Opening a window could cut the amount of coronavirus in a room by half, according to a new observational study of infected students in an isolated dormitory at the University of Oregon.
The study, posted online, is small and has not yet been published in a scientific journal. But it provides real evidence for several key principles, showing that the virus spreads from infected people to the air in a room; that the more virus they carry, the more the virus accumulates indoors; and that both natural and mechanical ventilation appear to reduce this viral load on the environment.
“Ventilation is one of the most important mitigation strategies we have at our disposal,” said Kevin Van Den Wymelenberg, who led the research and leads the Institute for Health in the Built Environment.
The researchers studied 35 University of Oregon students who tested positive for the coronavirus between January and May. All students then moved to single rooms in a Covid isolation dormitory for a 10-day isolation period.
The scientists placed petri dishes in each room and used an active air sampler to capture aerosols floating around the air. Several times a day, they also wiped various surfaces in the room, as well as students’ noses and mouths.
They then used PCR, or polymerase chain reaction, to determine whether the virus was present in each sample and, if so, at what levels.
The data confirmed that there was a clear correlation between the amount of virus students carried and the viral load of the environment. As the amount of virus in the nose and mouth of students decreased during their isolation period, so did the amount of virus in the air.
“There was a significant correlation between the nasal samples and the air samples in the room,” said Dr. VandenWymelenberg.
The viral load in the rooms was, on average, higher when the students were symptomatic than when they were symptom-free, although the scientists emphasized that even asymptomatic students shed a lot of virus. Several self-reported symptoms, including coughing, were specifically associated with higher environmental viral loads.
The researchers also calculated the percentage of mechanical ventilation for each room and asked students to rate how often the windows were open. They found that the viral load was on average about twice as high in rooms where the window was closed more than half the time.
“Ventilation is very important, and I think we’re just beginning to realize how important it is,” said Leslie Dietz, co-author of the study and researcher at the University of Oregon.
The study had several limitations, including the fact that it only included young adults and that symptoms and window data were self-reported. The researchers also noted that they did not measure how much of the virus in the room was viable or could infect other people.