By: Christopher Sirota, CPCU
Evidence is reportedly mounting that there is a risk that the novel coronavirus (SARS-CoV-2), which causes COVID-19, may be transmitted through the air as an aerosol emitted from an infected person. Until recently, concerns have reportedly been focused on transmission via large respiratory droplets directly from person to person or from contact with contaminated fomites (eg. surfaces like doorknobs, bed linens and handrails).
What is an aerosol?
According to a 2019 BMC Infectious Diseases research commentary, virus-related aerosols "refer to particles in suspension in a gas, such as small droplets in air" that are smaller than 5–10 μm in diameter, a size that is generally understood by experts to be able to penetrate various parts of the human respiratory system. A related April 2020 National Health Institute report regarding healthcare worker exposure to SARS-CoV-2 noted that "[s]neezing and coughing are effective aerosol generators, but all forms of expiration produce particles across a range of sizes."
Viral Viability of Aerosol transmission of SARS-CoV-2 Still Unclear
Some studies have reportedly identified the SARS-CoV-2 virus in samples of air, but uncertainty remains regarding how contagious that contaminated air might be.
A March 2020 commentary from the World Health Organization (WHO) highlights that "[i]n an analysis of 75,465 COVID-19 cases in China, airborne transmission was not reported." The WHO further explains that it is:
aware of other studies which have evaluated the presence of [SARS-CoV-2] RNA in air samples, but which are not yet published in peer-reviewed journals. It is important to note that the detection of RNA in environmental samples based on PCR-based assays is not indicative of viable virus that could be transmissible.
In drawing these conclusions, some researchers had reportedly analyzed potentially contaminated air in a hospital with COVID-19 patients.
The Centers for Disease Control and Prevention (CDC) published an early release of a study that examined samples from the air and fomites collected from a hospital in Wuhan, China from mid-February to early-March. During their research the study reportedly identified SARS-CoV-2 in samples from "floors, computer mice, trash cans, and sickbed handrails and was detected in air ≈4 meters from patients." Of note, the study did reference some limitations that should be considered including the fact that the "results of the nucleic acid test do not indicate the amount of viable virus. Second, for the unknown minimal infectious dose, the aerosol transmission distance cannot be strictly determined."
Aerosol Transmission Risk in Large Groups
According to the Wall Street Journal, a National Academy of Sciences study, which focused on the potential spread of COVID-19 during large gatherings, indicated that:
one minute of loud speech was enough to produce thousands of droplets that remain airborne for about 12 minutes, potentially able to infect anyone in the area. Similar studies have shown that virus-laden aerosols, particles smaller than droplets, can levitate for hours after being released in indoors spaces.
The article listed some example events linked to the spreading of COVID-19, like large church gatherings, a ski resort crowd, and several festivals; the article also noted that the researchers proposed a theory:
that banning mass public events where hundreds of attendees can infect themselves in the space of a few hours, along with other measures such as wearing face masks, might slow the pace of the new coronavirus’s progression to a manageable level even as shops and factories reopen.
Aerosol Transmission Concerns: Buildings and Planes
As many places and business have reportedly begun to reopen after COVID-19-related lockdowns, some experts have considered the safety of indoor air.
For example, Reuters reported about the general concern of aerosol transmission of SARS-CoV-2 within the cabin of commercial aircraft. Per the article, experts explained that, within aircraft, the risk of aerosol transmission may be much less than is perceived by the public, in part, because:
[half the air is] recycled through hospital-grade HEPA filters designed to remove some 99.97% of contaminants including viruses. The other half is flushed outside through valves.
Furthermore, according to Reuters, that cabin air is completely exchanged 20-30 times every hour, which is much more frequent than within an office building, which refreshes completely about four times an hour.
Speaking of buildings, Boston25 News has reported that some office building property owners in Boston are concerned about reopening buildings and the quality of the air and water within the buildings. According to the article, there are risk management recommendations to flush the air system of an office building for 48 hours before reopening. In addition, it is reportedly being suggested to increase the amount of fresh air that is mixed into a building's system and to adjust the humidity, since low humidity may enable a greater spread of the virus. Building owners that increase humidity reportedly may need to be careful not to inadvertently create an environment conducive to the development of mold. Lastly, the article noted that some of Boston's tallest office buildings may restrict the number of people per elevator car to four in order to help control the quality of the indoor air.