Inter-seasonal diversity of norovirus genotypes: Emergence and selection of virus variants

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.

Norovirus GII and astrovirus in shellfish from a mangrove region in Cananéia, Brazil: molecular detection and characterization

In recent years, annual cases of gastroenteritis have been reported in the world at high rates, suggesting an association with the consumption of shellfish with enteric viruses in their tissues. Anthropic activities are considered a source of environmental pollution and the main responsible for contamination by pathogenic microorganisms in aquatic environments. The objective of this study was to evaluate, by RT-semi-nested PCR, the presence of astrovirus (AstV) and norovirus genogroup II (NoV GII) in mussels (Mytella falcata) and oysters (Crassostrea brasiliana) collected in two sites of the Lagunar Complex of Cananéia, State of São Paulo, Brazil. A total of 150 samples of mussels and oysters (75 samples each) were analyzed. AstV was not identified in any shellfish sample. NoV GII was detected in 21 samples (14%), 8 mussel samples (38%), and 13 oyster samples (62%). From the 21 positive samples, 16 were analyzed by nucleotide sequencing. The molecular characterization revealed that Brazilian samples were grouped into clades along with other sequences from Brazil, Japan, and Mexico. There was 93.8-100% amino acid sequence similarity among the samples in this study and > 94.9% when compared with the strains isolated from clinical cases in Brazil. The screening of shellfish for the presence of health-significant enteric viruses can help prevent outbreaks among consumers and contribute to the improvement of the estuarine environment.

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.

Epidemiology and genotype diversity of norovirus infections among children aged <5 years following rotavirus vaccine introduction in Blantyre, Malawi

BACKGROUND

Following rotavirus vaccine introduction, norovirus has emerged as a significant pathogen associated with acute gastroenteritis among children in some high- and middle-income countries. In a case-control study following rotavirus vaccination in Malawi, we used PCR to test for multiple enteric pathogens in fecal samples from children aged <5 years hospitalized with diarrhea, and from asymptomatic community controls (Iturriza-Gómara et al. 2019).

OBJECTIVES

To describe the epidemiology and genotype diversity of norovirus infections among infants and young children in Blantyre, Malawi, following rotavirus vaccine introduction in 2012.

STUDY DESIGN

We analysed data from the case-control study to assess annual and agespecific norovirus prevalence and the presence of co-infection. Norovirus-containing specimens were amplified by PCR and sequenced to determined genotype.

RESULTS

Norovirus prevalence in cases was similar for each complete year of study (11.4% in 2013, 9.3% in 2014 and 11.2% in 2015). Prevalence of norovirus among children aged <6 months, 6-11 months, 12-23 months and 24+ months was 15.3% (11/72), 13.3% (44/331), 11.0% (24/219) and 6.6% (4/61) respectively in cases and 6.7% (2/30), 13.1% (30/229), 4.2% (8/192) and 7.1 (5/70) in controls. Co-pathogens were commonly detected in norovirus positive cases (77/83) and controls (44/45). Norovirus GII.4 was the most commonly identified genotype, comprising 48% and 41% of genotyped strains among cases and controls, respectively.

CONCLUSIONS

Norovirus disease prevalence was unchanged during the study period, and was greatest amongst infants. Frequent co-infection and asymptomatic shedding suggests intense community transmission of norovirus and other enteric pathogens in this low-income, African setting.

An interactive data visualisation application to investigate nosocomial transmission of infections

Background: Healthcare-associated infections represent a major threat to patient, staff and visitor safety. Identification of episodes that are likely to have resulted from nosocomial transmission has important implications for infection control. Routinely collected data on ward admissions and sample dates, combined with pathogen genomic information could provide useful insights. We describe a novel, open-source, application for visualising these data, and demonstrate its utility for investigating nosocomial transmission using a case study of a large outbreak of norovirus infection. Methods: We developed the application using Shiny, a web application framework for R. For the norovirus case study, cases were defined as patients who had a faecal sample collected at the hospital in a winter season that tested positive for norovirus. Patient demographics and ward admission dates were extracted from hospital systems. Detected norovirus strains were genotyped and further characterised through sequencing of the hypervariable P2 domain. The most commonly detected sub-strain was visualised using the interactive application. Results: There were 156 norovirus-positive specimens collected from 107 patients. The most commonly detected sub-strain affected 30 patients in five wards. We used the interactive application to produce three visualisations: a bar chart, a timeline, and a schematic ward plan highlighting plausible transmission links. Visualisations showed credible links between cases on the elderly care ward. Conclusions: Use of the interactive application provided insights into transmission in this large nosocomial outbreak of norovirus, highlighting where infection control practices worked well or could be improved. This is a flexible tool that could be used for investigation of any infection in any hospital by interactively changing parameters. Challenges include integration with hospital systems for extracting data. Prospective use of this application could inform better infection control in real time.

An interactive data visualisation application to investigate nosocomial transmission of infections

Background: Healthcare-associated infections represent a major threat to patient, staff and visitor safety. Identification of episodes that are likely to have resulted from nosocomial transmission has important implications for infection control. Routinely collected data on ward admissions and sample dates, combined with pathogen genomic information could provide useful insights. We describe a novel, open-source, application for visualising these data, and demonstrate its utility for investigating nosocomial transmission using a case study of a large outbreak of norovirus infection.

Methods: We developed the application using Shiny, a web application framework for R. For the norovirus case study, cases were defined as patients who had a faecal sample collected at the hospital in a winter season that tested positive for norovirus. Patient demographics and ward admission dates were extracted from hospital systems. Detected norovirus strains were genotyped and further characterised through sequencing of the hypervariable P2 domain. The most commonly detected sub-strain was visualised using the interactive application.

Results: There were 156 norovirus-positive specimens collected from 107 patients. The most commonly detected sub-strain affected 30 patients in five wards. We used the interactive application to produce three visualisations: a bar chart, a timeline, and a schematic ward plan highlighting plausible transmission links. Visualisations showed credible links between cases on the elderly care ward.

Conclusions: Use of the interactive application provided insights into transmission in this large nosocomial outbreak of norovirus, highlighting where infection control practices worked well or could be improved. This is a flexible tool that could be used for investigation of any infection in any hospital by interactively changing parameters. Challenges include integration with hospital systems for extracting data. Prospective use of this application could inform better infection control in real time.

