Norovirus GII.P16/GII.2-Associated Gastroenteritis, China, 2016

Measures for preventing norovirus outbreaks on campus in economically underdeveloped areas and countries: evidence from rural areas in Western China

Background

The outbreak of norovirus represents a significant public health emergency within densely populated, impoverished, and underdeveloped areas and countries. Our objective is to conduct an epidemiology study of a norovirus outbreak that occurred in a kindergarten located in rural western China. We aim to raise awareness and garner increased attention towards the prevention and control of norovirus, particularly in economically underdeveloped regions.

Methods

Retrospective on-site epidemiological investigation results, including data on school layout, case symptoms, onset time, disposal methods and sample testing results, questionnaire surveys, and case-control study were conducted in a kindergarten to analyze the underlying causes of the norovirus outbreak.

Results

A total of 15 cases were identified, with an attack rate of 44.12% (15/34). Among them, 10 cases were diagnosed through laboratory tests, and 5 cases were diagnosed clinically. Vomiting (100%, 15/15) and diarrhea (93.33%, 14/15) were the most common symptoms in the outbreak. Case control study revealed that cases who had close contact (<1 m) with the patient's vomitus (OR = 5.500) and those who had close contact with similar patients (OR = 8.000) had significantly higher ORs compared to the control participants. The current study demonstrated that improper handling of vomitus is positively associated with norovirus outbreak. The absence of standardized disinfection protocols heightens the risk of norovirus outbreaks.

Conclusion

To our knowledge, this study represents the first investigation into a norovirus outbreak in rural areas of western China. We aspire that amidst rapid economic development, a greater emphasis will be placed on the prevention and control of infectious diseases in economically underdeveloped areas and countries.

Establishment of a Nucleic Acid Detection Method for Norovirus GII.2 Genotype Based on RT-RPA and CRISPR/Cas12a-LFS

To establish a rapid detection method for norovirus GII.2 genotype, this study employed reverse transcription recombinase polymerase amplification (RT-RPA) combined with CRISPR/Cas12a and lateral flow strip (RT-RPA-Cas12a-LFS). Here, the genome of norovirus GII.2 genotype was compared to identify highly conserved sequences, facilitating the design of RT-RPA primers and crRNA specific to the conserved regions of norovirus GII.2. Subsequently, the reaction parameters of RT-RPA were optimized and evaluated using agar-gel electrophoresis and LFS. The results indicate that the conserved sequences of norovirus GII.2 were successfully amplified through RT-RPA at 37°C for 25 minutes. Additionally, CRISPR/Cas12a-mediated cleavage detection was achieved through LFS at 37°C within 10 minutes using the amplification products as templates. Including the isothermal amplification reaction time, the total time is 35 minutes. The established RT-RPA-Cas12a-LFS method demonstrated specific detection of norovirus GII.2, yielding negative results for other viral genomes, and exhibited an excellent detection limit of 10 copies/μl. The RT-RPA-Cas12a-LFS method was further compared with qRT-PCR by analyzing 60 food-contaminated samples. The positive conformity rate was 100%, the negative conformity rate was 95.45%, and the overall conformity rate reached 98.33%. This detection method for norovirus GII.2 genotype is cost-effective, highly sensitive, specific, and easy to operate, offering a promising technical solution for field-based detection of the norovirus GII.2 genotype.

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

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

Epidemiological Features of Human Norovirus Genotypes before and after COVID-19 Countermeasures in Osaka, Japan

We investigated the molecular epidemiology of human norovirus (HuNoV) in all age groups using samples from April 2019 to March 2023, before and after the COVID-19 countermeasures were implemented. GII.2[P16] and GII.4[P31], the prevalent strains in Japan before COVID-19 countermeasures, remained prevalent during the COVID-19 pandemic, except from April to November 2020; in 2021, the prevalence of GII.2[P16] increased among children. Furthermore, there was an increase in the prevalence of GII.4[P16] after December 2022. Phylogenetic analysis of GII.P31 RdRp showed that some strains detected in 2022 belonged to a different cluster of other strains obtained during the present study period, suggesting that HuNoV strains will evolve differently even if they have the same type of RdRp. An analysis of the amino acid sequence of VP1 showed that some antigenic sites of GII.4[P16] were different from those of GII.4[P31]. The present study showed high infectivity of HuNoV despite the COVID-19 countermeasures and revealed changes in the prevalent genotypes and mutations of each genotype. In the future, we will investigate whether GII.4[P16] becomes more prevalent, providing new insights by comparing the new data with those analyzed in the present study.

Prediction of Foodborne Norovirus Outbreaks in Coastal Areas in China in 2008-2018

Foodborne norovirus outbreak usually poses high risks in coastal areas in China. Owing to the influence of multiple climatic factors, it demonstrates typical seasonality and the hotspots gradually expanded northwards from 2008 to 2018. However, the complex mechanism of the onset of outbreaks makes accurate prediction difficult. Thus, it is in necessity to construct a predictive model for foodborne norovirus outbreaks in coastal areas based on environmental and geographical variables. A novel predictive nonlinear autoregressive model with exogenous inputs model was developed using 11 years of environmental and foodborne norovirus outbreak data collected from coastal areas in China. Five input variables (temperature, precipitation, elevation, latitude, and longitude) were screened through stepwise regression analysis. The predicted model developed in this study was able to reproduce 88.53% of outbreaks reported to the National Public Health Emergency Event Surveillance System (PHEESS) in the model development and 100% of outbreaks reported in the independent cross-validation since the system was first launched in China. In particular, foodborne norovirus outbreaks might occur when the probability is >0.6. The findings of this study suggest that foodborne norovirus outbreaks could be accurately predicted in coastal areas in China using the developed predictive model on a daily basis. The model output is most sensitive to temperature, followed by precipitation, and locations. The application of this predictive model is promising to improve local hygiene management levels, prevent foodborne norovirus outbreaks, and reduce the disease and economic costs in coastal areas in China.

Molecular epidemiology and genetic diversity of norovirus among hospitalized patients with acute gastroenteritis in Shandong, China, 2016-2018

Norovirus (NoV) infection is a leading cause of acute gastroenteritis (AGE) for people of all ages. Here, we reported the molecular epidemiology and genetic diversity of NoVs among hospitalized patients with AGE between 2016 and 2018 in Shandong Province, China. Two thousand sixty-nine AGE patients from sentinel hospitals were enrolled. The stool samples were collected and tested for NoVs by real-time RT-PCR. The RNA-dependent RNA polymerase (RdRp) and capsid gene of 163 strains were amplified and sequenced for genotyping. Phylogenetic analyses and genomic characterization were conducted with the VP1 and RdRp region of the full genome sequences. Four hundred seventy two (21.76%) samples were NoV-positive. The positive rate in 2016 was higher than those of 2017 and 2018. We observed diverse NoV genotypes. GII.2[P16] emerged in January 2017 and became the dominant genotype between May and June 2017. Phylogenetic analyses showed that our GII.2[P16] genomes clustered in the SC1 in VP1 region, while they belonged to the Emerging GⅡ.P16 (2015-2017) clade in RdRp region. Our GⅡ.4 strains displayed two amino acid mutations, positions R297H and D372N, in epitope A of the VP1 region. Our study highlighted that NoV is an important pathogen of viral AGE in Shandong and, therefore, it is necessary to strengthen its surveillance.

