Trends for Syndromic Surveillance of Norovirus in Emergency Department Data Based on Chief Complaints

BACKGROUND

This study compared trends in norovirus cases to determine whether chief complaint-based emergency department (ED) visit data could reflect trends of norovirus in Korea.

METHODS

The ED visits from the National Emergency Department Information System database and the weekly reported number of noroviruses from the sentinel surveillance system were collected between August 2017 and December 2020. The correlation between weekly norovirus cases and weekly ED visits considering the chief complaint and discharge diagnosis code was estimated using a 3-week moving average.

RESULTS

In total, 6 399 774 patients with chief complaints related to digestive system disease visited an ED. A higher correlation between reported norovirus cases and ED visit with chief complaint of vomiting and discharge diagnosis code of gastroenteritis and colitis of unspecified origin or other and unspecified gastroenteritis and colitis of infectious origin was observed (R = 0.88, P < .0001). The correlation was highest for the age group 0-4 years (R = 0.89, P < .0001). However, no correlation was observed between the reported norovirus cases and the number of ED visits with norovirus identified as a discharge diagnosis code.

CONCLUSIONS

ED visit data considering a combination of chief complaints and discharged diagnosis code would be useful for early detection of infectious disease trends.

Common and Potential Emerging Foodborne Viruses: A Comprehensive Review

Human viruses and viruses from animals can cause illnesses in humans after the consumption of contaminated food or water. Contamination may occur during preparation by infected food handlers, during food production because of unsuitably controlled working conditions, or following the consumption of animal-based foods contaminated by a zoonotic virus. This review discussed the recent information available on the general and clinical characteristics of viruses, viral foodborne outbreaks and control strategies to prevent the viral contamination of food products and water. Viruses are responsible for the greatest number of illnesses from outbreaks caused by food, and risk assessment experts regard them as a high food safety priority. This concern is well founded, since a significant increase in viral foodborne outbreaks has occurred over the past 20 years. Norovirus, hepatitis A and E viruses, rotavirus, astrovirus, adenovirus, and sapovirus are the major common viruses associated with water or foodborne illness outbreaks. It is also suspected that many human viruses including Aichi virus, Nipah virus, tick-borne encephalitis virus, H5N1 avian influenza viruses, and coronaviruses (SARS-CoV-1, SARS-CoV-2 and MERS-CoV) also have the potential to be transmitted via food products. It is evident that the adoption of strict hygienic food processing measures from farm to table is required to prevent viruses from contaminating our food.

Two successive outbreaks of acute gastroenteritis due to norovirus GII.6 in a holiday camp house

When two outbreaks occur in the same institution within a short period of time, an important health and social concern is generated. Two gastroenteritis outbreaks occurring a week apart in the same facility were reported in Lleida, Spain, in 2018. The objective of this study was to describe the clinical, epidemiological and microbiological investigation carried out and to determine the risk factors. Demographic data, food consumption and symptoms were collected. Health inspections of the facility were carried out. Risk ratio and their 95% confidence intervals were estimated for the implication of each food consumed. The attack rate was 89.7% in the first outbreak and 69.6% in the second outbreak. The most frequent symptoms in the first and second outbreak were abdominal pain (88.5% and 100%, respectively), vomiting (80.8% and 87.5%, respectively) and nausea (69.2% and 81.3%, respectively). The first outbreak was associated with the consumption of a salad and the second with a cheese omelet. Norovirus GII.6 was detected by RT-PCR and sequenced in both groups of students and in the food handlers who prepared the meals. These results highlight the importance of exclusion from work of food handlers with gastroenteritis, the adequate availability of mechanisms for correct hand washing and the correct cleaning of surfaces.

Significantly Longer Shedding of Norovirus Compared to Rotavirus and Adenovirus in Children with Acute Gastroenteritis

Worldwide, acute gastroenteritis (AGE) is a major cause of morbidity and mortality in children under 5 years of age. Viruses, including norovirus, rotavirus, and enteric adenovirus, are the leading causes of pediatric AGE. In this prospective cohort study, we investigated the viral load and duration of shedding of norovirus, rotavirus, and adenovirus in stool samples collected from 173 children (median age: 15 months) with AGE who presented to emergency departments (EDs) across Canada on Day 0 (day of enrollment), and 5 and 28 days after enrollment. Quantitative RT-qPCR was performed to assess the viral load. On Day 0, norovirus viral load was significantly lower compared to that of rotavirus and adenovirus (p < 0.001). However, on Days 5 and 28, the viral load of norovirus was higher than that of adenovirus and rotavirus (p < 0.05). On Day 28, norovirus was detected in 70% (35/50) of children who submitted stool specimens, while rotavirus and adenovirus were detected in 52.4% (11/24) and 13.6% (3/22) of children (p < 0.001), respectively. Overall, in stool samples of children with AGE who presented to EDs, rotavirus and adenovirus had higher viral loads at presentation compared to norovirus; however, norovirus was shed in stool for the longest duration.

Factors driving norovirus transmission in long-term care facilities: A case-level analysis of 107 outbreaks

Norovirus is the most common cause of gastroenteritis outbreaks in long-term care facilities (LTCFs) in the United States, causing a high burden of disease in both residents and staff. Understanding how case symptoms and characteristics contribute to norovirus transmission can lead to more informed outbreak control measures in LTCFs. We examined line lists for 107 norovirus outbreaks that took place in LTCFs in five U.S. states from 2015 to 2019. We estimated the individual effective reproduction number, R_i, to quantify individual case infectiousness and examined the contribution of vomiting, diarrhea, and being a resident (vs. staff) to case infectiousness. The associations between case characteristics and R_i were estimated using a multivariable, log-linear mixed model with inverse variance weighting. We found that cases with vomiting infected 1.28 (95 % CI: 1.11, 1.48) times the number of secondary cases compared to cases without vomiting, and LTCF residents infected 1.31 (95 % CI: 1.15, 1.50) times the number of secondary cases compared to staff. There was no difference in infectiousness between cases with and without diarrhea (1.07; 95 % CI: 0.90, 1.29). This suggests that vomiting, particularly by LTCF residents, was a primary driver of norovirus transmission. These results support control measures that limit exposure to vomitus during norovirus outbreaks in LTCFs.

