Coronavirus in the environment

While the information surrounding the transmission of SARS-CoV-2 is starting to be understood, how the virus stays in the environment remains unknown. Understanding how the virus operates in the environment is essential in preventing accidental transmission. Researchers have discovered SARS-CoV-2 in feces, raising concern about transmission through wastewater.

Another potential environmental exposure is via building air filters. As states are loosening restrictions and more people are returning to work, it is essential to understand how long SARS-CoV-2 can survive in air filters and whether that could pose a risk to those in the building.

Coronavirus in Wastewater

There is currently very little known on the survival of SARS-CoV-2 in environmental media such as water and wastewater.[1] However, in a study done in a Chinese hospital that collected fecal samples from SARS-CoV-2 positive patients, fecal samples remained positive for SARS-CoV-2 RNA for a mean of 27.9 days and was detected in a patient for 47 days after the first symptoms appeared.[2] Although presence of RNA does not always translate to infectability, the possible presence of virus in wastewater warrants investigation.

Despite the lack of research for SARS-CoV-2, we know that the stability of SARS-CoV-2 is similar to that of SARS-CoV in aerosols and surfaces, allowing us to apply the research from SARS-CoV and similar coronaviruses to SARS-CoV-2.[3] Even so, there are only a few studies that look at viral persistence of coronaviruses in wastewater. One 2005 study by Wang et al. looked at SARS-CoV from collected wastewater samples, and demonstrated that detection of SARS-CoV only persisted for 2 days in hospital wastewater, domestic sewage, and dechlorinated tap water at 20℃. The same study also discovered through RT-PCR that the SARS-CoV RNA could be barely detected on the 7th day of study in a 20℃ environment (room temperature) and persisted for 14 days under a 4℃ environment (refrigerator temperature).[4] In another study, the surrogate coronaviruses, transmissible gastroenteritis (TGEV) and mouse hepatitis (MHV), were sampled from wastewater and showed infectivity for up to 22 days.[5] Finally, another notable study demonstrates that the human coronavirus 229E (HCoV) collected from wastewater died off within 2-4 days at 23℃.[6]

The data shows a wide possible time range of persistence and while this may seem alarming, the WHO has stated that due to the enveloped structure of the SARS-CoV-2 virus, it is much less stable compared to non-enveloped human enteric viruses that are known waterborne transmissitters, such as the adenovirus, norovirus, rotavirus, and hepatitis A.[7] The WHO recommends usual sewage treatment but for workers to wear their proper PPE all the time and to be extra cautious in removing the PPE.

Coronavirus in Building Air Filters

There is currently no research done on the persistence of live forms of coronavirus on building air filters, but there are a few studies that report on the persistence of the live virus on varying surfaces. Building air filters are typically made from cotton, fiberglass, polyester, polypropylene, or any fibrous materials that collect particles.[8] Using this information, the data examining viral persistence on inanimate surfaces can be applied to the specific type of building air filter. Tabke 1 details the persistence of varying forms of the coronavirus on different surfaces.

It is important to note that residential and commercial ventilation systems typically require a minimum efficiency reporting value (MERV) of 8 which can capture 70-85% of particles ranging from 3.0 to 10.0 µm; however, most viruses range from 0.004 to 1.0 µm and would require a MERV of 13 or higher in addition to HEPA filters to be most effective (Dietz).[10]

Gaps in knowledge:

Very few studies have been done on the survival of RNA on the environment and on inanimate surfaces; future research should examine viral survival in wastewater and building air filters.