Changing predominance of norovirus strains in children with acute gastroenteritis in Shanghai, 2018-2021

Norovirus (NoV) is a major pathogen that causes acute gastroenteritis (AGE) in people of all ages, especially in children. In this study, we investigated the molecular epidemiological characteristics of NoV in children with AGE in Shanghai from 2018 to 2021. The overall detection rate of NoV was 11.9% (181/1545), with annual detection rates of 9.4% (36/381), 13.6% (29/213), 5.8% (13/226) and 14.2% (103/725), respectively. Of note, the prevalence of NoV in 2020 was significantly lower than that in 2018-2019 (10.9%, 65/594) (P ​= ​0.023) and 2021 (14.2%, 103/725) (P ​= ​0.000). The 181 NoV strains identified in this study were classified into the GI group (1.1%, 2/181), GII group (98.3%, 178/181) and GIX group (0.6%, 1/181) according to the VP1 gene. The most common NoV VP1 genotype was GII.4 Sydney_2012 (63.5%, 115/181), followed by GII.3 (19.9%, 36/181) and GII.2 (9.4%, 17/181). For P genotypes, 174 strains were sequenced successfully according to the RdRp gene, and the predominant genotype was GII.P16 (44.8%, 78/174), followed by GII.P31 (25.9%, 45/174) and GII.P12 (21.3%, 37/174). Among the 174 cases, GII.4 Sydney_2012[P16] (36.8%, 64/174) was the dominant genotype, followed by GII.4 Sydney_2012[P31] (25.3%, 44/174), GII.3[P12] (20.1%, 35/174) and GII.2[P16] (8.0%, 14/174). In particular, the dominant genotypes in Shanghai changed from GII.4 Sydney_2012[P31] in 2018-2019 to GII.4 Sydney_2012[P16] in 2020-2021. This is the first report to describe the epidemiological changes in NoV infection before and during the COVID-19 pandemic in Shanghai. These data highlight the importance of continuous surveillance for NoV in children with AGE in Shanghai.

Emergence of GII.4 Sydney[P16]-like Norovirus-Associated Gastroenteritis, China, 2020-2022

Newly evolved GII.4 Sydney[P16] norovirus with multiple residue mutations, already circulating in parts of China, became predominant and caused an abrupt increase in diagnosed norovirus cases among children with gastroenteritis in Shanghai during 2021-2022. Findings highlight the need for continuous long-term monitoring for GII.4 Sydney[P16] and emergent GII.4 norovirus variants.

Genetic characterization of rarely reported GII.3[P25] norovirus strain detected in patients with acute gastroenteritis in Huzhou, China, 2021

•The first genome of GII.3 [P25] strain isolated in China was determined by NGS. •About 19 unique amino acid substitutions were identified in the VP1 region of GII.3 [P25]. •Antigenic variation may have contributed to the re-emerge of GII.3 [P25] strains.

Molecular Evolutionary Analyses of the RNA-Dependent RNA Polymerase (RdRp) Region and VP1 Gene in Human Norovirus Genotypes GII.P6-GII.6 and GII.P7-GII.6

To understand the evolution of GII.P6-GII.6 and GII.P7-GII.6 strains, the prevalent human norovirus genotypes, we analysed both the RdRp region and VP1 gene in globally collected strains using authentic bioinformatics technologies. A common ancestor of the P6- and P7-type RdRp region emerged approximately 50 years ago and a common ancestor of the P6- and P7-type VP1 gene emerged approximately 110 years ago. Subsequently, the RdRp region and VP1 gene evolved. Moreover, the evolutionary rates were significantly faster for the P6-type RdRp region and VP1 gene than for the P7-type RdRp region and VP1 genes. Large genetic divergence was observed in the P7-type RdRp region and VP1 gene compared with the P6-type RdRp region and VP1 gene. The phylodynamics of the RdRp region and VP1 gene fluctuated after the year 2000. Positive selection sites in VP1 proteins were located in the antigenicity-related protruding 2 domain, and these sites overlapped with conformational epitopes. These results suggest that the GII.6 VP1 gene and VP1 proteins evolved uniquely due to recombination between the P6- and P7-type RdRp regions in the HuNoV GII.P6-GII.6 and GII.P7-GII.6 virus strains.

Epidemiology and genetic diversity of norovirus GII genogroups among children in Hubei, China, 2017-2019

Norovirus (NoV) is an important cause of viral acute gastroenteritis (AGE). To gain insights into the epidemiological characteristics and genetic diversity of NoV among children in Hubei, 1216 stool samples from children (≤ 5 years) obtained under AGE surveillance from January 2017 to December 2019 were analyzed. The results showed that NoV was responsible for 14.64% of AGE cases, with the highest detection rate in children aged 7-12 months (19.76%). Statistically significant differences were found between male and female infection rates (χ2 ​= ​8.108, P ​= ​0.004). Genetic analysis of RdRp and VP1 sequences showed that NoV GII genotypes were GII.4 Sydney [P31] (34.35%), GII.3 [P12] (25.95%), GII.2 [P16] (22.90%), GII.4 Sydney [P16] (12.98%), GII.17 [P17] (2.29%), GII.6 [P7] and GII.3 [P16] (each at 0.76%). GII.17 [P17] variants were divided into the Kawasaki323-like lineage and the Kawasaki308-like lineage. A unique recombination event was detected between strains of GII.4 Sydney 2012 and GII.4 Sydney 2016. Significantly, all GII.P16 sequences associated with GII.4/GII.2 obtained in Hubei were correlated with novel GII.2 [P16] variants that re-emerged in Germany in 2016. Antigenic site analysis of complete VP1 sequences from all GII.4 variants from Hubei identified notable variable residues of antibody epitopes. Genotyping under continuous AGE surveillance and observation of the antigenic sites of VP1 are important monitoring strategies for emerging NoV strains.

Epidemiological Characteristics of Norovirus Outbreaks in Shenyang from 2017 to 2021

Norovirus is one of the leading causes of acute gastroenteritis outbreaks worldwide. This study aimed to identify the epidemiological characteristics of norovirus outbreaks and to provide evidence for public health entities. Specimens and epidemiological survey data were collected to determine if there were differences in the attack rate of norovirus in terms of the year, season, transmission route, exposure setting, and region and to determine whether there were relationships between the reporting interval, the number of illnesses in a single outbreak and the duration of the outbreak. Norovirus outbreaks were reported throughout the year, with seasonal characteristics (i.e., high rates in spring and winter). Among all regions in Shenyang with the exception of Huanggu and Liaozhong, norovirus outbreaks had been reported, and the primary genotype was GII.2[P16]. Vomiting was the most common symptom. The main places of occurrence were childcare institutions and schools. The person-to-person route was the main transmission route. The median duration of norovirus was 3 days (IQR [interquartile range]: 2-6 days), the median reporting interval was 2 days (IQR: 1-4 days), the median number of illnesses in a single outbreak was 16 (IQR: 10-25); there was a positive correlation between these parameters. Norovirus surveillance and genotyping studies still need to be further strengthened to increase knowledge regarding the pathogens and their variant characteristics, to better characterize the patterns of norovirus outbreaks and to provide information for outbreak prevention. Norovirus outbreaks should be detected, reported and handled early. Public health entities and the government should develop corresponding measures for different seasons, transmission routes, exposure settings, and regions.

Functional and structural characterization of Norovirus GII.6 in recognizing histo-blood group antigens

Noroviruses (NoVs) are the primary cause of acute gastroenteritis worldwide. Histo-blood group antigens (HBGAs) are receptors or attachment factors that affect the prevalence and host susceptibility of NoVs. GII.6 NoV is one of the predominant genotypes in humans, which recognizes the type ABO secretor of HBGAs. However, the structural basis of GII.6 NoV's interaction with HBGAs receptors remains elusive. In this study, we investigated the binding features of the GII.6 strain to HBGAs using saliva- and glycan-ELISA assays and characterized the molecular basis of the GII.6 virus that recognizes H disaccharide. We showed that the GII.6 ​P domain recognized some A and O secretor's saliva samples, most B secretor's saliva samples, and H disaccharide antigen, but did not bind non-secretors' saliva. Further, we determined the crystal structures of GII.6 and its complex with H disaccharides at 1.7 ​Å, revealing that the P domain of GII.6 shares the conventional binding interface and mode of GII HBGAs. Single residue mutations at the GII.6-H binding sites could inhibit the binding of GII.6 to HBGAs, demonstrating that the interaction residues were crucial in maintaining NoV-glycan integrity. Finally, structural and sequence analyses showed that the major residues of the GII.6-H interaction were conserved among NoVs in the GII genogroup. Taken together, our study characterized the functional and structural features of GII.6 that allow it to interact with HBGAs, and shed light on NoV evolution, epidemiology, and anti-viral drug development.

