Noroviruses: The Most Common Pediatric Viral Enteric Pathogen at a Large University Hospital After Introduction of Rotavirus Vaccination

Norovirus Gastroenteritis among Hospitalized Patients, Germany, 2007-2012

We estimated numbers of hospitalizations for norovirus gastroenteritis (NGE) and associated medical costs in Germany, where norovirus testing is high because reimbursement is affected. We extracted aggregate data for patients hospitalized with a primary or secondary code from the International Classification of Diseases, 10th Revision (ICD-10), NGE diagnosis during 2007-2012 from the German Federal Statistics Office. We assessed reliability of the coding system in patient records from a large academic hospital. Approximately 53,000-90,000 NGE hospitalizations occurred annually in Germany (21,000-33,000 with primary and 32,000-57,000 with secondary ICD-10-coded NGE diagnoses). Rates of hospitalization with NGE as primary diagnosis were highest in children <2 years of age; rates of hospitalization with NGE as secondary diagnosis were highest in adults >85 years of age. The average annual reimbursed direct medical cost of NGE hospitalizations was €31-43 million. Among patients with a NGE ICD-10 code, 87.6% had positive norovirus laboratory results.

Data fitting approach more critical than exposure scenarios and treatment of censored data for quantitative microbial risk assessment

Recreational waters are a source of many diseases caused by human viral pathogens, including norovirus genogroup II (NoV GII) and enterovirus (EV). Water samples from the Arenales river in Salta, Argentina, were concentrated by ultrafiltration and analyzed for the concentrations of NoV GII and EV by quantitative PCR. Out of 65 samples, 61 and 59 were non-detects (below the Sample Limit of Detection limit, SLOD) for EV and NoV GII, respectively. We hypothesized that a finite number of environmental samples would lead to different conclusions regarding human health risks based on how data were treated and fitted to existing distribution functions. A quantitative microbial risk assessment (QMRA) was performed and the risk of infection was calculated using: (a) two methodological approaches to find the distributions that best fit the data sets (methods H and R), (b) four different exposure scenarios (primary contact for children and adults and secondary contact by spray inhalation/ingestion and hand-to-mouth contact), and (c) five alternatives for treating censored data. The risk of infection for NoV GII was much higher (and exceeded in most cases the acceptable value established by the USEPA) than for EV (in almost all the scenarios within the recommended limit), mainly due to the low infectious dose of NoV. The type of methodology used to fit the monitoring data was critical for these datasets with numerous non-detects, leading to very different estimates of risk. Method R resulted in higher projected risks than Method H. Regarding the alternatives for treating censored data, replacing non-detects by a unique value like the average or median SLOD to simplify the calculations led to the loss of information about the particular characteristics of each sample. In addition, the average SLOD was highly impacted by extreme values (due to events such as precipitations or point source contamination). Instead, using the SLOD or half- SLOD captured the uniqueness of each sample since they account for the history of the sample including the concentration procedure and the detection method used. Finally, substitution of non-detects by Zero is not realistic since a negative result would be associated with a SLOD that can change by developing more efficient and sensitive methodology; hence this approach would lead to an underestimation of the health risk. Our findings suggest that in most cases the use of the half-SLOD approach is appropriate for QMRA modeling.

Norovirus and rotavirus infections in children less than five years of age hospitalized with acute gastroenteritis in Indonesia

Rotaviruses and noroviruses are the most important viral causes of acute gastroenteritis in children. While previous studies of acute gastroenteritis in Indonesia mainly focused on rotavirus, here, we investigated the burden and epidemiology of norovirus and rotavirus disease. Children less than five years of age hospitalized with acute gastroenteritis were enrolled in this study from January to December 2015 at three participating hospitals. Rotavirus was detected by enzyme immunoassay (EIA), followed by genotyping by reverse transcription PCR (RT-PCR). Norovirus genogroups were determined by TaqMan-based quantitative RT-PCR. Among 406 enrolled children, 75 (18.47%), 223 (54.93%) and 29 (7.14%) cases were positive for norovirus, rotavirus and both viruses (mixed infections), respectively. Most cases clinically presented with fever, diarrhea, vomiting and some degree of dehydration. The majority (n = 69/75 [92%]) of the noroviruses identified belonged to genogroup II, and several genotypes were identified by sequencing a subset of samples. Among 35 samples tested for rotavirus genotype, the most prevalent genotype was G3P[8] (n = 30/35 [85.6%]). Our study suggests that the burden of norovirus diseases in Indonesian children should not be underestimated. It also shows the emergence of rotavirus genotype G3P[8] in Indonesia.

Structural and Antiviral Studies of the Human Norovirus GII.4 Protease

Norovirus is the leading cause of acute gastroenteritis worldwide with a yearly reported 700 million cases driving a $60 billion global socioeconomic burden. With no United States Food and Drug Administration approved therapeutics and the chance for severe chronic infection and life-threatening complications, researchers have identified the protease as a potential target. However, drug development has focused on the norovirus GI.1 strain despite its accounting for less than 5% of all outbreaks. Our lab aims to change focus for norovirus drug design from GI.1 to the highly infective GII.4, responsible for more than 50% of all outbreaks worldwide. With the first published crystal structure of the norovirus GII.4 protease, we have identified several significant differences in the structure and active site that have hindered development of a potent inhibitor targeting the norovirus GII.4 protease. With these new insights, we have begun designing compounds that demonstrate increased inhibition of the clinically most relevant norovirus GII.4 strain.

Human organoid cultures: transformative new tools for human virus studies

Studies of human infectious diseases have been limited by the paucity of functional models that mimic normal human physiology and pathophysiology. Recent advances in the development of multicellular, physiologically active organotypic cultures produced from embryonic and pluripotent stem cells, as well as from stem cells isolated from biopsies and surgical specimens are allowing unprecedented new studies and discoveries about host-microbe interactions. Here, we summarize recent developments in the use of organoids for studying human viral pathogens, including intestinal infections with human rotavirus, norovirus, enteroviruses and adenoviruses (intestinal organoids and enteroids), neuronal infections with Zika virus (cerebral organoids) and respiratory infections with respiratory syncytial virus in (lung bud organoids). Biologic discovery of host-specific genetic and epigenetic factors affecting infection, and responses to infection that lead to disease are possible with the use of organoid cultures. Continued development to increase the complexity of these cultures by including components of the normal host tissue microenvironment such as immune cells, blood vessels and microbiome, will facilitate studies on human viral pathogenesis, and advance the development of platforms for pre-clinical evaluation of vaccines, antivirals and therapeutics.

Significance of continuous rotavirus and norovirus surveillance in Indonesia

BACKGROUND

Diarrhea significantly contributes to the global burden of diseases, particularly in developing countries. Rotavirus and norovirus are the most dominant viral agents responsible for diarrheal disease globally. The aim of this review was to conduct a comprehensive assessment of rotavirus and norovirus study in Indonesia.

DATA SOURCES

Articles about rotavirus and norovirus surveillance in Indonesia were collected from databases, including PubMed and Google Scholar. Manual searching was performed to identify additional studies. Furthermore, relevant articles about norovirus diseases were included.

