Efficacy of Silver Dihydrogen Citrate and Steam Vapor against a Human Norovirus Surrogate, Feline Calicivirus, in Suspension, on Glass, and on Carpet

Efficacy of three EPA-registered antimicrobials and steam against two human norovirus surrogates on nylon carpets with two backing types

Carpet cleaning guidelines currently do not include the use of an antimicrobial, except after a bodily fluid event. To address this gap, we compared the efficacy of three antimicrobials-two hydrogen peroxide-based (H2O2) products (A and B) and one chlorine-based product (C)-and a steam treatment against two norovirus surrogates, specifically feline calicivirus (FCV) and Tulane virus (TuV). These tests were performed on nylon carpets with either water-permeable or waterproof backing types. The effect of repeated antimicrobial use on carpet properties was also evaluated. For a carpet with water-permeable backing, products A, B, and C achieved a 0.8, 3.1, and 0.9 log10 PFU/coupon reduction of FCV and 0.3, 2.5, and 0.4 log10 TCID50/coupon reduction of TuV, respectively, following a 30 min contact time. For carpet with waterproof backing, only product B achieved a 5.0 log10 PFU/coupon reduction of FCV and >3.0 log10 TCID50/coupon reduction of TuV, whereas products A and C achieved a 2.4 and 1.6 log10 PFU/coupon reduction of FCV and a 1.2 and 1.2 log10 TCID50/coupon reduction of TuV, respectively. Steam treatment achieved a ≥ 5.2 log10 PFU/coupon reduction of FCV and a > 3.2 log10 TCID50/coupon reduction of TuV in 15 seconds on the carpet with both backing types. The repeated use of products A and B decreased the tensile strength of the carpet backing, while use of product B resulted in cracks on carpet fibers. Overall, steam treatment for 15 seconds was efficacious on both carpet types, but only product B achieved efficacy after a 30-minute exposure on the carpet with waterproof backing.IMPORTANCECarpets are common in long-term care facilities, despite its potential as a vehicle for transmission of agents associated with healthcare-associated infections, including human norovirus (NoV). Presently, our understanding of carpet disinfection is limited; hence, there are no commercial antimicrobials against norovirus available for use on carpets. Our findings showed that steam treatment, which minimally affected the properties of carpet fibers and backing, was more efficacious against human norovirus surrogates on carpets compared to the three chemical antimicrobials tested. Additionally, the two surrogates were more sensitive to chemical antimicrobials on the carpet with waterproof backing compared to carpets with water-permeable backing. These findings can inform development of antimicrobials for use on carpets contaminated with human norovirus.

Use of a silver-based sanitizer to accelerate Escherichia coli die-off on fresh-cut lettuce and maintain produce quality during cold storage: Laboratory and pilot-plant scale tests

Outbreaks and product recalls involving romaine and iceberg lettuce are frequently reported in the United States. Novel technologies are needed to inactivate pathogens without compromising product quality and shelf life. In this study, the effects of a process aid composed of silver dihydrogen citrate, glycerin, and lactic acid (SGL) on Escherichia coli and Listeria monocytogenes concentrations on lettuce immediately after washing and during cold storage were evaluated. Sensory and quality attributes of fresh-cut iceberg lettuce were also evaluated. Laboratory results indicated that application of SGL solution for 30 s as a first step in the washing process resulted in a 3.15 log reduction in E. coli O157:H7 immediately after washing. For E. coli O157:H7 a significant difference between SGL treatment and all other treatments was maintained until day 7. On day zero, SGL led to a 2.94 log reduction of L. monocytogenes. However, there was no significant difference between treatments with or without SGL regardless of storage time. Pilot-plant results showed that samples receiving SGL spray followed by chlorinated flume wash exhibited a greater reduction (1.48 log) in nonpathogenic E. coli populations at the end of shelf life than other treatments (p < 0.05). Additional pilot plant tests were conducted to investigate the hypothesis that SGL residues could continue to impact microbial survival on the final washed lettuce. Results show that pathogens introduced subsequent to flume washing of lettuce pretreated with SGL solution were not affected by antimicrobial residues. The final quality and shelf life of flume washed lettuce were also unaffected by pretreatment with SGL. In conclusion, the results of this study demonstrate that this new technology has the potential to accelerate E. coli die-off on fresh-cut lettuce during cold storage and improve product safety, while not affecting quality throughout the shelf life of the finished products.

Evaluation of Virucidal Quantitative Carrier Test towards Bovine Viruses for Surface Disinfectants While Simulating Practical Usage on Livestock Farms

Livestock farming is affected by the occurrence of infectious diseases, but outbreaks can be prevented by effective cleaning and disinfection along with proper farm management. In the present study, bovine coronavirus (BCoV) and bovine rotavirus A (RVA) were inactivated using food additive-grade calcium hydroxide (FdCa(OH)2) solution, quaternary ammonium compound (QAC) and their mixture through suspension tests as the primary screening, and afterward via carrier tests using dropping or dipping techniques as the secondary screenings. Viruses in the aqueous phase can be easily inactivated in the suspension tests, but once attached to the materials, they can become resistant to disinfectants, and require longer times to be inactivated. This highlights the importance of thorough cleaning with detergent before disinfection, and keeping elevated contact durations of proper disinfectants to reduce viral contamination and decrease infectious diseases incidence in farms. It was also reaffirmed that the suspension and carrier tests are necessary to evaluate disinfectants and thus determine their actual use. Particularly, the mixture of QAC and FdCa(OH)2 was found to exhibit synergistic and broad-spectrum effects compared to their use alone, and is now recommended for use on livestock farms.

