This updated in-depth summary (previously released on December 21, 2020) is issued in response to new information that we received about updated definitions of aerosol particles that show that larger respiratory particles (<100 μm) can remain airborne for extended periods, and that in enclosed areas with poor ventilation, these aerosols containing infectious SARS-CoV-2 can spread beyond 6 feet and build up in a room. We apologize for not including this information in the earlier version of this summary.
Mitigation of SARS-CoV-2 transmission in indoor spaces is crucial, especially during the winter season when activities are mostly held in enclosed indoor environments. Understanding SARS-CoV-2 transmission mechanisms relating to ventilation of indoor air and what evidence-based environmental measures are available will be key to infection control. This document is a brief summary of published evidence on SARS-CoV-2 transmission mechanisms that relate to ventilation of indoor spaces and ventilation standards/best practices for minimizing spread. References are mainly drawn from the COVID-19 Literature Report (Lit Rep) team database and guidelines published by the CDC. References that appeared in the daily Lit Rep are marked with an asterisk*, and the summary is shown in the annotated bibliography below.
Executive Summary of Ventilation and SARS-CoV-2
- While evidence suggests that SARS-CoV-2 is commonly transmitted through close contact and respiratory droplets, updated definitions of aerosols show that larger respiratory particles (<100 μm) can remain airborne for extended periods. In enclosed areas with poor ventilation, these aerosols containing infectious SARS-CoV-2 can spread beyond 6 feet and build up in a room. A small number of studies have isolated viable virus from air samples in lab and clinical settings and SARS-CoV-2 airborne transmission beyond 6 feet has been observed in poorly ventilated and crowded indoor spaces.
- An expert panel assembled by the National Academies of Sciences, Engineering, and Medicine concluded that aerosols represent an important potential transmission pathway for SARS-CoV-2 based on multiple lines of evidence, but concluded that additional research is needed to definitively prove and quantify the role of the aerosol transmission pathway.
- While SARS-CoV-2 RNA has been detected in heating, ventilation, and air conditioning (HVAC) systems, viable virus was not isolated. There has been no documented evidence of SARS-CoV-2 transmission occurring through HVAC systems.
- Ventilation standards/best practices to reduce risk of SARS-CoV-2 transmission primarily include methods to decrease concentrations of aerosols that may carry infectious virus either through filtration of indoor air or circulation of cleaner air from outside.
- Ventilation standards/best practices alone are not enough to mitigate SARS-CoV-2 transmission. They should be implemented in conjunction with infection control measures that more directly address SARS-CoV-2 primary modes of transmission, such as reducing building occupancy to facilitate physical distancing, mask wearing, surface disinfection, and handwashing.
View the full report which contains:
- SARS-CoV-2 Transmission related to Ventilation
- Ventilation Standards/Best Practices
- Table of key studies
- Annotated Bibliography