RESULTS

A national surveillance of rotavirus-associated gastroenteritis has been conducted for years, resulting in substantial evidence about the high burden of the diseases in Indonesia. In contrast, norovirus infection received relatively lower attention and very limited data are available about the incidence and circulating genotypes. Norovirus causes sporadic and epidemic gastroenteritis globally. It is also emerging as a health problem in immunocompromised individuals. During post-rotavirus vaccination era, norovirus potentially emerges as the most frequent cause of diarrheal diseases.

CONCLUSIONS

Our review identifies knowledge gaps in Indonesia about the burden of norovirus diseases and the circulating genotypes. Therefore, there is a pressing need to conduct national surveillance to raise awareness of the community and national health authority about the actual burden of norovirus disease in Indonesia. Continuing rotavirus surveillance is also important to assess vaccine effectiveness and to continue tracking any substantial changes of circulating rotavirus genotypes.

The epidemiology of Norovirus in the Middle East and North Africa (MENA) region: a systematic review

Norovirus (NoV) is considered the second leading cause of viral acute gastroenteritis (AGE). To our knowledge, there are no systematic reviews assessing the role of NoV in AGE in the Middle East and North Africa (MENA) region. Consequently, we conducted an extensive systematic literature review on articles studying NoV in the 24 countries of the MENA region during the past 15 years (2000-2015). The methods and reporting were set according to the 2015 PRISMA-P and based on the elements from the international prospective register of systematic reviews (PROSPERO). We retrieved 38 studies meeting our predefined inclusion criteria and were used to extract full data. Studies reporting on NoV were conducted in 15 out of the 24 countries of the region. The reported NoV infection rates in MENA countries ranged between 0.82% and 36.84%. The majority of studies were clinical observational studies assessing NoV rates mainly among children. Participants were recruited from in- and outpatient clinics. NoV infection was reported all year round with with peaks observed mainly during cold months. GII.4 was the predominant genotype detected in stool of participants as reported by 16 out of 25 studies (64%). Overall, there is an increasing recognition of NoV as an important causative agent of AGE across all age groups in the MENA region. Further studies are needed to assess the national and the regional burden of NoV among different age groups, its molecular diversity and seasonal variability.

Estimated reductions in hospitalizations and deaths from childhood diarrhea following implementation of rotavirus vaccination in Africa

INTRODUCTION

Rotavirus is the leading cause of hospitalizations and deaths from diarrhea. 33 African countries had introduced rotavirus vaccines by 2016. We estimate reductions in rotavirus hospitalizations and deaths for countries using rotavirus vaccination in national immunization programs and the potential of vaccine introduction across the continent. Areas covered: Regional rotavirus burden data were reviewed to calculate hospitalization rates, and applied to under-5 population to estimate baseline hospitalizations. Rotavirus mortality was based on 2013 WHO estimates. Regional pre-licensure vaccine efficacy and post-introduction vaccine effectiveness studies were used to estimate summary effectiveness, and vaccine coverage was applied to calculate prevented hospitalizations and deaths. Uncertainties around input parameters were propagated using boot-strapping simulations. In 29 African countries that introduced rotavirus vaccination prior to end 2014, 134,714 (IQR 112,321-154,654) hospitalizations and 20,986 (IQR 18,924-22,822) deaths were prevented in 2016. If all African countries had introduced rotavirus vaccines at benchmark immunization coverage, 273,619 (47%) (IQR 227,260-318,102) hospitalizations and 47,741 (39%) (IQR 42,822-52,462) deaths would have been prevented. Expert commentary: Rotavirus vaccination has substantially reduced hospitalizations and deaths in Africa; further reductions are anticipated as additional countries implement vaccination. These estimates bolster wider introduction and continued support of rotavirus vaccination programs.

Comparison of three multiplex gastrointestinal platforms for the detection of gastroenteritis viruses

BACKGROUND

Viruses are major etiological agents of childhood gastroenteritis. In recent years, several molecular platforms for the detection of viral enteric pathogens have become available.

OBJECTIVE/STUDY DESIGN

We evaluated the performance of three multiplex platforms including Biofire's Gastrointestinal Panel (FilmArray), Luminex xTAG^® Gastrointestinal Pathogen Panel (GPP), and the TaqMan Array Card (TAC) for the detection of five gastroenteritis viruses using a coded panel of 300 archived stool samples.

RESULTS

The FilmArray detected a virus in 199 (96.1%) and the TAC in 172 (83.1%) of the 207 samples (187 samples positive for a single virus and 20 samples positive for more than one virus) whereas the GPP detected a virus in 100 (78.7%) of the 127 (97 positive for one virus and three positive for more than one virus) samples. Overall the clinical accuracy was highest for the FilmArray (98%) followed by TAC (97.2%) and GPP (96.9%). The sensitivity of the FilmArray, GPP and TAC platforms was highest for rotavirus (100%, 95.8%, and 89.6%, respectively) and lowest for adenovirus type 40/41 (97.4%, 57.9% and 68.4%). The specificity of the three platforms ranged from 95.6% (rotavirus) to 99.6% (norovirus/sapovirus) for the FilmArray, 99.6% (norovirus) to 100% (rotavirus/adenovirus) for GPP, and 98.9% (astrovirus) to 100% (rotavirus/sapovirus) for TAC.

CONCLUSION

The FilmArray demonstrated the best analytical performance followed by TAC. In recent years, the availability of multi-enteric molecular testing platforms has increased significantly and our data highlight the strengths and weaknesses of these platforms.

Human enteroviruses associated with and without diarrhea in Thailand between 2010 and 2016

Non-bacterial acute gastroenteritis (AGE) associated with virus infection affects individuals living in developing countries, especially children. To investigate whether shedding of certain human enterovirus (EV) is more frequently detected in the stool of individuals with AGE of unknown etiology than individuals without AGE symptoms, we tested fecal samples collected from 2,692 individuals with diarrhea between January 2010 and December 2016. Samples were tested for rotavirus, norovirus, and EV by reverse-transcription polymerase chain reaction (RT-PCR) and adenovirus by PCR. EV-positive samples were subjected to sequencing and phylogenetic analysis to identify EV species and types. Findings were compared to EV found in 1,310 fecal samples from individuals without AGE who were diagnosed with hand, foot, and mouth disease (HFMD). While the majority of viruses identified in AGE consisted of human rotavirus (22.7%), norovirus (11.4%) and adenovirus (9.3%), we identified EV (6.2%) belonging mainly to species B, C, and rhinovirus. In contrast, >92% of EV found without AGE symptoms belonged to species A. Although AGE symptoms are not often attributed to EV infection, EV was associated with diarrhea of unknown etiology at least in 3.4% of AGE cases. While CV-A6 was most likely to be found in stools of HFMD patients, rhinovirus A and C were the two most common EV species associated with AGE. Elucidating group-specific EV infection in diseases with and without AGE will be useful in assisting identification, clinical management, and the surveillance of EV infection in the community.

Prospects and Challenges in the Development of a Norovirus Vaccine

PURPOSE

Norovirus is the leading cause of acute epidemic gastroenteritis among children under the age of 5 years and adults in the United States and in adults worldwide, accounting for an estimated 20% of episodes of acute gastroenteritis across all ages. No effective vaccine is presently available. This article provides an overview of the current state of norovirus vaccine development, emphasizing barriers and challenges in the development of an effective vaccine, correlates of protection used to assess vaccine efficacy, and the results of clinical trials of the major candidate vaccines.