Norovirus: An Overview of Virology and Preventative Measures

Norovirus (NoV) is an enteric non-enveloped virus which is the leading cause of gastroenteritis across all age groups. It is responsible for around 200,000 deaths annually and outbreaks are common in small communities such as educational and care facilities. 40% of all NoV outbreaks occur in long-term and acute-care facilities, forming the majority of outbreaks. Nosocomial settings set ideal environments for ease of transmission, especially due to the presence of immunocompromised groups. It is estimated to cost global economies around £48 billion a year, making it a global issue. NoV is transmitted via the faecal-oral route and infection with it results in asymptomatic cases or gastrointestinal disease. It has high mutational rates and this allows for new variants to emerge and be more resistant. The classification system available divides NoV into 10 genogroups and 49 genotypes based on whole amino acid sequencing of VP1 capsid protein and partial sequencing of RdRp, respectively. The most predominant genotypes which cause gastroenteritis in humans include GI.1 and GII.4, where GII.4 is responsible for more extreme clinical implications such as hospitalisation. In addition, GII.4 has been responsible for 6 pandemic strains, the last of which is the GII.4 Sydney (2012) variant. In recent years, the successful cultivation of HuNoV was reported in stem cell-derived human intestinal enteroids (HIEs), which promises to assist in giving a deeper understanding of its underlying mechanisms of infection and the development of more personalized control measures. There are no specific control measures against NoV, therefore common practices are used against it such as hand washing. No vaccine is available, but the HIL-214 candidate passed clinical phase 2b and shows promise.

Evaluation of the Impact of Compliance with Mitigation Strategies and Frequency of Restaurant Surface Cleaning and Sanitizing on Control of Norovirus Transmission from Ill Food Employees Using an Existing Quantitative Risk Assessment Model

ABSTRACT

Reduction of foodborne illness caused by norovirus (NoV) continues to be a focus for the food safety community. Using a previously published quantitative risk assessment model, we evaluated more than 60 scenarios examining the impact of implementation of and compliance with risk management strategies identified in the U.S. Food and Drug Administration Food Code for (a) surface cleaning and sanitizing, (b) hand hygiene, (c) exclusion, or (d) restriction of ill employees. Implementation of and compliance with hand hygiene and ill food employee exclusion strategies had the largest impact on the predicted number of highly contaminated food servings and associated consumer illnesses. In scenarios in which gloves were always worn and hand washing compliance was 90%, the model estimated reductions in the number of highly contaminated food servings and ill consumers to 39 and 43% of baseline estimates (i.e., typical practice), respectively. Reductions were smaller when gloves were never worn. Hand washing compliance after using the restroom strongly impacted predicted numbers of highly contaminated servings and consumer illnesses. Ten percent compliance with removing or excluding ill food employees was predicted to increase the number of highly contaminated food servings and ill consumers to 221 and 213% of baseline estimates, respectively. Ninety-four percent compliance with exclusion of ill food employees was predicted to decrease these numbers to 69 and 71% of baseline estimates, respectively. Surface cleaning in food establishments had a relatively small impact on these measures. Restriction of food employees (removed from contact with food and food contact equipment and utensils) was not effective for reducing NoV illness unless this restriction included additional provisions. The results from this study can help risk managers prioritize mitigation strategies and their implementation for controlling the transmission of NoV and subsequent consumer foodborne illness.

HIGHLIGHTS

An open-access database of infectious disease transmission trees to explore superspreader epidemiology

Historically, emerging and reemerging infectious diseases have caused large, deadly, and expensive multinational outbreaks. Often outbreak investigations aim to identify who infected whom by reconstructing the outbreak transmission tree, which visualizes transmission between individuals as a network with nodes representing individuals and branches representing transmission from person to person. We compiled a database, called OutbreakTrees, of 382 published, standardized transmission trees consisting of 16 directly transmitted diseases ranging in size from 2 to 286 cases. For each tree and disease, we calculated several key statistics, such as tree size, average number of secondary infections, the dispersion parameter, and the proportion of cases considered superspreaders, and examined how these statistics varied over the course of each outbreak and under different assumptions about the completeness of outbreak investigations. We demonstrated the potential utility of the database through 2 short analyses addressing questions about superspreader epidemiology for a variety of diseases, including Coronavirus Disease 2019 (COVID-19). First, we found that our transmission trees were consistent with theory predicting that intermediate dispersion parameters give rise to the highest proportion of cases causing superspreading events. Additionally, we investigated patterns in how superspreaders are infected. Across trees with more than 1 superspreader, we found preliminary support for the theory that superspreaders generate other superspreaders. In sum, our findings put the role of superspreading in COVID-19 transmission in perspective with that of other diseases and suggest an approach to further research regarding the generation of superspreaders. These data have been made openly available to encourage reuse and further scientific inquiry.

This study compiles and standardizes reported infectious disease transmission trees to analyze trends in superspreader frequency and generation; these data support theories that intermediate dispersion parameters give rise to the highest proportion of cases causing superspreading events, and that superspreaders generate other superspreaders.

Elevated Fecal Mitochondrial DNA from Symptomatic Norovirus Infections Suggests Potential Health Relevance of Human Mitochondrial DNA in Fecal Source Tracking

An end goal of fecal source tracking (FST) is to provide information on risk of transmission of waterborne illnesses associated with fecal contamination. Ideally, concentrations of FST markers in ambient waters would reflect exposure risk. Human mtDNA is an FST marker that is exclusively human in origin and may be elevated in feces of individuals experiencing gastrointestinal inflammation. In this study, we examined whether human mtDNA is elevated in fecal samples from individuals with symptomatic norovirus infections using samples from the United States (US), Mozambique, and Bangladesh. We quantified hCYTB484 (human mtDNA) and HF183/BacR287 (human-associated Bacteroides) FST markers using droplet digital polymerase chain reaction. We observed the greatest difference in concentrations of hCYTB484 when comparing samples from individuals with symptomatic norovirus infections versus individuals without norovirus infections or diarrhea symptoms: log₁₀ increase of 1.42 in US samples (3,820% increase, p-value = 0.062), 0.49 in Mozambique (308% increase, p-value = 0.061), and 0.86 in Bangladesh (648% increase, p-value = 0.035). We did not observe any trends in concentrations of HF183/BacR287 in the same samples. These results suggest concentrations of fecal mtDNA may increase during symptomatic norovirus infection and that mtDNA in environmental samples may represent an unambiguously human source-tracking marker that correlates with enteric pathogen exposure risk.

