Respiratory viruses remain viable on inanimate, environmental surfaces (ie, fomites) for extended periods of time depending on temperature, humidity, and other factors.
Significance of fomites in the spread of respiratory disease and enteric viral disease.
Effective cleaning and surface disinfection practices reduce levels of infectious viruses and the potential for their spread.
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- et al.
Control of the spread of viruses in a long-term care facility using hygiene protocols.
Nevertheless, recontamination can occur at any time following the use of liquid disinfectants, which are typically wiped dry from surfaces after application. A number of self-disinfecting surface formulations have been developed during recent years.
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- Teixeria JP.
Self-disinfecting surfaces and infection control.
A continuously-active quaternary ammonium polymer applied to high-touch surfaces by certified technicians using electrostatic sprayers previously resulted in the reduced spread of antibiotic-resistant bacterial infections in clinical settings.
- Ellingson KD
- Pogreba-Brown K
- Gerba CP
- Elliott SP
Impact of a novel antimicrobial surface coating on health care-associated infections and environmental, at 2 urban hospitals.
The formulation was subsequently modified to increase cationic functionality for more efficient disruption of the lipid bilayers that comprise bacterial membranes and viral envelopes. Human coronavirus 229E (HCoV-229E), a seasonal enveloped respiratory pathogen of humans, has been employed as a surrogate for emergent coronaviruses to assess persistence, survival, and antiviral efficacy.
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- Del Giudice C
- Morelli M
- et al.
Persistence of SARS-CoV-2 in the environment and COVID-19 transmission risk from environmental matrices and surfaces.
The objective of this study was to assess the antiviral effectiveness of the new formulation following application to stainless steel coupons against SARS-related Coronavirus 2 (SARS-CoV-2) and HCoV-229E.
Acetone-washed, pre-autoclaved stainless-steel coupons (Type 304, unidirectional finish) coated with the reformulated quaternary ammonium polymer (SurfaceWise2) were supplied by Allied BioScience, Inc (Dallas, TX). An electrostatic sprayer mounted onto a robotic slide was used to coat the coupons, with coverage uniformity monitored by an x-ray fluorescence spectrometer. The coating was cured overnight under ambient conditions. Non-coated stainless-steel coupons were used as control surfaces. The carriers were not subjected to wear and abrasion testing prior to experimentation.
Human coronavirus 229E and the two cell lines used in the study, MRC-5 and Vero E6, were procured from the American Type Culture Collection (ATCC; Manassas, VA). SARS-CoV-2 Isolate USA-WA1/2020 was deposited by the Centers for Disease Control and Prevention and obtained through BEI Resources, The National Institute of Allergies and Infectious Disease (NIAID), and The National Institutes of Health (NIH). All laboratory work involving SARS-CoV-2 was conducted within a Biosafety Level 3 laboratory.
HCoV-229E (ATCC VR-740) and SARS-CoV-2 (BEI NR-52281) stocks were prepared according to the coronavirus propagation protocol described by Gundy et al.
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- Gerba CP
- Pepper IL
Survival of coronaviruses in water and wastewater.
using the MRC-5 (ATCC CCL-171) and Vero E6 (ATCC CRL-1586) cell lines, respectively. Stock virus concentrations were determined using the TCID50
(tissue culture infectious dose at the 50% endpoint) assay technique as described by Hierholzer and Killington (1996)
- Hierholzer JC
- Killington RA
- Stokes A
Virology Methods Manual.
, and quantified using the Spearman-Karber algorithm.
Antiviral efficacy of the coating was assessed using the American Society of Testing and Materials E1053-20 Method.