METHODS

We performed an unstructured literature review of published articles listed in PubMed in the field of norovirus vaccine development, with an emphasis on studies in humans.

FINDINGS

Two candidate vaccines have reached clinical trials, and a number of other candidates are in the preclinical stages of development. Multivalent vaccination may be effective in inducing broadly neutralizing antibodies protective against challenge with novel and heterologous norovirus strains. Most identified correlates of protection have not been validated in large-scale challenge studies, nor have the degrees to which these correlates covary been assessed.

IMPLICATIONS

Immune correlates of protection against norovirus infection need to be further developed to facilitate additional studies of the tolerability and efficacy of candidate norovirus vaccines in humans.

Frequency and molecular characterization of human norovirus in Erzurum, Turkey

BACKGROUND/AIM

There are limited studies on genotyping and phylogenetic analysis of norovirus in Turkey, and this has not previously been studied in the Eastern Anatolia region. The aim of the present study was to determine the norovirus profile in this region with genotyping and phylogenetic analysis.

MATERIALS AND METHODS

Included in the study were stool samples obtained from 427 people from different age groups in Eastern Anatolia. The nucleic acid samples isolated by the automatic system and nucleic acid sequence reactions and phylogenetic analyses were performed on RNA samples.

RESULTS

The presence of norovirus was detected in 86 (20.1%) of the 427 stool samples by RT-PCR analysis. Twenty-six samples selected randomly from norovirus-RNA positive samples were subjected to the sequence reaction. In 24 of the 26 samples, genogroup GII was determined, as well as one each from GI and GIV in sequence reactions. Four different genotypes were detected in genogroup GII, which were determined to be the dominant types. These were GII.1, GII.4, GII.16, and GII.21. The GI.6 and GIV.1 genotypes were determined in genogroups GI and GIV, respectively.

CONCLUSION

The high frequency and genetic diversity of these infections are risk factors for disease and so vaccine studies should be undertaken in consideration of this situation.

Glucose enhances rotavirus enterotoxin-induced intestinal chloride secretion

Rotavirus causes severe diarrhea in small children and is typically treated using glucose-containing oral rehydration solutions; however, glucose may have a detrimental impact on these patients, because it increases chloride secretion and presumably water loss. The rotavirus enterotoxin nonstructural protein 4 (NSP4) directly inhibits glucose-mediated sodium absorption. We examined the effects of NSP4 and glucose on sodium and chloride transport in mouse small intestines and Caco-2 cells. Mouse small intestines and Caco-2 cells were incubated with NSP4_114-135 in the presence/absence of glucose. Absorption and secretion of sodium and chloride, fluid movement, peak amplitude of intracellular calcium fluorescence, and expression of Ano1 and sodium-glucose cotransporter 1 were assessed. NHE3 activity increased, and chloride secretory activity decreased with age. Net chloride secretion increased, and net sodium absorption decreased in the intestines of 3-week-old mice compared to 8-week-old mice with NSP4. Glucose increased NSP4-stimulated chloride secretion. Glucose increased NSP4-stimulated increase in short-circuit current measurements (I _sc) and net chloride secretion. Ano1 cells with siRNA knockdown showed a significant difference in I _sc in the presence of NSP4 and glucose without a significant difference in peak calcium fluorescence intracellular when compared to non-silencing (N.S.) cells. The failure of glucose to stimulate significant sodium absorption was likely due to the inhibition of sodium-hydrogen exchange and sodium-glucose cotransport by NSP4. Since glucose enhances intestinal chloride secretion and fails to increase sodium absorption in the presence of NSP4, glucose-based oral rehydration solutions may not be ideal for the management of rotaviral diarrhea.

Prevalence of Rotavirus Genogroup A and Norovirus Genogroup II in Bassaseachic Falls National Park Surface Waters in Chihuahua, Mexico

In areas lacking potable water treatment, drinking contaminated water may represent a public health threat. In addition to enteropathogenic bacteria and parasites, fecal contamination in water environments is associated with the transmission of enteric viruses and other causal agents of infectious disease. Rotavirus and norovirus are the main enteric viral agents responsible for diarrheic outbreaks. The aim of the present study was to detect seasonal variation of rotavirus and norovirus in the surface water at Bassaseachic Falls National Park during 2013. Rivers and streams within and nearby this park were sampled once in each season during 2013. Viral concentration was carried out by a handmade filtration equipment, using a commercial electropositive membrane coupled with the virus absortion elution technique (VIRADEL©). Detection of rotavirus and norovirus was performed by SYBR Green reverse transcription-real time polymerase chain reaction (SYBR GREEN© RT-qPCR) analyses. Norovirus genogroup II was detected in samples collected in June and October 2013. In the case of rotavirus, genogroup A was detected in March and June. The presence of rotavirus and norovirus was related to viral acute diarrhea in children less than five years of age, who were inhabiting the sampled areas. This may indicates that the contaminated water was potentially a risk factor for regional diarrheic outbreaks.

Genomics and Foodborne Viral Infections

Foodborne viral illness, resulting from the consumption of contaminated food or water containing pathogenic viruses, remains a major public health problem globally with substantial economic impact. Major challenges regarding recognizing, detecting, characterizing, and effectively responding to foodborne viral threats to health exist. Adequate health crisis management is largely dependent on early detection of potential public health threats, which is hampered by changing trends in disease outbreaks, from localized clusters of disease in confined populations to dispersed outbreaks with excellent opportunity for further transmission. In addition, no precise and consistent global baseline syndrome and diagnostic surveillance information exists. An integrated multidisciplinary approach with a combination of sustained pathogen syndrome and diagnostic surveillance, genomics-based, and standardized global analytical networks gathering clinical, epidemiological and genetic data alike would be required to understand the dynamics of foodborne viral infection and to mitigate potential effects of future threats. A huge global effort in virus syndrome and diagnostic surveillance may be justified in the light of global health impact in general, and timely with the development of new metagenomics tools that hold the promise of not only identifying viral pathogens, but possibly the complete microbiome in a single assay.

Norovirus infections in young children in Lusaka Province, Zambia: clinical characteristics and molecular epidemiology

Background

The burden, clinical features, and molecular epidemiology of norovirus infection in young children in southern Africa are not well defined.

Methods

Using data from a health facility-based surveillance study of children <5 years in Lusaka Province, Zambia presenting with diarrhea, we assessed the burden of norovirus infection. A convenience sample of 454 stool specimens was tested for norovirus using reverse-transcriptase polymerase chain reaction (RT-PCR). RT-PCR positive samples underwent additional nucleotide sequencing for genogroup and genotype identification. Clinical features and severity of diarrheal illnesses were compared between norovirus-positive and -negative subjects using Chi-squared and t-tests.

Results

Norovirus was detected in 52/454 (11.5%) specimens tested. Abdominal pain, fever, and vomiting were the most common presenting features in norovirus-associated illnesses. However, there were no significant differences in the clinical features of norovirus-positive compared to norovirus-negative illnesses. Of 43 isolates that were available for sequencing, 31 (72.1%) were genogroup II (GII) and 12 (27.9%) were genogroup I (GI). The distribution of genotypes was diverse.

