Molecular Epidemiological Characteristics of Gastroenteritis Outbreaks Caused by Norovirus GII.4 Sydney [P31] Strains - China, October 2016-December 2020

Epidemics and diversity of norovirus variants with acute gastroenteritis outbreak in Hongshan District, Wuhan City, China, 2021-2023

BACKGROUND

Norovirus is the predominant pathogen causing foodborne illnesses and acute gastroenteritis (AGE) outbreaks worldwide, imposing a significant disease burden. This study aimed to investigate the epidemiological characteristics and genotypic diversity of norovirus outbreaks in Hongshan District, Wuhan City.

METHODS

A total of 463 AGE cases from 39 AGE-related outbreaks in Hongshan District between January 1, 2021, and June 30, 2023, were included in the study. Reverse transcription-polymerase chain reaction (RT-PCR) was used to identify norovirus types GI and GII in anal swab samples from all cases. Norovirus-positive samples were sequenced and analyzed for the open reading frame (ORF) 1/ORF2 hinge region.

RESULTS

26 norovirus infectious outbreaks were reported among 39 acute diarrheal outbreaks, including 14 outbreaks in kindergartens, 8 in elementary schools, and 4 in universities. Based on clinical symptoms and epidemiological investigations, a total of 1295 individuals were identified as having been exposed to norovirus, yielding an attack rate of 35.75 %. A higher proportion of outbreaks was observed during the winter and spring seasons (38.46 %). Additionally, norovirus-positive samples were subjected to sequencing and analysis of the open reading frame (ORF) 1/ORF2 hinge region. Genotypic data for norovirus was successfully obtained from 18 (69.23 %) of the infectious outbreaks, revealing 10 distinct recombinant genotypes. GII.4 Sydney 2012 [P31] and GII.17[P17] were the predominant strains in 2021 and 2022, GII.3 [P12] emerged as the dominant strain in 2023.

CONCLUSION

Norovirus outbreaks in Hongshan District predominantly occurred in crowded educational institutions, with peaks in the cold season and a high attack rate in universities. GII.3 [P12] has become the locally predominant strain.

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.

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.

Prevalence of Human Norovirus GII.4 Sydney 2012 [P31] between 2019 and 2021 among Young Children from Rural Communities in South Africa

Acute gastroenteritis (AGE) accounts for considerable morbidity and mortality in the paediatric population worldwide, especially in low-income countries. Human norovirus (HNoV), particularly GII.4 strains, are important agents of AGE. This study aimed to detect and characterise HNoV in children with and without AGE. Between 2019 and 2021, 300 stool samples (200 AGE and 100 without AGE) were collected from children below 5 years of age referred to the healthcare facilities of the rural communities of Vhembe District, South Africa. After detection using real-time RT-PCR, HNoV positive samples were subjected to RT-PCR and Sanger sequencing. Partial nucleotide sequences (capsid/RdRp) were aligned using the Muscle tool, and phylogenetic analysis was performed using MEGA 11. The nucleotides' percent identity among HNoV strains was compared using ClustalW software. A significant difference in HNoV prevalence between AGE children (37%; 74/200) and non-AGE (14%; 14/100) was confirmed (p < 0.0001). Genogroup II (GII) HNoV was predominant in AGE children (80%; 59/74), whereas most non-AGE children were infected by the GI norovirus genogroup (64%; 9/14). GII.4 Sydney 2012 [P31] strains were dominant (59%; 19/32) during the study period. A phylogenetic analysis revealed a close relationship between the HNoV strains identified in this study and those circulating worldwide; however, ClustalW showed less than 50% nucleotide similarity between strains from this study and those from previously reported norovirus studies in the same region. Our findings indicate significant changes over time in the circulation of HNoV strains, as well as the association between high HNoV prevalence and AGE symptoms within the study area. The monitoring of HuNoV epidemiology, along with stringent preventive measures to mitigate the viral spread and the burden of AGE, are warranted.

Molecular epidemiology analysis of symptomatic and asymptomatic norovirus infections in Chinese infants

BACKGROUND

Norovirus is a leading cause of acute gastroenteritis among children. Previous studies based on symptomatic infections indicated that mutations, rather than recombination drove the evolution of the norovirus ORF2. These characteristics were found in hospital-based symptomatic infections, whereas, asymptomatic infections are frequent and contribute significantly to transmission.

METHODS

We conducted the first norovirus molecular epidemiology analysis covering both symptomatic and asymptomatic infections derived from a birth cohort study in the northern China.

RESULTS

During the study, 14 symptomatic and 20 asymptomatic norovirus infections were detected in 32 infants. Out of the 14 strains that caused symptomatic infections, 12 strains were identified as GII.3[P12], and others were GII.4[P31]. Conversely, 17 asymptomatic infections were caused by GII.4[P31], two by GII.2[P16], and one by GII.4[P16]. Regardless of symptomatic and asymptomatic infections, the mutations were detected frequently in the ORF2 region, and almost all recombination were identified in the RdRp-ORF2 region. The majority of the mutations were located around the predefined epitope regions of P2 subdomain indicating a potential for immune evasion.

CONCLUSION

The role of symptomatic as well as asymptomatic infections in the evolution of norovirus needs to be evaluated continuously.