Evolutionary Constraints on the Norovirus Pandemic Variant GII.4_2006b over the Five-Year Persistence in Japan

Norovirus GII.4 is a major cause of global outbreaks of viral gastroenteritis in humans, and has evolved by antigenic changes under the constantly changing human herd immunity. Major shift in the pandemic GII.4 strain periodically occurs concomitant with changes in the antigenic capsid protein VP1. However, how the newly emerged strain evolves after the onset of pandemic remains unclear. To address this issue, we examined molecular evolution of a pandemic lineage, termed the GII.4_2006b, by using the full-length viral genome and VP1 sequences (n = 317) from stools collected at 20 sites in Japan between 2006 and 2011. Phylogenetic tree showed a radial diversification of the genome sequences of GII.4_2006b, suggesting a rapid genetic diversification of the GII.4_2006b population from a few ancestral variants. Impressively, amino acid sequences of the variable VP1 in given seasons remained as homogeneous as those of viral enzymes under annual increase in the nucleotide diversity in the VP1 coding region. The Hamming distances between the earliest and subsequent variants indicate strong constraints on amino acid changes even for the highly variable P2 subdomain. These results show the presence of evolutionary constraints on the VP1 protein and viral enzymes, and suggest that these proteins gain near maximal levels of fitness benefits in humans around the onset of the outbreaks. These findings have implications for our understanding of molecular evolution, mechanisms of the periodic shifts in the pandemic NoV GII.4 strains, and control of the NoV GII.4 pandemic strain.

Detection, fate and inactivation of pathogenic norovirus employing settlement and UV treatment in wastewater treatment facilities

It is accepted that discharged wastewaters can be a significant source of pathogenic viruses in receiving water bodies contributing to pollution and may in turn enter the human food chain and pose a risk to human health, thus norovirus (NoV) is often a predominant cause of gastroenteritis globally. Working with NoV poses particular challenges as it cannot be readily identified and detection by molecular methods does not assess infectivity. It has been proposed that the infectivity of NoV may be modelled through the use of an alternative virus; F-specific RNA (FRNA) bacteriophages; GA genotype and other FRNA bacteriophages have been used as a surrogate in studies of NoV inactivation. This study investigated the efficiency of novel pulsed ultraviolet irradiation and low pressure ultraviolet irradiation as a potential pathogen inactivation system for NoV and FRNA bacteriophage (GA) in secondary treated wastewaters. The role of UV dose and the impact of suspended solids concentration on removal efficiency were also examined. The study also investigated the role of settlement processes in wastewater treatment plants in removing NoV. While NoV inactivation could not be determined it was found that at a maximum UV dose of 6.9J/cm(2) (6900mJ/cm(2)) an average 2.4 log removal of FRNA bacteriophage (GA) was observed; indicating the potential need for high UV doses to remove NoV if FRNA bacteriophage prove a suitable indicator for NoV. The study found that increasing concentrations of suspended solids impacted on PUV efficiency however, it appears the extent of the impact may be site specific. Furthermore, the study found that settlement processes can play a significant role in the removal of FRNA bacteriophage, thus potentially NoV.

Viral gastrointestinal infections and norovirus genotypes in a paediatric UK hospital, 2014-2015

BACKGROUND

Diarrhoea in children is a common disease; understanding the incidence of causative viruses can aid infection control and vaccine development.

OBJECTIVES

Describe the incidence and characteristics of gastroenteric viruses including norovirus genotypes in a paediatric hospital cohort.

STUDY DESIGN

Norovirus, adenovirus, sapovirus, astrovirus, rotavirus qPCR and norovirus genotyping results for all stool specimens (n=4786; 1393 patients) at a UK paediatric tertiary referral hospital June 2014-July 2015.

RESULTS AND DISCUSSION

24% (329/1393) of patients were positive for a GI virus; the majority were positive for norovirus (44%, 144/329) or adenovirus (44%, 146/329). The overall incidence of rotavirus (2%) is reduced compared to pre-vaccination studies; however the incidence of other GI viruses has not increased. Norovirus infections had a significantly higher virus burden compared to other GI viruses (P ≤0.03); sapovirus infections had the lowest viral burden. The number of norovirus cases per month did not follow the typical winter seasonal trend of nationally reported outbreaks. The number of cases per month correlates with the number of hospital admissions (R=0.703, P=0.011); the number of admissions accounts for 50% of the variability in number of cases per month. The breadth of genotypes seen (48% non-GII.4), suggests a community source for many norovirus infections and has implications for vaccine development. All GI viruses caused chronic infections, with the majority (50-100%) in immunocompromised patients. Incidence or duration of infection in chronic norovirus infections did not differ between genotypes, suggesting host-mediated susceptibility.

Emergence in Taiwan of novel norovirus GII.4 variants causing acute gastroenteritis and intestinal haemorrhage in children

Norovirus is the leading cause of viral gastroenteritis globally. Norovirus genotype GII.4 is responsible for the majority of outbreaks, but new variants are continuously emerging. The objective of the study was to delineate the clinical manifestations and complications associated with these new norovirus GII.4 variants in children. We investigated norovirus infections from the community outbreak in October 2011-September 2012 and an earlier outbreak in 2006-2007, in northern Taiwan. Norovirus genotypes and their variants were validated using molecular methods. A norovirus outbreak started in mid-2011 and continued through 2012 in northern Taiwan. Hospitalized children infected by norovirus in 2012 showed a significantly higher incidence of intestinal haemorrhage, as indicated by grossly bloody faeces (P=0.012) and occult blood in faeces (P < 0.001), and also presented with more high fever >39 °C (P < 0.001), fever >38.5 °C (P < 0.001) and fever of any temperature >38 °C (P < 0.001), compared with children hospitalized in 2006-2007. Analysis of 20 near-full-length genome sequences indicated an emergence of GII.4 2012 variants in 2011-2012. Circulating noroviruses can be divided into two clusters: GII.4 2012a, which is identical to the newly reported strain GII.4 Sydney 2012, and GII.4 2012b, which is close to GII.4 2006b, the earlier predominant strain. The emerging new variants of norovirus GII.4 caused a distinct clinical syndrome of acute gastroenteritis with severe fever and a high rate of intestinal haemorrhage in children. The genetic diversity associated with changing clinical manifestations poses major obstacles to norovirus control.

Prevention of Nosocomial Transmission of Norovirus by Strategic Infection Control Measures

Background.

Nosocomial outbreaks of norovirus infection pose a great challenge to the infection control team.

Methods.

Between November 1, 2009, and February 28, 2010, strategic infection control measures were implemented in a hospital network. In addition to timely staff education and promotion of directly observed hand hygiene, reverse-transcription polymerase chain reaction for norovirus was performed as an added test by the microbiology laboratory for all fecal specimens irrespective of the request for testing. Laboratory-confirmed cases were followed up by the infection control team for timely intervention. The incidence of hospital-acquired norovirus infection per 1,000 potentially infectious patient-days was compared with the corresponding period in the preceding 12 months, and the incidence in the other 6 hospital networks in Hong Kong was chosen as the concurrent control. Phylogenetic analysis of norovirus isolates was performed.

Results.