A2B-COVID: A Tool for Rapidly Evaluating Potential SARS-CoV-2 Transmission Events

Identifying linked cases of infection is a critical component of the public health response to viral infectious diseases. In a clinical context, there is a need to make rapid assessments of whether cases of infection have arrived independently onto a ward, or are potentially linked via direct transmission. Viral genome sequence data are of great value in making these assessments, but are often not the only form of data available. Here, we describe A2B-COVID, a method for the rapid identification of potentially linked cases of COVID-19 infection designed for clinical settings. Our method combines knowledge about infection dynamics, data describing the movements of individuals, and evolutionary analysis of genome sequences to assess whether data collected from cases of infection are consistent or inconsistent with linkage via direct transmission. A retrospective analysis of data from two wards at Cambridge University Hospitals NHS Foundation Trust during the first wave of the pandemic showed qualitatively different patterns of linkage between cases on designated COVID-19 and non-COVID-19 wards. The subsequent real-time application of our method to data from the second epidemic wave highlights its value for monitoring cases of infection in a clinical context.

Associations of infection control measures and norovirus outbreak outcomes in healthcare settings: a systematic review and meta-analysis

BACKGROUND

Although most norovirus outbreaks in high-income countries occur in healthcare facilities, information on associations between control measures and outbreak outcomes in these settings is lacking.

METHODS

We conducted a systematic review/meta-analysis to assess associations between norovirus outbreak control measures and outcomes in hospitals and long-term care facilities (LTCFs), globally. Using regression analyses stratified by setting (hospital/LTCF), we compared durations, attack rates, and case counts for outbreaks in which control measures were reportedly implemented to those in which they were not.

RESULTS

We identified 102 papers describing 162 norovirus outbreaks. Control measures were reportedly implemented in 118 (73%) outbreaks and were associated with 0.6 (95% CI: 0.3-1.1) times smaller patient case counts and 0.7 (95% CI: 0.4, 1.0) times shorter durations in hospitals but 1.5 (95% CI: 1.1-2.2), 1.5 (95% CI: 1.0-2.1) and 1.6 (95% CI: 1.0-2.6) times larger overall, resident and staff case counts, respectively, and 1.4 (95% CI: 1.0-2.0) times longer durations in LTCFs.

CONCLUSIONS

Reported implementation of control measures was associated with smaller/shorter outbreaks in hospitals but larger/longer outbreaks in LTCFs. Control measures were likely implemented in response to larger/longer outbreaks in LTCFs, rather than causing them. Prospective observational or intervention studies are needed to determine effectiveness.

Predicted norovirus resurgence in 2021-2022 due to the relaxation of nonpharmaceutical interventions associated with COVID-19 restrictions in England: a mathematical modeling study

BACKGROUND

To reduce the coronavirus disease burden in England, along with many other countries, the government implemented a package of non-pharmaceutical interventions (NPIs) that have also impacted other transmissible infectious diseases such as norovirus. It is unclear what future norovirus disease incidence is likely to look like upon lifting these restrictions.

METHODS

Here we use a mathematical model of norovirus fitted to community incidence data in England to project forward expected incidence based on contact surveys that have been collected throughout 2020-2021.

RESULTS

We report that susceptibility to norovirus infection has likely increased between March 2020 and mid-2021. Depending upon assumptions of future contact patterns incidence of norovirus that is similar to pre-pandemic levels or an increase beyond what has been previously reported is likely to occur once restrictions are lifted. Should adult contact patterns return to 80% of pre-pandemic levels, the incidence of norovirus will be similar to previous years. If contact patterns return to pre-pandemic levels, there is a potential for the expected annual incidence to be up to 2-fold larger than in a typical year. The age-specific incidence is similar across all ages.

CONCLUSIONS

Continued national surveillance for endemic diseases such as norovirus will be essential after NPIs are lifted to allow healthcare services to adequately prepare for a potential increase in cases and hospital pressures beyond what is typically experienced.

Quantitative microbial risk assessment of human norovirus infection in environmental service workers due to healthcare-associated fomites

BACKGROUND

Healthcare-associated norovirus outbreaks place a large burden on healthcare staff. Environmental service workers (ESWs), however, remain understudied despite high contact with potentially contaminated surfaces. Understanding the magnitude of the risk of norovirus infection in healthcare ESWs can protect workers and improve infection control.

AIM

This study simulated the risk of norovirus infection for unprotected ESWs after a single fomite contact, assuming no disinfection or protective equipment, in norovirus-positive patient rooms. In addition, the risk of secondary surface transmission from norovirus-exposed ESWs was simulated.

METHODS

A quantitative microbial risk assessment employing two-dimensional Monte Carlo simulation with parameters extracted from the literature was used to estimate norovirus infection from multiple fomite contact scenarios defined by: norovirus source (patient vomit/diarrhoea), location (bathroom/patient room) and target outcome (ESW/secondary illness).

FINDINGS

Unprotected ESWs have a maximum estimated risk of norovirus infection of 33% (1:3) for a single fomite contact in a room where a norovirus-positive patient had a diarrhoeal event. Patient vomit events lead to fomite contact risk estimates that are four orders of magnitude lower than those for diarrhoeal events. The estimated risk of secondary illness from touching a common surface is as high as 25% (1:4) after single fomite exposure following a diarrhoeal event.

CONCLUSIONS

A single fomite contact may lead to sizable risk of norovirus infection in ESWs if personal protective equipment and disinfection are not used appropriately. ESWs can also transfer virus to secondary surfaces, initiating further infections. Interventions are needed to reduce fomite transfer of norovirus, and protect patients and staff from nosocomial infections.

Surveillance To Prevent the Spread of Norovirus Outbreak from Asymptomatic Food Handlers during the PyeongChang 2018 Olympics

ABSTRACT

Human noroviruses are major causes of nonbacterial gastroenteritis and are transmitted by both food and water, as well as person-to-person. Asymptomatic norovirus infection of food handlers may play a role in transmission. The outbreak of norovirus infections was recognized in the PyeongChang Winter Olympics, starting with security staff on 3 February 2018. The Ministry of Food and Drug Safety in the Republic of Korea conducted norovirus surveillance from asymptomatic food handlers of food-catering facilities related to the Olympics to prevent the spread of noroviruses. Rectal swab samples (707) from food handlers were collected and examined for noroviruses by using real-time reverse transcription PCR and conventional reverse transcription PCR. Five of 707 samples were identified as noroviruses. Genotypes of the norovirus-positive samples were determined with sequencing analysis. Identified genotypes of norovirus in asymptomatic food handlers included GI.3, GII.4, and GII.17. The GII.17 strain was prevalent among the genotypes, accounting for three of five detections. Food handlers with noroviruses detected in rectal swabs were excluded from cooking, and all food handled by infected food handlers was discarded. Surveillance of norovirus infection for food handlers contributed to preventing norovirus spread.

HIGHLIGHTS

Risk of environmental transmission of norovirus infection from prior room occupants

BACKGROUND

Environmental contamination of norovirus (NoV) is believed to be a significant source for further transmission in hospitals.

