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Background Globally, noroviruses cause infections year-round but have recognized winter seasonality in the Northern Hemisphere and yearly variations in incidence. With candidate norovirus vaccines in development, understanding temporal and geographic trends in norovirus disease is important to inform potential vaccination strategies and evaluate vaccine impact. Methods We analyzed data from the National Outbreak Reporting System (NORS) and CaliciNet on single-state norovirus outbreaks that occurred during August 2009–July 2019 in the contiguous United States. We defined norovirus season onset and offset as the weeks by which 10% and 90% of norovirus outbreaks in a surveillance year occurred, respectively, and duration as the difference in weeks between onset and offset. We compared norovirus seasons across surveillance years and geographic regions. Results During August 2009–July 2019, 24 995 single-state norovirus outbreaks were reported to NORS and/or CaliciNet. Nationally, the median norovirus season duration was 24 weeks, with onset occurring between October and December and offset occurring between April and May. Across all years combined, we observed a west-to-east trend in seasonality, with the earliest onset (October) and latest offset (May) occurring in western regions and the latest onset (December) and earliest offset (April) occurring in northeastern regions. Conclusions Timing and duration of the US norovirus season varied annually but generally occurred during October–May. Norovirus wintertime seasonality was less distinct in western regions and was progressively more pronounced moving east. Further understanding the drivers of spatiotemporal dynamics of norovirus could provide insights into factors that promote virus transmission and help guide future interventions.

Noroviruses are a leading cause of endemic and epidemic acute gastroenteritis in all age groups. However, in Latin America, there are limited and updated data regarding circulating genotypes. The aim of this study was to assess the prevalence and genetic diversity of norovirus outbreaks in Argentina from 2013 to 2018. Stool samples from 29 acute gastroenteritis (AGE) outbreaks were available for viral testing. Norovirus was detected in samples from 18 (62.1%) outbreaks (2 GI and 16 GII). Both GI outbreaks were typed as GI.6[P11] whereas 10 different GII genotypes were detected, in which GII.4 viruses were the most frequently detected (29.4%, associated with GII.P31 and GII.P16) followed by GII.1[P33] and GII.6[P7] (17.6% each). Like GII.4 viruses, GII.2 viruses were also detected in association with different polymerases (GII.P2 and GII.P16). Our findings underscore the importance of dual RNA-dependent RNA polymerase-VP1 typing since recombinant strains with new polymerase sequences emerge frequently suggesting a possible role in improved fitness of these viruses. This study represents the most recent multi-year assessment of the molecular epidemiology of norovirus strains associated with AGE outbreaks in Argentina. Molecular surveillance of norovirus has to be considered to monitor possible changes in dominant genotypes which may assist to inform the formulation of future vaccines.

Background In the United States, norovirus is the leading cause of healthcare-associated gastroenteritis outbreaks. To inform prevention efforts, we describe the epidemiology of norovirus outbreaks in long-term care facilities (LTCFs). Methods The Centers for Disease Control and Prevention (CDC) collect epidemiologic and laboratory data on norovirus outbreaks from US health departments through the National Outbreak Reporting System (NORS) and CaliciNet. Reports from both systems were merged, and norovirus outbreaks in nursing homes, assisted living, and other LTCFs occurring in 2009–2018 were analyzed. Data from the Centers for Medicare and Medicaid Services and the National Center for Health Statistics were used to estimate state LTCF counts. Results During 2009–2018, 50 states, Washington D.C., and Puerto Rico reported 13 092 norovirus outbreaks and 416 284 outbreak-associated cases in LTCFs. Participation in NORS and CaliciNet increased from 2009 to 2014 and median reporting of LTCF norovirus outbreaks stabilized at 4.1 outbreaks per 100 LTCFs (interquartile range [IQR]: 1.0–7.1) annually since 2014. Most outbreaks were spread via person-to-person transmission (90.4%), and 75% occurred during December–March. Genogroup was reported for 7292 outbreaks with 862 (11.8%) positive for GI and 6370 (87.3%) for GII. Among 4425 GII outbreaks with typing data, 3618 (81.8%) were GII.4. LTCF residents had higher attack rates than staff (median 29.0% vs 10.9%; P < .001). For every 1000 cases, there were 21.6 hospitalizations and 2.3 deaths. Conclusions LTCFs have a high burden of norovirus outbreaks. Most LTCF norovirus outbreaks occurred during winter months and were spread person-to-person. Outbreak surveillance can inform development of interventions for this vulnerable population, such as vaccines targeting GII.4 norovirus strains.