Of the 988 patients who were tested, 242 (25%) were positive for norovirus; 114 (47%) of those 242 patients had norovirus detected by our added test. Compared with the corresponding period in the preceding 12 months, the incidence of hospital-acquired norovirus infection decreased from 131 to 16 cases per 1,000 potentially infectious patient-days (P < .001 ), although the number of hospital-acquired infections was low in both the study period (n = 8) and the historical control periods (n = 11). The incidence of hospital-acquired norovirus infection in our hospital network (0.03 cases per 1,000 patient-days) was significantly lower than that of the concurrent control (0.06 cases per 1,000 patient-days) (P = .015). Forty-three (93%) of 46 norovirus isolates sequenced belonged to the genogroup II.4 variant.

Conclusions.

Strategic infection control measures with an added test maybe useful in controlling nosocomial transmission of norovirus.

Temporal dynamics of norovirus GII.4 variants in Brazil between 2004 and 2012

Noroviruses (NoVs) are the major cause of acute gastroenteritis outbreaks, and, despite a wide genetic diversity, genotype II.4 is the most prevalent strain worldwide. Mutations and homologous recombination have been proposed as mechanisms driving the epochal evolution of the GII.4, with the emergence of new variants in 1–3-year intervals causing global epidemics. There are no data reporting the dynamics of GII.4 variants along a specific period in Brazil. Therefore, to improve the understanding of the comportment of these variants in the country, the aim of this study was to evaluate the circulation of NoV GII.4 variants during a 9-year period in 3 out of 5 Brazilian regions. A total of 147 samples were sequenced, and a phylogenetic analysis of subdomain P2 demonstrated the circulation of six GII.4 variants, Asia_2003, Hunter_2004, Den Haag_2006b, Yerseke_2006a, New Orleans_2009, and Sydney_2012, during this period. The most prevalent variant was Den Haag_2006b, circulating in different Brazilian regions from 2006 to 2011. A Bayesian coalescent analysis was used to calculate the mean evolutionary rate of subdomain P2 as 7.3×10⁻³ (5.85×10⁻³–8.82×10⁻³) subst./site/year. These analyses also demonstrated that clade Den Haag_2006b experienced a rapid expansion in 2005 and another in 2008 after a period of decay. The evaluation of the temporal dynamics of NoV GII.4 in Brazil revealed a similar pattern, with few exceptions, to the worldwide observation. These data highlight the importance of surveillance for monitoring the emergence of new strains of NoV GII.4 and its impact on cases of acute gastroenteritis.

Detection and molecular characterisation of noroviruses in hospitalised children in Malawi, 1997-2007

Despite the increasing recognition of noroviruses as major pathogens associated with community-acquired diarrhoea in children, there are few studies from Africa. Long-term surveillance studies of rotavirus gastroenteritis in Malawian children have provided an opportunity to undertake a study of the importance and epidemiological features of norovirus infection in this population. Faecal specimens were collected from children <5 years of age admitted to hospital with acute diarrhoea, as well as from a comparison group of diarrhoea-free children, in Blantyre, Malawi between 1997 and 2007. Norovirus was detected using real-time PCR and strains genotyped by nucleotide sequence analysis. Norovirus was detected in 220/1,941 (11.3%) faecal specimens, comprising genogroup GI (1.8%), GII (9.4%) and mixed GI/GII (0.1%). The median age of children with norovirus was 6 months (range, 0-48 months). Norovirus was detected throughout the year, with peaks at the end of the rainy season (March) and towards the end of the dry season (August-November). Norovirus GII.4 was the most commonly detected genotype accounting for 70% of strains characterised, followed by GII.2 (6%), GII.6 (4%) and GII.12 (4%). Sub typing of GII.4 noroviruses demonstrated local circulation of strains prior to their subsequent detection in association with global epidemics of gastroenteritis. The prevalence of norovirus in children without diarrhoea was similar to the level in cases. This largest study to date of norovirus infection in African children indicates the potential role of paediatric surveillance in predicting the emergence of norovirus strains with global epidemic potential.

Virus-like Particle Vaccines for Norovirus Gastroenteritis

Gastroenteritis (GE) and its associated diarrheal diseases remain as one of the top causes of death in the world. Noroviruses (NoVs) are a group of genetically diverse RNA viruses that cause the great majority of nonbacterial gastroenteritis in humans. However, there is still no vaccine licensed for human use to prevent NoV GE. The lack of a tissue culture system and a small animal model further hinders the development of NoV vaccines.

Virus-like particles (VLPs) that mimic the antigenic architecture of authentic virions, however, can be produced in insect, mammalian, and plant cells by the expression of the capsid protein. The particulate nature and high-density presentation of viral structure proteins on their surface render VLPs as a premier vaccine platform with superior safety, immunogenicity, and manufacturability. Therefore, this chapter focuses on the development of effective NoV vaccines based on VLPs of capsid proteins. The expression and structure of NoV VLPs, especially VLPs of Norwalk virus, the prototype NoV, are extensively discussed. The ability of NoV VLPs in stimulating a potent systemic and mucosal anti-NoV immunity through oral and intranasal delivery in mice is presented.

The advantages of plant expression systems as a novel production platform for VLP-based NoV vaccines are discussed in light of their cost-effectiveness, production speed, and scalability. Recent achievements from the first successful demonstration of NoV VLP production in plant expression system under the current Good Manufacture Practice (cGMP) regulation by the US Food and Drug Administration (FDA) are detailed.

Moreover, results of human clinical trials demonstrating the safety and efficacy of insect and plant-derived NoV VLPs are also presented. Due to the diversity of capsid protein among different NoV strains and its rapid antigenic drift, we speculate that vaccine development should focus on multivalent VLP vaccines derived from capsid proteins of the most prevalent strains. With the very recent approval of the first plant-made biologics by the FDA, we also speculate that plant-based production systems will play an important role in manufacturing such multivalent VLP-based NoV vaccines.

Epidemiology and estimated costs of a large waterborne outbreak of norovirus infection in Sweden

A large outbreak of norovirus (NoV) gastroenteritis caused by contaminated municipal drinking water occurred in Lilla Edet, Sweden, 2008. Epidemiological investigations performed using a questionnaire survey showed an association between consumption of municipal drinking water and illness (odds ratio 4·73, 95% confidence interval 3·53–6·32), and a strong correlation between the risk of being sick and the number of glasses of municipal water consumed. Diverse NoV strains were detected in stool samples from patients, NoV genotype I strains predominating. Although NoVs were not detected in water samples, coliphages were identified as a marker of viral contamination. About 2400 (18·5%) of the 13 000 inhabitants in Lilla Edet became ill. Costs associated with the outbreak were collected via a questionnaire survey given to organizations and municipalities involved in or affected by the outbreak. Total costs including sick leave, were estimated to be ∼8 700 000 Swedish kronor (∼€0·87 million).

