Capturing norovirus transmission

PMAxx-RT-qPCR to Determine Human Norovirus Inactivation Following High-Pressure Processing of Oysters

Norovirus is the leading cause of viral gastroenteritis globally. While person-to-person transmission is most commonly reported route of infection, human norovirus is frequently associated with foodborne transmission, including through consumption of contaminated bivalve molluscan shellfish. Reverse transcription (RT)-qPCR is most commonly used method for detecting human norovirus detection in foods, but does not inform on its infectivity, posing challenges for assessing intervention strategies aimed at risk elimination. In this study, RT-qPCR was used in conjunction with a derivative of the photoreactive DNA binding dye propidium monoazide (PMAxx™) (PMAxx-RT-qPCR) to evaluate the viral capsid integrity of norovirus genogroup I and II (GI and GII) in shellfish following high pressure processing (HPP). Norovirus GI.3 and GII.4 bioaccumulated oysters were subjected to HPP at pressures of 300 and 450 MPa at 15 °C, and 300, 450 and 600 MPa at 20 °C. Samples were analysed using both RT-qPCR and PMAxx-RT-qPCR. For each sample, norovirus concentration (genome copies/g digestive tissue) determined by RT-qPCR was divided by the PMAxx-RT-qPCR concentration, giving the relative non-intact (RNI) ratio. The RNI ratio values relate to the amount of non-intact (non-infectious) viruses compared to fully intact (possible infectious) viruses. Our findings revealed an increasing RNI ratio value, indicating decreasing virus integrity, with increasing pressure and decreasing pressure. At 300 MPa, for norovirus GI, the median [95% confidence interval, CI] RNI ratio values were 2.6 [1.9, 3.0] at 15 °C compared to 1.1 [0.9, 1.8] at 20 °C. At 450 MPa, the RNI ratio values were 5.5 [2.9, 7.0] at 15 °C compared to 1.3 [1.0, 1.6] at 20 °C. At 600 MPa, the RNI ratio value was 5.1 [2.9, 13.4] at 20 °C. For norovirus GII, RT-qPCR and PMAxx-RT-qPCR detections were significantly reduced at 450 and 600 MPa at both 15 °C and 20 °C, with the median [95% CI] RNI ratio value at 300 MPa being 1.1 [0.8, 1.6]. Following HPP treatment, the use of PMAxx-RT-qPCR enables the selective detection of intact and potential infectious norovirus, enhancing our understanding of the inactivation profiles and supporting the development of more effective risk assessment strategies.

A narrative review of norovirus epidemiology, biology, and challenges to vaccine development

Norovirus is a leading cause of acute gastroenteritis (AGE) globally. AGE resulting from norovirus causes significant morbidity and mortality in countries of all income levels, particularly among young children and older adults. Prevention of norovirus AGE represents a unique challenge as the virus is genetically diverse with multiple genogroups and genotypes cocirculating globally and causing disease in humans. Variants of the GII.4 genotype are typically the most common genotype, and other genotypes cause varying amounts of disease year-to-year, with GII.2, GII.3, and GII.6 most prevalent in recent years. Noroviruses are primarily transmitted via the fecal-oral route and only a very small number of virions are required for infection, which makes outbreaks of norovirus extremely difficult to control when they occur. Settings like long-term care facilities, daycares, and hospitals are at high risk of outbreaks and can have very high attack rates resulting in substantial costs and disease burden. Severe cases of norovirus AGE are most common in vulnerable patient populations, such as infants, the elderly, and immunocompromised individuals, with available treatments limited to rehydration therapies and supportive care. To date, there are no FDA-approved norovirus vaccines; however, several candidates are currently in development. Given the substantial human and economic burden associated with norovirus AGE, a vaccine to prevent morbidity and mortality and protect vulnerable populations could have a significant impact on global public health.

