A systematic review of human norovirus survival reveals a greater persistence of human norovirus RT-qPCR signals compared to those of cultivable surrogate viruses

Persistence of Infectious Human Norovirus in Estuarine Water

Norovirus is the predominant cause of viral acute gastroenteritis globally. While person-to-person is the most reported transmission route, norovirus is also associated with waterborne and foodborne illness, including from the consumption of contaminated bivalve molluscan shellfish. The main cause of shellfish contamination is via the bioaccumulation of norovirus from growing waters impacted by human wastewater. However, data on the persistence of infectious norovirus in the environment are limited due to a lack of a human norovirus culture method in the past. In this study, we applied the recently established method of norovirus replication in human intestinal enteroids to determine the persistence of norovirus in artificial estuarine water at 25 ppt for up to 21 days at 4 °C and 16 °C in the dark. Infectious norovirus was detected for up to 21 days. The relative infectivity declined from 100 to 3% at day 21, with decay rate constants of 0.07 day-1 at 4 °C and 0.17 day-1 at 16 °C. There was no decrease in norovirus titres as measured by reverse transcription-droplet digital PCR (RT-ddPCR), confirming the lack of the relationship between norovirus infectivity and direct detection by PCR. The results confirm that norovirus can remain infectious for at least 3 weeks in an estuarine water environment, presenting associated health risks.

Heat inactivation of aqueous viable norovirus and MS2 bacteriophage

AIMS

This study aimed to compare the heat inactivation kinetics of viable human norovirus with the surrogate, MS2 bacteriophage as well as assess the decay of the RNA signal.

METHODS AND RESULTS

Human intestinal enteroids were used to analyze the heat inactivation kinetics of viable human norovirus compared to the surrogate MS2 bacteriophage, which was cultured using a plaque assay. Norovirus decay rates were 0.22 min-1, 0.68 min-1, and 1.11 min-1 for 50°C, 60°C, and 70°C, respectively, and MS2 bacteriophage decay rates were 0.0065 min-1, 0.045 min-1, and 0.16 min-1 for 50°C, 60°C, and 70°C, respectively. Norovirus had significantly higher decay rates than MS2 bacteriophage at all tested temperatures (P = .002-.007). No decrease of RNA titers as measured by reverse transcription-PCR for both human norovirus and MS2 bacteriophage over time was observed, indicating molecular methods do not accurately depict viable human norovirus after heat inactivation and treatment efficiency is underestimated.

CONCLUSIONS

Overall, our data demonstrate that MS2 bacteriophage is a conservative surrogate to measure heat inactivation and potentially overestimates the infectious risk of norovirus. Furthermore, this study corroborates that measuring viral RNA titers, as evaluated by PCR methods, does not correlate with the persistence of viable norovirus under heat inactivation.

Performance of Manufacturer Cleaning Recommendations Applied to 3D Food Ink Capsules for the Control of a Human Norovirus Surrogate

With the widespread availability of 3D food printing systems for purchase, users can customize their food in new ways. Manufacturer recommendations for cleaning these machines remain untested with regard to the prevention of foodborne pathogen transmission. This study aimed to determine if manufacturer cleaning recommendations for food ink capsules utilized in 3D food printers are adequate to control human norovirus (HuNoV). A HuNoV surrogate, Tulane virus (TuV; ~ 6 log₁₀ PFU/mL), was inoculated onto the interior surface of stainless steel food ink capsules. Capsules were either unsoiled or soiled with one of the following: butter, protein powder solution, powdered sugar solution, or a mixture containing all three food components. The capsules were allowed to dry and then one of three hygienic protocols was applied: manual washing (MW), a dishwasher speed cycle (DSC), or a dishwasher heavy cycle (DHC). The interaction effect between DSC and pure butter was a significant predictor of log reduction (P = 0.0067), with the pure butter and DSC combination achieving an estimated mean log reduction of 4.83 (95% CI 4.13, 5.59). The DSC was the least effective method of cleaning when compared with MW and the DHC. The 3-way interaction effects between wash type, soil, and capsule position were a significant predictor of log reduction (P = 0.00341). Capsules with butter in the DSC achieved an estimated mean log reduction of 2.81 (95% CI 2.80, 2.83) for the front-most position versus 6.35 (95% CI 6.33, 6.37) for the back-most position. Soil matrix, cleaning protocol, and capsule position all significantly impact capsule cleanability and potential food safety risk. The DHC is recommended for all capsules, and the corners should be avoided when placing capsules into the dishwasher. The current study seeks to provide recommendations for users of additive manufacturing and 3D food printing including consumers, restaurants, industry, and regulatory industries.

Inactivation of Human Norovirus GII.4 and Vibrio parahaemolyticus in the Sea Squirt (Halocynthia roretzi) by Floating Electrode-Dielectric Barrier Discharge Plasma

Human norovirus (HNoV) GII.4 and Vibrio parahaemolyticus may be found in sea squirts. Antimicrobial effects of floating electrode-dielectric barrier discharge (FE-DBD) plasma (5-75 min, N₂ 1.5 m/s, 1.1 kV, 43 kHz) treatment were examined. HNoV GII.4 decreased by 0.11-1.29 log copy/μL with increasing duration of treatment time, and further by 0.34 log copy/μL when propidium monoazide (PMA) treatment was added to distinguish infectious viruses. The decimal reduction time (D₁) of non-PMA and PMA-treated HNoV GII.4 by first-order kinetics were 61.7 (R² = 0.97) and 58.8 (R² = 0.92) min, respectively. V. parahaemolyticus decreased by 0.16-1.5 log CFU/g as treatment duration increased. The D₁ for V. parahaemolyticus by first-order kinetics was 65.36 (R² = 0.90) min. Volatile basic nitrogen showed no significant difference from the control until 15 min of FE-DBD plasma treatment, increasing after 30 min. The pH did not differ significantly from the control by 45-60 min, and Hunter color in "L" (lightness), "a" (redness), and "b" (yellowness) values reduced significantly as treatment duration increased. Textures appeared to be individual differences but were not changed by treatment. Therefore, this study suggests that FE-DBD plasma has the potential to serve as a new antimicrobial to foster safer consumption of raw sea squirts.

