Spread of COVID-19 occurs via airborne particles and droplets. People who are infected with COVID can release particles and droplets of respiratory fluids that contain the SARS CoV-2 virus into the air when they exhale (e.g., quiet breathing, speaking, singing, exercise, coughing, sneezing). The droplets or aerosol particles vary across a wide range of sizes – from visible to microscopic. Once infectious droplets and particles are exhaled, they move outward from the person (the source). These droplets carry the virus and transmit infection. Indoors, the very fine droplets and particles will continue to spread through the air in the room or space and can accumulate.
Since COVID-19 is transmitted through contact with respiratory fluids carrying the infectious SARS-CoV-2 virus, a person can be exposed by an infected person coughing or speaking near them. They can also be exposed by inhaling aerosol particles that are spreading away from the infected person. Transmission of COVID-19 from inhalation of virus in the air can occur at distances greater than six feet. Particles from an infected person can move throughout an entire room or indoor space. The particles can also linger in the air after a person has left the room – they can remain airborne for hours in some cases. Someone can also be exposed via splashes and sprays of respiratory fluids directly onto their mucous membranes. Spread may also sometimes occur through contact with contaminated surfaces, though this route is now considered less likely. See Science and Technical Resources related to Indoor Air and Coronavirus (COVID-19) or Indoor Air and COVID-19 Key References and Publications for technical information.
Though the risk of infection by breathing in particles carrying the virus generally decreases with distance from infected people and with time, some circumstances increase the risk of infection:
- Being indoors rather than outdoors, particularly in indoor environments where ventilation with outside air is inadequate
- Activities that increase emission of respiratory fluids, such as speaking loudly, singing, or exercising
- Prolonged time of exposure (e.g. longer than a few minutes)
- Crowded spaces, particularly if face coverings are inconsistently or improperly worn
There are straightforward steps that can be taken to reduce the potential for airborne transmission of COVID-19 and the focus of this material is on those measures. The layout and design of a building, as well as occupancy and type of heating, ventilation, and air conditioning (HVAC) system, can all impact potential airborne spread of the virus. Although improvements to ventilation and air cleaning cannot on their own eliminate the risk of airborne transmission of the SARS-CoV-2 virus, EPA recommends increasing ventilation with outdoor air and air filtration as important components of a larger strategy that may include physical distancing, wearing cloth face coverings or masks, surface cleaning , handwashing, and other precautions. Consult guidance from the Centers for Disease Control and Prevention (CDC) and local authorities on current guidelines on the use of masks.