Norovirus Outbreaks Research Articles

Genetic recombination and genotype diversity of norovirus GI in children with acute gastroenteritis in Thailand, 2015-2021

BackgroundHuman norovirus is a predominant etiological agent responsible for acute gastroenteritis across all age groups. Recently, norovirus recombinant strains have been reported as the cause of norovirus outbreaks in several settings and the strains that cause outbreaks mostly belong to the norovirus GII. However, yet, the norovirus GI recombinant strains have never been reported previously in Thailand. The aims of this study were to investigate the genetic recombination and genotype diversity of norovirus GI strains in children hospitalized with acute gastroenteritis in Chiang Mai, Thailand during a period of seven years from 2015 to 2021. MethodsA total of 2829 stool specimens were screened for norovirus GI by real-time PCR, and the polymerase and capsid genes were sequenced and analyzed. ResultsOf 2829 specimens tested, 12 (0.4%) were positive for norovirus GI. Of these, 7 out of 12 (58.3%) strains were identified as norovirus GI recombinant strains. Among 7 norovirus GI recombinant strains, 3, 3, and 1 were identified as GI.3[P13], GI.5[P4], and GI.6[P11], respectively. The remaining five strains were identified as non-recombinant strains of the GI.4[P4], GI.5[P5], and GI.6[P6] genotypes. ConclusionsThe findings highlight the genetic diversity and multiple intergenotype recombinant strains of norovirus GI circulating in children with acute gastroenteritis in Chiang Mai, Thailand from 2015 to 2021. The detection of multiple intergenotype norovirus GI recombinant strains further underscore the complexity of norovirus GI strains circulating in this region.

Asymptomatic norovirus infection during outbreaks in China: A systematic review and meta-analysis.

Acute gastroenteritis outbreaks may be caused by the excretion of norovirus (NoV) from asymptomatic individuals. Despite numerous studies involving asymptomatic NoV infection during outbreaks in China, a comprehensive assessment of its role has not been conducted, which is critical for emergency management. Our objective was to assess the prevalence of asymptomatic NoV infection during outbreaks in China. We conducted a comprehensive search of multiple databases, including PubMed, Web of Science, Cochrane Library, China National Knowledge Infrastructure, China Wanfang, and China Weipu, between January 1, 1997 and June 19, 2023. The retrieved articles and their references underwent screening, which utilized polymerase chain reaction-based assays for the detection of NoV in asymptomatic individuals during outbreaks that occurred in China. The primary summary data were the prevalence of asymptomatic NoV infection in outbreaks. We generated pooled estimates of asymptomatic prevalence in the population as a whole and in subgroups by using random-effect models. Of the 97 articles included, the pooled asymptomatic prevalence of NoV among 5117 individuals in outbreaks was 17.6% (95% confidence interval [CI]: 14.1-21.3). The asymptomatic prevalence of NoV GII (17.1%, 95% CI: 12.9-21.5) was similar to that of NoV GI (22.0%, 95% CI: 12.8-32.4). However, the proportion of asymptomatic individuals involved in NoV GII (57.44%) was significantly higher than that of NoV GI (5.12%), and NoV GII (75.26%) was reported much more frequently than NoV GI (14.43%) in the included articles. Meta-regression analysis of 11 possible influencing factors (geographic region, setting, season, sample type, genotype, transmission route, occupation, age, per capita income, study quality, and cases definition) showed that the source of heterogeneity might be related to the outbreak settings, per capita income, and study quality (p = 0.037, 0.058, and 0.026, respectively). Of particular note was the asymptomatic prevalence peaked in preschoolers (27.8%), afterward, it fell into trough in elementary and junior school children (10.5%), before the second peak located in adults (17.8%), and the elderly (25.2%). Prevalent genotypes reported include GII.4, followed by GII.17, GII.2, GII.3, GII.6, and so forth. The estimated asymptomatic prevalence of NoV during outbreaks in China was as high as 17.6%, with NoV GII dominating. In addition, genetic subtypes of NoV in outbreaks should be detected whenever possible. The role of asymptomatic individuals in NoV outbreaks cannot be ignored. This knowledge will help governments develop public health policies and emergency response strategies for outbreaks, assess the burden, and develop vaccines.