Background Diarrhea remains the leading cause of childhood illness in China. Better understanding of burden and etiology of diarrheal diseases is important for development of effective prevention measures. Methods Population-based diarrhea surveillance was conducted in Sanjiang (southern China) year-round and Zhengding (northern China) in autumn/winter. Stool specimens were collected from children, Key Points Currently bacterial and viral agents in the gastrointestinal tract are under-detected and poorly defined in developing countries. A new sensitive TAC assay provided comprehensive identification of microorganisms, including neglected pathogens, in Chinese children with moderate and severe diarrhea. Supplementary Information The online version contains supplementary material available at 10.1186/s13099-021-00428-2.

We report a norovirus GIV outbreak in the United States, 15 years after the last reported outbreak. During May 2016 in Wisconsin, 53 persons, including 4 food handlers, reported being ill. The outbreak was linked to individually prepared fruit consumed as a fruit salad. The virus was phylogenetically classified as a novel GIV genotype.

Noroviruses are a leading cause of acute gastroenteritis (AGE) among adults and children worldwide. NoroSurv is a global network for norovirus strain surveillance among children

Background Noroviruses are the leading cause of acute gastroenteritis outbreaks worldwide. Clarifying the viral, host, and environmental factors (epidemiologic triad) associated with severe outcomes can help target public health interventions. Methods Acute norovirus outbreaks reported to the National Outbreak Reporting System (NORS) in 2009-2016 were linked to laboratory-confirmed norovirus outbreaks reported to CaliciNet. Outbreaks were analyzed for differences in genotype (GII.4 vs non-GII.4), hospitalization, and mortality rates by timing, setting, transmission mode, demographics, clinical symptoms, and health outcomes. Results A total of 3747 norovirus outbreaks were matched from NORS and CaliciNet. Multivariable models showed that GII.4 outbreaks (n = 2353) were associated with healthcare settings (odds ratio [OR], 3.94 [95% confidence interval {CI}, 2.99-5.23]), winter months (November-April; 1.55 [95% CI, 1.24-1.93]), and older age of cases (≥50% aged ≥75 years; 1.37 [95% CI, 1.04-1.79]). Severe outcomes were more likely among GII.4 outbreaks (hospitalization rate ratio [RR], 1.54 [95% CI, 1.23-1.96]; mortality RR, 2.77 [95% CI, 1.04-5.78]). Outbreaks in healthcare settings were also associated with higher hospitalization (RR, 3.22 [95% CI, 2.34-4.44]) and mortality rates (RR, 5.65 [95% CI, 1.92-18.70]). Conclusions Severe outcomes more frequently occurred in norovirus outbreaks caused by GII.4 and those in healthcare settings. These results should help guide preventive interventions for targeted populations, including vaccine development.

BackgroundNoroviruses are the most common cause of epidemic and endemic acute gastroenteritis (AGE) worldwide. The burden of norovirus disease in low-income settings is poorly understood.MethodsWe tested stool samples from children less than 5 years of age with diarrhea who were admitted in a rural hospital in Bangladesh from 2010–2012 and from matched, healthy controls from the same catchment area.ResultsNorovirus was detected in 109 (18%) of 613 children with diarrhea and in 30 (15%) of 206 healthy controls. Most (n = 118; 85%) norovirus infections belonged to genogroup II (GII). Of these, GII.4 viruses were identified in 36 (33%) of the cases and in 6 (21%) of the controls. Other major genotypes included GII.3 (13%), GII.6 (11%), and GII.13 (11%) in the cases and GII.6 (17%) and GII.2 (14%) in the controls. The greatest risk of severe norovirus disease (Vesikari score ≥11) was associated with GII.4 infections. GII.4 viruses were the predominant genotype detected during the winter (55%) and rainy season (23%), while GII.3 (19%) and GII.13 (19%) viruses were the most prevalent genotypes during the summer. Vomiting was significantly associated with GII.4 infections, while longer durations of diarrhea were associated with GI.3 infections.ConclusionsFuture studies are needed to understand the high rates of virus shedding in children without AGE symptoms.

