An updated scientific brief posted by the Centers for Disease Control and Prevention Friday said the coronavirus can be spread via "very small fine droplets and aerosol particles" and that infection can happen farther than six feet from the source under certain conditions.
While the likelihood of being infected drops the farther away one gets from the source, the CDC said, "These transmission events have involved the presence of an infectious person exhaling virus indoors for an extended time (more than 15 minutes and in some cases hours) leading to virus concentrations in the air space sufficient to transmit infections to people more than 6 feet away, and in some cases to people who have passed through that space soon after the infectious person left."
The CDC said factors that exacerbate the spread of the virus in this way include enclosed spaces with poor ventilation, which can cause the concentration of particles in the air to build up. The agency also pointed out that increased exhalation, such as from those who are exercising, singing or shouting can increase the risk of SARS-CoV-2 transmission, along with prolonged exposure to those conditions, typically more than 15 minutes.
The CDC's most-recent guidance also says transmission can occur through exhaled particles on exposed mucous membranes, such as if an infected person coughs or sneezes on another person. The virus can also be spread if someone gets the virus on their hands and then touches mucous membranes, such as touching areas on the face, like the nose or eyes.
The CDC pointed out that there two primary factors which can help in reducing the chance of infection from droplets and particles: Distance and time.
"The risk for infection decreases with increasing distance from the source and increasing time after exhalation," the CDC highlighted in its updated guidance Friday.
The health agency said that its recommendations for reducing the spread remain the same: Use well-fitting masks, practice social distancing in everyday situations, try to avoid crowded spaces, especially indoors. Also, it is always important to practice good hygiene by washing hands thoroughly as well as cleaning surfaces.