University of Nebraska Medical Center researchers have found more evidence that the coronavirus may spread through tiny airborne particles, in addition to large respiratory droplets. They published their first study, Aerosol and surface contamination of SARS-CoV-2 observed in quarantine and isolation care, in the journal Scientific Reports. A preprint of their second study, The Infectious Nature of Patient-Generated SARS-CoV-2 Aerosol, shows that the aerosols are infectious.
What makes a virus airborne?
First, some terminology. What's the difference between an airborne virus and one that's not? The difference is droplet size. Joshua Santarpia, PhD, a researcher in both studies, explains the difference: "Airborne means that the infectious particles are small enough to be carried by the air." Smaller infectious droplets can be airborne, while larger infectious droplets are too heavy to float in midair.
Dr. Santarpia says, "There's an arbitrary line between calling a particle of a certain size either a droplet or an aerosol. It's more helpful to look at where the particle is produced – either in the lungs or the mouth."
When you cough or sneeze, you produce particles in your mouth (also called the oral cavity). These large particles fall to the ground.
Breathing and talking produces particles in the voice box (also called the larynx) and deep lungs. These small particles can float in the air. If these particles are infectious, the virus is airborne.
To sum up, COVID-19 spreads in three ways:
- Large respiratory droplets: Infectious germs spread from sneezing and coughing. Large respiratory droplets fall to the ground due to gravity.
- Airborne particles: Tiny droplets (sometimes called aerosols) float around in the air. Aerosols may hang around for several hours after an infectious person emits them.
- Contaminated surfaces: Surfaces that have been coughed on that someone else then touches. Like door handles or tissues. Scientists call these "fomites." The coronavirus can live on a surface for up to two days.
Researchers found likely infectious aerosols
In the first study, UNMC researchers reported that pieces of the virus were in patient rooms and even the hallways outside their rooms. The pieces of the virus had its genetic material – meaning they might be infectious.
Researchers found pieces of the coronavirus on:
- Cell phones
- TV remote controls
- Toilets
- Bedside tables
- Windowsills
- Floor underneath the beds
- Ventilation grates
- Air in the rooms
- Air in the hallway outside the room
In this newer study awaiting publication, they found the virus had replicated in some of the samples. A replicating virus is likely an infectious virus. This gives more evidence for airborne transmission.
Months earlier, before either study had taken place, Nebraska Medicine was prepared for the potential of airborne transmission. COVID-19 patients (and people suspected to have COVID-19) were placed in an area separate away from other patients. These separate areas had specially engineered negative airflow, meaning air couldn't leave the infected patient area. Expert health care providers donned full body protection to guard against airborne infection.
How does this change things?
Previously, we knew that the coronavirus spread through larger respiratory droplets. This is still true. Many public health guidelines (like the 6 feet of social distancing) were based on the virus spreading through the larger respiratory droplets. A cough travels about 6 feet before falling to the ground, so stay 6 feet away from others.
Now, with the real possibility of airborne transmission, guidelines should also consider airflow.
- Social distancing: Aerosols can travel farther than 6 feet. Even if you're 6 feet away, aerosols may be able to infect you. With airborne transmission, an enclosed space is riskier than an outdoors area
- Barriers: Shields or plexiglass barriers will still be effective against large respiratory droplets from coughs and sneezes – but less effective against aerosols
- Masks: Wearing a mask filters some infectious particles, which limits how many particles you're exposed to
"All these things add up," says Dr. Santarpia. "Done together, social distancing, masks and less frequent interactions will limit the spread of coronavirus."
Infectious aerosols explain asymptomatic transmission
If COVID-19 only spreads through large respiratory droplets, only people with symptoms should be able to infect others. If someone is sick with COVID-19, but never coughs or sneezes, how can they spread the coronavirus to healthy people?
This study gives the answer: tiny aerosols. The paper explains that infectious "aerosol particles are produced by individuals that have the COVID-19 disease, even in the absence of cough."
That's because breathing and talking can create infectious coronavirus aerosols. If someone doesn't have a cough, they can still be sick – and more importantly, they can still infect others with COVID-19. Aerosols explain asymptomatic transmission.
"The biggest implication of this new research is to be aware that an environment around a sick person is contaminated with COVID-19," says Dr. Santarpia. "The air and surfaces in a sick person's room can get you sick, too."