Conclusions

Noroviruses were detected in approximately 10% of young children with diarrhea in the Lusaka Province of Zambia, with GII representing the majority of infections. These findings support the role of norovirus in symptomatic diarrhea disease in Africa. Further studies are needed to confirm these observations and to evaluate prevention strategies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-017-2206-2) contains supplementary material, which is available to authorized users.

Viral Diarrhea

Viral gastroenteritis is among the most common illnesses affecting humans and has greatest impact at the extremes of age. The spectrum of disease can range from asymptomatic infections to severe disease with dehydration. In contrast to bacterial pathogens, enteric viruses cannot multiply outside their host; hence, the original inoculum into the common source determines infectivity. Prevention of contamination of food and water control primary cases, whereas careful nursing and handwashing prevent secondary cases. Effective vaccines are available and widely used to prevent rotaviral gastroenteritis, but vaccines for other causes of viral gastroenteritis are not yet available.

Detection of viruses in weekly stool specimens collected during the first 2 years of life: A pilot study of five healthy Australian infants in the rotavirus vaccine era

Several viruses are associated with gastroenteritis in infants. This pilot study, nested within a larger community-based project of early childhood infections, collected daily symptom data and 511 weekly stool samples from five healthy, fully vaccinated, term infants from birth until their second birthday. Real-time PCR assays were used to detect six enteric viruses. Frequent, silent shedding of one or more of the six viruses was observed, particularly involving adenovirus where shedding could be for up to 3 months without gastrointestinal symptoms. These pilot data demonstrate that a positive PCR result for enteric viruses may not always indicate the cause of childhood gastroenteritis. J. Med. Virol. 89:917-921, 2017. © 2016 Wiley Periodicals, Inc.

Norovirus antagonism of B-cell antigen presentation results in impaired control of acute infection

Human noroviruses are a leading cause of gastroenteritis, and so, vaccine development is desperately needed. Elucidating viral mechanisms of immune antagonism can provide key insight into designing effective immunization platforms. We recently revealed that B cells are targets of norovirus infection. Because noroviruses can regulate antigen presentation by infected macrophages and B cells can function as antigen-presenting cells, we tested whether noroviruses regulate B-cell-mediated antigen presentation and the biological consequence of such regulation. Indeed, murine noroviruses could prevent B-cell expression of antigen presentation molecules and this directly correlated with impaired control of acute infection. In addition to B cells, acute control required MHC class I molecules, CD8⁺ T cells, and granzymes, supporting a model whereby B cells act as antigen presenting cells to activate cytotoxic CD8⁺ T cells. This immune pathway was active prior to the induction of antiviral antibody responses. As in macrophages, the minor structural protein VP2 regulated B-cell antigen presentation in a virus-specific manner. Commensal bacteria were not required for the activation of this pathway and ultimately only B cells were required for the clearance of viral infection. These findings provide new insight into the role of B cells in stimulating antiviral CD8⁺ T-cell responses.

Norovirus Whole-Genome Sequencing by SureSelect Target Enrichment: a Robust and Sensitive Method

Norovirus full-genome sequencing is challenging due to sequence heterogeneity among genomes. Previous methods have relied on PCR amplification, which is problematic due to primer design, and transcriptome sequencing (RNA-Seq), which nonspecifically sequences all RNA, including host and bacterial RNA, in stool specimens. Target enrichment uses a panel of custom-designed 120-mer RNA baits that are complementary to all publicly available norovirus sequences, with multiple baits targeting each position of the genome, which overcomes the challenge of primer design. Norovirus genomes are enriched from stool RNA extracts to minimize the sequencing of nontarget RNA. SureSelect target enrichment and Illumina sequencing were used to sequence full genomes from 507 norovirus-positive stool samples with reverse transcription-real-time PCR cycle threshold (CT) values of 10 to 43. Sequencing on an Illumina MiSeq system in batches of 48 generated, on average, 81% on-target reads per sample and 100% genome coverage with >12,000-fold read depth. Samples included genotypes GI.1, GI.2, GI.3, GI.6, GI.7, GII.1, GII.2, GII.3, GII.4, GII.5, GII.6, GII.7, GII.13, GII.14, and GII.17. When outliers were accounted for, we generated >80% genome coverage for all positive samples, regardless of CT values. A total of 164 samples were tested in parallel with conventional PCR genotyping of the capsid shell domain; 164/164 samples were successfully sequenced, compared to 158/164 samples that were amplified by PCR. Four of the samples that failed capsid PCR analysis had low titers, which suggests that target enrichment is more sensitive than gel-based PCR. Two samples failed PCR due to primer mismatches; target enrichment uses multiple baits targeting each position, thus accommodating sequence heterogeneity among norovirus genomes.

Replication of Human Norovirus RNA in Mammalian Cells Reveals Lack of Interferon Response

Human noroviruses (HuNoVs), named after the prototype strain Norwalk virus (NV), are a leading cause of acute gastroenteritis outbreaks worldwide. Studies on the related murine norovirus (MNV) have demonstrated the importance of an interferon (IFN) response in host control of virus replication, but this remains unclear for HuNoVs. Despite the lack of an efficient cell culture infection system, transfection of stool-isolated NV RNA into mammalian cells leads to viral RNA replication and virus production. Using this system, we show here that NV RNA replication is sensitive to type I (α/β) and III (interleukin-29 [IL-29]) IFN treatment. However, in cells capable of a strong IFN response to Sendai virus (SeV) and poly(I·C), NV RNA replicates efficiently and generates double-stranded RNA without inducing a detectable IFN response. Replication of HuNoV genogroup GII.3 strain U201 RNA, generated from a reverse genetics system, also does not induce an IFN response. Consistent with a lack of IFN induction, NV RNA replication is enhanced neither by neutralization of type I/III IFNs through neutralizing antibodies or the soluble IFN decoy receptor B18R nor by short hairpin RNA (shRNA) knockdown of mitochondrial antiviral signaling protein (MAVS) or interferon regulatory factor 3 (IRF3) in the IFN induction pathways. In contrast to other positive-strand RNA viruses that block IFN induction by targeting MAVS for degradation, MAVS is not degraded in NV RNA-replicating cells, and an SeV-induced IFN response is not blocked. Together, these results indicate that HuNoV RNA replication in mammalian cells does not induce an IFN response, suggesting that the epithelial IFN response may play a limited role in host restriction of HuNoV replication.

IMPORTANCE

Human noroviruses (HuNoVs) are a leading cause of epidemic gastroenteritis worldwide. Due to lack of an efficient cell culture system and robust small-animal model, little is known about the innate host defense to these viruses. Studies on murine norovirus (MNV) have shown the importance of an interferon (IFN) response in host control of MNV replication, but this remains unclear for HuNoVs. Here, we investigated the IFN response to HuNoV RNA replication in mammalian cells using Norwalk virus stool RNA transfection, a reverse genetics system, IFN neutralization reagents, and shRNA knockdown methods. Our results show that HuNoV RNA replication in mammalian epithelial cells does not induce an IFN response, nor can it be enhanced by blocking the IFN response. These results suggest a limited role of the epithelial IFN response in host control of HuNoV RNA replication, providing important insights into our understanding of the host defense to HuNoVs that differs from that to MNV.

Epidemiology of Norovirus Infection Among Immunocompromised Patients at a Tertiary Care Research Hospital, 2010-2013

Background. Noroviruses are a major cause of infectious gastroenteritis worldwide, and viruses can establish persistent infection in immunocompromised individuals. Risk factors and transmission in this population are not fully understood.