Evolution of virulence in emerging epidemics

Theory predicts that selection for pathogen virulence and horizontal transmission is highest at the onset of an epidemic but decreases thereafter, as the epidemic depletes the pool of susceptible hosts. We tested this prediction by tracking the competition between the latent bacteriophage λ and its virulent mutant λcI857 throughout experimental epidemics taking place in continuous cultures of Escherichia coli. As expected, the virulent λcI857 is strongly favored in the early stage of the epidemic, but loses competition with the latent virus as prevalence increases. We show that the observed transient selection for virulence and horizontal transmission can be fully explained within the framework of evolutionary epidemiology theory. This experimental validation of our predictions is a key step towards a predictive theory for the evolution of virulence in emerging infectious diseases.

Clinical and molecular epidemiologic analyses of norovirus-associated sporadic gastroenteritis in adults from Beijing, China

Noroviruses (NoVs) are a major cause of nonbacterial acute gastroenteritis. The molecular epidemiology of NoV infections in China has not been well characterized. To study the incidence of NoV infections and the nature of the circulating NoV genotypes, 403 specimens were collected from adult outpatients with acute gastroenteritis in Beijing, China, between October 2007 and September 2008. Samples were examined for NoV by reverse transcriptase-polymerase chain reaction (RT-PCR) and sequences corresponding to both the NoV polymerase and capsid regions were characterized. Among the 403 specimens, 48 (11.9%) were positive for NoV and 1/3 NoV-associated gastroenteritis cases occurred during the colder months (November and December). Based on polymerase region sequences, 6 NoV genotypes (GII-4, GII-b, GII-6, GI-2, GI-3, and GI-4) were identified with GII-4 2006b being the most predominant genotype (37/48, 77.1%). Eleven distinct genotype sequences in polymerase and capsid regions were identified, indicating a genetic diversity among NoV isolates. This study suggested NoVs were an important pathogen responsible for sporadic acute gastroenteritis in adults in Beijing, China.

Molecular epidemiology of noroviruses in children and adults with acute gastroenteritis in Wuhan, China, 2007-2010

To study epidemiological features and genetic characteristics of noroviruses in children and adults with acute gastroenteritis, fecal specimens were collected in three hospitals from Jan. 2007 to May 2010 in Wuhan, China. Noroviruses were detected in 25.9 % (286/1103) and 24.6 % (202/822) of the specimens from children and adults, respectively, with genogroup II (GII) being predominant (99.2 %). The most frequent genotype among GII strains was GII.4 (2006b variant) (77.3 %) (72.0 % in children and 87.9 % in adults), followed by GII.3 (15.0 %) and GII.6 (3.4 %). Potential recombinant genotypes (polymerase/capsid) were detected in 51 GII strains (15.9 %), including the most frequent type, GII.12/GII.3 (28 strains), and GII.16/GII.2, detected for the first time in China, which were found in only children. The results indicated that genetically similar noroviruses were circulating among children and adults as a cause of gastroenteritis, except for some recombinant genotypes.

Worldwide molecular epidemiology of norovirus infection

Norovirus (NoV) is recognised as one of the emerging viruses causing infection in humans. It is the leading cause of outbreaks of viral gastro-enteritis worldwide. In children, NoV plays an increasing and important role in enteric infection, apart from rotavirus, especially in the post-rotavirus vaccine era. NoV-infected children usually present with typical clinical manifestations of acute viral gastro-enteritis, including vomiting and watery diarrhoea, and paediatric patients are more liable to have dehydration requiring hospitalisation. Other than these symptoms, severe or atypical complications associated with NoV infection include infantile convulsion, necrotising enterocolitis, and, rarely, disseminated disease involving multiple organs. Although most symptoms of NoV infection are self-limiting, recurrent infection is not uncommon in children as well as in the elderly. The rapid evolution and complex genetic diversity of NoV makes for difficulty in identification, classification and surveillance of the virus. Using molecular biological methods, clearer genetic and molecular features of the circulating NoV are now recognised. The emerging GII.4 genotype is currently responsible for 60-90% of outbreaks worldwide. Rapid transmission of NoV from person-to-person makes the infection difficult to control. In addition to personal hygiene such as hand-washing, prevention of NoV will depend largely on the development of an effective vaccine. Given the rapid evolution of the virus, continued molecular epidemiological surveillance is important.

Molecular epidemiology of canine norovirus in dogs from Portugal, 2007-2011

Background

Canine noroviruses (NoVs) have been recently described in south European countries and associated with outbreaks of diarrhea in kennels. Unlike human NoV which are known as an important cause of acute gastroenteritis, little is known about the role of canine NoV as pathogens in dogs as well as its epidemiological features.

Results

From 2007–2011, 256 stool samples were collected from dogs across Portugal and tested by RT-PCR for canine NoV. Viral fecal shedding was found to be 23% (60/256). All sequences contained the GLPSG amino acid motif characteristic of the RNA-dependent RNA-polymerase gene of NoVs and had a high nucleotide identity (range 98%–100%) to the canine NoV first described in Portugal. The highest shedding rate was detected during the winter months.

Conclusions

This study shows that canine NoV infection is endemic in the dog population of Portugal. Peak shedding was detected in the winter months, a well-known epidemiologic feature of human NoV infections.

Complete genomic sequence analysis of norovirus isolated from South Korea

The complete nucleotide and deduced amino acid sequences of the RNA genome of a recently isolated norovirus (NoV) from Korea, designated Hu/GII-4/CBNU2/2007/KR (CBNU2), were determined and characterized by phylogenetic comparison with several genetically diverse NoV sequences. The RNA genome of CBNU2 is 7,560 nucleotides in length, excluding the 3' poly (A) tract. It includes three open reading frames (ORFs): ORF1, which encodes the nonstructural polyprotein (5-5,104); ORF2, which encodes VP1 (5,085-6,707); and ORF3, which encodes VP2 (6,707-7,513). ORF2-based phylogenetic analysis revealed that CBNU2 belonged to the GII.4 genotype, the most prevalent genotype, and formed a cluster with NoVs isolated from Asian regions, between 2006 and 2008. Comparative analysis with the consensus sequence of 207 completely sequenced NoV genomes showed 47 mismatched nucleotides: 26 in ORF1, 14 in ORF2, and 7 in ORF3, resulting in 8 amino acid changes: 3 in ORF1, 2 in ORF2, and 3 in ORF3. Phylogenetic analysis with full genome ORF1, ORF2, and ORF3 nucleotide sequences obtained from CBNU2 and each of the other representative NoV genomes suggested that CBNU2 had not undergone recombination with any of the other NoVs. A SimPlot analysis further supported this finding.