Viable Norovirus Persistence in Water Microcosms

Human noroviruses are one of the leading causes of acute gastroenteritis worldwide. Based on quantitative microbial risk assessments, norovirus contributes the greatest infectious risk of any pathogen from exposure to sewage-contaminated water; however, these estimates have been based upon molecular (i.e., RNA-based) data as human norovirus has remained largely unculturable in the laboratory. Current approaches to assess the environmental fate of noroviruses rely on the use of culturable surrogate viruses and molecular methods. Human intestinal enteroids (HIEs) are an emerging cell culture system capable of amplifying viable norovirus. Here, we applied the HIE assay to assess both viable norovirus and norovirus RNA persistence in surface, tap, and deionized water microcosms. Viable norovirus decreased to below the detection limit in tap and deionized water microcosms and was measured in a single replicate in the surface water microcosm at study conclusion (28 days). Conversely, the norovirus RNA signal remained constant over the duration of the study, even when viable norovirus was below the limit of detection. Our findings demonstrate the disconnect between current environmental norovirus detection via molecular methods and viability as assessed through the HIE assay. These results imply that molecular norovirus monitoring is not inherently representative of infectious norovirus.

A metagenomic insight into the Yangtze finless porpoise virome

The Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis) inhabiting the Yantze River, China is critically endangered because of the influences of infectious disease, human activity, and water contamination. Viral diseases are one of the crucial factors that threatening the health of Yangtze finless porpoise. However, there are few studies which elaborate the viral diversity of Yangtze finless. Therefore, this study was performed to investigate the viral diversity of Yangtze finless by metagenomics. Results indicated that a total of 12,686,252 high-quality valid sequences were acquired and 2,172 virus reads were recognized. Additionally, we also obtained a total of 10,600 contigs. Phages was the most abundant virus in the samples and the ratio of DNA and RNA viruses were 69.75 and 30.25%, respectively. Arenaviridae, Ackermannviridae and Siphoviridae were the three most predominant families in all the samples. Moreover, the majority of viral genus were Mammarenavirus, Limestonevirus and Lambdavirus. The results of gene prediction indicated that these viruses play vital roles in biological process, cellular component, molecular function, and disease. To the best of our knowledge, this is the first report on the viral diversity of Yangtze finless porpoise, which filled the gaps in its viral information. Meanwhile, this study can also provide a theoretical basis for the establishment of the prevention and protection system for virus disease of Yangtze finless porpoise.

Recent Update on UV Disinfection to Fulfill the Disinfection Credit Value for Enteric Viruses in Water

Ultraviolet (UV) radiation alone or in combination with other oxidation processes is increasingly being considered for water disinfection because of stringent regulatory requirements for pathogen inactivation. To fulfill this requirement, an appropriate UV dose or fluence (mJ/cm²) is applied to combat enteric viruses in surface or treated water. There is a need for a cumulative review on the effectiveness of current and emerging UV technologies against various types of human enteric viruses. We extracted the kinetics data from 52 selected experimental studies on enteric virus inactivation using low pressure (LP-UV), medium pressure (MP-UV), UV-LED, and advanced oxidation processes (AOPs) and applied a simple linear regression analysis to calculate the range of UV fluence (mJ/cm²) needed for 4-log₁₀ inactivation. The inactivation of adenoviruses with LP-UV, MP-UV, and UV/H₂O₂ (10 mg/L) required the highest fluence, which ranged from 159 to 337, 45, and 115 mJ/cm², respectively. By contrast, when using LP-UV, the inactivation of other enteric viruses, such as the Caliciviridae and Picornaviridae family and rotavirus, required fluence that ranged from 19 to 69, 18 to 43, and 38 mJ/cm², respectively. ssRNA viruses exhibit higher sensitivity to UV radiation than dsRNA and DNA viruses. In general, as an upgrade to LP-UV, MP-UV is a more promising strategy for eliminating enteric viruses compared to AOP involving LP-UV with added H₂O₂ or TiO₂. The UV-LED technology showed potential because a lower UV fluence (at 260 and/or 280 nm wavelength) was required for 4-log₁₀ inactivation compared to that of LP-UV for most strains examined in this critical review. However, more studies evaluating the inactivation of enteric viruses by means of UV-LEDs and UV-AOP are needed to ascertain these observations.

Inactivation of Foodborne Viruses by UV Light: A Review

Viruses on some foods can be inactivated by exposure to ultraviolet (UV) light. This green technology has little impact on product quality and, thus, could be used to increase food safety. While its bactericidal effect has been studied extensively, little is known about the viricidal effect of UV on foods. The mechanism of viral inactivation by UV results mainly from an alteration of the genetic material (DNA or RNA) within the viral capsid and, to a lesser extent, by modifying major and minor viral proteins of the capsid. In this review, we examine the potential of UV treatment as a means of inactivating viruses on food processing surfaces and different foods. The most common foodborne viruses and their laboratory surrogates; further explanation on the inactivation mechanism and its efficacy in water, liquid foods, meat products, fruits, and vegetables; and the prospects for the commercial application of this technology are discussed. Lastly, we describe UV’s limitations and legislation surrounding its use. Based on our review of the literature, viral inactivation in water seems to be particularly effective. While consistent inactivation through turbid liquid food or the entire surface of irregular food matrices is more challenging, some treatments on different food matrices seem promising.

Optimizing Human Intestinal Enteroids for Environmental Monitoring of Human Norovirus

Human noroviruses (HuNoV) are the leading cause of gastrointestinal illness and environmental monitoring is crucial to prevent HuNoV outbreaks. The recent development of a HuNoV cell culture assay in human intestinal enteroids (HIEs) has enabled detection of infectious HuNoV. However, this complex approach requires adaptation of HIEs to facilitate HuNoV replication from environmental matrixes. Integrating data from 200 experiments, we examined six variables: HIE age, HIE basement membrane compounds (BMC), HuNoV inoculum processing, HuNoV inoculum volume, treatment of data below limit of detection (LOD), and cutoff criteria for determining positive HuNoV growth. We infected HIEs with HuNoV GII.4 Sydney positive stool and determined 1.4 × 103 genome equivalents per HIE well were required for HuNoV replication. HIE age had minimal effect on assay outcomes. LOD replacement and cutoff affected data interpretation, with lower values resulting in higher estimated HuNoV detection. Higher inoculum volumes lead to minimal decreases in HuNoV growth, with an optimal volume of 250uL facilitating capture of low concentrations of HuNoVs present in environmental isolates. Processing of HuNoV inoculum is valuable for disinfection studies and concentrating samples but is not necessary for all HIE applications. This work enhances the HuNoV HIE cell culture approach for environmental monitoring. Future HIE research should report cell age as days of growth and should clearly describe BMC choice, LOD handling, and positive cutoff.