Capsid Integrity Detection of Enteric Viruses in Reclaimed Waters

Climate change, unpredictable weather patterns, and droughts are depleting water resources in some parts of the globe, where recycling and reusing wastewater is a strategy for different purposes. To counteract this, the EU regulation for water reuse sets minimum requirements for the use of reclaimed water for agricultural irrigation, including a reduction in human enteric viruses. In the present study, the occurrence of several human enteric viruses, including the human norovirus genogroup I (HuNoV GI), HuNoV GII, and rotavirus (RV), along with viral fecal contamination indicator crAssphage was monitored by using (RT)-qPCR methods on influent wastewater and reclaimed water samples. Moreover, the level of somatic coliphages was also determined as a culturable viral indicator. To assess the potential viral infectivity, an optimization of a capsid integrity PMAxx-RT-qPCR method was performed on sewage samples. Somatic coliphages were present in 60% of the reclaimed water samples, indicating inefficient virus inactivation. Following PMAxx-RT-qPCR optimization, 66% of the samples tested positive for at least one of the analyzed enteric viruses, with concentrations ranging from 2.79 to 7.30 Log10 genome copies (gc)/L. Overall, most of the analyzed reclaimed water samples did not comply with current EU legislation and contained potential infectious viral particles.

Systematic literature review and meta-analysis on preventing and controlling norovirus outbreaks on cruise ships, 1990 to 2020: calling for behaviour change strategies of travellers

BackgroundOutbreaks of norovirus gastroenteritis aboard cruise ships may affect a large number of people, debilitate vulnerable travellers, disrupt vacations and cause economic losses to the cruise ship industry.AimWe aimed to identify risk factors for norovirus outbreaks on cruise ships and assess the effectiveness of prevention and control measures.MethodsWe conducted a systematic literature review searching PubMed and Scopus databases as well as grey literature for articles and reports describing norovirus outbreaks on cruise ships between 1990 and 2020. We also performed a meta-analysis of norovirus prevalence in passengers and crew members.ResultsData from 45 outbreaks on 26 cruise ships from 1990 to 2020 were identified in 13 articles and five reports, with a weighted average of prevalence (attack rate) for passengers of 7% (95% confidence interval (CI): 5.00-9.00) and for crew of 2% (95% CI: 0.00-3.00). Person-to-person was the most frequent mode of transmission in 35 of the 45 outbreaks (in 14 the only mode and in 21 as part of multiple transmission routes). Having an ill cabin mate (OR = 38.70; 95% CI: 13.51-110.86) was the most common risk factor. Six outbreak investigations reported poor hygiene, while four reported satisfactory hygiene in the cruise setting. Behavioural risk factors among travellers were investigated in three of the 13 studies.ConclusionsThe findings indicate a need for behavioural interventions to improve personal hygiene, symptom reporting and compliance with isolation measures, and for reconsidering current isolation policies where symptomatic and healthy individuals are isolated in the same cabin.

Complex norovirus transmission dynamics at hospital wards revealed by deep sequencing

Detailed knowledge regarding norovirus transmission within hospitals is limited. We investigated a norovirus hospital outbreak affecting 65 patients at five different wards. PCR showed that 61 (94%) of the patients were infected with genotype II.4 strains. Successful Ion Torrent deep sequencing of GII.4 positive samples from 59 patients followed by phylogenetic analysis revealed that all sequences but two clustered into four distinct clades. Two of the clades belonged to GII.4 Sydney 2012, while the other two belonged to GII.4 New Orleans 2009. One of the clades was predominant at two wards, while two clades were predominant at one ward each. The fourth clade was found in sporadic cases at several wards. Thus, at four out of five wards, variants from one clade were predominant. At one ward, a single clade accounted for all cases, while at three wards the predominant clade accounted for 60%-71% of cases. Analysis of quasispecies variation identified positions that could further discriminate between variants from separate wards. The results illustrate a complex transmission of healthcare-associated norovirus infections and show that sequencing can be used to discriminate between related and unrelated cases.