Molecular characteristics of norovirus in sporadic and outbreak cases of acute gastroenteritis and in sewage in Sichuan, China

Background

Norovirus is highly diverse and constant surveillance is essential for the prevention and control of norovirus gastroenteritis.

Methods

From 2015 to 2019, fecal samples were collected from sporadic cases and outbreaks of acute gastroenteritis reported to Sichuan center for disease control and prevention. Sewage samples were collected from a wastewater treatment plant in Sichuan. All samples were tested for norovirus by real-time reverse transcription polymerase chain reaction. Norovirus-positive clinical samples were sequenced by Sanger sequencing. Sewage samples were sequenced by amplicon and virome sequencing.

Results

A total of 1462 fecal samples were collected and 11 different norovirus genotypes were detected. GII.4 Sydney 2012[P31] and GII.3[P12] were the dominant genotypes in sporadic cases whereas GII.2[P16] and GII.17[P17] were the dominant genotypes in outbreaks. GII.3 was predominant in children 0–6 months of age during spring and summer, while GII.4 was predominant in children older than 6 months and in the autumn. The detection rate of GII.17[P17] increased with age. In sewage, 16 genotypes were detected. GII.3, GII.4, GI.1, and GI.2 were the dominant genotypes.

Conclusion

This study demonstrated that multiple norovirus genotypes co-circulate in Sichuan. It is vital to continuously trace the genetic diversity of norovirus to give a future perspective on surveillance needs and guide vaccine design and policy decisions.

Early evolution and transmission of GII.P16-GII.2 norovirus in China

Norovirus is the most common cause of acute gastroenteritis worldwide. During 2016-2017, a novel recombinant GII.P16-GII.2 genotype of norovirus suddenly appeared and over the next several years became the predominant strain in both China and worldwide. To better understand the origin and diffusion of the GII.P16-GII.2 genotype in China, we conducted molecular evolutionary analyses, including phylodynamics and phylogeography. Moreover, to trace person-to-person transmission of GII.P16-GII.2 norovirus, we applied the novel method, TransPhylo, to a historical phylogeny using sequences obtained from a publicly available database. A time-scaled phylogenetic tree indicated that the time to the most recent common ancestor of the GII.P16-GII.2 major capsid protein (VP1) gene diverged from the GII.P2-GII.2 VP1 gene at 2,001.03 with an evolutionary rate of 3.32 × 10-3 substitutions/site/year. The time to the most recent common ancestor of the GII.P16-GII.2 RNA-dependent RNA polymerase region diverged from the GII.P16-GII.4 RNA-dependent RNA polymerase region at 2,013.28 with an evolutionary rate of 9.44 × 10-3 substitutions/site/year. Of these 2 genomic regions, VP1 gene sequence variations were the most influenced by selective pressure. A phylogeographic analysis showed that GII.P16-GII.2 strains in China communicated most frequently with those in the United States, Australia, Thailand, and Russia, suggesting import from Australia to Taiwan and from the United States to Guangdong. TransPhylo analyses indicated that the basic reproductive number (R0) and sampling proportion (pi) of GII.P16-GII.2 norovirus were 1.99 (95% confidence interval: 1.58-2.44) and 0.76 (95% confidence interval: 0.63-0.88), respectively. Strains from the United States and Australia were responsible for large spread during the evolution and transmission of the virus. Coastal cities and places with high population densities should be closely monitored for norovirus.

Norovirus outbreaks in China, 2000-2018: A systematic review

To understand epidemiological characteristics of norovirus outbreaks in China from 2000 to 2018 the literature on norovirus outbreaks was identified by searching WANFANG, CNKI, PubMed, and Web of Science databases before 31 December 2018. Statistical analyses were performed using Statistical Product Service Solutions software. RStudio1.4.1717 and ArcGIS trial version were used for plotting bar graphs and maps. A total of 419 norovirus outbreaks were reported in the 394 included articles, which occurred between June 2000 and October 2018, showing an overall increasing trend. The majority of outbreaks occurred in schools (52.28%, 218/417) and kindergartens (55/417, 13.19%). Person-to-person transmission (41.64%, 137/329) was most common, followed by food-borne transmission (75/329, 22.80%) and water-borne transmission (72/329, 21.88%). GII was the most predominant norovirus genogroup, with GII.4, GII.17 and GII.2 being the dominant genotypes in 2007-2013, 2014-2015, 2016-2017, respectively. Increased outbreaks were associated with the prevalence of new variants. Most norovirus outbreaks were reported in the southeast of the country. The number of norovirus outbreaks was positively associated with the per capita gross domestic product and the year-end resident population. Norovirus outbreaks have become an important public health problem in China. It is necessary to establish surveillance in hospitals and nursing homes. Genotyping of noroviruses is important for monitoring the circulating strains and improving the vaccine design, so it should be carried out in more regions.

Updating a New Semi-nested PCR Primer Pair for the Specific Detection of GII Norovirus in Oysters

Oysters are major transmission vectors of noroviruses (NoVs) in the environment. Outbreaks of NoVs are often associated with the consumption of NoV-contaminated oysters. Laboratory confirmation of suspected oyster samples is a critical step in the surveillance and control of NoVs. Because of non-specific amplification, false-positive results are frequently obtained by semi-nested RT-PCR with the presently widely used primer set (G2SKF/G2SKR). Here, a novel universal PCR primer set N (NG2OF/NG2OR) specific for genogroup II (GII) NoVs was designed based on all GII NoV sequences available in public databases. Specific products were obtained with the primer set N when the NoV-positive oysters, spiked with each of five representative genotypes of GII NoVs (GII.17, GII.13, GII.4, GII.3, and GII.12), were subjected to analyzing. No products were detected with the primer set N for the NoV-negative oysters, while the primer set C gave various non-specific bands. Twenty-three out of 156 fresh oyster samples were NoV-positive with both the primer set N and the classic primer set, while eight were NoV-positive solely with the primer set N. Compared with the classic primer set, the newly designed primer set N had a higher detection rate and improved specificity for GII NoVs in oyster samples. These results show that the novel PCR primer pair is specific and applicable for the detection of GII NoVs in oysters.

6-Valent Virus-Like Particle-Based Vaccine Induced Potent and Sustained Immunity Against Noroviruses in Mice

Norovirus is a major cause of acute gastroenteritis worldwide, and no vaccine is currently available. The genetic and antigenic diversity of Norovirus presents challenges for providing broad immune protection, which calls for a multivalent vaccine application. In this study, we investigated the possibility of developing a virus-like particle (VLP)-based 6-valent Norovirus vaccine candidate (Hexa-VLPs) that covers GI.1, GII.2, GII.3, GII.4, GII.6, and GII.17 genotypes. Hexa-VLPs (30 µg) adjuvanted with 500 µg of aluminum hydroxide (alum) were selected as the optimal immunization dose after a dose-escalation study. Potent and long-lasting blockade antibody responses were induced by 2-or 3-shot Hexa-VLPs, especially for the emerging GII.P16-GII.2 and GII.17 (Kawasaki 2014) genotypes. Hexa-VLPs plus alum elicited Th1/Th2 mixed yet Th2-skewed immune responses, characterized by an IgG1-biased subclass profile and significant IL-4⁺ T-cell activation. Notably, simultaneous immunization with a mixture of six VLPs revealed no immunological interference among the component antigens. These results demonstrate that Hexa-VLPs are promising broad-spectrum vaccines to provide immunoprotection against major GI/GII epidemic strains in the future.