Viral gastroenteritis associated with genogroup II norovirus among U.S. military personnel in Turkey, 2009

The present study demonstrates that multiple NoV genotypes belonging to genogroup II contributed to an acute gastroenteritis outbreak at a US military facility in Turkey that was associated with significant negative operational impact. Norovirus (NoV) is an important pathogen associated with acute gastroenteritis among military populations. We describe the genotypes of NoV outbreak occurred at a United States military facility in Turkey. Stool samples were collected from 37 out of 97 patients presenting to the clinic on base with acute gastroenteritis and evaluated for bacterial and viral pathogens. NoV genogroup II (GII) was identified by RT-PCR in 43% (16/37) stool samples. Phylogenetic analysis of a 260 base pair fragment of the NoV capsid gene from ten stool samples indicated the circulation of multiple and rare genotypes of GII NoV during the outbreak. We detected four GII.8 isolates, three GII.15, two GII.9 and a sole GII.10 NoV. Viral sequences could be grouped into four clusters, three of which have not been previously reported in Turkey. The fact that current NoV outbreak was caused by rare genotypes highlights the importance of norovirus strain typing. While NoV genogroup II is recognized as causative agent of outbreak, circulation of current genotypes has been rarely observed in large number of outbreaks.

The epidemiology of published norovirus outbreaks: a review of risk factors associated with attack rate and genogroup

The purpose of this study was to examine global epidemiological trends in human norovirus (NoV) outbreaks by transmission route and setting, and describe relationships between these characteristics, viral attack rates, and the occurrence of genogroup I (GI) or genogroup II (GII) strains in outbreaks. We analysed data from 902 reverse transcriptase-polymerase chain reaction-confirmed, human NoV outbreaks abstracted from a systematic review of articles published from 1993 to 2011 and indexed under the terms 'norovirus' and 'outbreak'. Multivariate regression analyses demonstrated that foodservice and winter outbreaks were significantly associated with higher attack rates. Foodborne and waterborne outbreaks were associated with multiple strains (GI+GII). Waterborne outbreaks were significantly associated with GI strains, while healthcare-related and winter outbreaks were associated with GII strains. These results identify important trends for epidemic NoV detection, prevention, and control.

Molecular epidemiology of norovirus in Edinburgh healthcare facilities, Scotland 2007-2011

Norovirus (NoV) is a leading cause of outbreaks of gastroenteritis worldwide, and a major burden for healthcare facilities. This study investigated the NoV genotypes responsible for outbreaks in Edinburgh healthcare facilities between June 2008 and July 2011, and studied their temporal distribution to enable a better understanding of the epidemiology of the outbreaks. A total of 287 samples positive for NoV genogroup II (GII) RNA by reverse transcription-polymerase chain reaction (RT-PCR) during routine diagnostic testing were investigated. Nested RT-PCR (nRT-PCR) and sequencing was used to genotype the NoV strains. Overall, a total of 69 NoV strains belonging to six different genoclusters (GII.1, GII.2, GII.3, GII.4, GII.6, GII.13) were detected. The predominant genotype was GII.4 that included four variants, GII.4 2006a, GII.4 2006b, GII.4 2007 and GII.4 2010. Importantly, increases in NoV activity coincided with the emergence of new GII.4 strains, highlighting the need for an active surveillance system to allow the rapid identification of new strains.

Prevalence of norovirus GII-4 antibodies in Finnish children

Noroviruses (NoVs) are the second most common cause of viral gastroenteritis after rotavirus in children. NoV genotype GII-4 has emerged as the major type not only in outbreaks of NoV gastroenteritis but also endemic gastroenteritis among infants and young children worldwide. Using baculovirus-insect cell system virus-like particles (VLPs) of NoV genotype GII-4 and an uncommon genotype GII-12 were produced. These VLPs were used in enzyme-linked immunosorbent assays (ELISA) for detection of NoV-specific immunoglobulin G (IgG) and IgA antibodies in 492 serum specimens from Finnish children 0-14 years of age collected between 2006 and 2008. NoV IgG antibody prevalence was 47.3% in the age group 7-23 months and increased up to 91.2% after the age of 5 years. Avidity of NoV IgG antibodies was low in the primary infections while high avidity antibodies were detected in the recurrent infections of the older children. In GII-4 infections, the homologous antibody response to GII-4 VLPs was stronger than to GII-12 VLPs but cross-reactivity between GII-4 and GII-12 was observed. Binding of GII-4 VLPs to a putative carbohydrate antigen receptor H-type 3 could be blocked by sera from children not infected with NoV during a waterborne outbreak of acute gastroenteritis. Therefore, protection against NoV infection correlated with strong blocking activity.

Low prevalence of rotavirus and high prevalence of norovirus in hospital and community wastewater after introduction of rotavirus vaccine in Nicaragua

Rotavirus (RV) and norovirus (NoV) are major causes of pediatric diarrhea and are altogether associated with approximately 800,000 deaths in young children every year. In Nicaragua, national RV vaccination program using the pentavalent RV5 vaccine from Merck was implemented in October 2006. To determine whether RV vaccination decreased the overall number of RV infections, we investigated the occurrence of RV and NoV in wastewater in the city of León from July 2007 to July 2008 and compared these data with pre-vaccination data. The major finding was the low prevalence of RV compared to NoV in all sampling points (11% vs 44%, p<0.05), and that RV concentration was lower as compared to NoV. RV was observed mainly during the rainy season (July–September), and the majority of all RV detected (6/9) belonged to subgroup (SG) I. The partial VP7-gene obtained from one RV positive sample was similar (99% nt identity) to a G6 VP7-gene of bovine origin and similar to the corresponding gene of the vaccine strain (98%). Furthermore RV G-types 2 and 4 were found in the incoming wastewater. NoV strains were detected throughout the year, of which a majority (20/21) were of genotype GII.4. We conclude that the introduction of RV vaccination reduced the transmission of RV in the community in Nicaragua. However, the burden of diarrhea in the country remains high, and the high prevalence of NoVs in hospital and municipal wastewater is noteworthy. This study highlights the need for further assessment of NoV following RV vaccine introduction.

Evaluation and verification of the Seeplex Diarrhea-V ACE assay for simultaneous detection of adenovirus, rotavirus, and norovirus genogroups I and II in clinical stool specimens

Acute viral gastroenteritis is an intestinal infection that can be caused by several different viruses. Here we describe the evaluation and verification of Seeplex Diarrhea-V ACE (Seeplex DV), a novel commercial multiplex reverse transcription-PCR (RT-PCR) assay that detects 5 diarrheal pathogens, including adenovirus, rotavirus, norovirus genogroup I (GI) and GII, and astrovirus. We describe a retrospective study of 200 clinical specimens of which 177 were stool specimens previously tested for the presence of gastrointestinal viruses by electron microscopy (EM) and/or real-time RT-PCR (rRT-PCR). The remaining 23 specimens comprised other human pathogens of viral or bacterial origin. Discordant norovirus GI and GII results were resolved using a commercial kit; discordant adenovirus and rotavirus results were resolved using a home brew multiplex rRT-PCR assay. Diagnostic sensitivities and specificities were calculated before and after discordant analysis. After discordant analysis, estimated diagnostic sensitivities were 100% for adenovirus, rotavirus, and norovirus GI and 97% for norovirus GII. Diagnostic specificities after discordant analysis were 100% for adenovirus, rotavirus, and norovirus GI and 99.4% for norovirus GII. The 95% limits of detection were 31, 10, 2, and 1 genome equivalent per reaction for adenovirus, rotavirus, and norovirus GI and GII, respectively. The results demonstrate that the Seeplex DV assay is sensitive, specific, convenient, and reliable for the simultaneous detection of several viral pathogens directly in specimens from patients with gastroenteritis. Importantly, this novel multiplex PCR assay enabled the identification of viral coinfections in 12 (6.8%) stool specimens.