Vaccine value profile for norovirus

Norovirus is attributed to nearly 1 out of every 5 episodes of diarrheal disease globally and is estimated to cause approximately 200,000 deaths annually worldwide, with 70,000 or more among children in developing countries. Noroviruses remain a leading cause of sporadic disease and outbreaks of acute gastroenteritis even in industrialized settings, highlighting that improved hygiene and sanitation alone may not be fully effective in controlling norovirus. Strengths in global progress towards a Norovirus vaccine include a diverse though not deep pipeline which includes multiple approaches, including some with proven technology platforms (e.g., VLP-based HPV vaccines). However, several gaps in knowledge persist, including a fulsome mechanistic understanding of how the virus attaches to human host cells, internalizes, and induces disease.

Deformed wing virus of honey bees is inactivated by cold plasma ionized hydrogen peroxide

Deformed wing virus (DWV) is a widespread pathogen of Apis mellifera honey bees, and is considered a major causative factor for the collapse of infected honey bee colonies. DWV can be horizontally transmitted among bees through various oral routes, including via food sharing and by interactions of bees with viral-contaminated solid hive substrates. Cold plasma ionized hydrogen peroxide (iHP) is used extensively by the food production, processing and medical industries to clean surfaces of microbial contaminants. In this study, we investigated the use of iHP to inactivate DWV particles in situ on a solid substrate. iHP-treated DWV sources were ~105-fold less infectious when injected into naïve honey bee pupae compared to DWV receiving no iHP treatment, matching injected controls containing no DWV. iHP treatment also greatly reduced the incidence of overt DWV infections (i.e., pupae having >109 copies of DWV). The level of DWV inactivation achieved with iHP treatment was higher than other means of viral inactivation such as gamma irradiation, and iHP treatment is likely simpler and safer. Treatment of DWV contaminated hive substrates with iHP, even with honey bees present, may be an effective way to decrease the impacts of DWV infection on honey bees.

Environmental challenges of COVID-19 pandemic: resilience and sustainability - A review

The emergence of novel respiratory disease (COVID-19) caused by SARS-CoV-2 has become a public health emergency worldwide and perturbed the global economy and ecosystem services. Many studies have reported the presence of SARS-CoV-2 in different environmental compartments, its transmission via environmental routes, and potential environmental challenges posed by the COVID-19 pandemic. None of these studies have comprehensively reviewed the bidirectional relationship between the COVID-19 pandemic and the environment. For the first time, we explored the relationship between the environment and the SARS-CoV-2 virus/COVID-19 and how they affect each other. Supporting evidence presented here clearly demonstrates the presence of SARS-CoV-2 in soil and water, denoting the role of the environment in the COVID-19 transmission process. However, most studies fail to determine if the viral genomes they have discovered are infectious, which could be affected by the environmental factors in which they are found.The potential environmental impact of the pandemic, including water pollution, chemical contamination, increased generation of non-biodegradable waste, and single-use plastics have received the most attention. For the most part, efficient measures have been used to address the current environmental challenges from COVID-19, including using environmentally friendly disinfection technologies and employing measures to reduce the production of plastic wastes, such as the reuse and recycling of plastics. Developing sustainable solutions to counter the environmental challenges posed by the COVID-19 pandemic should be included in national preparedness strategies. In conclusion, combating the pandemic and accomplishing public health goals should be balanced with environmentally sustainable measures, as the two are closely intertwined.

Epidemiological and Genetic Characterization of Norovirus Outbreaks That Occurred in Catalonia, Spain, 2017–2019