Application of Chitosan Microparticles against Human Norovirus

ABSTRACT

Human norovirus (HuNoV) is the leading cause of foodborne illness outbreaks and the second most common cause of waterborne infections in the United States. The goal of this research was to investigate the antiviral activity of chitosan microparticles (CMs) against HuNoV GII.4 Sydney and its cultivable surrogate Tulane virus (TuV) in suspensions mimicking fecally contaminated water. CMs were prepared by cross-linking chitosan molecules with sodium sulfate, and the antiviral activity of CMs was assessed with an infectivity assay on TuV and by quantitative reverse transcription PCR on TuV and HuNoV. A 3% CM suspension in phosphate-buffered saline (pH 7.2) bound to TuV particles but had a negligible impact on virus infectivity (P > 0.05). A 10-min contact time resulted in a 1.5-log reduction in genomic copies per mL of TuV and HuNoV in fecal suspensions (P < 0.05). Despite the negligible impact on viral infectivity, CMs can moderately bind to infectious virus particles and help purify environmental water by removing these particles. In this study, TuV was a suitable surrogate for HuNoV with similar log reductions in fecal suspension. These findings highlight the potential application of CM as a novel treatment to minimize the spread of waterborne viral pathogens.

HIGHLIGHTS

The globally re-emerging norovirus GII.2 manifests higher heat resistance than norovirus GII.4 and Tulane virus

AIMS

To compare the heat stability of two globally prevalent human norovirus (HuNoV) strains (GII.2[P16] and GII.4[P16]) and a commonly used HuNoV surrogate, Tulane virus (TV).

METHODS AND RESULTS

With the use of a newly developed zebrafish larvae platform, we measured the change of infectivity of HuNoV GII.2[P16] and GII.4[P16] toward mild heat treatment at 55°C for 5 min. TV was tested with the same experimental design. As a result, the virus infectivity measurement clearly indicated the higher heat resistance of HuNoV GII.2[P16] (no reduction) than GII.4[P16] (>0.8-log TCID₅₀  ml^-1 reduction) and TV (2.5-log TCID₅₀  ml^-1 reduction). Further exploration revealed higher virus structural stability of HuNoV GII.2 than GII.4 strains by the use of different clinical samples with different evaluation methods.

CONCLUSION

The inactivation data generated from the surrogate virus TV cannot be used directly to describe the inactivation of HuNoV. The phylogenetic classification of HuNoVs may correlate with the virus stability and/or circulation dynamics.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study is expected to serve as an important reference when revisiting the numerous previous data evaluating HuNoV inactivation conditions in foods with the use of TV as the cultivable surrogate or with genuine HuNoV but using molecular methods. The higher resistance of NoV GII.2 strains than GII.4 strains toward inactivation treatment supplies a possible explanation for the global re-emerging of NoV GII.2 epidemic in recent years.

Detection and Quantification of Enteric Pathogens in Aerosols Near Open Wastewater Canals in Cities with Poor Sanitation

Urban sanitation infrastructure is inadequate in many low-income countries, leading to the presence of highly concentrated, uncontained fecal waste streams in densely populated areas. Combined with mechanisms of aerosolization, airborne transport of enteric microbes and their genetic material is possible in such settings but remains poorly characterized. We detected and quantified enteric pathogen-associated gene targets in aerosol samples near open wastewater canals (OWCs) or impacted (receiving sewage or wastewater) surface waters and control sites in La Paz, Bolivia; Kanpur, India; and Atlanta, USA, via multiplex reverse-transcription qPCR (37 targets) and ddPCR (13 targets). We detected a wide range of enteric targets, some not previously reported in extramural urban aerosols, with more frequent detections of all enteric targets at higher densities in La Paz and Kanpur near OWCs. We report density estimates ranging up to 4.7 × 10² gc per m_air³ across all targets including heat-stable enterotoxigenic Escherichia coli, Campylobacter jejuni, enteroinvasive E. coli/Shigella spp., Salmonella spp., norovirus, and Cryptosporidium spp. Estimated 25, 76, and 0% of samples containing positive pathogen detects were accompanied by culturable E. coli in La Paz, Kanpur, and Atlanta, respectively, suggesting potential for viability of enteric microbes at the point of sampling. Airborne transmission of enteric pathogens merits further investigation in cities with poor sanitation.

Advances and Future Perspective on Detection Technology of Human Norovirus

Human norovirus (HuNoV) is a food-borne pathogen that causes acute gastroenteritis in people of all ages worldwide. However, no approved vaccines and antiviral drugs are available at present. Therefore, the development of accurate and rapid detection technologies is important in controlling the outbreak of HuNoVs. This paper reviewed the research progress on HuNoV detection, including immunological methods, molecular detection and biosensor technology. Immunological methods and molecular detection technologies are still widely used for HuNoV detection. Furthermore, biosensors will become an emerging developmental direction for the rapid detection of HuNoVs because of their high sensitivity, low cost, easy operation and suitability for onsite detection.

Extraction of human noroviruses from leafy greens and fresh herbs using magnetic silica beads

Consumption of leafy greens and to a lesser extent fresh herbs has been associated with several foodborne outbreaks including human norovirus (HuNoV). However, the extraction and detection of viruses from these matrices present multiple challenges such as low recovery yields and relatively high PCR inhibition. A new magnetic silica bead based (MSB) extraction protocol was developed and used to recover norovirus from leafy greens and fresh herbs. The performance results were compared to the ISO 15216-1:2017 standard. The HuNoV GII.4 and GI.5 recovery yields from spiked lettuce using the MSB extraction protocol range from 33 to 82%. There was a good correlation between murine norovirus (MNV) and HuNoV recovery yields from fresh herbs and leafy greens. No reverse-transcriptase quantitative polymerase chain reaction (RT-qPCR) inhibition was detected from leafy green extracts using the MSB methodology. The selected commercial RT-qPCR detection kit had a major impact on RT-qPCR inhibition levels detected in the ISO 15216-1:2017 RNA extracts. RNase treatment was used to estimate genome recovery from HuNoV with intact capsids. This treatment resulted in similar HuNoV and MNV recovery yields. Between 2019 and 2020, the MSB protocol was used to conduct a survey of HuNoV in domestic and imported leafy greens and fresh herbs sold at retail in Canada. All of the 280 samples tested were negative. Overall, the use of MSB was shown to be an efficient approach to recover HuNoV from leafy greens and certain types of fresh herbs and to conduct surveys.

Recovery of Infectious Human Norovirus GII.4 Sydney From Fomites via Replication in Human Intestinal Enteroids

Contamination of fomites by human norovirus (HuNoV) can initiate and prolong outbreaks. Fomite swabbing is necessary to predict HuNoV exposure and target interventions. Historically, swab recovered HuNoV has been measured by molecular methods that detect viral RNA but not infectious HuNoV. The recent development of HuNoV cultivation in human intestinal enteroids (HIEs) enables detection of infectious HuNoV. It is unknown if the swabbing process and swab matrix will allow for cultivation of fomite recovered HuNoV. We used HIEs to culture swab-recovered HuNoV GII.4 Sydney from experimentally infected surfaces—a hospital bed tray (N = 32), door handle (N = 10), and sanitizer dispenser (N = 11). Each surface was swabbed with macrofoam swabs premoistened in PBS plus 0.02% Tween80. Swab eluate was tested for infectious HuNoV by cultivation in HIE monolayers. Infectious HuNoV can be recovered from surfaces inoculated with at least 10⁵ HuNoV genome equivalents/3 cm². In total, 57% (N = 53) of recovered swabs contained infectious HuNoV detected by HIEs. No difference in percent positive swabs was observed between the three surfaces at p = 0.2. We demonstrate that fomite swabbing can be combined with the HIE method to cultivate high titer infectious HuNoV from the environment, filling a significant gap in HuNoV detection. Currently, high titers of HuNoV are required to measure growth in HIEs and the HIE system precludes absolute quantification of infectious viruses. However, the HIE system can provide a binary indication of infectious HuNoV which enhances existing detection methods. Identification of infectious HuNoVs from swabs can increase monitoring accuracy, enhance risk estimates, and help prevent outbreaks.