Concentration and diversity of noroviruses detected in Luxembourg wastewaters in 2008-2009

Noroviruses (NoV) in 78 wastewater samples from Luxembourg were quantified, cloned, and sequenced in 2008-2009. The concentrations of NoV genogroup II and the relative occurrences of certain genotypes changed significantly during the winter season. NoV genogroup I was frequently detected by real-time reverse transcription-PCR (RT-PCR), albeit at 30-fold lower concentrations than for genogroup II, hampering attempts to assess overall genetic diversity by the cloning/sequencing approach.

A duplex real-time RT-PCR assay for the simultaneous genogroup-specific detection of noroviruses in both clinical and environmental specimens

Norovirus (NoV) is the major etiological agent causing foodborne and waterborne outbreaks worldwide. We developed a novel duplex real-time quantitative RT-PCR assay designed for the simultaneous detection of and discrimination between NoV genogroups GI and GII, by targeting the short junction region between ORF1 and ORF2, with sensitivity and efficiency comparable to those of each simplex RT-PCR assay. This new duplex assay was evaluated against clinical stool (n = 82) and environmental (groundwater or surface water, n = 60) specimens from South Korea, and the results were compared with those of conventional RT-PCR (cRT-PCR) assays. The duplex assay detected more positive samples than did the cRT-PCR for both clinical (74 vs. 71) and, more strikingly, environmental (24 vs. 10) specimens. No cross-reactivity against specimens containing other enteric viruses such as rotavirus, adenovirus, and poliovirus were observed. These results suggest that this newly developed duplex real-time RT-PCR assay can be used for the sensitive and simultaneous genogroup-specific detection of NoV in both clinical and environmental specimens.

The dynamics of norovirus outbreak epidemics: recent insights

Noroviruses are a major cause of gastroenteritis outbreaks worldwide. Norovirus outbreaks frequently occur as epidemics which appear to be related to both genetic and environmental factors. This review considers recent progress in understanding these factors. The norovirus genome undergoes continuous change and this appears to be important in the persistence of the virus in the community. Studies on the common GII.4 genotype have shown that some norovirus outbreak epidemics involving this genotype are correlated with specific changes in the genome. In contrast to the growing understanding of the role of genetic factors in norovirus outbreak epidemics, the role of environmental factors is less well understood. Topics reviewed here include long term excretion of norovirus in some individuals, long term survivability of norovirus in the environment, the role of meteorological factors in the control of norovirus outbreaks and the possible zoonotic transmission of the virus.

Waterborne norovirus outbreak in a municipal drinking-water supply in Sweden

During Easter 2009, almost 200 people resident in a small Swedish village fell ill with gastrointestinal symptoms. We conducted a retrospective cohort study and a molecular investigation in order to identify the source of the outbreak. Residents living in households connected to the public water network were at an increased risk of developing disease (relative risk 4·80, 95% confidence interval 1·68–13·73) compared to those with no connection to the public network. Norovirus genotype GI.3 was identified in stool samples from six patients and in a sample from the public water network. Contamination of one of the wells supplying the public water network was thought to be the source of the outbreak. This is a description of a norovirus outbreak linked to a municipal drinking-water supply in Sweden. Information from epidemiological and molecular investigations is of utmost importance to guide outbreak control measures and to prevent future outbreaks.

Norovirus: changing epidemiology, changing virology. The challenges for infection control

Norovirus infection is the commonest cause of outbreaks and sporadic cases of acute gastrointestinal disease in England and Wales. It is estimated that 4.5% of the population are infected by norovirus each year. Some years see more infections than others and occasionally peaks of summer time activity can occur. Current surveillance of norovirus is based on two main sources of information, routine laboratory reporting and reports of norovirus outbreaks. There are still significant barriers impeding a better understanding of the biology and epidemiology of noroviruses. Modern genetic techniques have shed light on ways in which the virus interacts with its host and evades the immune system. Some of these techniques have also led to new tools that may be useful in tracking outbreaks of norovirus, and in turn, to study the effect of potential intervention strategies, aimed at preventing or curtailing transmission within outbreaks.

Asymptomatic norovirus infections in Nicaraguan children and its association with viral properties and histo-blood group antigens

BACKGROUND

It has been previously reported that histo-blood group antigens (HBGAs) and particularly secretor status provides protection against symptomatic norovirus infection, but it remains unclear to what extent this includes asymptomatic infections in children.

METHODS

To explore whether HBGAs or certain viral genotypes are associated with asymptomatic norovirus infections in a pediatric population in Nicaragua, we investigated 163 children ≤5 years of age, without a recent history of diarrhea (≤10 days).

RESULTS

Asymptomatic norovirus infections were observed in 11.7% (19/163), with children ≤6 months of age being most frequently infected (16%). Of the 19 norovirus-positive children, 4 (21%) and 10 (53%) were infected with genogroups GI and GII, respectively, and 4 children (21%) were infected with viruses of both genogroups. Most children had ≥10 viral genomes per gram of feces. Nucleotide sequence analysis (15/19) revealed uncommon genotypes, such as, GII.7 (n = 5) and GII.2 (n = 3). An interesting observation was the low frequency of norovirus GII.4 strains among the asymptomatic children. AB blood type, Lewis a (Le) phenotype and nonsecretor genotype (sese) were not found among the asymptomatic children, but they occurred in population controls.

CONCLUSIONS

Frequency of asymptomatic norovirus infections was similar to that observed in symptomatic children from Nicaragua. Norovirus GII.2 and GII.7 were frequently detected but the globally dominating GII.4 was infrequent. Host genetic factors previously observed to be associated with protection against symptomatic norovirus infection were not found in this study.