Background Norovirus is the leading cause of epidemic and sporadic acute gastroenteritis (AGE) in the United States. Widespread prevalence necessitates implementation of accurate norovirus detection assays in clinical diagnostic laboratories. Objective To evaluate RIDA®GENE norovirus GI/GII real-time RT-PCR assay (RGN RT-PCR) using stool samples from patients with sporadic AGE. Study design Patients between 14 days to 101 years of age with symptoms of AGE were enrolled prospectively at four sites across the United States during 2014–2015. Stool specimens were screened for the presence of norovirus RNA by the RGN RT-PCR assay. Results were compared with a reference method that included conventional RT-PCR and sequencing of a partial region of the 5′end of the norovirus ORF2 gene. Results A total of 259 (36.0%) of 719 specimens tested positive for norovirus by the reference method. The RGN RT-PCR assay detected norovirus in 244 (94%) of these 259 norovirus positive specimens. The sensitivity and specificity (95% confidence interval) of the RGN RT-PCR assay for detecting norovirus genogroup (G) I was 82.8% (63.5–93.5) and 99.1% (98.0–99.6) and for GII was 94.8% (90.8–97.2) and 98.6% (96.9–99.4), respectively. Seven specimens tested positive by the RGN-RT PCR that were negative by the reference method. The fifteen false negative samples were typed as GII.4 Sydney, GII.13, GI.3, GI.5, GI.2, GII.1, and GII.3 in the reference method. Conclusions The RGN RT-PCR assay had a high sensitivity and specificity for the detection of norovirus in stool specimens from patients with sporadic AGE.

Background The family Caliciviridae consists of a genetically diverse group of RNA viruses that infect a wide range of host species including noroviruses and sapoviruses which cause acute gastroenteritis in humans. Typing of these viruses relies on sequence-based approaches, and therefore there is a need for rapid and accurate web-based typing tools. Objective To develop and evaluate a web-based tool for rapid and accurate genotyping of noroviruses and sapoviruses. Methods The Human Calicivirus Typing (HuCaT) tool uses a set of curated reference sequences that are compared to query sequences using a k-mer (DNA substring) based algorithm. Outputs include alignments and phylogenetic trees of the 12 top matching reference sequences for each query. Results The HuCaT tool was validated with a set of 1310 norovirus and 239 sapovirus sequences covering all known human norovirus and sapovirus genotypes. HuCaT tool assigned genotypes to all queries with 100 % accuracy and was much faster (17 s) than BLAST (150 s) or phylogenetic analyses approaches. Conclusions The web-based HuCaT tool supports rapid and accurate genotyping of human noroviruses and sapoviruses.

Highlights • We validated genogroup-specific one-step conventional RT-PCR assays (PC assays) for sequence-based dual typing of GI and GII norovirus strains. • The PC assays use a combination of oligonucleotide primers that target a genomic region spanning the 3’-end of ORF1 and 5’end of ORF2 of GI and GII noroviruses. • The PC assays are sensitive (5 to 50 copies/rx) and detect all currently identified norovirus P-types and capsid genotypes from different geographic regions. • The PC assays have been successfully implemented by CaliciNet USA and CaliciNet China., Background Noroviruses are the major cause of acute gastroenteritis (AGE) in people of all ages globally. Standardized genotyping is key for outbreak investigations and surveillance networks. Objective Here we describe the validation of a one-step conventional RT-PCR assay for sequence-based dual typing of GI and GII noroviruses. This polymerase (P) and capsid (C) dual typing assay uses a combination of previously published oligonucleotide primers amplifying a genomic region spanning the 3'-end of ORF1 and 5'end of ORF2 resulting in a 579 bp product for GI and 570 bp product for GII viruses. Results The limit of detection of the assay ranged from 5 to 50 copies of viral RNA per reaction for GI and GII. To validate the assay, we tested 2,663 noroviruspositive stool samples from outbreaks and sporadic cases of AGE in Bangladesh, Guatemala, Peru, and USA collected between 2010–2019, of which 2,392 (90 %) were genotyped successfully. Most of the known genotypes infecting humans (GI (n = 9) and GII (n = 23)) and P types (GI (n = 15), GII, (n = 20)) could be detected. The remaining 270 samples had low viral load (Ct > 30) by real-time RT-PCR. A panel of 166 samples positive for other enteric viruses (rotavirus, astrovirus, sapovirus, adenovirus type 40/41) tested negative. Conclusion The use of broadly reactive genotyping assays greatly strengthens exchange of standardized genotype data globally to monitor trends in genotype diversity which is important for both the development of vaccines and to measure their impact.

