**2. SARS-CoV-2 persistence in the environment and risk of transmission to humans**

The study of the persistence of SARS-CoV-2 in the environment is necessary, as this informs the need for and frequency of disinfection of those surfaces. This virus shows environmental persistence for a few hours to a few days. Several studies are now available to provide viral persistence data for various environmental surfaces, both porous and non-porous. Many of these studies also documented the virus persistence half-life or decay rate information on different surfaces and materials [9, 14–22]. This information allows one to estimate the amount of time necessary for the virus to decay to titers beneath an estimated human minimal infectious dose. As might be expected, the amount of time required depends, in part, on the initial contamination titer for the surface, the type of surface, and the temperature and relative humidity.

### **2.1 Environmental and surface persistence of SARS-CoV-2**

Previous research work related to the environmental persistence of coronavirus species was conducted on human coronavirus strain HCoV-229E [23]. This virus

#### *Environmental Persistence of SARS-CoV-2 and Disinfection of Work Surfaces in View… DOI: http://dx.doi.org/10.5772/intechopen.104520*

was found to survive for 2 hours to 9 days on various surfaces including metal, glass, and plastic. Moreover, the study also confirmed the temperature sensitivity of coronaviruses. Environmental temperatures in the range of 30–40°C were found to reduce the persistence of transmissible gastroenteritis virus (TGEV), Middle East respiratory syndrome coronavirus (MERS-CoV), and mouse hepatitis virus (MHV) [23]. At environmental temperatures above 40°C the virus is inactivated within hours to minutes [24]. However, based on the lack of experimental data available on the minimal human infectious doses of the human coronaviruses, it is difficult to say for how long the viruses may survive on different inanimate surfaces at levels actually capable of infecting a human host.

Subsequently, several studies have been conducted on environmental persistence of SARS-CoV-2 specifically (**Table 1**). The data on the survival of SARS-CoV-2 on different surfaces have revealed that viral persistence on prototypic high-touch environmental surfaces (HITES) mainly depends upon four factors: the type of surface (porosity), presence of organic matrix on the surface, temperature/ humidity, and time [9, 15–22, 25, 27]. The survival data analyses for SARS-CoV-2 demonstrate that the virus remains infectious for longer durations on hard nonporous surfaces, such as stainless steel and plastic, in comparison with cardboard or wood [15]. The presence of organic matrix during drying of SARS-CoV-2 on surfaces may lead to an increase in half-life of the virus [16, 17, 21]. However, in one of the studies it was demonstrated that SARS-CoV-2 exhibited a shorter half-life on a surface in the presence of human mucus and sputum in comparison to when dried in presence of matrix of culture medium [18]. In the absence of an organic load, the half-life of SARS-CoV-2 on plastic, glass, and aluminum surfaces was demonstrated as 35 hours, 7 hours, and 0.33 hours, respectively at 19–21°C and 45–55% relative humidity (RH) [17]. Similarly, the persistence half-life on stainless steel, wood, in a matrix of 10% suspension of human feces or human urine was demonstrated as 23 hours, 21 hours, 2.6 hours, and 16 hours, respectively at 25–27°C and 35% relative humidity [20]. In another study the persistence of SARS-CoV-2 in human sputum and mucus was found to be very close to that on porous surfaces, with half-lives of 1.9 and 3.5 hours, respectively [18]. These half-life values demonstrate that the SARS-CoV-2 may remain infectious for few days on HITES following a contamination event, if hygiene interventions are not implemented.

In one of the studies, infectious SARS-CoV-2 was detected at up to 10 days on mink fur, 5 days on plastic, 1 day on faux fur, and less than a day on various materials including faux leather, cotton, and polyester [22]. Further study revealed that UV light failed to inactivate the virus on pelts, probably due to mechanical protection by the fur. However, heat treatment at 60°C for 1 h was found sufficient to inactivate the virus on all the mentioned surfaces [22].

Other researchers have also evaluated the environmental persistence of the SARS-CoV-2 on different surfaces. In one such study, it was demonstrated that SARS-CoV-2 remained infectious for up to 1 day on wood and cloth, 2 days on a glass surface, 4 days on stainless steel and plastic surfaces, and up to 7 days on facemasks [9]. Similarly, in another study, it was found that SARS-CoV-2 remained infectious for up to 4 hours on a copper metal surface, 24 hours on a cardboard surface, and 72 hours on objects made of plastic and stainless-steel materials [25].