Changing Predominance of Norovirus Recombinant Strains GII.2[P16] to GII.4[P16] and GII.4[P31] in Thailand, 2017 to 2018

Human norovirus is a major virus that causes acute gastroenteritis in all age groups. Recently, norovirus recombinant strains have been reported as the cause of norovirus outbreaks. This study has investigated the distribution of norovirus genotypes and recombinant strains circulating in children hospitalized with diarrhea in Chiang Mai, Thailand from 2017 to 2018. A total of 882 stool specimens were tested for the presence of norovirus GI and GII by reverse transcription-PCR (RT-PCR) assay. Genotypes of the viruses were assessed by partial VP1 nucleotide sequencing and the representative strains were further characterized for norovirus recombinant strains by amplification of ORF1 (RdRp)/ORF2 (VP1 capsid) junction region. From a total of 882 stool samples, 131 (14.9%) were positive for norovirus, of which the majority of norovirus genogroups were norovirus GII, and only one was identified as norovirus GI. A wide variety of norovirus genotypes were detected in this study, including GI.5, GII.2, GII.3, GII.4, GII.6, GII.7, GII.13, GII.14, and GII.17 with the predominance of GII.2 (62.5%) in 2017 and GII.4 (57.0%) in 2018. Nevertheless, it should be noted that GII.4 remained the most predominant genotype (50.4%) in overall prevalence. Analysis of norovirus recombination revealed that several norovirus recombinant strains (GII.2[P16], GII.3[P16], GII.4[P16], GII.4[P31], GII.6[P7], GII.13[P16], and GII.14[P7]) had been identified with the predominance of GII.2[P16] in 2017 and changed to GII.4[P16] and GII.4[P31] in 2018. In conclusion, this study reported the detection of a wide variety of norovirus genotypes and several norovirus recombinant strains in Chiang Mai, Thailand from 2017 to 2018.

IMPORTANCE In the present study, the prevalence of norovirus infection in children with acute gastroenteritis in Chiang Mai, Thailand between 2017 and 2018 was 14.9%. A variety of norovirus genotypes were detected, including GI.5, GII.2, GII.3, GII.4, GII.6, GII.7, GII.13, GII.14, and GII.17 with the predominance of GII.4 genotype. In addition, several norovirus recombinant strains (GII.2[P16], GII.3[P16], GII.4[P16], GII.4[P31], GII.6[P7], GII.13[P16], and GII.14[P7]) had been identified. Our results revealed that GII.2[P16] was a predominant strain till the end of 2017 and then was replaced by GII.4[P16] and GII.4[P31] in 2018. The findings imply that norovirus recombinant strains emerged in Chiang Mai, Thailand and that circulating strains changes over time.

Global and regional circulation trends of norovirus genotypes and recombinants, 1995-2019: A comprehensive review of sequences from public databases

Human noroviruses are the leading global cause of viral gastroenteritis. Attempts at developing effective vaccines and treatments against norovirus disease have been stymied by the extreme genetic diversity and rapid geographic distribution of these viruses. The emergence and replacement of predominantly circulating norovirus genotypes has primarily been attributed to mutations on the VP1 capsid protein leading to genetic drift, and more recently to recombination events between the ORF1/ORF2 junction. However, large‐scale research into the historical and geographic distribution of recombinant norovirus strains has been limited in the literature. We performed a comprehensive historical analysis on 30,810 human norovirus sequences submitted to public databases between the years 1995 and 2019. During this time, 37 capsid genotypes and 56 polymerase types were detected across 90 different countries, and 97 unique recombinant genomes were also identified. GII.4, both capsid and polymerase, was the predominately circulating type worldwide for the majority of this time span, save for a brief swell of GII.17 and GII.2 capsid genotypes and a near‐total eclipse by GII.P16, GII.P21 and GII.P31 beginning in 2013. Interestingly, an analysis of 4067 recombinants found that 50.2% (N = 2039) of all recorded sequences belonged to three recently emerged recombinant strains: GII.2[P16], GII.4[P31], and GII.4[P16]. This analysis should provide an important historical foundation for future studies that evaluate the emergence and distribution of noroviruses, as well as the design of cross‐protective vaccines.

Human Norovirus Induces Aquaporin 1 Production by Activating NF-κB Signaling Pathway

Human norovirus (HuNoV) is one of the major pathogens of acute nonbacterial gastroenteritis. Due to the lack of a robust and reproducible in vitro culture system and an appropriate animal model, the mechanism underlying HuNoV-caused diarrhea remains unknown. In the current study, we found that HuNoV transfection induced the expression of aquaporin 1 (AQP1), which was further confirmed in the context of virus infection, whereas the enterovirus EV71 (enterovirus 71) did not have such an effect. We further revealed that VP1, the major capsid protein of HuNoV, was crucial in promoting AQP1 expression. Mechanistically, HuNoV induces AQP1 production through the NF-κB signaling pathway via inducing the expression, phosphorylation and nuclear translocation of p65. By using a model of human intestinal epithelial barrier (IEB), we demonstrated that HuNoV and VP1-mediated enhancement of small molecule permeability is associated with the AQP1 channel. Collectively, we revealed that HuNoV induced the production of AQP1 by activating the NF-κB signaling pathway. The findings in this study provide a basis for further understanding the significance of HuNoV-induced AQP1 expression and the potential mechanism underlying HuNoV-caused diarrhea.

Genetic diversity of norovirus associated with outbreaks in school children with acute gastroenteritis in Changzhou, China, 2018-2019

OBJECTIVE

Norovirus is one of the major causes of outbreaks and sporadic cases of acute gastroenteritis in school children. Obtaining local genotype diversity information regarding norovirus is important for developing and evaluating prevention strategies of the transmission of this virus in school children.

METHODS

Clinical specimens, obtained from the routine acute gastroenteritis surveillance network from 2018 to 2019, were primarily tested using commercial real-time PCR Kit. Samples with Ct value less than 25 were selected and used for complete genome sequencing and those with Ct value between 25 and 30 were selected and used for he partial VP1 and RdRp regions sequencing. Phylogenetic trees of the viral genome were constructed by using the neighbor-joining method with bootstrap analysis of 1,000 replicates in MEGA 6.0 RESULTS: Epidemiological surveillance of acute intestinal infections (n=384) showed high-level detection (73.18%) of human norovirus in school endemic acute gastroenteritis events in Changzhou, with obvious epidemic characteristics in autumn and winter. Through genotyping, it was found that 93.12% of norovirus were GII, including GII.2, GII.3, GII.4, GII.6, GII.7 and GII.17. By October 2019, two norovirus genotypes, GII.4[P31] and GII.17[P17], became the preponderant epidemic strains. Phylogenetic analysis of the new GII.17[P17] complete genomes showed close relationship with Miyagi strain identified in Japan in 2015, and GII.4[P31] showed close relationship with Jinan strain indentified in China in 2017.

CONCLUSION

The study highlights the emerging role of GII.4[P31] and GII.17[P17] in causing endemic acute gastroenteritis outbreaks at school children, in Changzhou, China in 2019. This article is protected by copyright. All rights reserved.

Evolutionary Analyses of Emerging GII.2[P16] and GII.4 Sydney [P16] Noroviruses

GII.2[P16] and GII.4 Sydney [P16] are currently the two predominant norovirus genotypes. This study sought to clarify their evolutionary patterns by analyzing the major capsid VP1 and RNA-dependent RNA polymerase (RdRp) genes. Sequence diversities were analyzed at both nucleotide and amino acid levels. Selective pressures were evaluated with the Hyphy package in different models. Phylogenetic trees were constructed by the maximum likelihood method from full VP1 sequences, and evolutionary rates were estimated by the Bayesian Markov Chain Monte Carlo approach. The results showed that (1) several groups of tightly linked mutations between the RdRp and VP1 genes were detected in the GII.2[P16] and GII.4[P16] noroviruses, and most of these mutations were synonymous, which may lead to a better viral fitness to the host; (2) although the pattern of having new GII.4 variants every 2–4 years has been broken, both the pre- and the post-2015 Sydney VP1 had comparable evolutionary rates to previously epidemic GII.4 variants, and half of the major antigenic sites on GII.4 Sydney had residue substitutions and several caused obvious changes in the carbohydrate-binding surface that may potentially alter the property of the virus; and (3) GII.4 Sydney variants during 2018–21 showed geographical specificity in East Asia, South Asia, and North America; the antigenic sites of GII.2 are strictly conserved, but the GII.2 VP1 chronologically evolved into nine different sublineages over time, with sublineage IX being the most prevalent one since 2018. This study suggested that both VP1 and RdRp of the GII.2[P16] and GII.4 Sydney [P16] noroviruses exhibited different evolutionary directions. GII.4[P16] is likely to generate potential novel epidemic variants by accumulating mutations in the P2 domain, similar to previously epidemic GII.4 variants, while GII.2[P16] has conserved predicted antigenicity and may evolve by changing the properties of nonstructural proteins, such as polymerase replicational fidelity and efficiency. This study expands the understanding of the evolutionary dynamics of GII.2[P16] and GII.4[P16] noroviruses and may predict the emergence of new variants.