An Investigation of a Norovirus Outbreak Linked to Contaminated Vegetables in Mueang District, Chanthaburi Province, Thailand, December 2021–January 2022

An Investigation of a Norovirus Outbreak Linked to Contaminated Vegetables in Mueang District, Chanthaburi Province, Thailand, December 2021–January 2022

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.

Characteristics and related factors of waterborne and foodborne infectious disease outbreaks before and after the onset of the COVID-19 pandemic (2017-2021) in the Republic of Korea: a descriptive study.

The incidence of waterborne and foodborne infectious diseases (WFIDs) continues to increase annually, attracting significant global attention. This study examined trends in WFID outbreaks in the Republic of Korea over the 5-year period before and during the coronavirus disease 2019 (COVID-19) pandemic and provided foundational data to establish measures for the prevention and control of WFID outbreaks. We analyzed 2,541 WFID outbreaks from 2017 to 2021 (42,805 cases) that were reported through the Integrated Disease Surveillance System of the Korea Disease Control and Prevention Agency. Outbreaks were defined as the occurrence of gastrointestinal symptoms in ≥2 individuals within a group with temporal and regional epidemiological associations. The related factors associated with WFID outbreaks during the observation period were statistically analyzed. The total number of WFID outbreaks significantly decreased in 2020 during the COVID-19 pandemic and increased to the pre-pandemic level in 2021. Different patterns were observed for each pathogen. The incidence of Salmonella outbreaks more than doubled, while norovirus outbreaks decreased significantly. WFID outbreaks in the Republic of Korea showed different patterns before and during the COVID-19 pandemic, influenced by infection control measures and changes in dietary consumption patterns. Outbreaks of some diseases increased, but the infection control measures applied during the pandemic resulted in a significant decrease in the overall number of WFID outbreaks. This highlights the importance of strengthening the management strategies for outbreak prevention through hygiene inspections, long-term monitoring, education, and promotion by conducting multidimensional analyses to understand the complex related factors.

Investigation of two norovirus outbreaks linked to drinking water contaminated with multiple GII strains in a rural county-Chongqing, China, 2021.

Norovirus is leading cause of non-bacterial gastroenteritis outbreaks globally, characterized by different strains prevalent in different countries and regions. Cases were defined as individuals experiencing diarrhea ≥3 times/24 h, and/or vomiting ≥2 times/24 h in two villages between January 28 and February 9, 2021. Investigations were conducted to identify causes. Cases were interviewed using a standardized in-person form to collect data on potential risk factors. A retrospective cohort study was conducted to investigate the role of the spring water supply as the outbreak source. Residents from neighboring villages with different water sources served as the unexposed population. Stool specimens, rectal swabs, and water samples were tested using quantitative real-time Polymerase Chain Reaction, with subsequent sequencing performed on pathogen-positive specimens. Village-specific attack rates were 21.93% (123/561) and 26.99% (88/326), respectively. Evidence from both epidemiological and laboratory tests was consistent. Drinking spring water was statistically associated with the two outbreaks (RR = 41.8 and 79.2, respectively). In both outbreaks, stool specimens, rectal swabs, and water samples tested positive for norovirus. Specifically, GII.2 (P16) and GII.17 (P17) were identified in outbreak A, and GII.4 Sydney (P16) and GII.1 (P16) in outbreak B. These two independent gastroenteritis outbreaks share similarities, both being linked to norovirus GII strains. The contaminated spring drinking water was identified as the probable source and was promptly closed and subjected to disinfection procedures. These findings reinforce the importance of implementing sanitation and environmental disinfection measures in rural areas, especially during the periods of increased rainfall.

Prevention, protocols, and lab capacity: lessons from a norovirus outbreak in the Algarve.

This brief report presents the findings of an epidemiological investigation into a large-scale outbreak of norovirus gastroenteritis that occurred in a hotel in Algarve, Portugal, in August 2022. A total of 244 cases were reported, primarily affecting Portuguese families, with the parents aged 40-50 years and the children aged 0-19 years. Reported symptoms included vomiting, nausea, abdominal pain, and diarrhoea. Norovirus genotype GI.3 [P3] was detected in stool samples from eight probable cases, while food samples tested negative for norovirus and common pathogenic bacteria. The investigation data collected suggest that the source of the outbreak was likely in the hotel's common areas, with subsequent person-to-person transmission in other areas. The final report emphasizes the importance of improving outbreak prevention and control measures, including the development of a foodborne outbreak investigation protocol, the establishment of an outbreak response team, and the enhancement of regional laboratory capacity.