AIM

To investigate the risk of acquiring NoV in a cleaned room previously occupied by a patient with NoV infection. The risk of having a roommate with recent NoV infection was also assessed.

METHODS

In a retrospective cohort, comprising 33,788 room stays at five infectious Disease wards in southern Sweden from 2013 to 2018, the risk of acquiring NoV infection after admission to an exposed or non-exposed room was analysed with uni- and multivariable statistical analysis, controlling for age, colonization pressure and any roommate. RNA sequencing of the NoV strains involved in suspected room transmission was also performed.

RESULTS

Five of the 1106 patients exposed to a room with a prior occupant with NoV infection and 49 in the non-exposed group acquired NoV infection. An association between NoV acquisition was found in the univariable analysis (odds ratio (OR) 3.3, P=0.01), but not when adjusting for potential confounders (OR 1.9, P=0.2). Sequencing of the NoV samples showed that only two of the five exposed patients with acquired NoV infection were infected by identical strains to the prior room occupant, inferring a room transmission risk of 0.2% (95% confidence interval 0.05-0.78%). None of the 52 patients who shared room with a roommate with NoV symptoms resolved for ≥48 h acquired NoV infection.

CONCLUSIONS

In absolute terms, the risk of room transmission of NoV is low. Discontinuation of isolation ≥48 h after resolution of symptoms seems adequate.

Predicted Norovirus Resurgence in 2021-2022 Due to the Relaxation of Nonpharmaceutical Interventions Associated with COVID-19 Restrictions in England: A Mathematical Modelling Study

BACKGROUND

To reduce the coronavirus disease burden in England, along with many other countries, the Government implemented a package of non-pharmaceutical interventions (NPIs) that have also impacted other transmissible infectious diseases such as norovirus. It is unclear what future norovirus disease incidence is likely to look like upon lifting these restrictions.

METHODS

Here we use a mathematical model of norovirus fitted to community incidence data in England to project forward expected incidence based on contact surveys that have been collected throughout 2020-2021.

RESULTS

We report that susceptibility to norovirus infection has likely increased between March 2020 to mid-2021. Depending upon assumptions of future contact patterns incidence of norovirus that is similar to pre-pandemic levels or an increase beyond what has been previously reported is likely to occur once restrictions are lifted. Should adult contact patterns return to 80% of pre-pandemic levels the incidence of norovirus will be similar to previous years. If contact patterns return to pre-pandemic levels there is a potential for the expected annual incidence to be up to 2-fold larger than in a typical year. The age-specific incidence is similar across all ages.

CONCLUSIONS

Continued national surveillance for endemic diseases such as norovirus will be essential after NPIs are lifted to allow healthcare services to adequately prepare for a potential increase in cases and hospital pressures beyond what is typically experienced.

Noroviruses-The State of the Art, Nearly Fifty Years after Their Initial Discovery

Human noroviruses are recognised as the major global cause of viral gastroenteritis. Here, we provide an overview of notable advances in norovirus research and provide a short recap of the novel model systems to which much of the recent progress is owed. Significant advances include an updated classification system, the description of alternative virus-like protein morphologies and capsid dynamics, and the further elucidation of the functions and roles of various viral proteins. Important milestones include new insights into cell tropism, host and microbial attachment factors and receptors, interactions with the cellular translational apparatus, and viral egress from cells. Noroviruses have been detected in previously unrecognised hosts and detection itself is facilitated by improved analytical techniques. New potential transmission routes and/or viral reservoirs have been proposed. Recent in vivo and in vitro findings have added to the understanding of host immunity in response to norovirus infection, and vaccine development has progressed to preclinical and even clinical trial testing. Ongoing development of therapeutics includes promising direct-acting small molecules and host-factor drugs.

Risk factors for norovirus infection in healthcare workers during nosocomial outbreaks: a cross-sectional study

Background

Norovirus outbreaks cause severe medico-socio-economic problems affecting healthcare workers and patients. The aim of the study was to investigate prevalence of norovirus infection and risk factors for infection in healthcare workers during nosocomial outbreaks.

Methods

A cross-sectional study of norovirus infections in healthcare workers was performed in seven outbreak wards in a large university hospital. Packs (swab for rectal sampling, and questionnaire) were posted to healthcare workers on notification of a ward outbreak. Rectal samples were examined with norovirus-specific real-time PCR. Replies from questionnaires were analysed using logistic regression models with norovirus genogroup (G)II positive findings as dependent variable. The results are expressed as odds ratios (OR) with 95% confidence intervals (CI). Sequencing and phylogenetic analyses (1040 nucleotides) were used to characterize norovirus strains from healthcare workers. Cluster analyses included norovirus GII.4 strains detected in ward patients during the ongoing outbreaks.

Results

Of 308 packs issued to healthcare workers, 129 (42%) were returned. norovirus GII was detected in 26 healthcare workers (20.2%). Work in cohort care (OR 4.8, 95% CI 1.4–16.3), work in wards for patients with dementia (OR 13.2, 95% CI 1.01–170.7), and having diarrhoea, loose stools or other gastrointestinal symptoms the last week (OR 7.7, 95% CI 2.5–27.2) were associated with increased norovirus prevalence in healthcare workers. Sequencing revealed norovirus GII.4 in healthcare workers samples, and strains detected in healthcare workers and ward patients during a given ward outbreak showed ≥ 99% similarity.

Conclusion

Norovirus positive findings in healthcare workers were strongly associated with symptomatic infection, close contact with sick patients, and dementia nursing.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13756-021-00979-8.

Characterizing Norovirus Transmission from Outbreak Data, United States

Norovirus is the leading cause of acute gastroenteritis outbreaks in the United States. We estimated the basic (R₀) and effective (R_e) reproduction numbers for 7,094 norovirus outbreaks reported to the National Outbreak Reporting System (NORS) during 2009–2017 and used regression models to assess whether transmission varied by outbreak setting. The median R₀ was 2.75 (interquartile range [IQR] 2.38–3.65), and median R_e was 1.29 (IQR 1.12–1.74). Long-term care and assisted living facilities had an R₀ of 3.35 (95% CI 3.26–3.45), but R₀ did not differ substantially for outbreaks in other settings, except for outbreaks in schools, colleges, and universities, which had an R₀ of 2.92 (95% CI 2.82–3.03). Seasonally, R₀ was lowest (3.11 [95% CI 2.97–3.25]) in summer and peaked in fall and winter. Overall, we saw little variability in transmission across different outbreaks settings in the United States.