Foodborne transmission accounts for 10% of outbreaks caused by GII.4, 27% by all other single genotypes, and 37% by mixtures of GII.4 and others, Worldwide, noroviruses are a leading cause of gastroenteritis. They can be transmitted from person to person directly or indirectly through contaminated food, water, or environments. To estimate the proportion of foodborne infections caused by noroviruses on a global scale, we used norovirus transmission and genotyping information from multiple international outbreak surveillance systems (Noronet, CaliciNet, EpiSurv) and from a systematic review of peer-reviewed literature. The proportion of outbreaks caused by food was determined by genotype and/or genogroup. Analysis resulted in the following final global profiles: foodborne transmission is attributed to 10% (range 9%%�?"11%) of all genotype GII.4 outbreaks, 27% (25%�?"30%) of outbreaks caused by all other single genotypes, and 37% (24%%�?"52%) of outbreaks caused by mixtures of GII.4 and other noroviruses. When these profiles are applied to global outbreak surveillance data, results indicate that �%^14% of all norovirus outbreaks are attributed to food.

Background Real-time reverse-transcriptase polymerase chain reaction (RT-PCR) is the state-of-the-art diagnostic for norovirus. Cycle threshold (Ct), an indicator of viral load, may be associated with symptomatic disease as well as demographic and outbreak characteristics. Methods Data on (1) outbreak and sporadic cases and (2) asymptomatic controls in the United States and Latin America were analyzed. With multivariate regression models, we assessed relationships between various factors and Ct values, and we calculated odds ratios (ORs) for the presence of symptoms and attributable fractions of norovirus. Receiver-operating characteristic analysis was performed to define an optimal Ct cutoff to identify disease-causing infections. Results Cycle threshold values were lower (ie, higher viral loads) among symptomatic cases (model-adjusted mean ± standard error: 25.3 ± 1.2) compared with asymptomatic controls (28.5 ± 1.4). Cycle threshold values were significantly different across age groups, norovirus genogroups, timing of specimen collection, outbreak settings, and transmission modes. Genogroup II (GII) Ct values were associated with presence of symptoms (OR = 1.1), allowing us to estimate that 16% of diarrheal disease was attributable to norovirus. The optimized Ct cutoff led to poor sensitivity and specificity for genogroup I and GII. Conclusions Cycle threshold values were associated with host, pathogen, and outbreak factors. Cycle threshold values may not effectively distinguish disease-causing infection for individual patients, but they are useful for epidemiological studies aiming to attribute disease.

Background: Nicaragua was the first developing nation to implement routine immunization with the pentavalent rotavirus vaccine (RV5). In this RV5-immunized population, understanding infectious etiologies of childhood diarrhea is necessary to direct diarrhea treatment and prevention efforts. Methods: We followed a population-based sample of children less than5 years in Leon, Nicaragua for diarrhea episodes through household visits. Information was obtained on RV5 history and sociodemographics. Stool samples collected during diarrhea episodes and among healthy children underwent laboratory analysis for viral, bacterial and parasitic enteropathogens. Detection frequency and incidence of each enteropathogen was calculated. Results: The 826 children in the cohort experienced 677 diarrhea episodes during 607.5 child-years of exposure time (1.1 episodes per child-year). At least 1 enteropathogen was detected among 61.1% of the 337 diarrheal stools collected. The most common enteropathogens among diarrheal stools were: norovirus (20.4%), sapovirus (16.6%), enteropathogenic Escherichia coli (11.3%), Entamoeba histolytica/dispar (8.3%), Giardia lamblia (8.0%) and enterotoxigenic E. coli (7.7%), with rotavirus detected among 5.3% of diarrheal stools. Enteropathogenic Escherichia coli and enterotoxigenic E. coli were frequently detected among stools from healthy children. Among children with diarrhea, norovirus was more commonly detected among younger children (less than2 years) and G. lamblia was more commonly detected among older children (2-4 years). The mean age of rotavirus detection was 34.6 months. Conclusions: In this Central American community after RV5 introduction, rotavirus was not commonly detected among children with diarrhea. Prevention and appropriate management of norovirus and sapovirus should be considered to further reduce the burden of diarrheal disease.