Methods. From 2010 through 2013, we conducted a retrospective review among immunocompromised patients (n = 268) enrolled in research studies at the National Institutes of Health Clinical Center and identified a subset of norovirus-positive patients (n = 18) who provided stool specimens for norovirus genotyping analysis.

Results. Norovirus genome was identified by reverse-transcription quantitative polymerase chain reaction in stools of 35 (13%) of the 268 immunocompromised patients tested, and infection prevalence was 21% (11 of 53) in persons with primary immune deficiencies and 12% (20 of 166) among persons with solid tumors or hematologic malignancies. Among 18 patients with norovirus genotyping information, norovirus GII.4 was the most prevalent genotype (14 of 18, 78%). Persistent norovirus infection (≥6 months) was documented in 8 of 18 (44%) individuals. Phylogenetic analysis of the GII.4 capsid protein sequences identified at least 5 now-displaced GII.4 variant lineages, with no evidence of their nosocomial transmission in the Clinical Center.

Conclusions. Norovirus was a leading enteric pathogen identified in this immunocompromised population. Both acute and chronic norovirus infections were observed, and these were likely community-acquired. Continued investigation will further define the role of noroviruses in these patients and inform efforts toward prevention and treatment.

High Prevalence and Increased Severity of Norovirus Mixed Infections Among Children 12-24 Months of Age Living in the Suburban Areas of Lima, Peru

In an active diarrhea surveillance study of children aged 12-24 months in Lima, Peru, norovirus was the most common pathogen identified. The percentage of mixed (bacterial and noroviral) infections was significantly higher among norovirus-positive samples (53%) than among norovirus-negative samples (12%). The combination of norovirus with the most common bacterial pathogens was associated with increased clinical severity over that of either single-pathogen norovirus or single-pathogen bacterial infections.

Narrowing of the Diagnostic Gap of Acute Gastroenteritis in Children 0-6 Years of Age Using a Combination of Classical and Molecular Techniques, Delivers Challenges in Syndromic Approach Diagnostics

BACKGROUND

Twenty-five percent to 50% of acute gastroenteritis (AGE) cases remain etiologically undiagnosed. Our main aim was to determine the most appropriate list of enteric pathogens to be included in the daily diagnostics scheme of AGE, ensuring the lowest possible diagnostic gap.

METHODS

Two hundred ninety seven children ≤6 years of age, admitted to hospital in Slovenia, October 2011 to October 2012, with AGE, and 88 ≤6 years old healthy children were included in the study. A broad spectrum of enteric pathogens was targeted with molecular methods, including 8 viruses, 6 bacteria and 2 parasites.

RESULTS

At least one enteric pathogen was detected in 91.2% of cases with AGE and 27.3% of controls. Viruses were the most prevalent (82.5% and 15.9%), followed by bacteria (27.3% and 10.2%) and parasites (3.0% and 1.1%) in cases and controls, respectively. A high proportion (41.8%) of mixed infections was observed in the cases. For cases with undetermined etiology (8.8%), stool samples were analyzed with next generation sequencing, and a potential viral pathogen was detected in 17 additional samples (5.8%).

CONCLUSIONS

Our study suggests that tests for rotaviruses, noroviruses genogroup II, adenoviruses 40/41, astroviruses, Campylobacter spp. and Salmonella sp. should be included in the initial diagnostic algorithm, which revealed the etiology in 83.5% of children tested. The use of molecular methods in diagnostics of gastroenteritis is preferable because of their high sensitivity, specificity, fast performance and the possibility of establishing the concentration of the target. The latter may be valuable for assessing the clinical significance of the detected enteric, particularly viral pathogens.

Characterization of a Novel Conformational GII.4 Norovirus Epitope: Implications for Norovirus-Host Interactions

Human noroviruses (NoVs) are the main etiological agents of acute gastroenteritis worldwide. While NoVs are highly diverse (more than 30 genotypes have been detected in humans), during the last 40 years most outbreaks and epidemics have been caused by GII.4 genotype strains, raising questions about their persistence in the population. Among other potential explanations, immune evasion is considered to be a main driver of their success. In order to study antibody recognition and evasion in detail, we analyzed a conformational epitope recognized by a monoclonal antibody (3C3G3) by phage display, site-directed mutagenesis, and surface plasmon resonance. Our results show that the predicted epitope is composed of 11 amino acids within the P domain: P245, E247, I389, Q390, R397, R435, G443, Y444, P445, N446, and D448. Only two of them, R397 and D448, differ from the homologous variant (GII.4 Den-Haag_2006b) and from a previous variant (GII.4 VA387_1996) that is not recognized by the antibody. A double mutant derived from the VA387_1996 variant containing both changes, Q396R and N447D, is recognized by the 3C3G3 monoclonal antibody, confirming the participation of the two sites in the epitope recognized by the antibody. Furthermore, a single change, Q396R, is able to modify the histo-blood group antigen (HBGA) recognition pattern. These results provide evidence that the epitope recognized by the 3C3G3 antibody is involved in the virus-host interactions, both at the immunological and at the receptor levels.

IMPORTANCE

Human noroviruses are the main cause of viral diarrhea worldwide in people of all ages. Noroviruses can infect individuals who had been previously exposed to the same or different norovirus genotypes. Norovirus genotype GII.4 has been reported to be most prevalent during the last 40 years. In the present study, we describe a novel viral epitope identified by a monoclonal antibody and located within the highly diverse P domain of the capsid protein. The evolution of this epitope along with sequential GII.4 variants has allowed noroviruses to evade previously elicited antibodies, thus explaining how the GII.4 genotype can persist over long periods, reinfecting the population. Our results also show that the epitope participates in the recognition of host receptors that have evolved over time, as well.

Detection of human norovirus in intestinal biopsies from immunocompromised transplant patients

Human noroviruses (HuNoVs) can often cause chronic infections in solid organ and haematopoietic stem cell transplant (HSCT) patients. Based on histopathological changes observed during HuNoV infections, the intestine is the presumed site of virus replication in patients; however, the cell types infected by HuNoVs remain unknown. The objective of this study was to characterize histopathological changes during HuNoV infection and to determine the cell types that may be permissive for HuNoV replication in transplant patients. We analysed biopsies from HuNoV-infected and non-infected (control) transplant patients to assess histopathological changes in conjunction with detection of HuNoV antigens to identify the infected cell types. HuNoV infection in immunocompromised patients was associated with histopathological changes such as disorganization and flattening of the intestinal epithelium. The HuNoV major capsid protein, VP1, was detected in all segments of the small intestine, in areas of biopsies that showed histopathological changes. Specifically, VP1 was detected in enterocytes, macrophages, T cells and dendritic cells. HuNoV replication was investigated by detecting the non-structural proteins, RdRp and VPg. We detected RdRp and VPg along with VP1 in duodenal and jejunal enterocytes. These results provide critical insights into histological changes due to HuNoV infection in immunocompromised patients and propose human enterocytes as a physiologically relevant cell type for HuNoV cultivation.