Study of Risk Factors for Total Attack Rate and Transmission Dynamics of Norovirus Outbreaks, Jiangsu Province, China, From 2012 to 2018

Objective: To describe the epidemiological characteristics of norovirus outbreaks in Jiangsu Province, utilize the total attack rate (TAR) and transmissibility (R_unc) as the measurement indicators of the outbreak, and a statistical difference in risk factors associated with TAR and transmissibility was compared. Ultimately, this study aimed to provide scientific suggestions to develop the most appropriate prevention and control measures.

Method: We collected epidemiological data from investigation reports of all norovirus outbreaks in Jiangsu Province from 2012 to 2018 and performed epidemiological descriptions, sequenced the genes of the positive specimens collected that were eligible for sequencing, created a database and calculated the TAR, constructed SEIAR and SEIARW transmission dynamic models to calculate R_unc, and performed statistical analyses of risk factors associated with the TAR and R_unc.

Results: We collected a total of 206 reported outbreaks, of which 145 could be used to calculate transmissibility. The mean TAR in was 2.6% and the mean R_unc was 12.2. The epidemiological characteristics of norovirus outbreaks showed an overall increasing trend in the number of norovirus outbreaks from 2012 to 2018; more outbreaks in southern Jiangsu than northern Jiangsu; more outbreaks in urban areas than in rural areas; outbreaks occurred mostly in autumn and winter. Most of the sites where outbreaks occurred were schools, especially primary schools. Interpersonal transmission accounted for the majority. Analysis of the genotypes of noroviruses revealed that the major genotypes of the viruses changed every 3 years, with the GII.2 [P16] type of norovirus dominating from 2016 to 2018. Statistical analysis of TAR associated with risk factors found statistical differences in all risk factors, including time (year, month, season), location (geographic location, type of settlement, type of premises), population (total number of susceptible people at the outbreak site), transmission route, and genotype (P < 0.05). Statistical analysis of transmissibility associated with risk factors revealed that only transmissibility was statistically different between sites.

Conclusions: The number of norovirus outbreaks in Jiangsu Province continues to increase during the follow-up period. Our findings highlight the impact of different factors on norovirus outbreaks and identify the key points of prevention and control in Jiangsu Province.

Aetiological Characteristics of Infectious Diarrhea in Yantai City, Shandong Province, China in 2017

This study aimed to analyse the pathogenic spectrum and epidemiological characteristics of infectious diarrhea in Yantai City, Shandong Province, China and provide a reference for its prevention and control. A total of 713 stool specimens collected within 3 days of diarrhea onset from January to December 2017 at secondary or higher hospitals in Yantai City were tested for 10 causative pathogens, using real-time polymerase chain reaction (RT-PCR). The top two rotaviruses and norovirus were analysed for typing and geographical distribution. The total positive rate was 46.56% (332/713), and 268 of 713 specimens contained at least one pathogen; 64 had at least two pathogens, accounting for 19.28% of the positive specimens (64/332). The positivity rates of rotavirus (RV), norovirus (NoVs) GI, norovirus (NoVs) GII, enterovirus universal (EV), enteric adenoviruses (EAdV), sapovirus (SaV), astrovirus (Astv), Salmonella (SE), Listeria monocytogenes (LiMo), and Vibrio parahaemolyticus (VP) were 20.06% (143/713), 1.82% (13/713), 12.84% (89/713), 10.66% (76/713), 4.07% (29/713), 0.42% (3/713), 2.38% (17/713), 1.54% (11/713), 1.82% (13/713), and 1.54% (11/713), respectively. Infectious diarrhea showed a high prevalence in young children aged 1-5 years, accounting for 48.6% of the total number of cases. Bacterial diarrhea was predominant in summer, and viral diarrhea was distributed throughout the year, without a significant seasonal pattern. Rotavirus is dominated by G9P, accounting for 81.82%, while norovirus is dominated by the GII type and has diverse characteristics. The aetiology of infectious diarrhea in Yantai is mainly viral, with RV, NoVs, EV, EAdV, and Astv being the most frequent pathogens. Continuous surveillance of infectious diarrhea diseases can help us understand its epidemiological and pathogenic characteristics, thereby taking targeted preventive and control measures in different seasons.

Understanding the relationship between norovirus diversity and immunity

Human noroviruses are the most common viral cause of acute gastroenteritis worldwide. Currently, there are no approved vaccines or specific therapeutics to treat the disease. Some obstacles delaying the development of a norovirus vaccine are: (i) the extreme diversity presented by noroviruses; (ii) our incomplete understanding of immunity to noroviruses; and (iii) the lack of a robust cell culture system or animal model for human noroviruses. Recent advances in in vitro cultivation of norovirus, novel approaches applied to viral genomics and immunity, and completion of vaccine trials and birth cohort studies have provided new information toward a better understanding of norovirus immunity. Here, we will discuss the complex relationship between norovirus diversity and correlates of protection for human noroviruses, and how this information could be used to guide the development of cross-protective vaccines.

What is the Potential Cause for the Predominance of GII.2[P16] Norovirus in Acute Gastroenteritis Outbreaks in China?

GII.2[P16] noroviruses (NoV) reemerged and rapidly became the main epidemic strain in acute gastroenteritis (AGE) outbreaks in Asian countries since 2016. The current GII.2 [P16] NoV showed the same antigenicity to the ones before 2016, but several unique amino acid substitutions existed in the RNA dependent RNA polymerase (RdRp) and other non-structural proteins, and the viral load of the current GII.2[P16] NoV was higher than those of other genotypes, it was estimated that the viral replication ability may have improved. However, other genotypes, such as GII.1 and GII.3, also had recombination with the novel RdRp, were not prevalent in AGE-outbreaks; thus, it was inferred that the capsid proteins also played an important role in the enhanced replication process. The viral infection could also be affected by other factors, such as the population genetic background, the climate and environment, and people’s lifestyles. Continued surveillance on genetic diversity and evolutionary pattern for the GII.2[P16] NoV is necessary.

Epidemiological characteristics and genetic diversity of norovirus infections among outpatient children with diarrhea under 5 years of age in Beijing, China, 2011-2018

Background

Human noroviruses are the leading cause of sporadic cases and outbreaks of viral acute gastroenteritis in all age groups worldwide.

Methods

Epidemiological data and fecal specimens were collected between January 2011 and December 2018 from 4911 children < 5 years of age with diarrhea in three districts of Beijing. From 2011 to 2013, One-Step Reverse Transcription Polymerase Chain Reaction (RT-PCR) was used to detect noroviruses, and from January 2014 to December 2018, norovirus GI and GII were screened using duplex quantitative real-time RT-PCR (qRT-PCR). One-Step RT-PCR and RT-seminested PCR were performed to amplify the RNA-dependent polymerase and capsid genes of noroviruses in positive sample. Amplified products were sequenced directly; norovirus was typed using the online Norovirus Genotyping Tool v2.0 and phylogenetic analyses were conducted using MEGA-X.

Results

From 2011 to 2018, noroviruses were detected in 16.5% of specimens from children with diarrhea. The highest prevalence was observed in children aged 12 to 23 months (22.4%, 319/1421), followed by children aged 6 to 11 months (17.6%, 253/1441). The highest prevalence of norovirus infections occurred in autumn followed by winter, spring, and summer. From 2011 to 2018, the most prevalent dual types (genotype and polymerase type) were GII.4 Sydney[P31] (51.6%, 239/463), followed by GII.3[P12] (24.0%, 111/463), GII.4 2006b[P4 2006b] (7.3%, 34/463), GII.2[P16] (5.0%, 23/463), GII.17[P17] (2.6%, 12/463) and GII.6[P7] (2.6%, 12/463). GII.4 2006b[P4 2006b] predominated in 2011 and 2012. GII.4 Sydney[P31] predominated from 2013 to 2018. In total, 15 genotypes, 15 P-types and 19 dual types were detected in this study, reflecting the genetic diversity.