Molecular characterization of human norovirus (HuNoV) genotypes enhances the understanding of viral features and illustrates distinctive evolutionary patterns. The aim of our study was to describe the prevalence of the genetic diversity and the epidemiology of the genotypes involved in HuNoV outbreaks in Catalonia (Spain) between 2017 and 2019. A total of 100 HuNoV outbreaks were notified with the predominance of GII (70%), followed by GI (27%) and mixed GI/GII (3%). Seasonality was observed for GII outbreaks only. The most prevalent genotypes identified were GII.4[P31] Sydney 2012, GII.4[P16] Sydney 2012 and GII.2[P16]. As compared to person-to-person (P/P) transmitted outbreaks, foodborne outbreaks showed significantly higher attack rates and lower duration. The average attack rate was higher in youth hostel/campgrounds compared to nursing homes. Only genotypes GI.4[P4], GII.2[P16], GII.4[P16], GII.4[P31] and GII.17[P17] were consistently detected every year, and only abundance of GII.2[P16] showed a negative trend over time. GII.4 Sydney 2012 outbreaks were significantly associated to nursing homes, while GII.2[P16] and GI.3[P3] were most frequently identified in youth hostel/campgrounds. The average attack rate was significantly higher when comparing GII.2[P16] vs. GI.4[P4], GII.2[P16] vs. GII.4[P31] Sydney 2012, and GII.6[P7] vs. GII.4[P31] Sydney 2012. No correlations were found between genotype and outbreak duration or age of affected individuals.

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

Noroviruses-The State of the Art, Nearly Fifty Years after Their Initial Discovery

Human noroviruses are recognised as the major global cause of viral gastroenteritis. Here, we provide an overview of notable advances in norovirus research and provide a short recap of the novel model systems to which much of the recent progress is owed. Significant advances include an updated classification system, the description of alternative virus-like protein morphologies and capsid dynamics, and the further elucidation of the functions and roles of various viral proteins. Important milestones include new insights into cell tropism, host and microbial attachment factors and receptors, interactions with the cellular translational apparatus, and viral egress from cells. Noroviruses have been detected in previously unrecognised hosts and detection itself is facilitated by improved analytical techniques. New potential transmission routes and/or viral reservoirs have been proposed. Recent in vivo and in vitro findings have added to the understanding of host immunity in response to norovirus infection, and vaccine development has progressed to preclinical and even clinical trial testing. Ongoing development of therapeutics includes promising direct-acting small molecules and host-factor drugs.

Association of environmental surface contamination with hand hygiene and infections in nursing homes: a prospective cohort study

Background

Little is known about the presence of infections in nursing home residents, the causative micro-organisms, how hand hygiene (HH) influences the presence of infections in residents, and the extent to which environmental contamination is associated with the incidence of infection among residents.

Aims

To establish if environmental contamination can be used as an indicator for HH compliance, and if environmental contamination is associated with the incidence of infection.

Methods

Environmental surface samples (ESS) were collected in an exploratory study as part of a HH intervention in 60 nursing homes. ESS results from three distinct surfaces (nurses' station, communal toilet and residents' shared living area) were compared with nurses' HH compliance and the incidence of infection among residents. Real-time polymerase chain reaction assays were used to detect norovirus genogroup I and II, rhinovirus and Escherichia coli. HH compliance was measured by direct observation. The incidence of infection was registered weekly.

Findings

Rhinovirus (nurses' station: 41%; toilet: 14%; living area: 29%), norovirus (nurses' station: 18%; toilet: 12%; living area: 16%) and E. coli (nurses' station: 14%; toilet: 58%; living area: 54%) were detected. No significant (P<0.05) associations were found between HH compliance and the presence of micro-organisms. An association was found between E. coli contamination and the incidence of disease in general (P=0.04). No other associations were found between micro-organisms and the incidence of disease.

Conclusion

Rhinovirus, norovirus and E. coli were detected on surfaces in nursing homes. No convincing associations were found between environmental contamination and HH compliance or the incidence of disease. This study provides reference data about surface contamination.

An outbreak of gastroenteritis by emerging norovirus GII.2[P16] in a kindergarten in Kota Kinabalu, Malaysian Borneo

