By Condair | All photos by IMD

With the increasing spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that results in coronavirus disease 19 (COVID-19), all citizens and other building owners and occupants have an opportunity to reduce the potential for transmission through BE mediated pathways.

Over the last decade, substantial research into the presence, abundance, diversity, function, and transmission of microbes in the built environment (BE) has taken place and revealed common pathogen exchange pathways and mechanisms. The synthesises this microbiology of the BE research and the known information about SARSCoV-2 to provide actionable and achievable guidance to BE decision makers, building operators, and all indoor occupants attempting to minimise infectious disease transmission through environmentally mediated pathways. We believe this information will be useful to corporate and public administrators and individuals responsible for building operations and environmental services in their decisionmaking process about whether to implement social distancing measures and for what duration. Increased spread of SARS-CoV-2 causing COVID-19 infections worldwide has brought increased attention and fears surrounding the prevention and control of SAR-CoV-2 from both the scientific community and the general public. More than 300 000 cases have been reported worldwide, with over 100 000 recovering.

While many of the typical precautions typical for halting the spread of SARS-CoV-2 are being implemented, other less common transmission pathways should also be considered and addressed to reduce further spread. Environmentally mediated pathways for infection by other pathogens have been a concern in buildings for decades, most notably in hospitals. Substantial research into the presence, abundance, diversity, function, and transmission of the microorganisms in the BE has taken place in recent years. This work has revealed common pathogen exchange pathways and mechanisms that could lend insights into potential methods to mediate the spread of SARS-2-CoV through BE mediated pathways.

The knowledge of the transmission dynamics of COVID 19 is
still currently developing especially in the HVACR industry.

In December 2019, a novel CoV (SARS-CoV-2) was identified in Wuhan, a major transport hub of central China. The earliest COVID-19 cases were linked to a large seafood market in Wuhan, initially suggesting a direct food source transmission pathway. Since that time, we have learned that person-to-person transmission is one of the main mechanisms of COVID-19 spread.

In the months since the identification of the initial cases, COVID-19 has spread to 192 countries and territories and there are approximately 349 187confirmed cases (as of 23 March 2020). The modes of transmission have been identified as host-tohuman and human-to-human. There is preliminary evidence that environmentally mediated transmission may be possible; specifically, that COVID-19 patients could be acquiring the virus through contact with abiotic (BE) surfaces.


The built environment (BE) is the collection of environments that humans have constructed, including buildings, cars, roads, public transport, and other human-built spaces. Since most humans spend >90% of their daily lives inside the BE, it is essential to understand the potential transmission dynamics of COVID-19 within the BE ecosystem and the human behaviour, spatial dynamics and building operational factors that potentially promote and mitigate the spread and transmission of COVID-19. BEs serve as potential transmission vectors for the spread of COVID-19 by forcing close interactions between individuals, by acting as fomites (objects or materials which are likely to carry infectious diseases), and through viral exchange and transfer through the air.

Shared workspaces such as co work environments rooms in homes cars bikes and other elements of the BE may increase the potential for environmentally mediated pathways of exposureShared workspaces such as co work environments rooms in
homes cars bikes and other elements of the BE may increase
the potential for environmentally mediated pathways of exposure.

The occupant density in buildings, influenced by building type and programme, occupancy schedule, and indoor activity, facilitates the accrual of human-associated microorganisms. Higher occupant density and increased indoor activity level typically increases social interaction and connectivity through direct contact as well as environmentally mediated contact (fomites).

The original cluster of patients were hospitalised in Wuhan with respiratory distress (Dec 2019), and approximately ten days later, the same hospital facility was utilising rt-PCR to diagnose patients with COVID-19. It is presumed that the number of infected patients increased because of transmissions that occurred within the hospital BE. The increased exposure risk associated with high occupant density and consistent contact was demonstrated with the COVID-19 outbreak that occurred on the Diamond Princess cruise ship in January 2020. Current estimates of contagiousness of SARS-CoV-2 (known as the R0), have been estimated from 1.5-3. R0 is defined as the average number of people who will contract a disease from one contagious person. For reference, measles has a famously high R0 of roughly 12-18, and influenza (flu) has an R0 of <2. However, within the confined spaces of the BE, the R0 of SARS-CoV-2 has been estimated to be significantly higher (estimates ranging from 5-14), with ~700 of the 3 711 passengers on board (~19%) contracting COVID-19 during their two-week quarantine on the ship. These incidents demonstrate the high transmissibility of COVID-19 as a result of confined spaces found within the BE. With consideration to the spatial layout of the cruise ship, the proximity of infected passengers to others likely had a major role in the spread of COVID-19.