Antiviral Effects of Pomegranate Peel Extracts on Human Norovirus in Food Models and Simulated Gastrointestinal Fluids

Human noroviruses (HuNoV) are the dominant cause of viral gastroenteritis in all age groups worldwide. In this study, we investigated the effects of pomegranate peel extract (PPE) on the reduction of HuNoV in different food models, on surfaces of fresh produce (green onion and cherry tomato), in low-fat milk, and simulated gastrointestinal fluids. The antiviral efficacy of PPE against HuNoV was evaluated by quantifying the number of residual virus genomes using a quantitative reverse transcription PCR (qRT-PCR) assay. Pomegranate peel, considered as a waste product of industrial processing, is known for beneficial health effects and broad antimicrobial activity due to the high content of phenolic compounds and tannins. PPE showed significant antiviral properties against HuNoV both in phosphate-buffered saline (PBS) and simulated gastric fluid. The reduction of HuNoV by pomegranate juice was lower than with PPE, which could be attributed to the lower content of antimicrobial compounds. A pretreatment of cherry tomato and green onion surfaces with PPE significantly reduced the amount of HuNoV particles that adhered to those surfaces during subsequent virus suspension treatment. A detrimental effect of PPE on HuNoV structure was confirmed by transmission electron microscopy. Our results indicate that PPE is a natural antiviral agent effective against food-borne noroviruses.

Reduction of Norovirus in Foods by Nonthermal Treatments: A Review

ABSTRACT

Human noroviruses are enteric pathogens that cause a substantial proportion of acute gastroenteritis cases worldwide regardless of background variables such as age, ethnicity, and gender. Although person-to-person contact is the general route of transmission, foodborne infections are also common. Thorough cooking eliminates noroviruses, but several food products such as berries, leafy vegetables, and mollusks undergo only limited heat treatment, if any, before consumption. Novel applications of nonthermal processing technologies are currently being vigorously researched because they can be used to inactivate pathogens and extend product shelf life with limited effects on nutrient content and perceived quality. These technologies, adopted from several industrial fields, include some methods already approved for food processing that have been applied in the food industry for years. However, a majority of the research has been conducted with bacteria and simple matrixes or surfaces. This review focuses on elimination of norovirus in food matrixes by use of nonthermal technologies in four categories: high hydrostatic pressure, light, irradiation, and cold atmospheric plasma. We discuss the properties of noroviruses, principles and inactivation mechanisms of select technologies, and main findings of relevant studies. We also provide an overview of the current status of the research and propose future directions for related work.

HIGHLIGHTS

Evaluation of Copper Alloy Surfaces for Inactivation of Tulane Virus and Human Noroviruses

ABSTRACT

This study evaluated the efficacy of copper alloy surfaces for inactivation of Tulane virus (TV), assessed by plaque assay and porcine gastric mucin-conjugated magnetic bead (PGM-MB) binding assay, followed by quantitative reverse transcription PCR (PGM-MB-RT-qPCR assay). In addition, the efficacy of a copper surface for inactivation of human norovirus (HuNoV) GII.4 Sydney and GI.3B Potsdam strains was evaluated by PGM-MB-RT-qPCR assay. Results of time-dependent inactivation of viruses on copper, bronze, and brass coupons revealed that 15 min of surface treatments of each of the copper and copper alloys achieved >4-log reduction of purified TV, as assessed by plaque assay, while up to 20 min of copper alloy surface treatments only achieved ∼2-log reduction, as assessed by PGM-MB-RT-qPCR assay. As assessed by PGM-MB-RT-qPCR assay, 10 min of copper surface treatments achieved reductions of 3 and 4 log units for HuNoVs GII.4 Sydney and GI.3B Potsdam, respectively. Results from this study suggest that even though PGM-MB-RT-qPCR assay underestimated the efficacy of copper alloy surface inactivation of TV, copper alloy surfaces were able to effectively inactivate TV and HuNoVs. Therefore, copper alloys can be used as a preventive measure to prevent HuNoV infection and are an effective surface treatment for HuNoVs.

HIGHLIGHTS

Human Intestinal Enteroids to Evaluate Human Norovirus GII.4 Inactivation by Aged-Green Tea

Human noroviruses are the leading cause of epidemic and sporadic acute gastroenteritis worldwide and the most common cause of foodborne illness in the United States. Several natural compounds, such as aged-green tea extract (aged-GTE), have been suggested as ingestible antiviral agents against human norovirus based on data using murine norovirus and feline calicivirus as surrogates. However, in vitro data showing their effectiveness against infectious human norovirus are lacking. We tested the activity of aged-GTE to inhibit human norovirus in a human intestinal enteroids (HIEs) model and Tulane virus in LLC-monkey kidney (LLC-MK2) cell culture. HIE monolayers pretreated with aged-GTE at different temperatures showed complete inhibition of human norovirus GII.4 replication at concentrations as low as 1.0 mg/ml for 37°C, 1.75 mg/ml for 21°C, and 2.5 mg/ml for 7°C. In contrast, a moderate decrease in Tulane virus infectivity of 0.85, 0.75, and 0.65 log TCID₅₀/ml was observed for 2.5 mg/ml aged-GTE at 37, 21, and 7°C, respectively. Our findings demonstrate that GTE could be an effective natural compound against human norovirus GII.4, while only minimally effective against Tulane virus.

Interaction between norovirus and Histo-Blood Group Antigens: A key to understanding virus transmission and inactivation through treatments?