Outbreaks of diarrhea in kindergartens are underreported and frequently go unnoticed in developing countries. To better understand the etiology this study was performed during an outbreak of diarrhea in a kindergarten in Sabah, Malaysia. Outbreak investigation was performed according to the standard procedures. In this outbreak a total of 34 (36.5%) children and 4 (30.8%) teachers suffered from gastroenteritis. Stool samples from seven children and 13 teachers were tested for rotavirus and norovirus. During the investigation stool samples were collected and sent in cold chain to the laboratory. The samples were subjected to rotavirus enzyme linked immunosorbent assay, and reverse transcription PCR for norovirus. All samples were negative for rotavirus but positive for norovirus. To determine the genogroup and genotype of norovirus, nucleotide sequencing of the amplicons was performed. All norovirus from the outbreak was of genotype GII.2[16]. To determine the relatedness of the strains phylogenetic analysis was done using neighbor-joining method. Phylogenetically these strains were highly related to GII.2[P16] noroviruses from China and Japan. This study provided evidence that a diarrheal outbreak in a kindergarten was caused by GII.2[P16] norovirus which is an emerging strain in East Asia and Europe.

Characterization of Norovirus and Other Human Enteric Viruses in Sewage and Stool Samples Through Next-Generation Sequencing

This study aimed to optimize a method to identify human enteric viruses in sewage and stool samples using random primed next-generation sequencing. We tested three methods, two employed virus enrichment based on the binding properties of the viral capsid using pig-mucin capture or by selecting viral RNA prior to library preparation through a capture using the SureSelect target enrichment. The third method was based on a non-specific biophysical precipitation with polyethylene glycol. Full genomes of a number of common human enteric viruses including norovirus, rotavirus, husavirus, enterovirus and astrovirus were obtained. In stool samples full norovirus genome were detected as well as partial enterovirus genome. A variety of norovirus sequences was detected in sewage samples, with genogroup II being more prevalent. Interestingly, the pig-mucin capture enhanced not only the recovery of norovirus and rotavirus but also recovery of astrovirus, sapovirus and husavirus. Documenting sewage virome using these methods provides information for molecular epidemiology and may be useful in developing strategies to prevent further spread of viruses.

Human noroviruses: recent advances in a 50-year history

PURPOSE OF REVIEW

Noroviruses are a major cause of gastroenteritis. This review summarizes new information on noroviruses that may lead to the development of improved measures for limiting their human health impact.

RECENT FINDINGS

GII.4 strains remain the most common human noroviruses causing disease, although GII.2 and GII.17 strains have recently emerged as dominant strains in some populations. Histo-blood group antigen (HBGA) expression on the gut mucosa drives susceptibility to different norovirus strains. Antibodies that block virus binding to these glycans correlate with protection from infection and illness. Immunocompromised patients are significantly impacted by norovirus infection, and the increasing availability of molecular diagnostics has improved infection recognition. Human noroviruses can be propagated in human intestinal enteroid cultures containing enterocytes that are a significant primary target for initiating infection. Strain-specific requirements for replication exist with bile being essential for some strains. Several vaccine candidates are progressing through preclinical and clinical development and studies of potential antiviral interventions are underway.

SUMMARY

Norovirus epidemiology is complex and requires continued surveillance to track the emergence of new strains and recombinants, especially with the continued progress in vaccine development. Humans are the best model to study disease pathogenesis and prevention. New in-vitro cultivation methods should lead to better approaches for understanding virus-host interactions and ultimately to improved strategies for mitigation of human norovirus-associated disease.

Transmissibility of Norovirus in Urban Versus Rural Households in a Large Community Outbreak in China

BACKGROUND

Norovirus is a leading cause of outbreaks of acute infectious gastroenteritis worldwide, yet its transmissibility within households and associated risk factors remain unknown in developing countries.

METHODS

Household, demographic, and clinical data were collected from a semi-urban area in south China where an outbreak occurred in the winter of 2014. Using a Bayesian modeling framework, we assessed the transmissibility and potential risk modifiers in both urban and rural households.

RESULTS

In urban apartment buildings, the secondary attack rates were 84% (95% credible interval [CI] = 60%, 96%) among households of size two and 29% (95% CI = 9.6%, 53%) in larger households. In the rural village, secondary attack rate estimates were lower than the urban setting, 13% (0.51%, 54%) for households of size two and 7.3% (0.38%, 27%) for larger households. Males were 31% (95% CI = 3%, 50%) less susceptible to the disease than female. Water disinfection with chlorine was estimated to reduce environmental risk of infection by 60% (95% CI = 26%, 82%), and case isolation was estimated to reduce person-to-person transmission by 65% (95% CI = 15%, 93%). Nausea and vomiting were not associated with household transmission.

