Science highlight – COVID-19 indoors

COVID-19 in built environments: what the science says

Considerations to reduce the transmission of COVID-19

Original article by Dietz L, et al., March 2020, in mSystems (peer-review pending)

In the Science Highlight blog posts, we digest the latest scientific publications about COVID-19.

Dietz et al cover

In this paper, submitted for peer review in March 2020, the authors offer a review of the scientific literature about SARS-CoV-2 — the virus responsible for COVID-19 — focusing on ways to mitigate contamination in Built Environments, defined as the collection of environments that humans have constructed, including buildings, cars, roads, public transport, and other human-built spaces. Although the transmission of coronavirus has only been documented through respiratory droplet spread and not through deposition on carrier surfaces so far, the authors cite preliminary evidence that COVID-19 patients could be acquiring the virus through contact with surfaces (2, 3). Therefore, a better understanding of built environments variables can help facility and operations managers make actionable decisions about whether and how to implement safety measures and for what duration.

A little bit about the COVID-19 virus

The betacoronavirus SARS-CoV-2 is responsible for COVID-19. It is an RNA virus, meaning that it carries and “injects” its genetic material (viral RNA) into a cell in order to reproduce. Viral RNA contains the blueprints for all of the components of a particular virus. The viral genetic material is then replicated by the host cell. RNA virus typically infect mammals, including humans and bats.

In order to infect a new host, the virus needs to be in contact with one or more of that individual’s cells. This happens more easily in close quarters such as in built environments/ buildings. Not only do built environments force close interactions between individuals, they also act as contamination vectors via objects or materials which are likely to carry infectious diseases, and through the air. As individuals move through the built environments, there is direct and indirect contact with the surfaces around them. Viral particles can be directly deposited and resuspended due to airflow patterns in the indoor environment such as foot fall, walking, and thermal plumes from warm human bodies. These resuspended viral particles can then resettle back onto surfaces.

Once infected, individuals with COVID-19 shed viral particles before, during, and after developing symptoms. Whenever an individual makes contact with a surface, there is an exchange of microbial life, including a transfer of viruses from the individual to the surface and vice-versa. Evidence suggests that surfaces can potentially be contaminated with SARS-CoV-2 particles from infected individuals through bodily secretions such as saliva, nasal fluid, contact with soiled hands, and the settling of aerosolized viral particles and large droplets spread via talking, sneezing, coughing, and vomiting. The knowledge of the transmission dynamics of COVID-19 is still currently developing, but based upon studies on related viruses such as SARS-, MERS-CoV, preliminary data on SARSCoV-2, and CDC recommendations, it seems likely that SARS-CoV-2 can potentially persist on surfaces anywhere from a couple of hours up to nine days.

While transmission of coronavirus has only been documented through respiratory droplet spread, steps should nonetheless still be taken to clean and disinfect all surfaces under the assumption that active virus may be transmitted through these abiotic surfaces. To mitigate contamination, non-healthcare-setting social distancing measures should be observed in at-risk built environments. These measures, such as closing high-occupancy areas such as schools and workplaces act to prevent disease transmission by reducing typical person-to-person contact, decreasing the possibility of surface contamination by those that are shedding viral particles, and decreasing the possibility of airborne, particle transmission between individuals in the same room or close proximity.

Recommendations to reduce contamination in built environments

Conceptualization of SARS-CoV-2 deposition. (a) Viral particles accumulate in the lungs and upper respiratory tract (b) droplets and aerosolized viral particles are expelled from the body through daily activities and can spread to nearby surroundings and individuals (c) Viral particles, excreted from the mouth and nose, are often found on the hands and (d) can be spread to commonly touched items such as computers, glasses, faucets, and countertops. Source: Dietz et al., 2020 (1)

Within the built environments, environmental precautions that can be taken to potentially prevent the spread of SARS-CoV-2. This article, supported by scientific literature and the CDC guidelines, suggests the following.

1) Chemically deactivate viral particles on surfaces using approved cleaning agents. 62-71% ethanol is effective at eliminating MERS and SARS. This ethanol concentration is the same as most typical alcohol-based hand sanitizers, suggesting that properly applied hand sanitizer may be a valuable tool against the spread of COVID-19 in built environments.

2) Administrators and building operators should post signage about the effectiveness of personal hygiene such as proper handwashing

3) Items should be removed from sink areas to ensure aerosolized water droplets do not carry viral particles onto commonly used items. Countertops around the sinks should be cleaned using bleach or an alcohol-based cleaner on a regular basis.

4) Building HVAC operational practices can also reduce the potential for the spread of SARS-CoV-2.

5) Previous research has found that relative humidity above 40% is detrimental to the survival of many viruses, including coronaviruses in general. Maintaining a relative humidity between 40%-60% within the built environments may help to limit the spread and survival of SARS-CoV-2. Targeted in-room humidification is another option to consider,

6) Daylight has been shown to help decrease the infection of humans by microorganisms.

7) Reorganize the office to promote social distancing

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