Transmissibility quantification of norovirus outbreaks in 2016-2021 in Beijing, China.

The transmissibility is a crucial feature for norovirus, yet its quantitative estimation has been limited. Our objective was to estimate the basic reproduction number (R0 ) of norovirus and investigate its variation characteristics. Norovirus outbreaks reported from September 2016 to August 2021 in Beijing were analyzed. The susceptible-infected-removed compartment model was established to estimate R0 . Linear regression models and logistic regression models were used to explore the factors affecting the transmissibility of norovirus. The overall median R0 of norovirus was estimated as 2.1 (interquartile range [IQR] 1.8-2.5), with 650 norovirus outbreaks. The transmissibility of norovirus varied by year, outbreak setting and genotype. The R0 of norovirus during September 2019 to August 2020 (median 2.1, IQR 1.8-2.4) and September 2020 to August 2021 (median 2.0, IQR 1.7-2.3) was lower than that of September2016 to August 2017 (median 2.3, IQR 1.8-2.7) (β = 0.94, p = 0.05; β = 0.93, p = 0.008). The R0 of norovirus for all other settings was lower than that for kindergarten (median 2.4, IQR 2.0-2.9) (primary school: median 2.0, IQR 1.7-2.4, β = 0.94, p = 0.001; secondary school: median 1.7, IQR 1.5-2.0, β = 0.87, p < 0.001; college: median 1.7, IQR 1.5-1.8, β = 0.89, p = 0.03; other closed settings: median 1.8, IQR 1.5-2.0, β = 0.90, p = 0.004). GⅡ.2[P16] outbreaks had a median R0 of 2.2 (IQR 1.8-2.7), which was higher than that for GⅡ.6[P7] outbreaks (median 1.8, IQR: 1.8-2.0, odds ratio = 0.19, p = 0.03; GⅡ.2[P16] as reference) and mixed-genotype outbreaks (median 1.7, IQR: 1.5-1.8, β = 0.92, p = 0.02; mixed-genotype as reference).In kindergartens and primary schools, norovirus shows increased transmissibility, emphasizing the vulnerable population and high-risk settings. Furthermore, the transmissibility of norovirus may change over time and with virus evolution, necessitating additional research to uncover the underlying mechanisms.

Genotypic diversity and recombination of norovirus GI.6[P11] associated acute gastroenteritis outbreaks in Beijing, China, from 2016 to 2019.

Norovirus (NoV) is the leading pathogen responsible for global acute gastroenteritis (AGE) outbreaks and sporadic cases. NoV evolves through gene mutation and recombination, leading to the emergence of new strains capable of causing global epidemics. This study aimed to learn the epidemiological characteristics of 39 GI.6[P11] NoV outbreaks in Beijing, China, from 2016 to 2019 and to analyze the genetic diversity and phylogenetic process of GI.6[P11] strains. The Bayesian phylogenetic analysis of partial VP1 and RNA-dependent RNA polymerase (RdRp) genes showed that GI.6[P11] strains were clustered into four subclades. Eleven whole genome sequences were obtained through the amplicon sequencing with 16 pairs of newly designed primers. The phylogenetic trees based on the whole genome and ORF1, 2, and 3 showed that the clustering of the 11 strains was consistent with that of partial VP1 and RdRp genes. The Bayesian inference revealed that the most recent ancestor (TMRCA) for the four subclades of the phylogenetic tree based on the whole genome sequences was 2012.42, 2014.81, 2011.74, and 2015.53, respectively. The recombination sites of GI.6[P11] strains in Beijing were located near the ORF1/2 junction. The histo-blood group antigens (HBGA) binding sites of GI.6[P11] strains in Beijing were conserved and there were some unique amino acid mutations in non-structural proteins in the ORF1 region.