Conclusions

There were significant epidemiological characteristics and genetic diversity among outpatient children with norovirus infections < 5 years of age in Beijing from 2011 to 2018. These characteristics differ from those of norovirus outbreaks in Beijing. The complete genome sequences of each genotype are needed to better understand norovirus evolutionary mechanisms.

GII.P16-GII.2 Recombinant Norovirus VLPs Polarize Macrophages Into the M1 Phenotype for Th1 Immune Responses

Norovirus (NoV) is a zoonotic virus that causes diarrhea in humans and animals. Outbreaks in nosocomial settings occur annually worldwide, endangering public health and causing serious social and economic burdens. The latter quarter of 2016 witnessed the emergence of the GII.P16-GII.2 recombinant norovirus throughout Asia. This genotype exhibits strong infectivity and replication characteristics, proposing its potential to initiate a pandemic. There is no vaccine against GII.P16-GII.2 recombinant norovirus, so it is necessary to design a preventive vaccine. In this study, GII.P16-GII.2 type norovirus virus-like particles (VLPs) were constructed using the baculovirus expression system and used to conduct immunizations in mice. After immunization of mice, mice were induced to produce memory T cells and specific antibodies, indicating that the VLPs induced specific cellular and humoral immune responses. Further experiments were then initiated to understand the underlying mechanisms involved in antigen presentation. Towards this, we established co-cultures between dendritic cells (DCs) or macrophages (Mø) and naïve CD4+T cells and simulated the antigen presentation process by incubation with VLPs. Thereafter, we detected changes in cell surface molecules, cytokines and related proteins. The results indicated that VLPs effectively promoted the phenotypic maturation of Mø but not DCs, as indicated by significant changes in the expression of MHC-II, costimulatory factors and related cytokines in Mø. Moreover, we found VLPs caused Mø to polarize to the M1 type and release inflammatory cytokines, thereby inducing naïve CD4+ T cells to perform Th1 immune responses. Therefore, this study reveals the mechanism of antigen presentation involving GII.P16-GII.2 recombinant norovirus VLPs, providing a theoretical basis for both understanding responses to norovirus infection as well as opportunities for vaccine development.

Norovirus Foodborne Outbreak Associated With the Consumption of Ice Pop, Southern Brazil, 2020

Norovirus is a major cause of foodborne-associated acute gastroenteritis (AGE) outbreaks worldwide. Usually, food products are contaminated either during harvesting or preparation, and the most common products associated to norovirus outbreaks are raw or undercooked bivalve shellfish, fruits (frozen berries) and ready-to-eat produce. In the present study, we investigated an AGE outbreak caused by norovirus associated with the consumption of ice pops in southern Brazil. Clinical stool samples from patients and ice pops samples were collected and analyzed for viruses' detection. By using RT-qPCR and sequencing, we detected the uncommon genotype GII.12[P16] in clinical samples and GII.12 in samples of ice pop. Strains shared identity of 100% at nucleotide level strongly suggesting the consumption of ice pops as the source of the outbreak.

Epidemiology and evolution of Norovirus in China

Norovirus (NoV) has been recognized as a leading cause of gastroenteritis worldwide. This review estimates the prevalence and genotype distribution of NoV in China to provide a sound reference for vaccine development. Studies were searched up to October 2020 from CNKI database and inclusion criteria were study duration of at least one calendar year and population size of >100. The mean overall NoV prevalence in individuals with sporadic diarrhea/gastroenteritis was 16.68% (20796/124649, 95% CI 16.63-16.72), and the detection rate of NoV was the highest among children. Non-GII.4 strains have replaced GII.4 as the predominant caused multiple outbreaks since 2014. Especially the recombinant GII.P16-GII.2 increased sharply, and virologic data show that the polymerase GII.P16 rather than VP1 triggers pandemic. Due to genetic diversity and rapid evolution, predominant genotypes might change unexpectedly, which has become major obstacle for the development of effective NoV vaccines.

Prevalence of GII.4 Sydney Norovirus Strains and Associated Factors of Acute Gastroenteritis in Children: 2019/2020 Season in Guangzhou, China

Norovirus, the leading cause of non-bacterial acute gastroenteritis (AGE) worldwide, is constantly mutating. Continuous monitoring of the evolution of epidemic genotypes and emergence of novel genotypes is, therefore, necessary. This study determined the prevalence and clinical characteristics of norovirus strains in AGE in Guangzhou, China in 2019/2020 season. This study included children aged 2-60 months diagnosed with AGE in Guangzhou Women and Children Hospital, from August 2019 to January 2020. Norovirus was detected by real-time polymerase chain reaction and clinical data were obtained. Genotyping and phylogenetic analyses were performed with partial gene sequence fragments located within the open reading frames 1 and 2. During the study period, 168 children (61.3% males) were confirmed as norovirus infectious AGE. The main symptoms were diarrhoea and vomiting and 38 patients (22.6%) had seizures. Norovirus was mainly prevalent in October and November, and GII.4 Sydney[P31] was the major genotype circulating in Guangzhou. The phylogenetic tree showed that the Guangzhou strains had high homology with the strains circulating in 2017-2019 worldwide. GII.4 Sydney was the main prevalent norovirus genotype in Guangzhou from August 2019 to January 2020, which had more severe diarrhoea than those of other genotypes. These findings provide a valuable reference for the prevention, control, and treatment of norovirus in the future.

Genome-wide analyses of human noroviruses provide insights on evolutionary dynamics and evidence of coexisting viral populations evolving under recombination constraints

Norovirus is a major cause of acute gastroenteritis worldwide. Over 30 different genotypes, mostly from genogroup I (GI) and II (GII), have been shown to infect humans. Despite three decades of genome sequencing, our understanding of the role of genomic diversification across continents and time is incomplete. To close the spatiotemporal gap of genomic information of human noroviruses, we conducted a large-scale genome-wide analyses that included the nearly full-length sequencing of 281 archival viruses circulating since the 1970s in over 10 countries from four continents, with a major emphasis on norovirus genotypes that are currently underrepresented in public genome databases. We provided new genome information for 24 distinct genotypes, including the oldest genome information from 12 norovirus genotypes. Analyses of this new genomic information, together with those publicly available, showed that (i) noroviruses evolve at similar rates across genomic regions and genotypes; (ii) emerging viruses evolved from transiently-circulating intermediate viruses; (iii) diversifying selection on the VP1 protein was recorded in genotypes with multiple variants; (iv) non-structural proteins showed a similar branching on their phylogenetic trees; and (v) contrary to the current understanding, there are restrictions on the ability to recombine different genomic regions, which results in co-circulating populations of viruses evolving independently in human communities. This study provides a comprehensive genetic analysis of diverse norovirus genotypes and the role of non-structural proteins on viral diversification, shedding new light on the mechanisms of norovirus evolution and transmission.

Norovirus is a highly diverse enteric pathogen. The large genomic database accumulated in the last three decades advanced our understanding of norovirus diversity; however, this information is limited by geographical bias, sporadic times of collection, and missing or incomplete genome sequences. In this multinational collaborative study, we mined archival samples collected since the 1970s and sequenced nearly full-length new genomes from 281 historical noroviruses, including the first full-length genomic sequences for three genotypes. Using this novel dataset, we found evidence for restrictions in the recombination of genetically disparate viruses and that diversifying selection results in new variants with different epidemiological profiles. These new insights on the diversification of noroviruses could provide baseline information for the study of future epidemics and ultimately the prevention of norovirus infections.

Molecular Evolution of Human Norovirus GII.2 Clusters

Background

The human norovirus GII.2 outbreak during the 2016–2017 winter season was of unprecedented scale and geographic distribution.

Methods

We analyzed 519 complete VP1 gene sequences of the human norovirus GII.2 genotype sampled during the 2016–2017 winter season, as well as prior (dating back to 1976) from 7 countries. Phylodynamic analyses of these sequences were performed using maximum likelihood and Bayesian statistical frameworks in order to estimate viral evolutionary and population dynamics associated with the outbreak.