SARS-CoV-2 infectivity has been found to persist over a wide range of ambient temperatures and pH values, but the virus was found to be susceptible to temperatures above 40°C [24] and standard disinfection procedures (**Table 1**) [15]. The environmental survivability of the virus depends on various factors, such as types of material, surfaces, temperature, and humidity. For instance, it has been shown that SARS-CoV-2 may remain viable for up to 4 hours on a copper surface, and up to 72 hours on a stainless steel or plastic surface (**Table 1**) [25]. Similarly, this virus


#### **Table 1.**

*Persistence of SARS-CoV-2 on different prototypic environmental surfaces.*

may survive for up to 1 day on cloth and wood, 2 days on a glass surface, and up to 7 days on the outer surface of a regular medical mask along with a wide range of ambient temperature and pH values of 3–10 [9]. However, in another study it was

#### *Environmental Persistence of SARS-CoV-2 and Disinfection of Work Surfaces in View… DOI: http://dx.doi.org/10.5772/intechopen.104520*

demonstrated that the stability of SARS-CoV (a related betacoronavirus) may rapidly decrease after exposure to low pH (pH < 3) and high temperature (>65°C) [28].

The surface viability of SARS-CoV-2 was demonstrated in one of the experiments using plaque assay followed by viral RNA extraction and detection [14]. The study showed that infectious viruses may persist for the longest duration on a surgical mask and stainless steel, with an overall reduction in infectivity of 99.9% by 122 and 114 hours, respectively. On polyester shirt and banknote, the infectivity of SARS-CoV-2 reduced to 99.9% within 2.5 hours and 75 hours, respectively. Further study revealed that SARS-CoV-2 is most stable on nonporous hydrophobic surfaces. The viral RNA was also found highly stable on surfaces, and only 1 log10 reduction in recovery was observed in three weeks [14]. However, in comparison to viral RNA, the infectivity of SARS-CoV-2 reduced more rapidly on surfaces. The level of infectivity SARS-CoV-2 may become undetectable within 2 days on environmental surfaces. This indicates that mere detection of viral RNA on surfaces does not prove the presence of infectious SARS-CoV-2 [14].

Studies have also been conducted to evaluate the survival time of coronaviruses in food matrices. It has been demonstrated that MERS-CoV may survive up to 72 hours in food at 40°C [29]. In a similar study, a lower persistence of human coronavirus 229E (HCoV-229E) was found in comparison to poliovirus 1 (PV-1) on lettuce stored at 40°C [27]. Further, the study revealed that HCoV-229E was not detected on lettuce samples after four days of storage at 40°C and no virus was identified after ten days of spiking of HCoV-229E on another fruit sample (strawberries) [27]. Recent evidence suggests that coronaviruses may remain stable at low temperatures on food and surfaces for an extended period. This suggest that, theoretically, SARS-CoV-2 transmission through foods or food packaging when stored under these conditions [30]. An experimental study under laboratory conditions revealed that SARS-CoV-2 remained highly stable at freezing (−10 to −80°C) and refrigerated (4°C) temperatures on poultry, meat, fish, and swine skin for 14–21 days [30]. Similarly, in another study SARS-CoV-2 was found stable on swine skin even after 14 days at 4°C [19]. These studies suggest that SARS-CoV-2 might remain infectious for a prolonged period in food stored at low temperature. In another study, SARS-CoV-2 was isolated from the swab samples of imported frozen cod outer package surfaces, which showed that the frozen food industry may transmit SARS-CoV-2 virus to other countries and regions [31]. Therefore, based upon available data, it can be hypothesized that contaminated cold-storage foods may pose a risk for SARS-CoV-2 transmission. Since coronaviruses are thermolabile and thus susceptible to traditional heat treatments of cooking (70°C), consumption of cooked foods should not pose risk of transmission of these viruses. Consumption of uncooked or frozen food should be avoided during a coronvirus outbreak to avoid possible transmission of virus.

### **2.2 SARS-CoV-2 survival on atmospheric particulate matter**

Airborne particulate matter may also transmit the causative agent of COVID-19. In hospital wards, SARS-CoV-2 RNA has been recovered from air samples collected in greater amounts than recovered from outdoor premises [32]. The study suggests that air might be a route of virus transmission. The aerosol-generating mechanisms in healthcare facilities are a major cause of concern. For instance, researchers have demonstrated the possibility of airborne diffusion of the virus from aerosols and suspended particles in the air at hospitals in Wuhan (China) [33] and Omaha (USA) [34]. The initial study confirmed the persistence of 1 to 113 genomic copies/m3 of SARS-CoV-2 in the air in Wuhan Hospital during gatherings of high numbers of people. With the reduction in the number of patients and adequate sanitization

and disinfection, viral RNA was not detected [33]. Similarly, at Nebraska Medical Center, Omaha (USA), 63.2% positivity for the presence of SARS-CoV-2 RNA was detected in analyzed air samples, with 2 to 9 genomic copies/L of virus [34].

The atmospheric pollutants and particulate matter (PM10 and PM2.5) may also be linked with the spread of respiratory viral infections, because particulate matter may act as a carrier (vehicle) for viruses [35]. Researchers have confirmed the increased transmission of SARS-CoV-2 through PM10 in Italy [36]. Therefore, it is assumed that air pollution and particulate matter in the air may contribute to the spread of COVID-19. Periodic air monitoring may be needed to mitigate the risk of transmission of the virus in the most highly impacted environments.