Factors associated with the detection of norovirus among asymptomatic adults

OBJECTIVES

Little is known about asymptomatic norovirus infection and its risk factors in healthy adults. This study investigated detection of norovirus in stool and its associated factors among asymptomatic healthy adults in a high-income country.

METHODS

This prospective cross-sectional study-conducted between February 2016 and January 2017 at a teaching hospital in Japan-included apparently healthy adults aged ≥18 years who underwent voluntary health check-ups. Our primary outcome was detection of norovirus in stool specimens confirmed by real-time RT-PCR. We evaluated descriptive statistics and associated factors, including demographics, social habits, and clinical parameters.

RESULTS

Among 15 532 participants, 4536 (29.2%, mean age 58.0 (standard deviation 11.8) years, male 44.6%) were enrolled, and 112 (2.5%, GI 57, GII 54, GI + GII 1) were norovirus-positive. Monthly prevalence rates of the GI norovirus were consistent throughout the year, while those of GII were high in May. Participants aged <40 and ≥ 80 years had higher rates of GII norovirus detection. Participants who occasionally consume alcohol, especially wine (odds ratio (OR) 0.17, 95% confidence interval (CI) 0.04-0.68), had lower norovirus detection rates than abstainers. Participants with untreated dyslipidaemia and a low high-density lipoprotein (HDL) cholesterol level had higher detection rates than those with treated dyslipidaemia (OR 1.48, 95%CI 1.07-2.05) and a normal HDL cholesterol level (OR 2.60, 95%CI 1.46-4.61). Some gastrointestinal and female genital diseases were associated with norovirus detection.

CONCLUSIONS

The norovirus detection rate in asymptomatic adults was 2.5%. Participants with specific lifestyles or medical histories may have higher risks of asymptomatic norovirus infection.

Modeling the Potential Impact of Norovirus Vaccination Among DoD Forces

INTRODUCTION

Norovirus, a contagious disease that spreads rapidly in close-quartered communities, has a debilitating effect in military settings, affecting troops' health, productivity, and mission-readiness. This research presents a model of norovirus transmission, testing the vaccination's effectiveness in military training centers.

METHODS

Transmission was modeled using structured ordinary differential equations, including symptomatic and asymptomatic infection, genetic resistance, vaccination, and herd-immunity effects, within a hypothetical cohort of trainees and support staff. The modeled vaccine had an efficacy of 72%, 4 weeks after a single dose in phase 2 clinical trials. The transmission model was calibrated against data from a norovirus outbreak in a university setting. Sensitivity and uncertainty analyses were performed on 22 parameters.

RESULTS

The greatest reduction in norovirus cases resulted from prophylactic environmental decontamination and vaccination of trainee and staff populations. These combined interventions prevented more than 6,800 cases of norovirus over the 10-year simulated period-a 15% reduction over the baseline scenario of no interventions. Implementing vaccination and environmental decontamination with an outbreak response threshold of 0.1%, prevented more than 5,300 infections; raising the threshold to 0.2% to 0.5% significantly reduced effectiveness. Environmental decontamination and contact reduction alone had little impact on overall norovirus cases.

CONCLUSIONS

Given vaccine characteristics, the model predicted that up to 15% of norovirus cases occurring in training settings over a 10-year period could be prevented by vaccinating all trainees and staff members immediately upon arrival on-base combined with continuous environmental decontamination. There was an impact on morbidity from implementing vaccination of trainees, alone and in combination with staff members. However, vaccinating staff alone prevented few cases over the simulation period, indicating the importance of trainees in norovirus transmission. Likewise, the negligible impact of environmental decontamination or contact reduction alone highlights the importance of addressing both person-to-person and environmental transmission together to minimize illnesses and training downtime.

Norovirus Infections in Kidney Transplant Recipients

BACKGROUND

Norovirus (NoV) infection frequently progresses to chronic disease after kidney transplant (KTx). This study aims to assess potential risk factors helping to determine patients at risk of chronic NoV infection and to analyse the effect of NoV on allograft outcome. Additionally, we assessed the effectiveness of intravenous immunoglobulin (IVIg) therapy for chronic NoV infection.

METHODS

The study enrolled 60 KTx patients requiring hospitalization because of NoV infection. Clinical parameters, severity of NoV infection and potential risk factors were evaluated. Outcome parameters were clinical symptoms, rehospitalizations, persistent shedding of virus and effects on allograft function.

RESULTS

Patients were divided into 2 groups: 29 had acute NoV infection only, 31 progressed to chronic NoV infection. Chronic NoV infection was defined as a recurrence of clinical symptoms plus redetection of NoV in stool. Lymphocyte-depleting induction therapy and diabetes mellitus were independent risk factors for chronic infection. For patients with chronic NoV infection, length of stay in hospital was significantly prolonged (p= 0.024). Allograft function remained impaired in the chronic NoV group 6 and 12 months after initial admission.IVIg was administered to 18 patients with chronic NoV infection. No further clinical symptoms of NoV infection occurred in 13 (72%) of these patients. However, NoV was still detectable in stool specimens from 10 (77%) of these patients.

CONCLUSIONS

Chronic NoV infection is associated with reduced allograft function. Administration of IVIg to patients with chronic NoV infection seems beneficial in achieving freedom from clinical symptoms, despite limited effects on shedding of virus.

Strongly Heterogeneous Transmission of COVID-19 in Mainland China: Local and Regional Variation

Background: The outbreak of novel coronavirus disease 2019 (COVID-19) started in the city of Wuhan, China, with a period of rapid initial spread. Transmission on a regional and then national scale was promoted by intense travel during the holiday period of the Chinese New Year. We studied the variation in transmission of COVID-19, locally in Wuhan, as well as on a larger spatial scale, among different cities and even among provinces in mainland China.

Methods: In addition to reported numbers of new cases, we have been able to assemble detailed contact data for some of the initial clusters of COVID-19. This enabled estimation of the serial interval for clinical cases, as well as reproduction numbers for small and large regions.

Findings: We estimated the average serial interval was 4.8 days. For early transmission in Wuhan, any infectious case produced as many as four new cases, transmission outside Wuhan was less intense, with reproduction numbers below two. During the rapid growth phase of the outbreak the region of Wuhan city acted as a hot spot, generating new cases upon contact, while locally, in other provinces, transmission was low.

Interpretation: COVID-19 is capable of spreading very rapidly. The sizes of outbreak in provinces of mainland China mainly depended on the numbers of cases imported from Wuhan as the local reproduction numbers were low. The COVID-19 epidemic should be controllable with appropriate interventions (suspension of public transportation, cancellation of mass gatherings, implementation of surveillance and testing, and promotion of personal hygiene and face mask use).