Antiviral targets of human noroviruses

Human noroviruses are major causative agents of sporadic and epidemic gastroenteritis both in children and adults. Currently there are no licensed therapeutic intervention measures either in terms of vaccines or drugs available for these highly contagious human pathogens. Genetic and antigenic diversity of these viruses, rapid emergence of new strains, and their ability to infect a broad population by using polymorphic histo-blood group antigens for cell attachment, pose significant challenges for the development of effective antiviral agents. Despite these impediments, there is progress in the design and development of therapeutic agents. These include capsid-based candidate vaccines, and potential antivirals either in the form of glycomimetics or designer antibodies that block HBGA binding, as well as those that target essential non-structural proteins such as the viral protease and RNA-dependent RNA polymerase. In addition to these classical approaches, recent studies suggest the possibility of interferons and targeting host cell factors as viable approaches to counter norovirus infection. This review provides a brief overview of this progress.

Prevalence and molecular characterization of human noroviruses and sapoviruses in Ethiopia

Viral gastroenteritis is a major public health problem worldwide. In Ethiopia, very limited studies have been done on the epidemiology of enteropathogenic viruses. The aim of this study was to detect and characterize noroviruses (NoVs) and sapoviruses (SaVs) from acute gastroenteritis patients of all ages. Fecal samples were collected from diarrheic patients (n = 213) in five different health centers in Addis Ababa during June-September 2013. The samples were screened for caliciviruses by reverse transcription polymerase chain reaction (RT-PCR) using universal and genogroup-specific primer pairs. Phylogenetic analyses were conducted using the sequences of the PCR products. Of the clinical samples, 25.3 % and 4.2 % were positive for NoV and SaV RNA, respectively. Among the norovirus positives, 22 were sequenced further, and diverse norovirus strains were identified: GI (n = 4), GII (n = 17) and GIV (n = 1). Most strains were GII (n = 17/22: 77.2 %), which were further divided into three different genotypes (GII.4, GII.12/GII.g recombinant-like and GII.17), with GII.17 being the dominant (7/17) strain detected. GI noroviruses, in particular GI.4 (n = 1), GI.5 (n = 2) and GI.8 (n = 1), were also detected and characterized. The GIV strain detected is the first from East Africa. The sapoviruses sequenced were also the first reported from Ethiopia. Collectively, this study showed the high burden and diversity of noroviruses and circulation of sapoviruses in diarrheic patients in Ethiopia. Continued surveillance to assess their association with diarrhea is needed to define their epidemiology, disease burden, and impact on public health.

Whole genome analysis of Vietnamese G2P[4] rotavirus strains possessing the NSP2 gene sharing an ancestral sequence with Chinese sheep and goat rotavirus strains

Because imminent introduction into Vietnam of a vaccine against Rotavirus A is anticipated, baseline information on the whole genome of representative strains is needed to understand changes in circulating strains that may occur after vaccine introduction. In this study, the whole genomes of two G2P[4] strains detected in Nha Trang, Vietnam in 2008 were sequenced, this being the last period during which virtually no rotavirus vaccine was used in this country. The two strains were found to be >99.9% identical in sequence and had a typical DS-1 like G2-P[4]-I2-R2-C2-M2-A2-N2-T2-E2-H2 genotype constellation. Analysis of the Vietnamese strains with >184 G2P[4] strains retrieved from GenBank/EMBL/DDBJ DNA databases placed the Vietnamese strains in one of the lineages commonly found among contemporary strains, with the exception of the NSP2 and NSP4 genes. The NSP2 genes were found to belong to a previously undescribed lineage that diverged from Chinese sheep and goat rotavirus strains, including a Chinese rotavirus vaccine strain LLR with 95% nucleotide identity; the time of their most recent common ancestor was 1975. The NSP4 genes were found to belong, together with Thai and USA strains, to an emergent lineage (VIII), adding further diversity to ever diversifying NSP4 lineages. Thus, there is a need to enhance surveillance of locally-circulating strains from both children and animals at the whole genome level to address the effect of rotavirus vaccines on changing strain distribution.

Recent advances in understanding norovirus pathogenesis

Noroviruses constitute a family of ubiquitous and highly efficient human pathogens. In spite of decades of dedicated research, human noroviruses remain a major cause of gastroenteritis and severe diarrheal disease around the world. Recent findings have begun to unravel the complex mechanisms that regulate norovirus pathogenesis and persistent infection, including the important interplay between the virus, the host immune system, and commensal bacteria. Herein, we will summarize recent research developments regarding norovirus cell tropism, the use of M cells, and commensal bacteria to facilitate norovirus infection, and virus, host, and bacterial determinants of persistent norovirus infections. J. Med. Virol. 88:1837-1843, 2016. © 2016 Wiley Periodicals, Inc.

Temporal Changes in Pediatric Gastroenteritis after Rotavirus Vaccination in Quebec

BACKGROUND

Rotavirus and norovirus are among the leading causes of pediatric gastroenteritis. We examined the relative burden of pediatric gastroenteritis by etiology and compared the clinical severity of rotavirus and norovirus cases after the November 2011 implementation of publicly funded rotavirus vaccination program in Quebec.

METHODS

Prospective, active surveillance for acute gastroenteritis among children aged 8 weeks to less than 3 years of age was implemented at 3 hospitals. Participant demographics, clinical histories and stools were collected; stools were tested for rotavirus, norovirus and sapovirus. Risk and absolute differences of several clinical severity outcomes were compared by etiology with adjustment for patient age.

RESULTS

From February 2012 to May 2014, 734 eligible active surveillance patients were recruited, and stools from 705 (96.0%) were tested and included in study analyses. Of these, 20.4% [95% confidence interval (CI): 16.5-24.3%] were rotavirus positive and 25.5% (95% CI: 21.3-29.8%) were norovirus positive, representing a difference of 5.1% (95% CI: 0.1-10.1%). When stratified by year, rotavirus and norovirus prevalence were similar from June 2012 to May 2013, but rotavirus prevalence was 21.4% (95% CI: 14.3-28.5%) lower than norovirus from June 2013 to May 2014. On average, rotavirus patients were more likely to be febrile, dehydrated, hospitalized and report more diarrheal episodes at the height of illness in comparison with norovirus patients of the same age.

CONCLUSIONS

Norovirus infections were more prevalent than rotavirus infections among pediatric gastroenteritis cases hospitalized or seeking emergency care. Rotavirus cases were, on average, more clinically severe than norovirus cases among participants of the same age.

Norovirus as the cause of medically attended gastroenteritis: a hospital-based experience

Gastroenteritis remains an important cause of morbidity and mortality worldwide. With the introduction of vaccines against rotavirus, interest has shifted to understanding the epidemiology of norovirus (NoV). While the importance of NoV in gastroenteritis outbreaks is well established, its role in sporadic gastroenteritis is less known. To better define the role of NoV as a cause of sporadic gastroenteritis we investigated its prevalence in the patients seen in our paediatric hospital with special emphasis on its seasonal and age distribution. Over a 12-month period discarded stool specimens submitted to our paediatric hospital for testing of an infectious aetiology were retrieved and additionally tested for NoV by real-time reverse transcriptase–polymerase chain reaction; demographical and clinical information were also obtained. Overall, NoV was the single most commonly identified pathogen and found in 68/892 (7·6%) total specimens or 68/258 (26%) of pathogen-positive specimens. The highest rates of NoV were detected in children aged 6 months to 4 years (50/332, 15·1%) and presenting between October and January (46/314, 14·7%). NoV has become the main cause of gastroenteritis in our paediatric population.