Isolated norovirus GII.7 strain within an extended GII.4 outbreak

Noroviruses are a major cause of viral gastroenteritis and have been detected with increasing prevalence in recent years. Currently, two main genogroups GI and GII with an increasing number of subtypes are differentiated. Because of a high genetic variability new variants emerge constantly allowing epidemiological tracing of viruses from year to year and location to location. A 282 bp sequence at the 5'end of the capsid gene was analyzed in isolates originating from the University hospital, Technische Universität München. Phylogenetic analysis was based on 20 GII positive samples from an outbreak in March/April 2006 and 8 samples from the following winter season 2006-2008. In the initial outbreak two distinct genotypes were identified. The GII.4 strain 2006a found in the majority of outbreaks in 2006 worldwide was isolated from all but two patients. These two individuals were infected with a GII.7 strain clustering mainly with isolates from Asia. Of note, they excreted noroviral RNA for 81 and 27 days, respectively. Longitudinal analysis of an extended 1381 bp sequence revealed positive selection in the P2 domain. The variant was very similar to GII.7 strains isolated in 1990 and 1994 suggesting slow evolution with evidence of recombination according to the SimPlot analysis. Strains found in the following years 2006-2008 clustered around the isolate GII.4 2006b, characterized in the spring of 2006 and reaching a high prevalence in 2006-2007. The results provide an insight into norovirus evolution at a University hospital over 3 years and describe intraindividual evolution within a patient infected chronically.

Complete genome sequence and phylogenetic analysis of a recombinant Korean norovirus, CBNU1, recovered from a 2006 outbreak

We have determined the complete nucleotide and deduced amino acid sequences of the RNA genome of CBNU1, a human norovirus (NoV) recovered from a 2006 outbreak in South Korea. The genome of 7547 nucleotides, excluding a 3'-poly(A) tail of 11-105 nucleotides, encodes three overlapping open reading frames (ORFs): ORF1 (nucleotides 5-5104), ORF2 (nucleotides 5085-6731), and ORF3 (nucleotides 6731-7495). In a comparison to 108 other currently available completely sequenced NoVs representing all five genogroups (GI-GV) except GIV, the CBNU1 strain was highly similar to GII.3 NoVs. Multiple sequence alignments of the completely sequenced NoV genomes revealed five hypervariable regions throughout their genomes: two in ORF1, one in ORF2, and two in ORF3. At both the nucleotide and amino acid levels, genome-based phylogenetic analyses invariably showed that the CBNU1 strain was most closely related to three GII.3 NoVs: the American Texas/TCH04-577 and the two Japanese Saitama U18 and Saitama U201 strains; furthermore, these genome-based phylogenetic topologies corresponded most closely to those based on the ORF2 genes, as compared to those based on the ORF1 and ORF3 genes. Subsequent ORF2-based phylogenetic analyses of a selection of 126 other NoVs representing all 19 GII genotypes, in combination with genome-based Simplot analyses, showed that the CBNU1 strain was a recombinant GII.3 NoV with a breakpoint at the ORF1/ORF2 junction between two putative parent-like strains, Guangzhou/NVgz01 and Texas/TCH04-577. Overall, the CBNU1 strain represents the first Korean human NoV whose genome has been completely sequenced and for which its relationship with a large panel of genetically diverse NoVs has been extensively characterized.

Phylodynamic reconstruction reveals norovirus GII.4 epidemic expansions and their molecular determinants

Noroviruses are the most common cause of viral gastroenteritis. An increase in the number of globally reported norovirus outbreaks was seen the past decade, especially for outbreaks caused by successive genogroup II genotype 4 (GII.4) variants. Whether this observed increase was due to an upswing in the number of infections, or to a surveillance artifact caused by heightened awareness and concomitant improved reporting, remained unclear. Therefore, we set out to study the population structure and changes thereof of GII.4 strains detected through systematic outbreak surveillance since the early 1990s. We collected 1383 partial polymerase and 194 full capsid GII.4 sequences. A Bayesian MCMC coalescent analysis revealed an increase in the number of GII.4 infections during the last decade. The GII.4 strains included in our analyses evolved at a rate of 4.3-9.0x10(-3) mutations per site per year, and share a most recent common ancestor in the early 1980s. Determinants of adaptation in the capsid protein were studied using different maximum likelihood approaches to identify sites subject to diversifying or directional selection and sites that co-evolved. While a number of the computationally determined adaptively evolving sites were on the surface of the capsid and possible subject to immune selection, we also detected sites that were subject to constrained or compensatory evolution due to secondary RNA structures, relevant in virus-replication. We highlight codons that may prove useful in identifying emerging novel variants, and, using these, indicate that the novel 2008 variant is more likely to cause a future epidemic than the 2007 variant. While norovirus infections are generally mild and self-limiting, more severe outcomes of infection frequently occur in elderly and immunocompromized people, and no treatment is available. The observed pattern of continually emerging novel variants of GII.4, causing elevated numbers of infections, is therefore a cause for concern.

Tracking environmental norovirus contamination in a pediatric primary immunodeficiency unit

Norovirus strains were detected in two patients and in environmental swabs from a pediatric primary immunodeficiency unit in London, United Kingdom, during an infection control incident in November and December 2007. Detailed analyses of the gene encoding the P2 domain demonstrated that the majority of the strains were not related to the patients and that the environmental contamination was most likely due to secondary transfer by the hands of staff or visitors.

Genetic characterization of genogroup I norovirus in outbreaks of gastroenteritis

In this study, we demonstrate that differences within the P2 domain of norovirus genogroup I (GI) strains can be used to segregate outbreaks which are unrelated, whereas complete conservation within this region allows tracking of strains that are part of a single outbreak and likely to have a common source.

Community incidence of norovirus-associated infectious intestinal disease in England: improved estimates using viral load for norovirus diagnosis

Existing estimates of the incidence of infectious intestinal disease (IID) caused by norovirus are based on electron microscopy or reverse transcription-polymerase chain reaction (RT-PCR). Neither method accurately represents norovirus disease burden: Electron microscopy has poor diagnostic sensitivity, and RT-PCR has poor diagnostic specificity. In this study, viral load measurements were used to identify cases of norovirus-associated IID and to produce new incidence estimates for England. IID cases were ascertained in the Study of Infectious Intestinal Disease in England (1993-1996), and stool specimens were tested by semiquantitative real-time RT-PCR for norovirus. The age-adjusted community incidence of norovirus-associated IID was 4.5/100 person-years (95% credibility interval: 3.8, 5.2), equating to 2 million episodes/year. Among children aged less than 5 years, the community incidence was 21.4/100 person-years (95% credibility interval: 15.9, 27.7), and the incidence of consultations to general practitioners for norovirus-associated IID was 3.2/100 person-years (95% credibility interval: 2.6, 3.8), with 100,000 children visiting their general practitioner for norovirus-associated IID each year. Norovirus is the most common cause of IID in the community in England and is responsible for a similar number of pediatric primary care consultations as rotavirus.