Significance of norovirus in occupational health: a review of published norovirus outbreaks in Central and Northern Europe

Objectives

Globally, norovirus (NoV) is the leading cause of gastroenteritis infection among all ages. The development of prevention strategies in the field of occupational health requires a detailed knowledge about the impact of the disease on employees. This review article aims not only at evaluating the burden of NoV outbreaks on staff but also at discussing implications for future prevention strategies.

Methods

Published NoV outbreaks in Central and Northern Europe were identified via a systematic literature search. Additionally, published NoV outbreaks in Germany were detected via a manual literature search. Key epidemiological data, as the number of symptomatic staff, was then extracted. The proportion of affected employees was calculated for each dataset (single NoV outbreaks or aggregated data of multiple outbreaks).

Results

Overall, 116 datasets were extracted from 72 relevant articles. 144,852 persons were affected by NoV gastroenteritis, 25,408 out of them (17.5%) were employees. 23,874 (94.0%) of them fell sick during outbreaks in hospitals and related settings. NoV cases among personnel in food establishments were reported only sporadically (mean ratio: 0.01).

Conclusions

Employees in hospitals and community facilities seem quantitatively to be most vulnerable towards NoV epidemics. Therefore, high quality of prevention measures in these settings, respective compliance with prevention strategies should have the highest priority. The disease can be considered as an occupational disease, even regularly without long-term consequences. Following work safety rules, a vaccination for vulnerable groups should be recommended if the vaccine development turns out to be successful.

Electronic supplementary material

The online version of this article (10.1007/s00420-020-01543-4) contains supplementary material, which is available to authorized users.

A foodborne norovirus outbreak in a nursing home and spread to staff and their household contacts

On 16 March 2018, a nursing home notified a possible acute gastroenteritis outbreak that affected 11 people. Descriptive and case-control studies and analysis of clinical and environmental samples were carried out to determine the characteristics of the outbreak, its aetiology, the transmission mechanism and the causal food. The extent of the outbreak in and outside the nursing home was determined and the staff factors influencing propagation were studied by multivariate analysis. A turkey dinner on March 14 was associated with the outbreak (OR 4.22, 95% CI 1.11-16.01). Norovirus genogroups I and II were identified in stool samples. The attack rates in residents, staff and household contacts of staff were 23.49%, 46.22% and 22.87%, respectively. Care assistants and cleaning staff were the staff most frequently affected. Cohabitation with an affected care assistant was the most important factor in the occurrence of cases in the home (adjusted OR 6.37, 95% CI 1.13-36.02). Our results show that staff in close contact with residents and their household contacts had a higher risk of infection during the norovirus outbreak.

Quantifying the roles of vomiting, diarrhea, and residents vs. staff in norovirus transmission in U.S. nursing home outbreaks

The role of individual case characteristics, such as symptoms or demographics, in norovirus transmissibility is poorly understood. Six nursing home norovirus outbreaks occurring in South Carolina, U.S. from 2014 to 2016 were examined. We aimed to quantify the contribution of symptoms and other case characteristics in norovirus transmission using the reproduction number (R_Ei) as an estimate of individual case infectivity and to examine how transmission changes over the course of an outbreak. Individual estimates of R_Ei were calculated using a maximum likelihood procedure to infer the average number of secondary cases generated by each case. The associations between case characteristics and R_Ei were estimated using a weighted multivariate mixed linear model. Outbreaks began with one to three index case(s) with large estimated R_Ei’s (range: 1.48 to 8.70) relative to subsequent cases. Of the 209 cases, 155 (75%) vomited, 164 (79%) had diarrhea, and 158 (76%) were nursing home residents (vs. staff). Cases who vomited infected 2.12 (95% CI: 1.68, 2.68) times the number of individuals as non-vomiters, cases with diarrhea infected 1.39 (95% CI: 1.03, 1.87) times the number of individuals as cases without diarrhea, and resident-cases infected 1.53 (95% CI: 1.15, 2.02) times the number of individuals as staff-cases. Index cases tended to be residents (vs. staff) who vomited and infected considerably more secondary cases compared to non-index cases. Results suggest that individuals, particularly residents, who vomit are more infectious and tend to drive norovirus transmission in U.S. nursing home norovirus outbreaks. While diarrhea also plays a role in norovirus transmission, it is to a lesser degree than vomiting in these settings. Results lend support for prevention and control measures that focus on cases who vomit, particularly if those cases are residents.

The majority of all norovirus outbreaks reported to the CDC occur in long-term care facilities (LTCFs), including nursing homes, where older residents are at risk for more severe or prolonged infection. Because there is currently no publicly available norovirus vaccine, sound control measures are key to controlling norovirus outbreaks, but there is little evidence that standard control measures are effective in reducing the size and/or duration of LTCF norovirus outbreaks. Hence, studies leading to a better understanding of disease spread and prevention of additional cases, and thus more effective control measures, are needed. To this end, we aimed to quantify factors associated with norovirus transmission and to examine how transmission changes over the course of an outbreak. We show that vomiting and, to a lesser extent, diarrhea are critical in initiating and sustaining norovirus transmission in U.S. nursing home norovirus outbreaks. We also show that nursing home residents, rather than staff, are the primary drivers of transmission. Results suggest that control measures focusing on cases who vomit, particularly if those cases are residents, would be most effective at curtailing norovirus transmission in these settings.

Successful control of norovirus outbreak in a pediatric ward with multi-bed rooms

BACKGROUND

Norovirus outbreaks in health care facilities are difficult to prevent and control.

METHODS

We describe a norovirus outbreak that occurred in a single pediatric ward with multi-bed rooms.

RESULTS

The outbreak began with 4 clustered cases with acute diarrhea in a pediatric ward between December 22 and 25, 2017. A total of 10 cases were identified during the outbreak, with a cumulative incidence of 8.77%. The median age of the cases was 10 months. Symptoms lasted for a median of 7.5 days, and norovirus shed in stool for a median of 19.5 days. The first 5 cases consecutively developed diarrhea; 4 of them were in the same room. The sixth case, which was linked with the clustered cases, had stayed in the intensive care unit and infected 3 other patients during the stay. After these 4 cases were transferred back to the ward, an additional patient was infected. Strict infection control measures were implemented, and the outbreak was successfully terminated 24 days after the initial case.

CONCLUSIONS

Controlling norovirus outbreak in a pediatric ward with multi-bed rooms is challenging. Early detection of the outbreak and prompt implementation of strict infection control measures are critical.