A 1-Year Study on the Detection of Human Enteric Viruses in New Caledonia

Human enteric viruses occur in high concentrations in wastewater and can contaminate receiving environmental waters. Due to the lack of data on the prevalence of enteric viruses in New Caledonia, the presence and the concentrations of enteric viruses in wastewater and seawater were determined. Untreated wastewater and seawater samples were collected monthly for 1 year from a wastewater treatment plant (WWTP) and from the WWTP's outlet, located directly on a popular recreational beach. Samples were tested for norovirus genogroups I and II (NoV GI and GII), astroviruses (AsV), sapoviruses (SaV), enteroviruses (EV), hepatitis A viruses (HAV), rotaviruses (RoV), human adenoviruses (HAdV) and human polyomaviruses (HPyV). To support these data, faecal samples from cases of gastroenteritis were tested for the first time for NoV and detected in the population. NoV GI, NoV GII, EV, SaV, HAdV and HPyV were detected in all wastewaters, RoV in 75% and AsV in 67%. HAV were not detected in wastewater. Overall, 92% of seawater samples were positive for at least one virus. HPyV were detected most frequently in 92% of samples and at concentrations up to 7.7 × 10(3) genome copies/L. NoV GI, NoV GII, EV, SaV, RoV and HAdV were found in 33, 66, 41, 33, 16 and 66% of seawater samples, respectively. AsV were not detected in seawater. This study reports for the first time the presence of NoV and other enteric viruses in New Caledonia and highlights the year-round presence of enteric viruses in the seawater of a popular beach.

The influence of commensal bacteria on infection with enteric viruses

The intestinal microbiota exerts a marked influence in the mammalian host, both during homeostasis and disease. However, until very recently, there has been relatively little focus on the potential effect of commensal microorganisms on viral infection of the intestinal tract. In this Progress article, I review the recent advances that elucidate the mechanisms by which enteric viruses use commensal bacteria to enhance viral infectivity. These mechanisms segregate into two general categories: the direct facilitation of viral infection, including bacterial stabilization of viral particles and the facilitation of viral attachment to host target cells; and the indirect skewing of the antiviral immune response in a manner that promotes viral infection. Finally, I discuss the implications of these interactions for the development of vaccines and novel therapeutic approaches.

Clinical and Microbiologic Assessment of Cases of Pediatric Community-associated Clostridium difficile Infection Reveals Opportunities for Improved Testing Decisions

BACKGROUND

Most children with Clostridium difficile infection (CDI) experience community onset of CDI symptoms.

METHODS

We retrospectively compared hospital-onset healthcare facility-associated CDI cases to community-associated (CA) CDI cases diagnosed by Cepheid Xpert tcdB polymerase chain reaction (PCR) at an academic children's hospital over a 1-year period. Saved stools from CDI cases additionally underwent anaerobic stool culture and multiplex gastrointestinal pathogen PCR testing.

RESULTS

Compared with 25 hospital-onset healthcare facility-associated CDI cases, the 74 CA-CDI cases were more frequently <2 years old (18% vs. 0%, P = 0.034) and less frequently had antibiotic exposure in the past 30 days (26% vs. 88%, P < 0.0001), proton pump inhibitor exposure (16% vs. 36%, P = 0.036) or a gastrostomy tube (11% vs. 32%, P = 0.013). Among children diagnosed with CA-CDI, 19 (26%) had no identified CDI risk factors (immunocompromised; gastrostomy tube; recent antibiotic, proton pump inhibitor or inpatient/outpatient healthcare exposures). Clinical testing for viral pathogens was uncommon among children thought to have CA-CDI. Multiplex PCR testing of saved stool samples failed to identify C. difficile among 23% of cases diagnosed with CA-CDI by the Cepheid Xpert tcdB PCR assay. CDI antibiotic therapy was provided to nearly all patients testing positive by tcdB PCR irrespective of CDI risk factors.

CONCLUSIONS

Many children diagnosed with CA-CDI by PCR lack CDI risk factors and have discordant results when additional CDI testing methods are performed, suggesting overdiagnosis of CDI in children with community-onset diarrhea. More selective CDI testing of low-risk pediatric patients is needed to more accurately diagnose CDI and limit unnecessary CDI antibiotic treatment in children.

Regulation of Norovirus Virulence by the VP1 Protruding Domain Correlates with B Cell Infection Efficiency

Human noroviruses are a leading cause of gastroenteritis across the globe, but the pathogenic mechanisms responsible for disease are not well established. The availability of a murine norovirus model system provides the opportunity to elucidate viral and host determinants of virulence in a natural host. For example, previous studies have revealed that the protruding domain of the murine norovirus capsid protein VP1, specifically residue 296 of VP1, regulates virulent infection. We identified a panel of nonsynonymous mutations in the open reading frame 2 (ORF2) gene encoding VP1 that arose in persistently infected mice and tested whether these mutations conferred phenotypic changes to viral replication and virulence. Consistent with previous studies, we demonstrate that a glutamic acid at position 296 results in attenuation. For the first time, we also demonstrate that a lysine at this position is sufficient to confer virulence on an otherwise attenuated murine norovirus strain. Moreover, our studies reveal a direct correlation between the efficiency of viral replication in B cells and virulence. These data are especially striking because mutations causing reduced B cell replication and attenuation had minimal effects on the ability of the virus to replicate in macrophages. Thus, norovirus infection of B cells may directly contribute to disease outcome.

IMPORTANCE

Human noroviruses are a major global cause of disease, yet we know very little about their pathogenic mechanisms. The availability of a murine norovirus model system facilitates investigation of noroviruses in a natural host organism and the identification of viral and host determinants of pathogenesis. We have identified a panel of mutations arising in the viral capsid protein VP1 during persistent infection of mice. Our data reveal that the protruding domain of VP1 regulates the ability of the virus to replicate in B cells, and this directly correlates with virulence. Importantly, mutations impairing B cell infection had minimal effects on macrophage infection, revealing a potentially critical role for B cell infection in norovirus pathogenesis.

Norovirus mechanisms of immune antagonism

Noroviruses are a leading cause of gastroenteritis outbreaks globally. Several lines of evidence indicate that noroviruses can antagonize or evade host immune responses, including the absence of long-lasting immunity elicited during a primary norovirus exposure and the ability of noroviruses to establish prolonged infections that are associated with protracted viral shedding. Specific norovirus proteins possessing immune antagonist activity have been described in recent years although mechanistic insight in most cases is limited. In this review, we discuss these emerging strategies used by noroviruses to subvert the immune response, including the actions of two nonstructural proteins (p48 and p22) to impair cellular protein trafficking and secretory pathways; the ability of the VF1 protein to inhibit cytokine induction; and the ability of the minor structural protein VP2 to regulate antigen presentation. We also discuss the current state of the understanding of host and viral factors regulating the establishment of persistent norovirus infections along the gastrointestinal tract. A more detailed understanding of immune antagonism by pathogenic viruses will inform prevention and treatment of disease.

