifying systems. Keeping windows open is another useful way to dilute standing air.
“If you’re indoors, you need to be bringing in fresh air and wearing a mask and reducing the time you’re in there,” he said. ““If you’re outside and you’re wearing a mask and keeping 6 feet, your probability of getting the virus is very, very low.
“If you’re outside and in close proximity your odds go up, but if you keep even 6 feet and wear a mask, the chances are quite low.”
As Michiganders move toward colder months, the likelihood of outdoor gatherings diminishes. It also becomes more challenging to bring fresh air indoors.
“Just keep in mind as we go toward winter, if there isn’t a deadly second wave, it would be the first global pandemic in history with no large second wave,” Capecelatro said.
“I recommend wearing a mask and trying not to spend long durations indoors with people. Look into air purifiers and opening windows when you can.”
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