[On Statistical Underreporting of Norovirus-Infections: Insights from Register Data of Two Local Public Health Authorities]

BACKGROUND

Only laboratory-confirmed norovirus (NoV) cases have to be notified to the Robert Koch Institute (RKI) since 2011, but not other, e. g. clinical-epidemiological cases. It can be assumed that the extent of underreporting of NoV cases in Germany has significantly increased since then.

OBJECTIVES

To discuss the extent of underreporting, we wanted to find out how many laboratory tests were carried out during gastroenteritis outbreaks. Furthermore, the significance of NoV outbreaks in occupational health is discussed.

MATERIALS AND METHODS

Of all pseudonymized gastroenteritis outbreak data reported to 2 local health authorities between 2011 and 2015, the proportion of NoV outbreaks and reported cases of infection among employees in hospitals and community facilities (nursing homes for the elderly, day-care centers, schools) confirmed by laboratory tests was calculated retrospectively.

RESULTS

Only a few gastroenteritis outbreaks in day-care centers were etiologically diagnosed, so that only 6% and less could be classified as NoV outbreaks. In nursing homes for the elderly, about half of the outbreaks were classified as NoV, in hospitals almost all of them. Employees accounted for up to 23% of those affected in NoV outbreaks.

CONCLUSIONS

The low level of laboratory diagnostics carried out during gastroenteritis outbreaks in day-care centers suggests a considerable number of hidden NoV cases. The significant proportion of staff relative to the total number of infected persons during the outbreaks highlights the importance of the burden of NoV outbreaks as a topic in occupational health. Further, large-scale prospective studies are needed to empirically substantiate these initial findings.

Norovirus shedding among symptomatic and asymptomatic employees in outbreak settings in Shanghai, China

Background

Norovirus (NoV) is recognized as a leading cause of acute gastroenteritis (AGE) outbreaks in settings globally. Studies have shown that employees played an important role in the transmission mode during some NoV outbreaks. This study aimed to investigate the prevalence of NoV infection and duration of NoV shedding among employees during NoV outbreaks, as well as factors affecting shedding duration.

Methods

Specimens and epidemiological data were collected from employees who were suspected of being involved in the transmission or with AGE symptoms during NoV outbreaks in Xuhui District, Shanghai, from 2015 to 2017. Specimens were detected using real-time RT-PCR to determine whether or not employees had become infected with NoV. Specimens were collected every 3–7 days from NoV-infected employees until specimens became negative for NoV.

Results

A total of 421 employees were sampled from 49 NoV outbreaks, and nearly 90% of them (377/421) were asymptomatic. Symptomatic employees showed significantly higher prevalence of NoV infection than asymptomatic ones (70.5% vs. 17.0%, P < 0.01). The average duration of NoV shedding was 6.9 days (95% confidence interval: 6.1–7.7 days) among 88 NoV-infected individuals, and was significantly longer in symptomatic individuals than in asymptomatic ones (9.8 days vs. 5.6 days, P < 0.01). In Cox proportional-hazards model, after adjusting age and gender, symptoms was the only factor associated with duration of NoV shedding.

Conclusions

Compared with asymptomatic employees, symptomatic employees had higher prevalence of NoV infection and longer durations of NoV shedding. Since NoV shedding duration among NoV-infected employees tends to be longer than their isolation time during outbreaks, reinforcement of hygiene practices among these employees is especially necessary to reduce the risk of virus secondary transmissions after their return to work.

Probabilistic modeling for an integrated temporary acquired immunity with norovirus epidemiological data

Integration of acquired immunity into microbial risk assessment for illness incidence is of no doubt essential for the study of susceptibility to illness. In this study, a probabilistic model was set up as dose response for infection and a mathematical derivation was carried out by integrating immunity to obtain probability of illness models. Temporary acquire immunity from epidemiology studies which includes six different Norovirus transmission scenarios such as symptomatic individuals infectious, pre- and post-symptomatic infectiousness (low and high), innate genetic resistance, genogroup 2 type 4 and those with no immune boosting by asymptomatic infection were evaluated. Simulated results on illness inflation factor as a function of dose and exposure indicated that high frequency exposures had immense immunity build up even at high dose levels; hence minimized the probability of illness. Using Norovirus transmission dynamics data, results showed, and immunity included models had a reduction of 2-6 logs of magnitude difference in disease burden for both population and individual probable illness incidence. Additionally, the magnitude order of illness for each dose response remained largely the same for all transmission scenarios; symptomatic infectiousness and no immune boosting after asymptomatic infectiousness also remained the same throughout. With integration of epidemiological data on acquired immunity into the risk assessment, more realistic results were achieved signifying an overestimation of probable risk of illness when epidemiological immunity data are not included. This finding supported the call for rigorous integration of temporary acquired immunity in dose-response in all microbial risk assessments.

Norovirus and rotavirus infections in children less than five years of age hospitalized with acute gastroenteritis in Indonesia

Rotaviruses and noroviruses are the most important viral causes of acute gastroenteritis in children. While previous studies of acute gastroenteritis in Indonesia mainly focused on rotavirus, here, we investigated the burden and epidemiology of norovirus and rotavirus disease. Children less than five years of age hospitalized with acute gastroenteritis were enrolled in this study from January to December 2015 at three participating hospitals. Rotavirus was detected by enzyme immunoassay (EIA), followed by genotyping by reverse transcription PCR (RT-PCR). Norovirus genogroups were determined by TaqMan-based quantitative RT-PCR. Among 406 enrolled children, 75 (18.47%), 223 (54.93%) and 29 (7.14%) cases were positive for norovirus, rotavirus and both viruses (mixed infections), respectively. Most cases clinically presented with fever, diarrhea, vomiting and some degree of dehydration. The majority (n = 69/75 [92%]) of the noroviruses identified belonged to genogroup II, and several genotypes were identified by sequencing a subset of samples. Among 35 samples tested for rotavirus genotype, the most prevalent genotype was G3P[8] (n = 30/35 [85.6%]). Our study suggests that the burden of norovirus diseases in Indonesian children should not be underestimated. It also shows the emergence of rotavirus genotype G3P[8] in Indonesia.

High transmissibility of norovirus among infants and school children during the 2016/17 season in Osaka, Japan

The number of person-to-person transmitted norovirus cases (n = 4,712) in school children in Osaka, Japan, during 2016/17 was the largest since 2012/13. Norovirus outbreaks were reported by 101 schools including 53 nursery schools (1,927 cases), 18 kindergartens (1,086 cases) and 30 elementary schools (1,699 cases). The dominant genotype among outbreaks was GII.P16-GII.2 (57.4%; 58/101), followed by GII.P2-GII.2 (8.9%; 9/101) and GII.P7-GII.6 (5.9%; 6/101). GII.4 was not detected despite dominance in previous years.