Human noroviruses (HuNoVs) are a main cause of acute gastroenteritis worldwide. They are frequently involved in foodborne and waterborne outbreaks. Environmental transmission of the virus depends on two main factors: the ability of viral particles to remain infectious and their adhesion capacity onto different surfaces. Until recently, adhesion of viral particles to food matrices was mainly investigated by considering non-specific interactions (e.g. electrostatic, hydrophobic) and there was only limited information about infectious HuNoVs because of the absence of a reliable in vitro HuNoV cultivation system. Many HuNoV strains have now been described as having specific binding interactions with human Histo-Blood Group Antigens (HBGAs) and non-HBGA ligands found in food and the environment. Relevant approaches to the in vitro replication of HuNoVs were also proposed recently. On the basis of the available literature data, this review discusses the opportunities to use this new knowledge to obtain a better understanding of HuNoV transmission to human populations and better evaluate the hazard posed by HuNoVs in foodstuffs and the environment.

Evaluation of Bead-Based Assays for the Isolation of Foodborne Viruses from Low-Moisture Foods

ABSTRACT

Foodborne viruses such as norovirus and hepatitis A virus (HAV) are highly transmissible, persistent in the environment, and resistant to many conventional inactivation methods. Foods can become contaminated with these viruses either at the source of harvest or during food handling and processing. Multiple lines of evidence suggest that foodborne viruses can survive desiccation and dry conditions. Several foodborne virus outbreaks have been linked to low-moisture foods (LMFs), indicating that these foods can be vehicles of virus transmission. However, the efficiencies of common virus extraction methodologies have not been examined with LMFs. We adapted the International Organization for Standardization (ISO) 15216-1:2017 method for virus recovery for use with chocolate, pistachios, and cornflakes. We also developed a magnetic bead assay for the recovery of HAV from LMFs and used the porcine gastric mucin-coated magnetic beads (PGM-MBs) to extract norovirus surrogates, feline calicivirus (FCV), and murine norovirus (MNV) from the same LMFs. The efficiency of virus recovery using the bead-based assay was then compared with that of the ISO 15216-1:2017 method. In chocolate and pistachios, the recovery rates with the PGM-MB method were 5.6- and 21.3-fold higher, respectively, for FCV and 1.65- and 18-fold higher, respectively, for MNV than those with the ISO 15216-1:2017 method. However, the PGM-MB method failed to recover MNV and FCV from cornflakes. The recovery rates for HAV in chocolate, pistachios, and corn flakes with the magnetic bead method were 11.5-, 3-, and 5.6-fold higher, respectively, than those with the ISO 15216-1:2017 method. Thus, depending upon the food matrix and the target virus, the bead-based assays can be used to efficiently and rapidly extract viruses from LMFs.

HIGHLIGHTS

Required Chlorination Doses to Fulfill the Credit Value for Disinfection of Enteric Viruses in Water: A Critical Review

A credit value of virus inactivation has been assigned to the disinfection step in international and domestic guidelines for wastewater reclamation and reuse. To fulfill the credit value for water disinfection, water engineers need to apply an appropriate disinfection strength, expressed as a CT value (mg × min/L), which is a product of disinfectant concentration and contact time, against enteric viruses in wastewater. In the present study, we extracted published experimental data on enteric virus inactivation using free chlorine and monochloramine and applied the Tobit analysis and simple linear regression analysis to calculate the range of CT values (mg × min/L) needed for 4-log₁₀ inactivation. Data were selected from peer-reviewed papers containing kinetics data of virus infectivity and chlorine residual in water. Coxsackie B virus and echovirus require higher CT values (lower susceptibility) for 4-log₁₀ inactivation than adenovirus and a human norovirus surrogate (murine norovirus) with free chlorine. On the other hand, adenovirus has lower susceptibility to monochloramine compared to murine norovirus, coxsackievirus, and echovirus. The factors that influence the required CT value are virus type, pH, water temperature, and water matrix. This systematic review demonstrates that enteroviruses and adenovirus are appropriate representative enteric viruses to evaluate water disinfection using free chlorine and monochloramine, respectively.

Virus inactivation in groundwater in a postglacial lava field in arctic climate

Outbreaks of viral gastroenteritis are often connected to contaminated drinking water. The assessment of the water quality relies on the cultivation of indicator bacteria, and little is known of the fate of viruses in groundwater, especially in arctic regions. In Iceland, the groundwater temperature is between 3 and 6°C. The aim of this study was to determine virus inactivation at low temperature in a groundwater microcosm and in a borehole in a postglacial lava field. Two phage species that are commonly used as surrogates for norovirus were used, MS2 and PhiX174. Dialysis bags were used for the samples, and a device was constructed to hold many samples at a time and protect the samples in the borehole. No significant decrease of infective PhiX174 phages in the borehole or of the MS2 phages in the microcosm was observed. A slightly significant decrease of PhiX174 in the microcosm was noticed, with one log reduction time of 476 days. On the other hand, a significant reduction in MS2 was found in the field test, where the time needed for 90% reduction was 12·5 days. The results showed that an infective virus can exist in groundwater for months or years in arctic regions and a great difference may exist between results from microcosm and field tests. SIGNIFICANCE AND IMPACT OF THE STUDY: This study reveals that arctic regions are highly sensitive to virus contamination as an infective virus may exist in groundwater for years at low temperature. The results also show that the virus inactivation observed in field tests may differ considerably from the inactivation observed in laboratory microcosms. The results emphasize the importance of large protection zones around drinking water intakes as well as good wastewater treatment so that the likelihood of faecal contamination of groundwater is reduced.

Effects of pH Variability on Peracetic Acid Reduction of Human Norovirus GI, GII RNA, and Infectivity Plus RNA Reduction of Selected Surrogates

With increasing interest in peracetic acid (PAA) as a disinfectant in water treatment processes, this study determined PAA treatment effects on human noroviruses (hNoVs) genotype I (GI) and genotype II (GII) as well as effects on bacteriophage MS2 and murine norovirus (MNV) in relation to pH. Across all pH conditions, PAA achieved between 0.2 and 2.5 log₁₀ reduction of hNoVs over 120 min contact time in buffer solution as measured by reverse transcription-qPCR (RT-qPCR). The PAA treatments produced similar RT-qPCR reductions of MS2 and MNV, in the range of 0.2-2.7 log₁₀. Infectivity assays achieved > 4 log₁₀ reduction of both MS2 and MNV in buffer solution after 120 min contact time. Comparing PAA activity across varying pH, disinfection at pH 8.5, in general, resulted in less reduction of infectivity and molecular signals compared to pH conditions of 6.5 and 7.5. This difference was most pronounced for reductions in infectivity of MNV and MS2, with as much as 2.7 log₁₀ less reduction at pH 8.5 relative to lower pH conditions. This study revealed that PAA was an effective disinfectant for treatment of hNoV GI and GII, MS2 and MNV, with greatest virus reduction observed for MS2 and MNV infectivity. RT-qPCR reductions of MS2 and MNV were lower than concurrent MS2 and MNV infectivity reductions, suggesting that observed hNoV RT-qPCR reductions may underestimate reductions in hNoV infectivity achieved by PAA. Although virus disinfection by PAA occurred at all evaluated pH levels, PAA is most effective at pH 6.5-7.5.