Results

Our results revealed an increase in the genetic diversity of human norovirus GII.2 during the recent Asian outbreak and diversification was characterized by at least eight distinct clusters. Bayesian estimation of viral population dynamics revealed a highly fluctuating effective population size, increasing in frequency during the past 15 years.

Conclusion

Despite an increasing viral diversity, we found no evidence of an elevated evolutionary rate or significant selection pressure in human norovirus GII.2, indicating viral evolutionary adaptation was not responsible for the volatility of or spread of the virus during this time.

Norovirus Outbreak Surveillance, China, 2016-2018

CaliciNet China, a network of provincial, county, and city laboratories coordinated by the Chinese Centers for Disease Control and Prevention, was launched in October 2016 to monitor the epidemiology and genotype distribution of norovirus outbreaks in China. During October 2016–September 2018, a total of 556 norovirus outbreaks were reported, and positive fecal samples from 470 (84.5%) outbreaks were genotyped. Most of these outbreaks were associated with person-to-person transmission (95.1%), occurred in childcare centers or schools (78.2%), and were reported during November–March of each year (63.5%). During the 2-year study period, 81.2% of all norovirus outbreaks were typed as GII.2[P16]. In China, most norovirus outbreaks are reported by childcare centers or schools; GII.2[P16] is the predominant genotype. Ongoing surveillance by CaliciNet China will provide information about the evolving norovirus genotype distribution and outbreak characteristics important for the development of effective interventions, including vaccines.

Serological surveillance of noroviruses in a community-based prospective cohort: a study protocol

INTRODUCTION

Noroviruses are the leading cause of viral acute gastroenteritis affecting all age groups. Since 2014, the previous rarely reported GII.P17-GII.17 and recombinant GII.P16-GII.2 norovirus emerged, replacing GII.4 predominant genotype, causing increased outbreaks in China and other countries. Meanwhile, GII.4/2012 Sydney strain has re-emerged as the dominant variant in many places in 2015-2018. The role of herd immunity as the driving force during these new emerging or re-emerging noroviruses is poorly defined. Serological surveillance studies on community-based prospective cohort on norovirus are highly needed.

METHODS AND ANALYSES

This study will include 1000 out of 9798 participants aged 18 years and above from Caofeidian district, Tangshan city, northern China. Baseline data on sociodemographic characteristics and blood samples were collected in 2013-2014. Blood collection will be replicated annually throughout the cohort until 2023. Saliva samples were also collected in 2016. The seroprevalence and seroincidence of blockade antibodies against norovirus genotypes of GII.P17-GII.17, GII.P16-GII.2, the re-emerged GII.4/2012 and potential novel pandemic variants will be evaluated by ELISA. Associations between genotype blockade antibodies and sociodemographic factors and human histo-blood group antigens will be evaluated using univariate and multivariate analysis. The dynamics of herd immunity duration will be estimated in this longitudinal surveillance.

ETHICS AND DISSEMINATION

The study has been approved by the Ethical Committees of the Staff Hospital of Jidong oil-field of China National Petroleum Corporation. This study will provide insight into the seroprevalence and seroincidence of noroviruses, and their relationships with sociodemographic characteristics and genetic susceptibility. It will also explain herd immunity of the emerged and re-emerged genotypes or variants. The study will further enable an understanding of the mechanism driving the replacement of norovirus genotypes. Research findings will be disseminated in peer-reviewed journals and at scientific meetings.

Epidemiology of norovirus gastroenteritis in hospitalized children under five years old in western China, 2015-2019

OBJECTIVES

Norovirus is associated with one-fifth of all gastroenteritis cases, but basic epidemiological data is lacking, especially in developing countries. As long-term surveillance on norovirus gastroenteritis is scarce in western China, this study aims to update the epidemiological knowledge of norovirus gastroenteritis and to characterize the genotypes of norovirus strains.

METHODS

Stool samples were collected from hospitalized children under 5 years old with gastroenteritis in Chengdu, China. All samples were tested for norovirus as well as rotavirus, sapovirus, enteric adenovirus, and astrovirus by real-time RT-PCR. RdRp and VP1 genes were sequenced in norovirus-positive samples to investigate viral phylogenies.

RESULTS

Of the 1181 samples collected from 2015 to 2019, 242 (20.5%) were positive for norovirus. Among norovirus-positive cases, 65 cases had co-infection with another virus; norovirus/enteric adenovirus was most frequently detected (50.8%, 33/65). The highest positive rate was observed in children aged 13-18 months (23.7%, 68/287). Norovirus infection peaked in autumn (36.6%, 91/249), followed by summer (20.3%, 70/345). Pearson correlation analysis showed significant correlation between the norovirus-positive rate and humidity (r = 0.773, P < 0.05). GII.4 Sydney 2012 [P31] (48.5%, 79/163) and GII.3 [P12] (35.6%, 58/163) were the dominant norovirus strains.

CONCLUSIONS

Norovirus has become one of the most common causes of viral gastroenteritis in children under 5 years old in western China. Continuous monitoring is imperative for predicting the emergence of new epidemic strains and for current vaccine development.

Molecular epidemiology and genetic diversity of norovirus infection in children hospitalized with acute gastroenteritis in East Java, Indonesia in 2015-2019

Noroviruses are recognized as a leading cause of outbreaks and sporadic cases of acute gastroenteritis (AGE) among individuals of all ages worldwide, especially in children <5 years old. We investigated the epidemiology of noroviruses among hospitalized children at two hospitals in East Java, Indonesia. Stool samples were collected from 966 children with AGE during September 2015-July 2019. All samples were analyzed by reverse transcription-polymerase chain reaction (RT-PCR) for the amplification of both the RNA-dependent RNA polymerase (RdRp) and the capsid genes of noroviruses. The genotypes were determined by phylogenetic analyses. In 2015-2019, noroviruses were detected in 12.3% (119/966) of the samples. Children <2 years old showed a significantly higher prevalence than those ≥2 years old (P = 0.01). NoV infections were observed throughout the year, with the highest prevalence in December. Based on our genetic analyses of RdRp, GII.[P31] (43.7%, 31/71) was the most prevalent RdRp genotype, followed by GII.[P16] (36.6%, 26/71). GII.[P31] was a dominant genotype in 2016 and 2018, whereas GII.[P16] was a dominant genotype in 2015 and 2017. Among the capsid genotypes, the most predominant norovirus genotype from 2015 to 2018 was GII.4 Sydney_2012 (33.6%, 40/119). The most prevalent genotype in each year was GII.13 in 2015, GII.4 Sydney_2012 in 2016 and 2018, and GII.3 in 2017. Based on the genetic analyses of RdRp and capsid sequences, the strains were clustered into 13 RdRp/capsid genotypes; 12 of them were discordant, e.g., GII.4 Sydney[P31], GII.3[P16], and GII.13[P16]. The predominant genotype in each year was GII.13[P16] in 2015, GII.4 Sydney[P31] in 2016, GII.3[P16] in 2017, and GII.4 Sydney[P31] in 2018. Our results demonstrate high detection rates and genetic diversity of norovirus GII genotypes in pediatric AGE samples from Indonesia. These findings strengthen the importance of the continuous molecular surveillance of emerging norovirus strains.

Molecular epidemiology and changes in genotype diversity of norovirus infections in acute gastroenteritis patients in Huzhou, China, 2018

Norovirus is an important causative agent of acute gastroenteritis worldwide, affecting people of all ages. Stool samples collected from patients with clinical symptoms of acute gastroenteritis in all age groups at the diarrhea outpatient department of the First People's Hospital in Huzhou were analyzed to gain insight into the prevalence and genetic characteristics of norovirus. From January to December 2018, a total of 551 specimens were screened for norovirus by real-time reverse transcription-polymerase chain reaction (RT-PCR). RT-PCR was used for genomic amplification and sequencing of the RNA-dependent RNA polymerase and capsid gene of the positive samples. Genotypes of norovirus were assigned using the norovirus Noronet typing tool and phylogenetic analysis. About 100 (18.1%) specimens were identified as norovirus positive. GII genogroup was the main genogroup identified (83.0%; 83/100). About 42 (42.0%) samples were successfully sequenced and genotyped by RT-PCR. Since one of the samples was dual infection, so we got 43 virus finally. Nine norovirus GII genotypes and four norovirus GI genotypes were detected in Huzhou during our research period. The main two norovirus GII genotypes were GII.2[P16] (54.8%; 23/43) and GII.17[P17] (11.9%; 5/43). We characterized the molecular epidemiology of norovirus infection in acute gastroenteritis patients during 2018. GII genogroup was the main genogroup identified. The dominance norovirus genotype circulating in the population of Huzhou was GII.2[P16] in 2018.