Global prevalence of asymptomatic norovirus infection in outbreaks: a systematic review and meta-analysis

BackgroundAlthough many studies on asymptomatic norovirus infection in outbreaks have been conducted globally, structured data (important for emergency management of outbreaks) on the prevalence of this epidemic are still not available. This study assessed the global prevalence of asymptomatic norovirus infection in outbreaks.MethodsWe identified publications on asymptomatic infections from norovirus outbreaks by searching the PubMed, Embase, Cochrane Library, Medline, and Web of Science databases and screening references from the articles reviewed. Prevalence of asymptomatic norovirus infection in outbreaks was employed as the primary summary data. The random-effects model of the meta-analysis was fitted to generate estimates of the prevalence in the overall and subgroup populations.ResultsIn total, 44 articles with a sample size of 8,115 asymptomatic individuals were included. The estimated pooled prevalence of asymptomatic norovirus infection in outbreaks was 21.8% (95%CI, 17.4–27.3). The asymptomatic prevalence of norovirus GII (20.1%) was similar to that of GI (19.8%); however, the proportion prevalence of asymptomatic individuals involved in the former (33.36%) was significantly higher than that of in the latter (0.92%) and the former (93.18%) was reported much more frequently than the latter (15.91%) in the included articles. These studies had significant heterogeneity (I2 = 92%, τ2 = 0.4021, P < 0.01). However, the source of heterogeneity could not be identified even after subgroup analysis of 10 possible influencing factors (geographical area, outbreak settings, outbreak seasons, sample types, norovirus genotypes, transmission routes, subjects’ occupations, subjects’ age, per capita national income, and clear case definition). Meta-regression analysis of these 10 factors demonstrated that the geographical area could be partly responsible for this heterogeneity (P = 0.012).ConclusionsThe overall pooled asymptomatic prevalence of norovirus in outbreaks was high, with genome II dominating. Asymptomatic individuals may play an important role in norovirus outbreaks. This knowledge could help in developing control strategies and public health policies for norovirus outbreaks.

Evaluation of the transmissibility of norovirus and the effectiveness of prevention and control measures for schools in Jiangsu Province

Objective This study aims to estimate the transmissibility of norovirus outbreaks in schools by different transmission routes, and to evaluate the effects of isolation, school-closure and disinfection measures under different intervention intensities, finally, scientific prevention and control suggestions are proposed. Method 23 outbreaks of norovirus infectious diarrhea occurring in Jiangsu Province’s school from 2012-2018 were selected and fitted to the model. The data includes various types of school places and pathogen genotype. A ‘SEIAQRW’ model with two transmission routes was established. The transmissibility of each outbreak was assessed using effective reproduction number, the efficacy of different intervention measures and intensities were evaluated by calculating the total attack rate and peak incidence. Results The mean effective reproduction number of noroviruses was estimated to be 8.92 for the human-to-human route of transmission and 2.19 for the water or food-to-human route of transmission. When all symptomatic cases were isolated, the median peak incidence for both transmission routes both being less than 1.8%. There was a smaller reduction in total attack rate compared to peak incidence, the median total attack rate for the two transmission routes decreased by 17.59% and 42.09%, respectively. When the effect of school-closure or disinfection is more than 90%, the total attack rate and peak incidence in the human-to-human route are reduced by more than 90% compared to no intervention, and the peak incidence in the water or food-to-human routes can be reduced to less than 1.4%, but the reduction in the total attack rate is only 50% or so. Conclusion Norovirus outbreaks have a high rate of transmission in schools. In the case of norovirus outbreaks, isolation should be complemented by other interventions, and the implementation of high-intensity school closures or disinfection of the external environment can be effective in reducing the spread of the virus.

Notes from the Field: Outbreak of Norovirus Linked to a Food Establishment - Illinois, November 2022.

Notes from the Field: Outbreak of Norovirus Linked to a Food Establishment - Illinois, November 2022.

Notes from the Field: Cruise Ship Norovirus Outbreak Associated with Person-to-Person Transmission - United States Jurisdiction, January 2023.

Notes from the Field: Cruise Ship Norovirus Outbreak Associated with Person-to-Person Transmission - United States Jurisdiction, January 2023.

Prevalence and Etiological Characteristics of Norovirus Infection in China: A Systematic Review and Meta-Analysis.