Efficacy of EPA-registered disinfectants against two human norovirus surrogates and Clostridioides difficile endospores

AIMS

To determine the efficacy of a panel of nine EPA-registered disinfectants against two human norovirus (HuNoV) surrogates (feline calicivirus [FCV] and Tulane virus [TuV]) and Clostridioides difficile endospores.

METHODS AND RESULTS

Nine EPA-registered products, five of which contained H2 O2 as active ingredient, were tested against infectious FCV, TuV and C. difficile endospores using two ASTM methods, a suspension and carrier test. Efficacy claims against FCV were confirmed for 8 of 9 products. The most efficacious product containing H2 O2 as ingredient achieved a >5.1 log reduction of FCV and >3.1 log reduction of TuV after 5 min, and >6.0 log reduction of C. difficile endospores after 10 min. Of the five products containing H2 O2 , no strong correlation (R2  = 0.25, p = 0.03) was observed between disinfection efficacy and H2 O2 concentration. Addition of 0.025% ferrous sulphate to 1% H2 O2 solution improved efficacy against FCV, TuV and C. difficile.

CONCLUSION

Disinfectants containing H2 O2 are the most efficacious disinfection products against FCV, TuV and C. difficile endospores. Product formulation, rather than the concentration of H2 O2 in a product, impacts the efficacy of a disinfection product.

SIGNIFICANCE AND IMPACT OF STUDY

H2 O2 -based disinfectants are efficacious against surrogate viruses for HuNoV and C. difficile endospores.

Factors Impacting Persistence of Phi6 Bacteriophage, an Enveloped Virus Surrogate, on Fomite Surfaces

The persistence of Phi6 (Φ6) bacteriophage on surfaces commonly encountered in consumer-facing environments was evaluated. Φ6 has been utilized as a surrogate for enveloped viruses, including SARS-CoV-2—the causative agent of COVID-19—due to structural similarities, biosafety level 1 (BSL-1) status, and ease of use. Φ6 persistence on fomites was evaluated by characterizing the impact of the inoculum matrix (artificial saliva, phosphate-buffered saline [PBS], tripartite), inoculum level (low and high), and surface type (nonporous—aluminum, stainless steel, plastic, touchscreen, vinyl; porous—wood). Φ6 was inoculated onto surfaces at low and high inoculum levels for each inoculum matrix and incubated (20.54 ± 0.48°C) for up to 168 h. Φ6 was eluted from the surface and quantified via the double agar overlay assay to determine virus survival over time. For nonporous surfaces inoculated with artificial saliva and PBS, significantly higher D values were observed with high inoculum application according to the 95% confidence intervals. In artificial saliva, D values ranged from 1.00 to 1.35 h at a low inoculum and 4.44 to 7.05 h at a high inoculum across inoculation matrices and surfaces. D values for Φ6, regardless of the inoculum level, were significantly higher in tripartite than in artificial saliva and PBS for nonporous surfaces. In contrast with artificial saliva or PBS, D values in tripartite at low inoculum (D values ranging from 45.8 to 72.8 h) were greater than those at high inoculum (D values ranging from 26.4 to 45.5 h) on nonporous surfaces. This study characterized the impact of the inoculum matrix, inoculum level, and surface type on Φ6 survival on various surfaces relevant to fomite transmission in public settings.

IMPORTANCE An important consideration in virus contact transmission is the transfer rate between hands and surfaces, which is driven by several factors, including virus persistence on inanimate surfaces. This research characterized Φ6 persistence on surfaces commonly encountered in public settings based on various factors. The inoculum matrix, which simulates the route of transmission, can impact virus persistence, and three separate matrices were evaluated in this study to determine the impact on Φ6 persistence over time. The number of microorganisms has also been suggested to impact persistence, which was evaluated here to simulate real-world contamination scenarios on six surface types. Results from this study will guide future research utilizing Φ6 or other surrogates for enveloped viruses of public health concern.