Multicenter Evaluation of the Xpert Norovirus Assay for Detection of Norovirus Genogroups I and II in Fecal Specimens

Norovirus is the most common cause of sporadic gastroenteritis and outbreaks worldwide. The rapid identification of norovirus has important implications for infection prevention measures and may reduce the need for additional diagnostic testing. The Xpert Norovirus assay recently received FDA clearance for the detection and differentiation of norovirus genogroups I and II (GI and GII), which account for the vast majority of infections. In this study, we evaluated the performance of the Xpert Norovirus assay with both fresh, prospectively collected (n = 914) and frozen, archived (n = 489) fecal specimens. A Centers for Disease Control and Prevention (CDC) composite reference method was used as the gold standard for comparison. For both prospective and frozen specimens, the Xpert Norovirus assay showed positive percent agreement (PPA) and negative percent agreement (NPA) values of 98.3% and 98.1% for GI and of 99.4% and 98.2% for GII, respectively. Norovirus prevalence in the prospective specimens (collected from March to May of 2014) was 9.9% (n = 90), with the majority of positives caused by genogroup II (82%, n = 74). The positive predictive value (PPV) of the Xpert Norovirus assay was 75% for GI-positive specimens, whereas it was 86.5% for GII-positive specimens. The negative predictive values (NPV) for GI and GII were 100% and 99.9%, respectively.

Viruses in Rodent Colonies: Lessons Learned from Murine Noroviruses

Noroviruses (NoVs) are highly prevalent, positive-sense RNA viruses that infect a range of mammals, including humans and mice. Murine noroviruses (MuNoVs) are the most prevalent pathogens in biomedical research colonies, and they have been used extensively as a model system for human noroviruses (HuNoVs). Despite recent successes in culturing HuNoVs in the laboratory and a small animal host, studies of human viruses have inherent limitations. Thus, owing to its versatility, the MuNoV system-with its native host, reverse genetics, and cell culture systems-will continue to provide important insights into NoV and enteric virus biology. In the current review, we summarize recent findings from MuNoVs that increase our understanding of enteric virus pathogenesis and highlight similarities between human and murine NoVs that underscore the value of MuNoVs to inform studies of HuNoV biology. We also discuss the potential of endemic MuNoV infections to impact other disease models.

Human norovirus culture in B cells

Human noroviruses (HuNoVs) are a leading cause of foodborne disease and severe childhood diarrhea, and they cause a majority of the gastroenteritis outbreaks worldwide. However, the development of effective and long-lasting HuNoV vaccines and therapeutics has been greatly hindered by their uncultivability. We recently demonstrated that a HuNoV replicates in human B cells, and that commensal bacteria serve as a cofactor for this infection. In this protocol, we provide detailed methods for culturing the GII.4-Sydney HuNoV strain directly in human B cells, and in a coculture system in which the virus must cross a confluent epithelial barrier to access underlying B cells. We also describe methods for bacterial stimulation of HuNoV B cell infection and for measuring viral attachment to the surface of B cells. Finally, we highlight variables that contribute to the efficiency of viral replication in this system. Infection assays require 3 d and attachment assays require 3 h. Analysis of infection or attachment samples, including RNA extraction and RT-qPCR, requires ∼6 h.

A decade of norovirus disease risk among older adults in upper-middle and high income countries: a systematic review

BACKGROUND

Noroviruses (NoVs) are the most common cause of acute gastroenteritis (AGE) causing both sporadic and outbreak-associated illness. Norovirus (NoV) infections occur across all ages but certain sub-groups are considered at increased risk due to heightened transmission and/or symptom severity. Older adults are potentially at high risk of NoV-associated illness due to frequent outbreaks in long-term care facilities (LTCFs) and severe health outcomes following infection. Elucidation of NoV risk among older adults will support prevention, treatment and control efforts.

METHODS

We conducted a systematic literature review to summarize the published risk estimates of NoV-associated illness, hospitalization and death among individuals aged 65 years and older. A structured search using defined NoV and gastroenteritis (GE) terms was performed in the PubMed and EMBASE databases of human studies published between January 1, 2003 and May 16, 2013.

RESULTS

We identified 39 studies from high income (HI) and upper-middle income (UMI) countries. Thirty-six percent of publications provided risk estimates based on laboratory-confirmed or epidemiologically-linked population-based surveillance data using molecular diagnostic methods. Over the study period, estimated annual NoV rates and extrapolated number of cases among older adults in HI and UMI countries were: 29-120/10,000 or 1.2-4.8 million NoV-associated illnesses; 18-54/10,000 or 723,000-2.2 million NoV-associated outpatient visits; 1-19/10,000 or 40,00-763,000 NoV-associated inpatient visits; 0.04-0.32/10,000 or 2000-13,000 NoV-associated deaths. NoV was responsible for approximately 10-20 % of GE hospitalizations and 10-15 % of all-cause GE deaths among older adults. Older adults experienced a heightened risk of nosocomial infections. Those in LTCFs experience frequent NoV outbreaks and the range in attack rates was 3-45 %, case hospitalization rates 0.5-6 % and case fatality rates 0.3-1.6 %.

CONCLUSIONS

Older adults are at increased risk of severe NoV-associated health outcomes. NoV-associated hospitalization rates were higher, more severe, resulted in longer stays and incurred greater costs than for younger patients. NoV-associated mortality rates were approximately 200 % higher among individuals 65 years and older compared to <5 years. The burden of NoV among older adults is expected to rise along with societal aging and increased need for institutionalized care. NoV prevention in older adults, including potential vaccination, may significantly impact risk of severe illness.

Norovirus Antigen Detection with a Combination of Monoclonal and Single-Chain Antibodies

The performance of a norovirus antigen detection assay was assessed using monoclonal antibody NV23 and single-chain antibody HJT-R3-A9 to identify both virus-like particles and virus-containing fecal samples. The detection of 25 different norovirus genotypes as recombinant virus-like particles or in clinical samples was dependent on virus or antigen concentration.

Noroviruses as a Cause of Diarrhea in Immunocompromised Pediatric Hematopoietic Stem Cell and Solid Organ Transplant Recipients

Case reports describe significant norovirus gastroenteritis morbidity in immunocompromised patients. We evaluated norovirus pathogenesis in prospectively enrolled solid organ (SOT) and hematopoietic stem cell transplant (HSCT) patients with diarrhea who presented to Texas Children's Hospital and submitted stool for enteric testing. Noroviruses were detected by real-time reverse transcription polymerase chain reaction. Clinical outcomes of norovirus diarrhea and non-norovirus diarrhea patients, matched by transplanted organ type, were compared. Norovirus infection was identified in 25 (22%) of 116 patients, more frequently than other enteropathogens. Fifty percent of norovirus patients experienced diarrhea lasting ≥14 days, with median duration of 12.5 days (range 1-324 days); 29% developed diarrhea recurrence. Fifty-five percent of norovirus patients were hospitalized for diarrhea, with 27% requiring intensive care unit (ICU) admission. One HSCT recipient developed pneumatosis intestinalis. Three HSCT patients expired ≤6 months of norovirus diarrhea onset. Compared to non-norovirus diarrhea patients, norovirus patients experienced significantly more frequent ICU admission (27% vs. 0%, p = 0.02), greater serum creatinine rise (median 0.3 vs. 0.2 mg/dL, p = 0.01), and more weight loss (median 1.6 vs. 0.6 kg, p < 0.01). Noroviruses are an important cause of diarrhea in pediatric transplant patients and are associated with significant clinical complications.