SYBR Green based real-time RT-PCR assay for detection and genotype prediction of bovine noroviruses and assessment of clinical significance in Norway

A novel SYBR Green based real-time RT-PCR assay for detection of genogroup III bovine noroviruses (BoNoV) was developed and the assay applied to 419 faecal samples from calves with and without diarrhoea. The samples were obtained from 190 Norwegian dairy and beef herds. BoNoV was detected in 49.6% of the samples from 61.1% of the herds indicating that BoNoV is ubiquitous in Norway. The overall prevalence was not significantly different in diarrhoea and non-diarrhoea samples. Analyses of polymerase gene sequences revealed both genotype III/1 and III/2 with genotype III/2 (Newbury2-like) being the most prevalent. Detected capsid sequences were restricted to Newbury2-like and the chimeric Bo/Thirsk10/00/UK strain. The RNA polymerase genotypes of the circulating BoNoVs in Norway were predicted by melting temperature analysis. Additional data from a challenge experiment suggest that a high proportion of young calves are shedding low levels of BoNoV for a prolonged time after recovering from the associated diarrhoea. The findings may explain some of the discrepancies in detection rates from previous studies and explain why some studies have failed to detect significant prevalence differences between calves with and without diarrhoea. It may also shed new light on some epidemiological aspects of norovirus infections.

Norovirus RNA in the blood of a child with gastroenteritis and convulsions--A case report

Potential extra-intestinal spread is an important issue in understanding the pathogenesis of NoV disease. A previously healthy 14-month-old boy was admitted to the Pediatric Emergency Department of the University-Hospital of Parma, Italy, for afebrile convulsions in a gastroenteritis episode. Bacterial culture and microscopic examination on cerebrospinal fluid (CSF) yielded negative results as well as PCRs and reverse-transcription PCRs (RT-PCRs) for neurotropic viruses performed either on CSF or plasma. Stools were subjected to electron microscopy and conventional cell culture, yielding negative results. NoV was found in stools and plasma by nested RT-PCR targeting the NoV polymerase gene. The nucleotide sequences obtained from the two specimens showed 100% identity, demonstrating that the strain invading the blood stream was from the intestine, and, in comparison with GenBank sequences, they belonged to NoV genotype GII.4, "2006b" variant. The child had no abnormal electrolyte balance and no fever that could justify seizures, encouraging the hypothesis that NoV could be the cause of the neurologic disorder. These findings further induce to review the current concept of human NoV focused on intestinal infection.

Molecular changes associated with altered patterns of norovirus outbreak epidemics in Victoria, Australia, in 2006 to 2007

Noroviruses (NoVs) are now considered the most common cause of outbreaks of nonbacterial gastroenteritis, but the factors which control the incidence of NoVs are poorly understood. In 2006, the pattern of NoV outbreak epidemics in Victoria, Australia, changed compared to the pattern for 2002 to 2005 and 2007. This study examined molecular correlates of the changed NoV periodicity. For the period of 2002 to 2007, 8,507 fecal specimens from 1,495 gastroenteritis outbreaks were tested for NoV by reverse transcription-PCR, and 1,018 NoV outbreaks were identified. Nucleotide sequence analysis was used to define genotypes and GII.4 variants. For 2002 to 2007, GII.4 was the predominant genotype. For the period of 2002 to 2005 and 2007, a single NoV outbreak epidemic occurred in warmer months of each year, but in 2006 two epidemics occurred in 1 year, one in colder months and one in warmer months of the year. For 2002 to 2007, four major GII.4 variants, "2002 Oxford/Farmington Hills," "2004 Hunter," "2006a," and "2006b," were identified. Each NoV outbreak epidemic was linked principally to one of these four variants, and there was a time link, a delay of 2 to 6 months, between the first detection of a GII.4 variant and the first outbreak epidemic in which it was the principal variant. The unusual 2006 pattern of outbreak epidemics can then be correlated with the appearance of two GII.4 variants within a short space of time, resulting in two outbreak epidemics in a short space of time, i.e., in the 1 year. This study provides a potentially greater ability to predict the characteristics of NoV epidemics.

Viral gastroenteritis

The virology, immunology, diagnosis, clinical symptoms, treatment, epidemiology and prevention measures relating to the most common viral causes of acute gastroenteritis (rotaviruses, human caliciviruses, astroviruses and enteric adenoviruses) are briefly reviewed. Uncommon viral causes of acute gastroenteritis and viruses causing gastroenteritis in immunodeficient patients are mentioned. The main change over the past three years has been the development, licensing and wide application of new live attenuated rotavirus vaccines.

Characterisation of a GII-4 norovirus variant-specific surface-exposed site involved in antibody binding

Background

The human noroviruses are a highly diverse group of viruses with a single-stranded RNA genome encoding a single major structural protein (VP1), which has a hypervariable domain (P2 domain) as the most exposed part of the virion. The noroviruses are classified on the basis of nucleotide sequence diversity in the VP1-encoding ORF2 gene, which divides the majority of human noroviruses into two genogroups (GI and GII). GII-4 noroviruses are the major aetiological agent of outbreaks of gastroenteritis around the world. During a winter season the diversity among the GII-4 noroviruses has been shown to fluctuate, driving the appearance of new virus variants in the population. We have previously shown that sequence data and in silico modelling experiments suggest there are two surface-exposed sites (site A and site B) in the hypervariable P2 domain. We predict these sites may form a functional variant-specific epitope that evolves under selective pressure from the host immune response and gives rise to antibody escape mutants.

Results

In this paper, we describe the construction of recombinant baculoviruses to express VLPs representing one pre-epidemic and one epidemic variant of GII-4 noroviruses, and the production of monoclonal antibodies against them. We use these novel reagents to provide evidence that site A and site B form a conformational, variant-specific, surface-exposed site on the GII-4 norovirus capsid that is involved in antibody binding.

Conclusion

As predicted by our earlier study, significant amino acid changes at site A and site B give rise to GII-4 norovirus epidemic variants that are antibody escape mutants.

A foodborne norovirus outbreak at a manufacturing company

Over 400 office workers from the same unit of a manufacturing company in Stockholm County, Sweden, fell ill with gastroenteritis. A retrospective cohort study of office workers in the affected unit demonstrated that canteen visitors on one day had an increased risk of illness [risk ratio (RR) 27·1, 95% confidence interval (CI) 15·7–46·8] compared to non-visitors. A second study, investigating canteen visitors' consumption of particular food items, showed that both tomatoes from the salad buffet (RR 5·6, 95% CI 3·2–9·6) and hamburgers (RR 4·9, 95% CI 2·4–9·8) were the most likely vehicles of infection. Norovirus GI.3 (Desert Shield) was identified in stool samples from three office workers and from a food handler who prepared the tomatoes for the salad buffet and hamburger ingredients before vomiting at the workplace on 12 November. The outbreak could have been prevented if the food items prepared by the food handler some hours before vomiting had not been served.