Survival of E. coli O157:H7, Salmonella Typhimurium, HAdV2 and MNV-1 in river water under dark conditions and varying storage temperatures

The ability of Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, Human adenovirus serotype 2 (HAdV2) and Murine Norovirus 1 (MNV-1) to survive in river water at -20, 4, room temperature (~24 °C) and 37 °C, were evaluated under dark conditions. The tested surface water was obtained from the main Nile River in the Dokki area, Giza and sterilized by autoclaving. The pathogens were inoculated separately in the autoclaved river water. Each microcosm was sampled and the test microorganisms counted after zero (immediately following inoculation), 1, 7, 15, 30, 60, 90 and 120 days. Physicochemical parameters including pH, turbidity, electrical conductivity, dissolved oxygen, total dissolved solids, total alkalinity, biological oxygen demand, chemical oxygen demand, nitrates and nitrites, and sulphate, were also measured. For HAdV2, the highest decay rates were observed at 37 °C and room temperature compared to 4 and -20 °C. A similar trend was found for the MNV-1, although unlike the HAdV2, the decay rate was higher at -20 than at 4 °C. Also, 4 °C was the best temperature for the survival of MNV-1 (T₉₀ = 76.9 days), E. coli O157:H7 (T₉₀ = 103 days) and Salmonella Typhimurium (T₉₀ = 105 days). The least survival of the pathogens, except MNV-1, was recorded at 37 °C. These results indicate that under dark conditions and low temperatures, enteric pathogens could be stable for extended periods. No significant statistical correlation was observed between the experimental temperatures and the infectivity of the viral particles. This study provided useful information about the stability of these pathogens in the Nile River water and could serve as an early warning when considering the water of the river for agricultural irrigation or household use in areas with limited or no access to potable water.

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.

Foodborne viruses: Detection, risk assessment, and control options in food processing

In a recent report by risk assessment experts on the identification of food safety priorities using the Delphi technique, foodborne viruses were recognized among the top rated food safety priorities and have become a greater concern to the food industry over the past few years. Food safety experts agreed that control measures for viruses throughout the food chain are required. However, much still needs to be understood with regard to the effectiveness of these controls and how to properly validate their performance, whether it is personal hygiene of food handlers or the effects of processing of at risk foods or the interpretation and action required on positive virus test result. This manuscript provides a description of foodborne viruses and their characteristics, their responses to stress and technologies developed for viral detection and control. In addition, the gaps in knowledge and understanding, and future perspectives on the application of viral detection and control strategies for the food industry, along with suggestions on how the food industry could implement effective control strategies for viruses in foods. The current state of the science on epidemiology, public health burden, risk assessment and management options for viruses in food processing environments will be highlighted in this review.

Norovirus: The Burden of the Unknown

Human noroviruses (HNoVs) are primarily transmitted by the fecal-oral route, either by person-to-person contact, or by ingestion of contaminated food or water as well as by aerosolization. Moreover, HNoVs significantly contribute to foodborne diseases being the causative agent of one-fifth of acute gastroenteritis worldwide. As a consequence of globalization, transnational outbreaks of foodborne infections are reported with increasing frequency. Therefore, in this review, state-of-the-art information regarding molecular procedures for human norovirus detection in food as well common food processing technologies have been summarized. Besides, the purpose of this chapter is to consolidate basic information on various aspects of HNoVs and to summarize food processing technologies that can potentially be applied in the food industry.

Impacts of virus processing on human norovirus GI and GII persistence during disinfection of municipal secondary wastewater effluent

Noroviruses cause significant global health burdens and waterborne transmission is a known exposure pathway. Chlorination is the most common method of disinfection for water and wastewater worldwide. The purpose of this study was to investigate the underlying causes for discrepancies in human norovirus (hNoV) resistance to free chlorine that have been previously published, and to assess hNoV GI and GII persistence during disinfection of municipal secondary wastewater (WW) effluent. Our results reveal that choice of hNoV purification methodology prior to seeding the viruses in an experimental water matrix influences disinfection outcomes in treatment studies. Common hNoV purification processes such as solvent extraction and 0.45-μm filtration were ineffective in removing high levels of organics introduced into water or wastewater samples when seeding norovirus positive stool. These methods resulted in experimental water matrices receiving an additional 190 mg/L as Cl₂ of 15-s chlorine demand and approximately 440 mg/L as Cl₂ of 30-min chlorine demand due to seeding norovirus positive stool at 1% w/v. These high organic loads impact experimental water chemistry and bias estimations of hNoV persistence. Advanced purification of norovirus positive stool using sucrose cushion ultracentrifugation and ultrafiltration reduced 15-s chlorine demands by 99% and TOC by 93% for loose (i.e. unformed diarrhea) stools. Using these methods, hNoV GI and GII persistence was investigated during free chlorination of municipal WW. A suite five of kinetic inactivation models was fit to viral reverse transcription-qPCR reduction data, and model predicted CT values for 1, 2, and 3 log₁₀ reduction of hNoV GI in municipal WW by free chlorine were 0.3, 2.1, and 7.8 mg-min/L, respectively. Model predicted CT values for reduction of hNoV GII in WW were 0.4, 2.0, and 7.0 mg-min/L, respectively. These results indicate that current WW treatment plant disinfection practices employing free chlorine are likely protective for public health with regards to noroviruses, and will achieve at least 3-log reduction of hNoV GI and GII RNA despite previous reports of high hNoV resistance.

Inactivation of Human Norovirus Genogroups I and II and Surrogates by Free Chlorine in Postharvest Leafy Green Wash Water

Human noroviruses (hNoVs) are a known public health concern associated with the consumption of leafy green vegetables. While a number of studies have investigated pathogen reduction on the surfaces of leafy greens during the postharvest washing process, there remains a paucity of data on the level of treatment needed to inactivate viruses in the wash water, which is critical for preventing cross-contamination. The objective of this study was to quantify the susceptibility of hNoV genotype I (GI), hNoV GII, murine norovirus (MNV), and bacteriophage MS2 to free chlorine in whole leaf, chopped romaine, and shredded iceberg lettuce industrial leafy green wash waters, each sampled three times over a 4-month period. A suite of kinetic inactivation models was fit to the viral reduction data to aid in quantification of concentration-time (CT) values. Results indicate that 3-log10 infectivity reduction was achieved at CT values of less than 0.2 mg · min/liter for MNV and 2.5 mg · min/liter for MS2 in all wash water types. CT values for 2-log10 molecular reduction of hNoV GI in whole leaf and chopped romaine wash waters were 1.5 and 0.9 mg · min/liter, respectively. For hNoV GII, CT values were 13.0 and 7.5 mg · min/liter, respectively. In shredded iceberg wash water, 3-log10 molecular reduction was not observed for any virus over the time course of experiments. These findings demonstrate that noroviruses may exhibit genogroup-dependent resistance to free chlorine and emphasize the importance of distinguishing between genogroups in hNoV persistence studies.IMPORTANCE Postharvest washing of millions of pounds of leafy greens is performed daily in industrial processing facilities with the intention of removing dirt, debris, and pathogenic microorganisms prior to packaging. Modest inactivation of pathogenic microorganisms (less than 2 log10) is known to occur on the surfaces of leafy greens during washing. Therefore, the primary purpose of the sanitizing agent is to maintain microbial quality of postharvest processing water in order to limit cross-contamination. This study modeled viral inactivation data and quantified the free-chlorine CT values that processing facilities must meet in order to achieve the desired level of hNoV GI and GII reduction. Disinfection experiments were conducted in industrial leafy green wash water collected from a full-scale fresh produce processing facility in the United States, and hNoV GI and GII results were compared with surrogate molecular and infectivity data.

