Scientists at Pacific Northwest National Laboratory in Richland have found an unexpected way that the coronavirus that causes COVID-19 may be infecting people.
A new study investigated one way that the virus may remain viable in the air more than 200 feet away from an infected person and after the infected person has left the room.
Conclusions are not definitive, but they do raise the possibility that changes should be considered in how buildings are ventilated to prevent the airborne spread of the virus that caused COVID-19.
“There are reports of people becoming infected with a coronavirus downwind of an infected person or in a room several minutes after an infected person has exited that room,” said Leonard Pease, the corresponding author of a PNNL study published in the February issue of the journal International Communications in Heat and Mass Transfer.
Mucus may be to blame, according to PNNL.
As early as the 1930s research has shown that some contaminated respiratory droplets are so large and heavy that they fall to the ground after a cough or sneeze, posing little risk of being breathed in by another person.
Others are so small and light that they dry out almost immediately, rendering them no longer infectious.
But a study done with computer modeling at PNNL in Eastern Washington shows that the mucus that coats respiratory droplets that people spew from their lungs may help keep viral particles within the droplets damp and infectious for longer than previously understood.
“Perhaps infections respiratory droplets persist longer than we have realized,” Pease said.
The team estimated that droplets encased in mucus could remain damp for up to 30 minutes and travel up to 200 feet in the air.
The possibility has implications for how ventilation in buildings may be used to either protect people from infection with the coronavirus or inadvertently increase the chances they could be infected.
Researchers studied how the coronavirus might spread through the air by using artificial, virus-like particles encased in two substances to stand in for human mucus — cow mucus and a compound derived from brown seaweed that is used as a thickening agent in ice cream.
The particles were released with an airbrush to simulate a person coughing for one minute and then tracked from room to room using ultraviolet light.
They found that increasing ventilation quickly reduced the airborne particles in the room where they were released. But levels then spiked in adjoining rooms.
“If you are in a downstream room and you’re not the source of the virus, you probably are not better off with more ventilation,” Pease said.
But in some situations ventilation still could help prevent infections.
Increasing the air exchange where crowds gather — such as at school assemblies — can help reduce contaminated particles.
But for normal work and school conditions, it can spread contamination throughout all rooms of the building, researchers concluded.