Noroviruses evolve by antigenic drift and recombination, which occurs most frequently at the junction between the non-structural and structural protein coding genomic regions. In 2015, a novel GII.P16-GII.4 Sydney recombinant strain emerged, replacing the predominance of GII.Pe-GII.4 Sydney among US outbreaks. Distinct from GII.P16 polymerases detected since 2010, this novel GII.P16 was subsequently detected among GII.1, GII.2, GII.3, GII.10 and GII.12 viruses, prompting an investigation on the unique characteristics of these viruses. Norovirus positive samples (n = 1807) were dual-typed, of which a subset (n = 124) was sequenced to yield near-complete genomes. CaliciNet and National Outbreak Reporting System (NORS) records were matched to link outbreak characteristics and case outcomes to molecular data and GenBank was mined for contextualization. Recombination with the novel GII.P16 polymerase extended GII.4 Sydney predominance and increased the number of GII.2 outbreaks in the US. Introduction of the novel GII.P16 noroviruses occurred without unique amino acid changes in VP1, more severe case outcomes, or differences in affected population. However, unique changes were found among NS1/2, NS4 and VP2 proteins, which have immune antagonistic functions, and the RdRp. Multiple polymerase-capsid combinations were detected among GII viruses including 11 involving GII.P16. Molecular surveillance of protein sequences from norovirus genomes can inform the functional importance of amino acid changes in emerging recombinant viruses and aid in vaccine and antiviral formulation.

We report an increase in the proportion of genotype GI.6 norovirus outbreaks in the United States from 1.4% in 2010 to 7.7% in 2012 (p

During 2012, global detection of a new norovirus (NoV) strain, GII.4 Sydney, raised concerns about its potential effect in the United States. We analyzed data from NoV outbreaks in 5 states and emergency department visits for gastrointestinal illness in 1 state during the 2012–13 season and compared the data with those of previous seasons. During August 2012–April 2013, a total of 637 NoV outbreaks were reported compared with 536 and 432 in 2011–2012 and 2010–2011 during the same period. The proportion of outbreaks attributed to GII.4 Sydney increased from 8% in September 2012 to 82% in March 2013. The increase in emergency department visits for gastrointestinal illness during the 2012–13 season was similar to that of previous seasons. GII.4 Sydney has become the predominant US NoV outbreak strain during the 2012–13 season, but its emergence did not cause outbreak activity to substantially increase from that of previous seasons.

Background Norovirus (NoV) is the leading cause of epidemic gastroenteritis worldwide. The lack of a cell culture has significantly hampered the development of effective therapies against human NoV. Clinically approved nucleoside and non-nucleoside analogues have been used successfully against RNA viruses. Methods In this study, we evaluated the efficacy of four nucleoside analogues (2′-C-MeC, 2′-F-2′-C-MeC, β-D-N(4)-hydroxycytidine [NHC] and lamivudine) on Norwalk virus (NV) RNA levels and protein expression in NV replicon-harbouring cells (HG23 cells), and their efficacy in blocking murine norovirus (MNV) replication in RAW 264.7 cells. Results 2′-C-MeC and 2′-F-2′-C-MeC reduced MNV RNA levels and infectivity in RAW 264.7 cells in a concentration- and time-dependent manner. The median effective concentrations (EC50) of 2′-C-MeC and 2′-F-2′-C-MeC were 6.9 μM and 12.7 μM, respectively. 2′-C-MeC, 2′-F-2′-C-MeC and NHC reduced NV RNA levels and protein expression in HG23 cells. For the NV replicon, the EC50 of 2′-C-MeC (1.3 μM) was comparable to the antiviral activity of NHC (1.5 μM) and twofold more potent than 2′-F-2′-C-MeC (3.2 μM). The combination of 2′-C-MeC/ ribavirin resulted in modest synergistic activity, whereas NHC/ribavirin was antagonistic for NV replication in HG23 cells. Conclusions The antiviral activity of 2′-C-MeC against strains of two different NoV genogroups and the low EC50 suggest that this nucleoside analogue may be effective against the more prevalent GII NoVs. In the absence of a vaccine, antiviral agents could be an effective intervention to control the spread of human NoV in populations at a high risk for NoV disease.

To identify the prevalence and genetic variability of noroviruses in dogs, we tested fecal samples by using reverse transcription–PCR. We found canine norovirus in 40% and 9% of dogs with and without diarrhea, respectively. The virus was genetically unrelated to other noroviruses and constitutes a tentative new genogroup.

TOC Summary: The launch of CaliciNet in March 2009 was a milestone., CaliciNet, the outbreak surveillance network for noroviruses in the United States, was launched in March 2009. As of January 2011, twenty state and local health laboratories had been certified to submit norovirus sequences and epidemiologic outbreak data to CaliciNet. During the network’s first year, 552 outbreaks were submitted to CaliciNet, of which 78 (14%) were associated with foodborne transmission. A total of 395 (72%) outbreaks were typed as GII.4, of which 298 (75%) belonged to a new variant, GII.4 New Orleans, which first emerged in October 2009. Analysis of the complete capsid and P2 region sequences confirmed that GII.4 New Orleans is distinct from previous GII.4 variants, including GII.4 Minerva (2006b).