Reduction of Human Norovirus GI, GII, and Surrogates by Peracetic Acid and Monochloramine in Municipal Secondary Wastewater Effluent

The objective of this study was to characterize human norovirus (hNoV) GI and GII reductions during disinfection by peracetic acid (PAA) and monochloramine in secondary wastewater (WW) and phosphate buffer (PB) as assessed by reverse transcription-qPCR (RT-qPCR). Infectivity and RT-qPCR reductions are also presented for surrogate viruses murine norovirus (MNV) and bacteriophage MS2 under identical experimental conditions to aid in interpretation of hNoV molecular data. In WW, RT-qPCR reductions were less than 0.5 log₁₀ for all viruses at concentration-time (CT) values up to 450 mg-min/L except for hNoV GI, where 1 log₁₀ reduction was observed at CT values of less than 50 mg-min/L for monochloramine and 200 mg-min/L for PAA. In PB, hNoV GI and MNV exhibited comparable resistance to PAA and monochloramine with CT values for 2 log₁₀ RT-qPCR reduction between 300 and 360 mg-min/L. Less than 1 log₁₀ reduction was observed for MS2 and hNoV GII in PB at CT values for both disinfectants up to 450 mg-min/L. Our results indicate that hNoVs exhibit genogroup dependent resistance and that disinfection practices targeting hNoV GII will result in equivalent or greater reductions for hNoV GI. These data provide valuable comparisons between hNoV and surrogate molecular signals that can begin the process of informing regulators and engineers on WW treatment plant design and operational practices necessary to inactivate hNoVs.

Persistence of Norovirus GII Genome in Drinking Water and Wastewater at Different Temperatures

Human norovirus (NoV) causes waterborne outbreaks worldwide suggesting their ability to persist and survive for extended periods in the environment. The objective of this study was to determine the persistence of the NoV GII genome in drinking water and wastewater at three different temperatures (3 °C, 21 °C, and 36 °C). The persistence of two NoV GII inoculums (extracted from stool) and an indigenous NoV GII were studied. The samples were collected for up to one year from drinking water and for up to 140 days from wastewater. Molecular methods (RT-qPCR) were used to assess the decay of the NoV genome. Decay rate coefficients were determined from the fitted decay curves using log-linear and/or non-linear model equations. Results showed significant differences in the decay kinetics of NoV genome between the temperatures, matrices, and virus strains. The persistence of NoV was higher in drinking water compared to wastewater, and the cold temperature assisted persistence at both matrices. Differences between the persistence of NoV strains were also evident and, particularly, indigenous NoVs persisted better than spiked NoVs in wastewater. The decay constants obtained in this study can be utilized to assess the fate of the NoV genome in different water environments.

Potential Approaches to Assess the Infectivity of Hepatitis E Virus in Pork Products: A Review

The zoonotic transmission of hepatitis E, caused by the hepatitis E virus (HEV), is an emerging issue. HEV appears common in pigs (although infected pigs do not show clinical signs), and evidence suggests that a number of hepatitis E cases have been associated with the consumption of undercooked pork meat and products. Little information is available on whether cooking can eliminate HEV, since there is currently no robust method for measuring its infectivity. HEV infectivity can be clearly demonstrated by monitoring for signs of infection (e.g., shedding of virus) in an animal model. However, this approach has several disadvantages, such as lack of reproducibility and unsuitability for performing large numbers of tests, high costs, and not least ethical considerations. Growth in cell culture can unambiguously show that a virus is infectious and has the potential for replication, without the disadvantages of using animals. Large numbers of tests can also be performed, which can make the results more amenable to statistical interpretation. However, no HEV cell culture system has been shown to be applicable to all HEV strains, none has been standardized, and few studies have demonstrated their use for measurement of HEV infectivity in food samples. Nonetheless, cell culture remains the most promising approach, and the main recommendation of this review is that there should be an extensive research effort to develop and validate a cell culture-based method for assessing HEV infectivity in pork products. Systems comprising promising cell lines and HEV strains which can grow well in cell culture should be tested to select an assay for effective and reliable measurement of HEV infectivity over a wide range of virus concentrations. The assay should then be harnessed to a procedure which can extract HEV from pork products, to produce a method suitable for further use. The method can then be used to determine the effect of heat or other elimination processes on HEV in pork meat and products, or to assess whether HEV detected in any surveyed foodstuffs is infectious and therefore poses a risk to public health.

Building research in diet and cognition: The BRIDGE randomized controlled trial

Obesity has been linked to cognitive impairment, cognitive decline and dementia. Given that 38.5% of U.S. adults 60years and older are obese and these numbers are rapidly increasing, strategies to decouple obesity from cognitive decline are needed. Innovative lifestyle strategies that may postpone the onset of subclinical symptoms or even arrest the transition to overt dementia in at-risk individuals are critically needed. Poor diet is central to the development of obesity and diet may affect cognition. Adherence to a Mediterranean Diet (MedDiet) is associated with reduced risk of cognitive impairment and dementia. Furthermore, weight loss through caloric restriction improves cognitive function. This paper describes the Building Research in Diet and CoGnition (BRIDGE) study, a randomized trial examining the effect of the MedDiet, with and without weight loss, on cognitive functioning in obese older adults. Obese (BMI≥30 and ≤50kg/m2) older adults (≥55years) (n=180) will be randomized in a 2:2:1 allocation scheme to: Typical Diet Control; MedDiet alone, without weight loss; or MedDiet lifestyle intervention to promote weight loss and weight loss maintenance. Both MedDiet intervention groups will meet for one individual session and 27 group sessions over an 8-month period. Individuals in the control group will not receive instruction on changing lifestyle habits. Outcomes will be assessed at baseline, 8 and 14months. The primary outcome is cognitive functioning; secondary outcomes will include changes in body weight, diet, cardiovascular, metabolic, and inflammatory biomarkers.