CONCLUSIONS

Norovirus is highly contagious within households, in particular in small households in urban communities. Our results suggest that water disinfection and case isolation are associated with reduction of outbreaks in resource-limited communities.

Noroviruses in raw sewage, secondary effluents and reclaimed water produced by sand-anthracite filters and membrane bioreactor/reverse osmosis system

The importance of noroviruses (NoVs) in the epidemiology of waterborne diseases has increased globally in the last decades. The present study aimed to monitor genogroup I and II noroviruses in different treatment stages of four wastewater treatment plants (WWTPs) in the metropolitan São Paulo. WWTPs consist of secondary (activated sludge) and tertiary treatments (coagulation, sand-anthracite filters, membrane bioreactor (MBR)/reverse osmosis (RO) and chlorination). Raw sewage (500mL) and treated effluents (1L) were concentrated by celite and reclaimed water (40L) by hollow-fiber ultrafiltration system. Quantitative (qPCR) and nested PCR with nucleotide sequencing were used for quantification and molecular characterization. NoVs were widely distributed in raw wastewater samples (83.3%-100% NoV GI and 91.6%-100% NoV GII) and viral loads varied from 3.8 to 6.66log₁₀gcL^-1 for NoV GI and 3.8 to 7.3log₁₀gcL^-1 for NoV GII. Mean virus removal efficiencies obtained for activated sludge processes ranged from 0.3 to 0.8 log₁₀ for NoV GI and 0.4 to 1.4 log₁₀ for NoV GII. NoVs were not detected in the reuse water produced by MBR/RO system, while sand-anthracite filters resulted in a NoV GI and GII decay of 1.1-1.6 log₁₀ and 0.7-1.6 log₁₀, respectively. A variety of genotypes (GI.2, GI.3a, GI.3b, GI.5, GII.1, GII.4 Sydney 2012, GII.5, GII.6, GII.17) was observed, with a predominance of GI.2 and GII.17 in the different genogroups. These results corroborate with recent data about the entry and dissemination of the emerging genotype GII.P17-GII.17 Kawasaki 2014 in the country, and may indicate a change in the epidemiological patterns of norovirus strains circulation in this region. This is the first large-scale study to evaluate burden and genotypes of noroviruses in WWTPs in Brazil, providing a rapid diagnosis of viruses circulating in the population.

Comprehensive Study on Enteric Viruses and Indicators in Surface Water in Kyoto, Japan, During 2014-2015 Season

Certain enteric viruses that are present in the water environment are potential risk factors of waterborne infections. To better understand the impact of viruses in water, both enteric viruses and their potential indicators should be comparatively investigated. In this study, occurrences of GI- and GII-noroviruses (NoVs), sapovirus (SaV), rotavirus (RoV), Aichi virus 1 (AiV-1), enterovirus (EV), and pepper mild mottle virus (PMMoV) were quantitatively determined in surface water samples in Japan. Additionally, the genotype distribution of GI- and GII-NoVs was determined using a next-generation amplicon sequencing. PMMoV was the most abundant virus regardless of season and location, indicating its usefulness as an indicator for the viral contamination of water. Other potential indicators, AiV and EV, were less abundant than GII-NoV. Viruses other than PMMoV showed seasonality, i.e., EV and other viruses (NoVs, SaV, RoV, and AiV-1) became prevalent during summer and winter, respectively. SaV showed a relatively high abundance at a location that was affected by untreated wastewater. Regarding NoV genotypes, GI.1, GI.2, GI.4, GI.5, GI.6, GII.3, GII.4, GII.6, and GII.17 were found from the surface water samples. GII.4 and GII.17 seemed to have contributed to the high abundance of GII-NoV in the samples. Interestingly, GII.17 strains became prevalent in the water samples before becoming prevalent among gastroenteritis patients in Japan. These findings provide further insights into the properties of viruses as contaminants in the water environment.