ASTM International. ASTM E1053-20. Standard practice to assess virucidal activity of chemicals intended for disinfection of inanimate, nonporous environmental surfaces. 2020. Accessed April 15, 2020. https://www.astm.org/Standards/E1053.htm
Modifications to the method were 1) the use of stainless-steel coupons, and 2) preapplication of the polymer coating to the coupons followed by inoculation of virus. Test 1 against HCoV-229E (Table 1
) was performed by inoculating 0.10 mL of stock virus onto polymer-coated and noncoated control coupons (25.81 cm2
) mounted into sterile Petri dishes, with spreading over the surface to within ∼0.32 cm of the perimeter edge. The coupons were incubated (22-23°C; 30-50% relative humidity) for 2 hours with the Petri dish lids on. Swabs predipped in Letheen Broth Base (LBB; Neogen Corp., Lansing, MI) were used for product neutralization and to harvest viruses from carriers. The swabs were placed into tubes containing 1 mL of LBB and vortexed vigorously. The suspensions were immediately passed through Sephadex G-10 gel columns by centrifugation (5 minutes at 3,500 × g
). Subsequent tests against HCoV-229E (Test 2) and SARS-CoV-2 were modified by the addition of 5% soil in the form of fetal bovine serum (FBS), and by decreasing the carrier size and viral inoculum volume (Table 1
). A wash method was also employed by rinsing the carriers 4-5 times using 1 mL of LBB, with further virus detachment using a cell scraper. Gel filtration followed as described. Neutralized suspensions underwent 1:10 serial dilutions using minimal essential media (Mediatech, Inc., Manassas, VA) followed by plating onto host cell monolayers in 96-well trays (6 replicates per dilution). Following incubation at 35°C in a 5% CO2
atmosphere, wells were scored for the presence of cytopathogenic effects and cytotoxicity. The method of neutralization was also validated per ASTM E1053-20
(data not shown). Additional assay parameters are listed in Table 1
Table 1Experimental parameters for human coronavirus 229E and SARS-CoV-2 antiviral efficacy testing
The reformulated quaternary ammonium coating achieved >99.9% reduction of HCoV-229E and SARS-CoV-2 during the 2-hour contact time in the absence and presence of 5% organic soil (Table 2
). The wash method for harvesting the carriers facilitated greater recovery of viruses compared to the swab method. Cytotoxicity was observed in the lowest plated dilution (100
) of Vero E6 cells, while no toxic effects were evident on MRC-5 cells at the 100
Table 2Viral recovery (log10) and reduction of HCoV-229E and SARS-CoV-2 on quaternary ammonium polymer-coated coupons relative to noncoated stainless steel carriers at 2 hours *,
CPE, cytopathogenic effects; N.A., Not applicable; N.D., Not determined.
All noncoated control and coated coupons tested in triplicate (n = 3) per contact time, except for coated test coupons against SARS-CoV-2 (n = 6).
The results demonstrate similar reductions of >99.9% (>3-log10) for HCoV-229E and SARS-CoV-2 following 2 hours of exposure to the reformulated quaternary ammonium coating applied to stainless steel coupons. However, further studies are warranted to assess effectiveness following application to a variety of nonporous and porous surface types. Recovery levels of both viruses from noncoated study controls after 2 hours suggest comparative rates of inactivation on Type 304 stainless steel under the environmental conditions implemented, although a larger sample size would be preferable to confirm statistical significance. Cytotoxic effects were observed after plating undiluted (100) neutralized filtrates from coated carriers onto Vero E6 host cells, while none were observed on MRC-5 cells. Widespread cell monolayer damage in the absence of infectious viruses typifies cytotoxicity; therefore, dilutions that display such effects are not utilized to calculate log10 reductions. However, they are determinative in establishing assay detection limits which can vary by orders of magnitude as observed for the HCoV-229E and SARS-CoV-2 assays (≤0.50 log10 and ≤1.50 log10, respectively).
Surface-active coatings that have antiviral capabilities are not meant to substitute for regular cleaning and disinfection practices, but rather serve as an additional barrier for reducing human exposure to infectious viruses that may be present on fomites.
- Rutala WA
- Gergen MF
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- Weber DJ
Antimicrobial activity of a continuously active disinfectant against healthcare pathogens.
With the recent detection of infectious SARS-CoV-2 from the bedside table, remote control, bed rails, and flooring in the hospital room of an infected patient,
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- Sohn Y
- et al.
Environmental contamination in the isolation rooms of COVID-19 patients with severe pneumonia requiring mechanical ventilation or high-flow oxygen therapy.
the importance of effective hygiene protocols for environmental surfaces remains imperative.