The Effect of Heat and Free Chlorine Treatments on the Surface Properties of Murine Norovirus

Heat and free chlorine are among the most efficient and commonly used treatments to inactivate enteric viruses, but their global inactivation mechanisms have not been elucidated yet. These treatments have been shown to affect at least the capsid proteins of viruses and thus may affect the surface properties (i.e. electrostatic charge and hydrophobicity) of such particles. Our aim was to study the effects of heat and free chlorine on surface properties for a murine norovirus chosen as surrogate for human norovirus. No changes in the surface properties were observed with our methods for murine norovirus exposed to free chlorine. Only the heat treatment led to major changes in the surface properties of the virus with the expression of hydrophobic domains at the surface of the particles after exposure to a temperature of 55 °C. No modification of the expression of hydrophobic domains occurred after exposure to 60 °C, and the low hydrophobic state exhibited by infectious and inactivated particles after exposure to 60 °C appeared to be irreversible for inactivated particles only, which may provide a means to discriminate infectious from inactivated murine noroviruses. When exposed to a temperature of 72 °C or to free chlorine at a concentration of 50 mg/L, the genome became available for RNases.

Capturing norovirus transmission

Human norovirus is a leading cause of gastroenteritis and is efficiently transmitted between humans and around the globe. The burden of norovirus infections in the global community and in health-care settings warrant the availability of outbreak prevention strategies and control measures that are tailored to the pathogen, outbreak setting and population at risk. A better understanding of viral and host determinants of transmission would aid in developing and fine-tuning such efforts. Here, we describe mechanisms of transmission, available model systems for studying norovirus transmission and their strengths and weaknesses as well as future research strategies.

Persistence and Elimination of Human Norovirus in Food and on Food Contact Surfaces: A Critical Review

This critical review addresses the persistence of human norovirus (NoV) in water, shellfish, and processed meats; on berries, herbs, vegetables, fruits, and salads; and on food contact surfaces. The review focuses on studies using NoV; information from studies involving only surrogates is not included. It also addresses NoV elimination or inactivation by various chemical, physical, or processing treatments. In most studies, persistence or elimination was determined by detection and quantification of the viral genome, although improved methods for determining infectivity have been proposed. NoV persisted for 60 to 728 days in water, depending on water source. It also persisted on berries, vegetables, and fruit, often showing <1-log reduction within 1 to 2 weeks. NoV was resilient on carpets, Formica, stainless steel, polyvinyl chloride, and ceramic surfaces; during shellfish depuration; and to repeated freeze-thaw cycles. Copper alloy surfaces may inactivate NoV by damaging viral capsids. Disinfection was achieved for some foods or food contact surfaces using chlorine, calcium or sodium hypochlorite, chlorine dioxide, high hydrostatic pressure, high temperatures, pH values >8.0, freeze-drying, and UV radiation. Ineffective disinfectants included hydrogen peroxide, quaternary ammonium compounds, most ethanol-based disinfectants, and antiseptics at normally used concentrations. Thorough washing of herbs and produce was effective in reducing, but not eliminating, NoV in most products. Washing hands with soap generally reduced NoV by <2 log. Recommendations for future research needs are provided.

Thermal Stability of Hepatitis E Virus as Estimated by a Cell Culture Method

Hepatitis E virus (HEV) is an increasingly recognized zoonotic pathogen. Transmission is suspected to occur from infected pigs or wild boars to humans through direct contact, environmental pathways, or contaminated food. However, the physical and chemical stability of HEV is largely unknown, because suitable cell culture methods for infectivity measurement are missing. Here, we developed a titration method using infection of the cell line A549/D3 with HEV genotype 3 strain 47832c and subsequent counting of focus-forming units by immunofluorescence, which allowed HEV infectivity measurements within a 4-log-dilution range. Long-term storage of HEV in cell culture medium at different temperatures indicated a phase of rapid virus inactivation, followed by a slower progression of virus inactivation. Infective HEV was detected up to 21 days at 37°C, up to 28 days at room temperature, and until the end of the experiment (56 days) with a 2.7-log decrease of infectious virus at 4°C. Heat treatment for 1 min resulted in moderate decreases of infectivity up to 60°C, 2- to 3.5-log decreases between 65°C and 75°C, and no remaining virus was detected at temperatures of ≥80°C. Heating for 70°C resulted in a 3.6-log decrease after 1.5 min and the absence of detectable virus (>3.9-log decrease) after 2 min. The data were used to calculate predictive heat inactivation models for HEV. The results may help estimate HEV stability in the environment or food. The established method may be used to study other aspects of HEV stability in the future.

IMPORTANCE

In this study, a cell culture method was developed which allows the measurement of hepatitis E virus (HEV) infectivity. Using this system, the stability of HEV at different time-temperature combinations was assessed, and a predictive model was established. The obtained data may help estimate HEV stability in the environment or food, thus enabling an assessment of the relative risks of HEV infection through distinct routes and by distinct types of food in the future.

Abiotic Stress and Phyllosphere Bacteria Influence the Survival of Human Norovirus and Its Surrogates on Preharvest Leafy Greens

Foodborne outbreaks of human noroviruses (HuNoVs) are frequently associated with leafy greens. Because there is no effective method to eliminate HuNoV from postharvest leafy greens, understanding virus survival under preharvest conditions is crucial. The objective of this study was to evaluate the survival of HuNoV and its surrogate viruses, murine norovirus (MNV), porcine sapovirus (SaV), and Tulane virus (TV), on preharvest lettuce and spinach that were subjected to abiotic stress (physical damage, heat, or flood). We also examined the bacteria culturable from the phyllosphere in response to abiotic stress and in relation to viral persistence. Mature plants were subjected to stressors 2 days prior to inoculation of the viruses on leaves. We quantified the viral RNA, determined the infectivity of the surrogates, and performed bacterial counts on postinoculation days (PIDs) 0, 1, 7, and 14. For both plant types, time exerted significant effects on HuNoV, MNV, SaV, and TV RNA titers, with greater effects being seen for the surrogates. Infectious surrogate viruses were undetectable on PID 14. Only physical damage on PID 14 significantly enhanced HuNoV RNA persistence on lettuce, while the three stressors differentially enhanced the persistence of MNV and TV RNA. Bacterial counts were significantly affected by time and plant type but not by the stressors. However, bacterial counts correlated significantly with HuNoV RNA titers on spinach and with the presence of surrogate viruses on both plant types under various conditions. In conclusion, abiotic stressors and phyllosphere bacterial density may differentially influence the survival of HuNoV and its surrogates on lettuce and spinach, emphasizing the need for the use of preventive measures at the preharvest stage.