Differences in Illness Severity among Circulating Norovirus Genotypes in a Large Pediatric Cohort with Acute Gastroenteritis

Norovirus is a major pathogen identified in children with acute gastroenteritis (AGE), little is known about the strain's diversity and their clinical severity. Stool and/or rectal swabs were collected from children ≤18 years of age recruited at emergency departments (ED), and a provincial nursing advice phone line due to AGE symptoms in the province of Alberta, Canada between December 2014 and August 2018. Specimens were tested using a reverse transcription real time PCR and genotyped by Sanger sequencing. The Modified Vesikari Scale score (MVS) was used to evaluate the disease severity. The objectives are to identify the Genogroup and Genotype distribution and to compare illness severity between the GI and GII genogroups and to complete further analyses comparing the GII genotypes identified. GII.4 was the genotype most commonly identified. Children with GII.4 had higher MVS scores (12.0 (10.0, 14.0; p = 0.002)) and more prolonged diarrheal (5 days (3.0, 7.8)) and vomiting (3.2 days (1.7, 5.3; p < 0.001)) durations compared to other non GII.4 strains. The predominant strain varied by year with GII.4 Sydney[P31] predominant in 2014/15, GII.4 Sydney[P16] in 2015/16 and 2017/18, and GII.3[P12] in 2016/17. Genogroup II norovirus strains predominated in children with AGE with variance between years; clinical severity associated with different strains varied with episodes being most severe among GII.4 infected children.

Human norovirus detection in bivalve shellfish in Brazil and evaluation of viral infectivity using PMA treatment

Noroviruses are the most common cause of gastroenteritis outbreaks in humans and bivalve shellfish consumption is a recognized route of infection. Our aim was to detect and characterize norovirus in bivalves from a coastal city of Brazil. Nucleic acid was extracted from the bivalve's digestive tissue concentrates using magnetic beads. From March 2018 to June 2019, 77 samples were screened using quantitative RT-PCR. Noroviruses were detected in 41.5%, with the GII being the most prevalent (37.7%). The highest viral load was 3.5 × 106 and 2.5 × 105 GC/g in oysters and mussels, respectively. PMA-treatment demonstrated that a large fraction of the detected norovirus corresponded to non-infectious particles. Genetic characterization showed the circulation of the GII.2[P16] and GII.4[P4] genotypes. Norovirus detection in bivalves reflects the anthropogenic impact on marine environment and serves as an early warning for the food-borne disease outbreaks resulting from the consumption of contaminated molluscs.

Rapid detection of norovirus genogroup II in clinical and environmental samples using recombinase polymerase amplification

Norovirus is the leading cause of acute gastroenteritis all over the world, and the most genotype that causes its epidemic is norovirus genogroup II (NoVs GII). Rapid detection of NoVs is important because it can facilitate timely diagnosis. In this study, we designed universal specific primers and an Exo probe to hybridize to all genetic clusters of NoVs GII based on the conserved region at the ORF1-ORF2 junction of the genome. For the first time, we established a rapid and reliable reverse transcription recombinase polymerase amplification (RT-RPA) method for the detection of NoVs GII within 20 min. This method can specifically amplify NoVs GII, and the detection limit was as low as 1.66 × 10² copies/μL. The method was validated in terms of LOD, accuracy, and specificity. We tested 55 real samples including foods, water, and feces. The results showed a sensitivity of 96% and specificity of 100% to NoVs GII. The whole procedure can be operated by a mobile suitcase laboratory, which is useful for resource-limited diagnostic laboratories. This novel real-time RT-RPA assay is an accurate tool for point-of-care testing of NoVs, providing practical support for norovirus-caused disease diagnosis and prevention.

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

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

An increasing prevalence of non-GII.4 norovirus genotypes in acute gastroenteritis outbreaks in Huzhou, China, 2014-2018

Since 2014, novel non-GII.4 norovirus (NoV) genotypes continue to be reported as the main cause of outbreaks worldwide. In this study, we analyzed the epidemiological and genetic features of NoV outbreaks from July 2014 to June 2018 in Huzhou, China. A total of 450 stool samples collected from 51 AGE outbreaks were tested for NoVs by real-time RT PCR. Partial polymerase and capsid sequences of NoV-positive samples were amplified and sequenced for phylogenetic analysis. NoVs were found to be responsible of 84.3% of AGE outbreaks in Huzhou over the past 5 years. Most NoV outbreaks were reported in the cool months (November-March) and occurred in primary schools and kindergartens. Changes in the diversity of genotypes and the distribution of predominant types were observed in recent years. At least eight genotypes were identified, and 91.9% of the genotyped outbreaks were caused by non-GII.4 strains. The top three circulating genotypes during the study period were GII.2[P16], GII.3[P12], and GII.17[P17]. The predominant NoV genotypes in outbreaks have changed from GII.4 variants to GII.17[P17] in 2014-2015, GII.3[P12] in 2015-2016, and then GII.2[P16] in 2016-2018. Non-GII.4 NoVs play an increasingly important role in outbreaks in Huzhou. Continuous surveillance is needed to monitor the emergence of novel NoV strains and help control NoV outbreaks in the next epidemic season.

Genotype-Specific Neutralization of Norovirus Is Mediated by Antibodies Against the Protruding Domain of the Major Capsid Protein

Human noroviruses are the most common viral agents of acute gastroenteritis. Recently, human intestinal enteroids were shown to be permissive for norovirus infection. We tested their suitability as a system to study norovirus neutralization. Hyperimmune sera raised against virus-like particles (VLPs) representing different genotypes showed highly specific neutralization activity against GII.4 and GII.6 noroviruses. Carbohydrate blocking assays and neutralization exhibited similar patterns in antibody responses. Notably, sera produced against chimeric VLPs that presented swapped structural shell and protruding (P) domains, from different genotypes showed that neutralization is primarily mediated by antibodies mapping to the P domain of the norovirus capsid protein. This study provides empirical information on the antigenic differences among genotypes as measured by neutralization, which could guide vaccine design.

Molecular Epidemiology of GI.3 Norovirus Outbreaks from Acute Gastroenteritis Surveillance System in Taiwan, 2015-2019

Norovirus is the leading cause of food-borne disease outbreaks. We conducted this study to examine the incidence and molecular characteristics of norovirus genogroup I infections from acute gastroenteritis outbreaks in Taiwan. Between January 2015 and June 2019, 2121 acute gastroenteritis clusters were reported to Taiwan CDC, of which 351 (16.5%) clusters were positive for NoV GI, and GI.3 was the most prevalent (36.8%) during the study period. The GI.3 infections were significantly higher than non-GI.3 infections in the age groups of 0-5 and 6-18 years. The phylogenetic analysis of the MCC tree revealed that VP1 genes were divided into 3 groups: the GI.P3-GI.3 strains in Taiwan were genetically close to Japan and the GI.Pd-GI.3 strains were segregated into 2 other groups which were genetically closely related to China. In addition, 7 GI.Pd-GI.3 recombinants were identified circulating in Taiwan between 2018 and 2019, and the prevalence of GI.Pd-GI.3 should be monitored to assess whether this could become the new predominant strains in neighboring Asian countries or other parts of the world. Both GI.P3-GI.3 and GI.Pd-GI.3 strains cocirculate, the recombination among these two lineages occurs frequently, contributing to the genetic diversity and multiple occurrences of different norovirus lineages, and their rapid evolution makes future control more difficult. Continued surveillance and timely interventions are critical to understand the complexity of norovirus gene variation and to monitor the new emerging norovirus strains.