Norovirus is a common cause of sporadic cases and outbreaks of gastroenteritis worldwide, although its prevalence and the dominant genotypes responsible for gastroenteritis outbreaks remain obscure. A systematic review was conducted on norovirus infection in China between January 2009 and March 2021. A meta-analysis and beta-binomial regression model were used to explore the epidemiological and clinical characteristics of norovirus infection and the potential factors contributing to the attack rate of the norovirus outbreaks, respectively. A total of 1132 articles with 155,865 confirmed cases were included, with a pooled positive test rate of 11.54% among 991,786 patients with acute diarrhea and a pooled attack rate of 6.73% in 500 norovirus outbreaks. GII.4 was the predominant genotype in both the etiological surveillance and outbreaks, followed by GII.3 in the etiological surveillance, and GII.17 in the outbreaks, with the proportion of recombinant genotypes increasing in recent years. A higher attack rate in the norovirus outbreaks was associated with age group (older adults), settings (nurseries, primary schools, etc.) and region (North China). The nation-wide pooled positive rate in the etiological surveillance of norovirus is lower than elsewhere in the global population, while the dominant genotypes are similar in both the etiological surveillance and the outbreak investigations. This study contributes to the understanding of norovirus infection with different genotypes in China. The prevention and control of norovirus outbreaks during the cold season should be intensified, with special attention paid to and enhanced surveillance performed in nurseries, schools and nursing homes from November to March.

High prevalence of norovirus GII.4 Sydney among children with acute gastroenteritis in Bangladesh, 2018–2021

BackgroundActive molecular surveillance and rapid diagnosis method to track an outbreak of norovirus in Bangladesh is lacking. This study aims to determine the genotypic diversity, molecular epidemiology and evaluate a rapid diagnosis method. MethodsA total of 404 fecal specimens were collected from children aged below 60 months from January 2018 to December 2021. All samples were analyzed by reverse transcriptase polymerase chain reaction molecular sequencing of partial VP1 nucleotide. Immunochromatography kit (IC, IP Rota/Noro) was evaluated against reference test method. ResultsWe found norovirus in 6.7 % (27 of 404) fecal specimens. A wide diversity of norovirus genotype including GII.3, GII.4, GII.5, GII.6, GII.7, and GII.9 were detected. Norovirus strain GII.4 Sydney-2012 was the most predominant (74 %, 20 of 27) followed by GII.7 (7.4 %), GII.9 (7.4 %), GII.3 (3.7 %), GII.5 (3.7 %) and GII.6 (3.7 %), respectively. Co-infection of rotavirus and norovirus (19 [4.7 %] of 404) was the most prevalent. We found higher odds of prolonged health impact [OR 1.93 (95 % CI 0.87–3.12) (p = .001)] among patients with co-infection. The incidence of norovirus was significant among the children below 24 months (p = 0.001). Significant relation of temperature with the cases of norovirus was detected (p = 0.001). The IC kit provided high specificity (99.3 %) and sensitivity (100 %) for the detection of norovirus. ConclusionsThis study will provide an integrated insight on the genotypic diversity and rapid identification method of norovirus in Bangladesh.

Spatio-temporal distribution and influencing factors of norovirus outbreaks in Beijing, China from 2016 to 2020

BackgroundNoroviruses are a leading cause of acute gastroenteritis (AGE) worldwide. The geographical characteristics of norovirus outbreaks in Beijing and their influencing factors remain unknown. This study aimed to explore the spatial distributions, geographical characteristics, and influencing factors of norovirus outbreaks in Beijing, China.MethodsEpidemiological data and specimens were collected through the AGE outbreak surveillance system in all 16 districts of Beijing. Data on spatial distribution, geographical characteristics, and influencing factors of norovirus outbreaks were analyzed using descriptive statistics methods. We measured spatial, geographical clustering of high- or low-value deviance from random distribution using Z-scores and P-values as statistical significance measures with Global Moran’s I statistics and Getis-Ord Gi in ArcGIS. Linear regression and correlation methods were used to explore influencing factors.ResultsBetween September 2016 and August 2020, 1,193 norovirus outbreaks were laboratory-confirmed. The number of outbreaks varied seasonally, typically peaking in spring (March to May) or winter (October to December). Outbreaks primarily occurred around central districts at the town level, and spatial autocorrelation was evident in both the entire study period and in individual years. Hotspots of norovirus outbreaks in Beijing were primarily found in contiguous areas between three central districts (Chaoyang, Haidian, Fengtai) and four suburban districts (Changping, Daxing, Fangshan, Tongzhou). The average population numbers, mean number of all schools, and mean number of kindergartens and primary schools for towns in central districts and hotspot areas were higher than those in suburban districts and non-hotspot areas respectively. Additionally, population numbers and densities of kindergartens and primary schools were influencing factors at the town level.ConclusionsHotspots of norovirus outbreaks in Beijing were in contiguous areas between central and suburban districts with high populations, and high kindergarten and primary school densities were the likely driving forces. Outbreak surveillance needs to focus on contiguous areas between central and suburban districts with increased monitoring, medical resources, and health education.