Tissue Distribution and Visualization of Internalized Human Norovirus in Leafy Greens

Lettuce has been implicated in human norovirus (HuNoV) outbreaks. The virus is stable on the leaf surface for at least 2 weeks; however, the dynamics of virus internalization have not been fully investigated. The purpose of this study was to assess the internalization and distribution of HuNoV and two surrogate viruses, porcine sapovirus (SaV) and Tulane virus (TV), in lettuce and spinach. Viral inoculations through the roots of seedlings and the petiole of leaves from mature plants were performed, and the viruses were tracked on days 1 and 6 post-root inoculation and at 16 h and 72 h post-petiole inoculation. Confocal microscopy was used to visualize root-internalized HuNoV. In both lettuce and spinach, (i) HuNoV was internalized into the roots and leaves at similar RNA titers, whereas surrogate viruses were more restricted to the roots, (ii) all three viruses were stable inside the roots and leaves for at least 6 days, and (iii) HuNoV disseminated similarly inside the central veins and leaf lamina, whereas surrogate viruses were more restricted to the central veins. Infectious TV, but not SaV, was detectable in all tissues, suggesting that TV has greater stability than SaV. HuNoV was visualized inside the roots' vascular bundle and the leaf mesophyll of both plants. In conclusion, using surrogate viruses may underestimate the level of HuNoV internalization into edible leaves. The internalization of HuNoV through roots and cut leaves and the dissemination into various spinach and lettuce tissues raise concerns of internal contamination through irrigation and/or wash water.IMPORTANCE Human noroviruses are the leading cause of foodborne outbreaks, with lettuce being implicated in the majority of outbreaks. The virus causes acute gastroenteritis in all age groups, with more severe symptoms in children, the elderly, and immunocompromised patients, contributing to over 200,000 deaths worldwide annually. The majority of deaths due to HuNoV occur in the developing world, where limited sanitation exists along with poor wastewater treatment facilities, resulting in the contamination of water resources that are often used for irrigation. Our study confirms the ability of lettuce and spinach to internalize HuNoV from contaminated water through the roots into the edible leaves. Since these leafy greens are consumed with minimal processing that targets only surface pathogens, the internalized HuNoV presents an added risk to consumers. Thus, preventive measures should be in place to limit the contamination of irrigation water. In addition, better processing technologies are needed to inactivate internalized viral pathogens.

Waterborne outbreak of gastroenteritis on the KwaZulu-Natal Coast, South Africa, December 2016/January 2017

An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A total of 126 cases and 62 controls were included in the analysis. The odds of developing gastroenteritis were 6.0 times greater among holiday makers than residents (95% confidence interval (CI) 2.0-17.7). Swimming in the lagoon increased the odds of developing gastroenteritis by 3.3 times (95% CI 1.06-10.38). Lagoon water samples tested positive for norovirus (NoV) GI.6, GII.3 and GII.6, astrovirus and rotavirus. Eleven (55%) stool specimens were positive for NoV with eight genotyped as GI.1 (n = 2), GI.5 (n = 3), GI.6 (n = 2), and GI.7 (n = 1). A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. Restriction to swimming in the lagoon was apparently ineffective at preventing the outbreak, possibly due to inadequate enforcement, communication and signage strategies.

Viral shedding and clinical status of feline-norovirus-infected cats after reinfection with the same strain

Norovirus (NoV) infection is the most common cause of acute gastroenteritis in humans of all ages worldwide. When cats are experimentally infected with feline norovirus (FNoV), they develop symptoms of acute gastroenteritis. Therefore, FNoV infection may serve as an animal model for the disease caused by human norovirus infection. In this study, we examined whether FNoV of cats infected with genogroup GVI are protected from reinfection with the same strain. The blood anti-FNoV IgG level was inversely correlated with the viral load in stool samples and the clinical score of FNoV-infected cats, but complete prevention of reinfection was not observed. These findings were similar to the results of a reinfection experiment with NoV in human volunteers.

