Persistence of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Virus and Viral RNA in Relation to Surface Type and Contamination Concentration

Abstract

The transmission of SARS-CoV-2 is likely to occur through a number of routes, including contact with contaminated surfaces. Many studies have used RT-PCR analysis to detect SARS-CoV-2 RNA on surfaces but seldom has viable virus been detected. This paper investigates the viability over time of SARS-CoV-2 dried onto a range of materials and compares viability of the virus to RNA copies recovered, and whether virus viability is concentration dependant. Viable virus persisted for the longest time on surgical mask material and stainless steel with a 99.9% reduction in viability by 122 and 114 hours respectively. Viability of SARS-CoV-2 reduced the fastest on a polyester shirt, with a 99.9% reduction within 2.5 hours. Viability on the bank note was reduced second fastest, with 99.9% reduction in 75 hours. RNA on all the surfaces exhibited a one log reduction in genome copy recovery over 21 days. The findings show that SARS-CoV-2 is most stable on non-porous hydrophobic surfaces. RNA is highly stable when dried on surfaces with only one log reduction in recovery over three weeks. In comparison, SARS-CoV-2 viability reduced more rapidly, but this loss in viability was found to be independent of starting concentration. Expected levels of SARS-CoV-2 viable environmental surface contamination would lead to undetectable levels within two days. Therefore, when RNA is detected on surfaces it does not directly indicate presence of viable virus even at high CT values. Importance This study shows the impact of material type on the viability of SARS-CoV-2 on surfaces. It demonstrates that the decay rate of viable SARS-CoV-2 is independent of starting concentration. However, RNA shows high stability on surfaces over extended periods. This has implications for interpretation of surface sampling results using RT-PCR to determine the possibility of viable virus from a surface, where RT-PCR is not an appropriate technique to determine viable virus. Unless sampled immediately after contamination it is difficult to align RNA copy numbers to quantity of viable virus on a surface.

Drying of virus-containing particles: modelling effects of droplet origin and composition

“…Abrupt changes in hydration may be more disruptive than gradual changes [22]. Inactivation is particularly slow when droplets dry onto non-porous surfaces [71][72][73], for reasons that are not clear: water activity in surface deposits depends on ambient RH in the same way as in aerosol droplets large enough for the Kelvin effect to be ignored. Fractionation of solutes during surface drying [70,74,75] might lead to salt-free areas where the virus can survive in dried form at higher RH, or inactivation may occur at the air-water interface [76] or due to local capillary forces [77].…”

SARS-CoV-2 RNA and Supermarket Surfaces: A Real or Presumed Threat?

“…The survival and persistence of SARS-CoV-2 on surfaces appear to be conditioned by characteristics of the material as well as temperature and humidity. A recent study [14] showed that UK SARS-CoV-2 strain, England 02/2020 remains viable for longer periods on hydrophobic surfaces (up to seven days) as compared with hydrophilic surfaces (three days).…”

Porous surfaces: stability and recovery of coronaviruses

“…Further differences in methodology that could affect the findings include the viral titre applied to the surface, which varies between studies (table 1). Paton et al [75] reported no significant difference ( p > 0.05) in SARS-CoV-2 decay on stainless steel between high (5.6 log 10 PFU) and low (3.6 log 10 PFU) inocula suggesting that inactivation is not associated with the viral load. Conversely, SARS-CoV-2 was detectable on paper for 30 min at 7.8 log 10 initial titre, with a 2.58 log 10 decline over this time period [11], compared to approximately 3.5 log 10 reduction over 5 days at 6.0 log 10 initial titre [74].…”

“…The droplet spreads due to capillary action between the contact line and fibres present on the porous surface, resulting in a modified effective-wetted area due to the voids of porous materials, which leads to enhanced disjoining pressure within the film, thereby accelerating film evaporation [85]. The absorption of droplets within hydrophilic materials also spreads virions over a larger surface area which prevents aggregation [75]. Desiccation may lead to the viral lipid envelope undergoing phase changes and oxidation, and Maillard reactions may occur within proteins, rendering the virus noninfectious.…”

“…Biphasic decay patterns may be caused by a heterogeneous population or the aggregation of viruses, which increases stability; this could lead to initial reductions of free virions followed by a slower rate of decay of aggregated virus [99]. Changes in salt concentration and pH encourage viral aggregate formation due to reduced electrostatic repulsion between viral surface proteins [75,88,100]. Aggregation is highly dependent on (i) the type of virus, hence why as the isoelectric points of viruses vary pH can mediate aggregation; (ii) the type of salts in solution (cation, anion, monovalent, divalent); and (iii) the overarching role that electrostatic and hydrophobic forces play in aggregate formation [99].…”