In vitro virucidal efficacy of a dry steam disinfection system against Human Coronavirus, Human Influenza Virus, and Echovirus

This in vitro study was aimed to assess the efficacy of dry steam in inactivating Human Coronavirus OC43 (HCoV-OC43) as surrogate of SARS-CoV-2, Human Influenza Virus A/H1N1/WSN/33 and Echovirus 7 on stainless steel, polypropylene, and cotton. The virus models were chosen on the basis of their transmission route and environmental resistance. Tests were carried out under a laminar flow cabinet, where two panels of each material were contaminated with a viral suspension. The inocula were left to dry and then the virus on untreated panel (control) was collected by swabbing in order to determine the initial titer. The other panel was treated using a professional vacuum cleaner equipped with a dry steam generator. Dry steam is generated in a boiler where tap water is heated up to 155 °C at 5.5 bar pressure and then during the passage along the flexible hose the temperature decreases to a value between 100 °C and 110 °C at the output. The dry steam was applied for four sec with a window wiper on metal and plastic panels or a brush covered by a microfiber cap on cotton, simulating the steam application during routine cleaning. After the treatment, infectious virus possibly remained on the surface was collected following the same swabbing procedure applied for controls. HCoV-OC43 and Echovirus 7 were titrated by end-point method on HCT-8 line cells and Vero cells, respectively, while Human Influenza Virus was quantified by plaque reduction assay on MDCK cells. Dry steam resulted effective against the three viruses on all tested materials, achieving a mean Log₁₀ reduction factor ≥4 in viral titer of treated samples compared with controls according to UNI EN 14476:2019. Thus, dry steam may be proposed as an ease to use, effective, fast, and nontoxic alternative to chemicals for surface disinfection without damaging materials. Therefore, this device could be employed not only in healthcare facilities but also in occupational, domestic, and community settings, with advantages for environment and human health.

Efficacy of novel aqueous photo-chlorine dioxide against a human norovirus surrogate, bacteriophage MS2 and Clostridium difficile endospores, in suspension, on stainless steel and under greenhouse conditions

AIMS

The efficacy of a novel photochemical method for generating chlorine dioxide (photoClO₂ ) was evaluated against human noroviruses (HuNoV) surrogate, bacteriophage MS2, and Clostridium difficile endospores.

METHODS AND RESULTS

Chlorine dioxide was generated by mixing 1% sodium chlorite with 10 parts-per-million (ppm) Eosin Y and irradiating with a photo-activator-excitable light. PhotoClO₂ efficacy was assessed against bacteriophage MS2 and C. difficile endospores in suspension, on hard surfaces and greenhouse conditions under soiled and unsoiled conditions. The estimated effective photoClO₂ produced and consumed was 20·39 ± 0·16 ppm at a rate of 8·16 ppm per min in a 1% sodium chlorite solution. In suspension, MS2 phage was reduced by 3·35 and >5·10 log₁₀ PFU per ml in 120 and 90 min, with and without soil, respectively. At the same time, when dried on stainless steel surface, MS2 phage was reduced by >4·53 log₁₀ PFU per carrier in 30 min under both conditions. On the other hand, C. difficile endospores in suspension were reduced by 2·26 and 3·65 log₁₀ CFU per ml in 120 min with and without soiling, respectively. However, on stainless steel surface, maximal reductions of the C. difficile endospores were 0·8 and 1·5 log₁₀ CFU per carrier with and without soiling, respectively, and a maximal reduction of 2·97 log₁₀ CFU per carrier under greenhouse conditions at 24 h.

CONCLUSIONS

Overall, photoClO₂ showed promise as a technology to control HuNoV contamination on environmental surfaces but requires further optimization and testing against C. difficile endospores.

SIGNIFICANCE AND IMPACT OF THE STUDY

Results from this investigation will serve as a model for how to generate and quantify photoClO₂ and how to appropriately evaluate this new class of disinfectants against environmentally resilient pathogens: viruses and bacterial endospores.

Sanitizing agents for virus inactivation and disinfection

Viral epidemics develop from the emergence of new variants of infectious viruses. The lack of effective antiviral treatments for the new viral infections coupled with rapid community spread of the infection often result in major human and financial loss. Viral transmissions can occur via close human-to-human contact or via contacting a contaminated surface. Thus, careful disinfection or sanitization is essential to curtail viral spread. A myriad of disinfectants/sanitizing agents/biocidal agents are available that can inactivate viruses, but their effectiveness is dependent upon many factors such as concentration of agent, reaction time, temperature, and organic load. In this work, we review common commercially available disinfectants agents available on the market and evaluate their effectiveness under various application conditions. In addition, this work also seeks to debunk common myths about viral inactivation and highlight new exciting advances in the development of potential sanitizing agents.

Control of norovirus infection

PURPOSE OF REVIEW

The purpose of the review is to provide an update on control measures for norovirus (NoV), which is the most commonly implicated pathogen in acute gastroenteritis and outbreaks, causing major disruption in nurseries, schools, hospitals and care homes.

RECENT FINDINGS

Important developments include the discovery that virus particles, previously considered to be the infectious unit, also occur in clusters, which appear to be more virulent than individual virus particles; a working culture system using human stem-cell derived enteroids; promising results from early phase clinical trials of candidate NoV vaccines, which appear to be safe and immunogenic; chronic NoV affects patients with primary and secondary immune deficiencies. Although several treatments have been used none are supported by well designed clinical trials; infection control procedures are effective if properly implemented.

SUMMARY

NoV remains an important cause of morbidity and mortality. Although there are exciting developments on the vaccine front, the mainstay of control remains good hand hygiene, adherence to infection control procedures and limiting contamination of food, water and the wider environment. Once vaccines are available there will be important decisions to be made about how best to implement them.