Risk factors for hospital norovirus outbreaks: impact of vomiting, genotype, and multi-occupancy rooms

BACKGROUND

Norovirus is frequently introduced to the hospital and is a frequent cause of hospital outbreaks. Recognition of the factors that facilitate or impede norovirus transmission is an important step to effectively prevent hospital outbreaks.

AIM

To investigate risk factors for norovirus outbreaks in hospital settings.

METHODS

Clinical data, ward setting, and norovirus genotype were collected from all 65 norovirus-positive index cases in outbreaks and all 186 sporadic norovirus cases at 192 wards in southern Sweden during 2010-2012 in a nested case-control study. Uni- and multivariate statistical analyses were conducted.

FINDINGS

Outbreak was independently associated with the number of patients sharing a room with the norovirus case (odds ratio (OR): 1.9 per additional patient in the room; P < 0.01), vomiting (OR: 2.6; P = 0.04), age >80 years (OR: 3.2; P < 0.01), comorbidity (OR: 2.3; P = 0.05), and onset of symptoms after admission to the ward (OR: 3.5; P < 0.01) in the multivariate analysis. Infection with genotype GII.4 was found to be strongly associated with outbreak in the univariate analysis (OR: 5.7; P < 0.01). Moreover, associations between GII.4 and vomiting (OR: 2.5; P = 0.01) and old age (OR: 4.3: P < 0.01) were found.

CONCLUSION

This is the first study to investigate clinical, ward and genotype risk factors for norovirus hospital outbreaks. Recognition of these factors may help direct and prioritize infection control actions based on the outbreak risk. The results also suggest that the outbreak association with GII.4 partly may be explained by an enhanced ability to induce vomiting.

Foodborne Norovirus State of Affairs in the EU Rapid Alert System for Food and Feed

The European Union Rapid Alert System for Food and Feed (EU RASFF) database is an invaluable instrument for analyzing notifications involving norovirus in food. The aim of this work was to carry out a thorough research of the alert and border rejection notifications submitted in the RASFF database from its onset until 31 August 2017. Some conclusions of interest were: (i) Denmark, France, Italy, the Netherlands and Norway have contributed the majority of alert notifications as notifying countries, (ii) France and Serbia have been cited more often in alert notifications as countries of origin, (iii) Italy and Spain have submitted the majority of border rejection notifications, (iv) Third Countries implicated more frequently in border rejection notifications for norovirus in bivalve molluscs were Vietnam and Tunisia, whereas in fruits and vegetables were China and Serbia, (v) "risk dispersion" from norovirus-contaminated food was narrow since, in just over half of all alert notifications and all of the border rejection notifications, only up to three countries were involved, and (vi) both raw (oysters and berries) and cooked (mussels) food products can present a health risk to consumers. The information retrieved from the RASFF database on norovirus-contaminated food could prove helpful in the planning of future norovirus risk analysis endeavors.

Norovirus Cell Tropism Is Determined by Combinatorial Action of a Viral Non-structural Protein and Host Cytokine

Cellular tropism during persistent viral infection is commonly conferred by the interaction of a viral surface protein with a host receptor complex. Norovirus, the leading global cause of gastroenteritis, can be persistently shed during infection, but its in vivo cellular tropism and tropism determinants remain unidentified. Using murine norovirus (MNoV), we determine that a small number of intestinal epithelial cells (IECs) serve as the reservoir for fecal shedding and persistence. The viral non-structural protein NS1, rather than a viral surface protein, determines IEC tropism. Expression of NS1 from a persistent MNoV strain is sufficient for an acute MNoV strain to target IECs and persist. In addition, interferon-lambda (IFN-λ) is a key host determinant blocking MNoV infection in IECs. The inability of acute MNoV to shed and persist is rescued in Ifnlr1-/- mice, suggesting that NS1 evades IFN-λ-mediated antiviral immunity. Thus, NS1 and IFN-λ interactions govern IEC tropism and persistence of MNoV.