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.

The survival of newer variants of SARS-CoV-2 on a representative surface has been compared to the established UK circulating isolate to determine whether enhanced environmental stability could play a part in their increased transmissibility. Stainless steel coupons were inoculated with liquid cultures of the three variants, with coupons recovered over seven days and processed for recoverable viable virus using plaque assay. After drying, there was no significant difference in inactivation rates between variants, indicating that there is no increased environmental persistence from the new variants.

Octenidine based disinfection products are becoming increasingly popular for infection control of multidrug resistant (MDR) Gram-negative isolates. When a waste trap was removed from a hospital and allowed to acclimatise in a standard tap rig in our laboratory, it was shown that Klebsiella pneumoniae, Pseudomonas aeruginosa, Citrobacter and Enterobacter spp. were readily isolated. This study aimed to understand the potential impact of prolonged exposure to low doses of a commercial product containing octenidine on these bacteria. Phenotypic and genotypic analysis showed that P. aeruginosa strains had increased tolerance to octenidine which was characterised by mutations in the Tet-repressor SmvR. Enterobacter species demonstrated increased tolerance to many other cationic biocides, though not octenidine, as well as the antibiotics ciprofloxacin, chloramphenicol and ceftazidime through mutations in another Tet-repressor RamR. Citrobacter species with mutations in RamR and MarR were identified following octenidine exposure and this is linked to development of resistance to ampicillin, piperacillin and chloramphenicol as well as an increased MIC level for ciprofloxacin. Isolates were able to retain fitness as characterised by growth, biofilm formation and virulence in Galleria mellonella, after prolonged contact with octenidine, although there were strain to strain differences. These results demonstrate that continued low-level octenidine exposure in a simulated sink-trap environment selects for mutations which affect smvR. It may also promote microbial adaptation to other cationic biocides and cross-resistance to antibiotics, whilst not incurring a fitness cost. This suggests that hospital sink traps may act as a reservoir for more biocide tolerant organisms. Importance Multi-drug resistant (MDR) strains of bacteria are a major clinical problem and several reports have linked outbreaks of MDR bacteria with bacterial populations in hospital sinks. Biocides such as octenidine are used clinically in body washes and other products such as wound dressings for infection control. Therefore, increased tolerance to these biocides would be detrimental to infection control processes. Here, we exposed bacterial populations originally from hospital sink traps to repeated dosing with an octenidine containing product over several weeks and observed how particular species adapted. We found mutations in genes related to biocide and antibiotic susceptibility which resulted in increased tolerance, although this was species dependent. Bacteria which became more tolerant to octenidine also showed no loss of fitness. This shows that prolonged octenidine exposure has the potential to promote microbial adaptation in the environment and that hospital sink traps may act as a reservoir for increased biocide and antibiotic tolerant organisms.

Human transmission is believed to occur primarily through direct transfer of infectious droplets or aerosols. However, fomite transmission through contact with contaminated surfaces may also play an important role.

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 124 and 113 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 cotton was reduced second fastest, with 99.9% reduction in 72 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.