As individuals move through the BE, there is direct and indirect contact with the surfaces around them. Viral particles can be directly deposited and resuspended due to natural airflow patterns, mechanical airflow patterns, or other sources of turbulence 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 fomites. 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. Once infected, individuals with COVID-19 shed viral particles before, during, and after developing symptoms. These viral particles can then settle onto abiotic objects in the BE and potentially serve as reservoirs for viral transmission. Evidence suggests that fomites can potentially be contaminated with SARSCoV-2 particles from infected individuals through bodily secretions such as saliva, nasal fluid, contact with soiled hands, and the settling of aerosolised viral particles and large droplets spread via talking, sneezing, coughing, and vomiting. A study on environmental contamination from the MERS-CoV demonstrated that nearly every touchable surface in a hospital housing MERS-CoV patients had been contaminated with the virus, and a survey of a hospital room with a quarantined COVID-19 patient demonstrated extensive environmental contamination.

The knowledge of the transmission dynamics of COVID-19 is still currently developing, but based upon studies on SARS-, MERS-CoV, preliminary data on SARSCoV-2, and CDC (Centers for Disease Control and Prevention) recommendations, it seems likely that SARS-CoV-2 can potentially persist on fomites anywhere from a couple of hours up to nine days. However, it should be noted that there are no documented cases to date of a coronavirus infection originating from a fomite. There is, however, preliminary data demonstrating the presence of SARS-CoV-2 in stool, indicating that transmission can potentially occur through the fecal-oral pathway. While transmission of coronavirus has only been documented through respiratory droplet spread and not through deposition on fomites, steps should still be taken to clean and disinfect all potential sources of SARS-nCoV-2 under the assumption that active virus may be transmitted through these abiotic surfaces.

Previously, it has been confirmed that SARS can be, and is most often, transmitted through droplets. Based upon previous investigation into SARS, spread through aerosolisation remains a potential secondary transmission method, especially within the BE that contain heating, ventilation, and air conditioning (HVAC) units. Mitigation of viral transmission through BE air delivery systems is most often reliant on inline filtration media. Residential and commercial systems typically require a minimum efficiency reporting value (MERV) of 8, which is rated to trap 70-85% of particles ranging from 3.0-10.0 microns, a strategy employed to minimise impacts to cooling coils and other HVAC equipment.

Higher MERV ratings are required in these settings to filter incoming outside air based on local outdoor particulate levels. Protective environment rooms in hospitals require the most stringent minimum filtration efficiency. A MERV 7 or greater is required as a first filter before heating and cooling equipment, and a second high-efficiency particulate air (HEPA) filter is placed downstream of cooling coils and fans. HEPA filters are rated to remove at least 99.97% of particles down to 0.3 microns. In most residential and commercial buildings, these are often MERV -5 to MERV -11, and in critical healthcare settings, MERV -12 or higher and HEPA filters are used.

MERV -13 filters have the potential to remove microbes and other particles ranging from 0.3-10.0 microns. HEPA filters are also able to filter out particles 0.3 microns and larger. Most viruses, including coronaviruses, range from 0.004 – 1.0 microns, limiting the effectiveness of these filtration techniques against pathogens such as SARSCoV-2. Furthermore, no filter is perfect. Recently, it has been found that gaps in the edges of filters in hospitals has been a contributing factor of the failure of filters to eliminate pathogens from the shared air environment.

In recent years, the sharing economy has created environments where multiple people share the same spaces. It is possible that infectious disease transmission may be impacted by this shift to the sharing economy. Shared workspaces such as co-work environments, rooms in homes, cars, bikes, and other elements of the BE may increase the potential for environmentally mediated pathways of exposure. In cases where alternate modes of transportation were previously single occupancy vehicles, these trips are now often replaced with rideshare programs or transportation network companies, the potential for exposure may increase.


The spread of COVID-19 is a rapidly developing situation, but there are steps that can be taken, inside and outside of the BE, to help prevent the spread of disease.

Within the BE, environmental precautions that can be taken to potentially prevent the spread of SARS-CoV-2 include chemical deactivation of viral particles on surfaces. It has been demonstrated that 62-71% ethanol is effective at eliminating MERS and SARS. This ethanol concentration is the same as most typical alcohol-based hand sanitisers, suggesting that properly applied hand sanitiser may be a valuable tool against the spread of SARS-CoV-2 in the BE. Items should be removed from sink areas to ensure aerosolised water droplets do not carry viral particles onto commonly used items, and countertops around sinks should be cleaned using bleach or an alcohol-based cleaner on a regular basis. 

Part 2 will be published in the next issue of RACA Journal.

Source: 2019 Novel Coronavirus Outbreak: A Review of the Current Literature and Built Environment Considerations to Reduce Transmission


Documented by Dr Walter Hugentobler, this literature review gives valuable information for building operators on actions they can take to mitigate the spread of COVID-19.

Alongside the regular advice we hear from governments on hand washing and social distancing, its finding show that increasing air exchange rate, maintaining indoor humidity at 40-60%RH (not achievable in winter without active humidification) and increasing natural light can all play a positive role.

The scientific studies referenced in the literature review provide valuable insight into how we can create a healthier built environment, not just at a time of crisis but in our everyday lives. For instance, if hospitals and public places kept their indoor humidity at the recommended 40-60%RH, many lives would be saved every year from reduced flu transmission alone.