Molecular Epidemiology and Genetic Diversity of Norovirus in Young Children in Phnom Penh, Cambodia

Global prevalence and genotype distribution of norovirus infection in children with gastroenteritis: A meta-analysis on 6 years of research from 2015 to 2020

In the post rotavirus vaccine era, norovirus (NoV) plays an increasingly important role in epidemic and sporadic gastroenteritis among children. This study was designed to provide an updated meta-analytic review of the prevalence of NoV among paediatric patients with gastroenteritis and to clarify the relationship between NoV infection and gastroenteritis. Systematic searches of the literature for potentially relevant studies were carried out from 1 January 2015 to 29 May 2020. The inverse variance method was chosen for weighting of the studies, and the random-effects model was used to analyse data. To determine the association between NoV infection and gastroenteritis in children, pooled odds ratio (OR) and its 95% confidence interval (CI) were computed for case-control studies. The pooled prevalence of NoV infection among 12,0531 children with gastroenteritis from 45 countries across the world was 17.7% (95% CI: 16.3%-19.2%). There were 28 studies with a case-control design, and the pooled prevalence of NoV infection among 11,954 control subjects was 6.7% (95% CI: 5.1%-8.8%). The pooled OR of the association of NoV infection and gastroenteritis was 2.7 (95% CI: 2.2-3.4). The most common NoV genotypes were GII.4 (59.3%) and GII.3 (14.9%). The highest frequency of NoV was found in the age group below 1 year. Our findings indicated a substantial burden of gastroenteritis caused by NoV globally, with GII.4 and GII.3 the major genotypes responsible for the majority of NoV-associated gastroenteritis cases among children. Younger age and male sex can be considered risk factors for NoV-associated gastroenteritis among children.

Identification of GII.14[P7] norovirus and its genomic mutations from a case of long-term infection in a post-symptomatic individual

Norovirus is a leading cause of acute gastroenteritis worldwide. Norovirus shedding typically lasts one week to one month after the onset of diarrhea in immunocompetent hosts. The occurrence of mutations in the genome during infection has contributed to the evolution of norovirus. It has been suggested that genomic mutations in the P2-domain of capsid protein VP1, the major antigenic site for virus clearance, are involved in the evasion of host immunity and prolonged shedding of norovirus. In our previous study, we found a case of long-term shedding of GII.14 norovirus in a post-symptomatic immunocompetent individual that lasted about three months. In this study, we characterized the genomic sequence of the GII.14 strain to gain insight into the context of long-term shedding. By sequencing a 4.8 kb region of the genome corresponding to half of ORF1 and the entire ORF2 and ORF3, which encode several non-structural proteins and the structural proteins VP1 and VP2, the GII.14 strain was found to be classified as recombinant GII.14[P7]. Six point-mutations occurred during the three-month period of infection in a time-dependent manner in the genomic regions encoding RNA-dependent RNA polymerase, VP1, and VP2. Three of the six mutations were sense mutations, but no amino acid substitution was identified in the P2-domain of VP1. These results suggest that there is a mechanism by which long-term shedding of norovirus occurs in immunocompetent individuals independent of P2-domain mutations.

Genetic Diversity Among Genogroup II Noroviruses and Progressive Emergence of GII.17 in Wastewaters in Italy (2011-2016) Revealed by Next-Generation and Sanger Sequencing

Noroviruses (NoV) are a major cause of gastroenteritis worldwide. Recently, a novel variant of NoV GII.17 (GII.P17_GII.17 NoV), termed Kawasaki 2014, has been increasingly reported in NoV outbreaks in Asia, and has also been described in Europe and North America. In this study, sewage samples were investigated to study the occurrence and genetic diversity of NoV genogroup II (GII) along a 6-year period. Moreover, the spread of GII.17 strains (first appearance and occurrence along time) was specifically assessed. A total of 122 sewage samples collected from 2011 to 2016 from four wastewater treatment plants in Rome (Italy) were initially tested using real-time RT-(q)PCR for GII NoV. Positive samples were subsequently subjected to genotypic characterization by RT-nested PCRs using broad-range primes targeting the region C of the capsid gene of GII NoV, and specific primers targeting the same region of GII.17 NoV. In total, eight different genotypes were detected with the broad-range assay: GII.1 (n = 6), GII.2 (n = 8), GII.3 (n = 3), GII.4 (n = 13), GII.6 (n = 3), GII.7 (n = 2), GII.13 (n = 2), and GII.17 (n = 3), with the latter two genotypes detected only in 2016. Specific amplification of GII.17 NoV was successful in 14 out of 110 positive samples, spanned over the years 2013-2016. The amplicons of the broad-range PCR, pooled per year, were further analyzed by next-generation sequencing (NGS) for a deeper analysis of the genotypes circulating in the study period. NGS confirmed the circulation of GII.17 NoV since 2013 and detected, beyond the eight genotypes identified by Sanger sequencing, three additional genotypes regarded as globally uncommon: GII.5, GII.16, and GII.21. This study provides evidence that GII.17 NoV Kawasaki has been circulating in the Italian population before its appearance and identification in clinical cases, and has become a major genotype in 2016. Our results confirm the usefulness of wastewater surveillance coupled with NGS to study the molecular epidemiology of NoV and to monitor the emergence of NoV strains.