Influence of herd immunity on norovirus: a long-term field study of repeated viral gastroenteritis outbreaks at the same facilities

BackgroundViral acute gastroenteritis (AG) is detected worldwide annually. Outbreaks caused by viruses associated with gastroenteritis have been reported repeatedly at the same facilities in Yokohama, Japan over several years. We investigated the statuses of these repeated outbreaks to consider herd immunity at the facility level.MethodsBetween September 2007 and August 2017, 1459 AG outbreaks were reported at 1099 facilities. Stool samples were collected for virological testing, and the norovirus gene was amplified and sequenced to determine the genotype using the N-terminal region of the capsid.ResultsThe outbreaks were caused by norovirus, sapovirus, rotavirus A, and rotavirus C. Norovirus was consistently predominant over the 10-year period. Of 1099 facilities, 227 reported multiple outbreaks, of which norovirus-only combinations accounted for 76.2%. More outbreaks were due to different genotype combinations than the same genotype combinations. For facilities that experienced two norovirus outbreaks, the average interval between outbreaks was longer for groups with the same combinations than for groups with different genogroup or genotype combinations, although no statistically significant differences were observed. At 44 facilities, outbreaks occurred repeatedly during the same AG season, and most exhibited combinations of different norovirus genotypes or viruses. Among 49 combinations with the same norovirus genotype at the same facilities over 10 years, the most prevalent genotypes were combinations of genogroup II genotype 4 (GII.4), followed by GII.2, GII.6, GII.3, GII.14, and GI.3. The mean interval between outbreaks was 31.2 ± 26.8 months for all combinations, and the mean intervals were longer for non-GII.4 genotype cases than for GII.4 cases, and statistically significant differences were observed (t-test, P < 0.05). Additionally, these average intervals were longer for kindergarten/nursery schools and primary schools than for nursing homes for older adults (t-test, P < 0.05).ConclusionsRepeated AG outbreaks at the same facilities in Yokohama during the 10-year study period included mainly norovirus combinations. Herd immunity at the facility level was maintained for at least the same AG season. Norovirus genotype-specific herd immunity was maintained for an average of 31.2 months during the study period, and these intervals differed depending on genotype.

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.

Guidelines for the management of norovirus outbreaks in acute and community health and social care settings

Guidelines for the management of norovirus outbreaks in acute and community health and social care settings

Epidemiology of GII.4 and GII.2 norovirus outbreaks in closed and semi-closed institutions in 2017 and 2018

Norovirus infections are a leading cause of acute gastroenteritis outbreaks worldwide, with genotypes GII.2 and GII.4 being the most prevalent. The aim of this study was to compare the characteristics of GII.2 and GII.4 norovirus outbreaks reported in Catalonia in closed or semi-closed institutions in 2017 and 2018. The epidemiological and clinical characteristics of GII.2 and GII.4 outbreaks were compared using the chi-square test or Fisher's exact test for categorical variables and the Mann–Whitney U test for continuous variables. Odds ratios and their 95% confidence intervals were estimated. 61 outbreaks were reported: GII.4 was the causative agent in 12 outbreaks (30%) and GII.2 in 9 outbreaks (22.5%). GII.2 outbreaks were detected more frequently in schools or summer camps (66.7%) and GII.4 outbreaks in nursing homes (91.7%) (p = 0.01). Ninety-three people were affected in GII.2 outbreaks and 94 in GII.4 outbreaks. The median age was 15 years (range: 1–95 years) in GII.2 outbreaks and 86 years (range: 0–100 years) in GII.4 outbreaks (p < 0.001). Nausea, abdominal pain, and headache were observed more frequently in persons affected by GII.2 outbreaks (p < 0.05). Symptomatic cases presented a higher viral load suggestive of greater transmission capacity, although asymptomatic patients presented relevant loads indicative of transmission capacity.