Transmissibility of Norovirus in Urban Versus Rural Households in a Large Community Outbreak in China

BACKGROUND

Norovirus is a leading cause of outbreaks of acute infectious gastroenteritis worldwide, yet its transmissibility within households and associated risk factors remain unknown in developing countries.

METHODS

Household, demographic, and clinical data were collected from a semi-urban area in south China where an outbreak occurred in the winter of 2014. Using a Bayesian modeling framework, we assessed the transmissibility and potential risk modifiers in both urban and rural households.

RESULTS

In urban apartment buildings, the secondary attack rates were 84% (95% credible interval [CI] = 60%, 96%) among households of size two and 29% (95% CI = 9.6%, 53%) in larger households. In the rural village, secondary attack rate estimates were lower than the urban setting, 13% (0.51%, 54%) for households of size two and 7.3% (0.38%, 27%) for larger households. Males were 31% (95% CI = 3%, 50%) less susceptible to the disease than female. Water disinfection with chlorine was estimated to reduce environmental risk of infection by 60% (95% CI = 26%, 82%), and case isolation was estimated to reduce person-to-person transmission by 65% (95% CI = 15%, 93%). Nausea and vomiting were not associated with household transmission.

CONCLUSIONS

Norovirus is highly contagious within households, in particular in small households in urban communities. Our results suggest that water disinfection and case isolation are associated with reduction of outbreaks in resource-limited communities.

The Population-Level Impacts of Excluding Norovirus-Infected Food Workers From the Workplace: A Mathematical Modeling Study

Norovirus is the leading cause of acute gastroenteritis and foodborne disease in the United States. The Food and Drug Administration recommends that food workers infected with norovirus be excluded from the workplace while symptomatic and for 48 hours after their symptoms subside. Compliance with this recommendation is not ideal, and the population-level impacts of changes in food-worker compliance have yet to be quantified. We aimed to assess the population impacts of varying degrees of compliance with the current recommendation through the use of a compartmental model. We modeled the number and proportion of symptomatic norovirus cases averted annually in the US population (using data from 1983-2014) in specific age groups (children aged <5 years, children aged 5-17 years, adults aged 18-64 years, and adults aged ≥65 years) under various scenarios of food-worker exclusion (i.e., proportion compliant and days of postsymptomatic exclusion) in comparison with a referent scenario which assumed that 66.6¯% of norovirus-symptomatic food workers and 0% of postsymptomatic food workers were excluded from work. Overall, we estimated that 6.0 million cases of norovirus have already been avoided annually under the referent scenario and that 6.7 million (28%) more cases might be avoided through 100% compliance with the current recommendations. Substantial population-level benefits were predicted from improved compliance in exclusion of norovirus-infected food workers from the workplace-benefits that may be realized through policies or programs incentivizing self-exclusion.

Estimating the incidence of norovirus acute gastroenteritis among US and European international travelers to areas of moderate to high risk of traveler's diarrhea: a prospective cohort study protocol

Background

Acute gastroenteritis (AGE) is the leading cause of illness among returning travelers seeking medical care. Multiple types of enteric pathogens can cause travel-acquired AGE and, while bacterial pathogens have a predominant role, the importance of viruses, such as norovirus, is increasingly recognized. There is a lack of information on travel-acquired norovirus incidence among symptomatic and asymptomatic individuals irrespective of healthcare-seeking behavior. Our aim is to estimate the incidence of travel-acquired AGE due to norovirus and to characterize the burden of disease among international travelers from the United States and Europe.

Methods

We describe a prospective cohort study implemented in five US and European sites to estimate the role of AGE due to norovirus among adult international travelers. We enrolled individuals aged 18 years and older who are traveling to regions of moderate-high risk of AGE, or via cruise ship with an international port stop, with a trip duration of 3–15 days. The study will generate a wide range of health and travel-related data for pre-, during, and up to 6-months post-travel. We will identify laboratory-confirmed travel-acquired norovirus infections among both symptomatic and asymptomatic individuals from self-collected whole stool samples tested via quantitative RT-PCR. Coinfections will be identified in a subset of travelers with AGE using a multiplex molecular-based assay.

Discussion

This study is unique in design and breadth of data collected. The prospective collection of health and behavioral data, as well as biologic samples from travelers irrespective of symptoms, will provide useful data to better understand the importance of norovirus AGE among international travelers. This study will provide data to estimate the incidence of norovirus infections and AGE and the risk of post-infectious sequelae in the 6-month post-travel period serving as a baseline for future norovirus AGE vaccination studies. This study will contribute valuable information to better understand the role of norovirus in travel-acquired AGE risk and the impact of these infections on a broad set of outcomes.

Who is the infector? Epidemic models with symptomatic and asymptomatic cases

What role do asymptomatically infected individuals play in the transmission dynamics? There are many diseases, such as norovirus and influenza, where some infected hosts show symptoms of the disease while others are asymptomatically infected, i.e. do not show any symptoms. The current paper considers a class of epidemic models following an SEIR (Susceptible  →  Exposed  →  Infectious  →  Recovered) structure that allows for both symptomatic and asymptomatic cases. The following question is addressed: what fraction ρ of those individuals getting infected are infected by symptomatic (asymptomatic) cases? This is a more complicated question than the related question for the beginning of the epidemic: what fraction of the expected number of secondary cases of a typical newly infected individual, i.e. what fraction of the basic reproduction number R₀, is caused by symptomatic individuals? The latter fraction only depends on the type-specific reproduction numbers, while the former fraction ρ also depends on timing and hence on the probabilistic distributions of latent and infectious periods of the two types (not only their means). Bounds on ρ are derived for the situation where these distributions (and even their means) are unknown. Special attention is given to the class of Markov models and the class of continuous-time Reed-Frost models as two classes of distribution functions for latent and infectious periods. We show how these two classes of models can exhibit very different behaviour.

Quantifying the relative effects of environmental and direct transmission of norovirus

Norovirus is a common cause of outbreaks of acute gastroenteritis in health- and child-care settings, with serial outbreaks also frequently observed aboard cruise ships. The relative contributions of environmental and direct person-to-person transmission of norovirus have hitherto not been quantified. We employ a novel mathematical model of norovirus transmission, and fit the model to daily incidence data from a major norovirus outbreak on a cruise ship, and examine the relative efficacy of potential control strategies aimed at reducing environmental and/or direct transmission. The reproduction number for environmental and direct transmission combined is [Formula: see text] [6.1,9.5], and of environmental transmission alone is [Formula: see text] [0.9,2.6]. Direct transmission is overwhelmingly due to passenger-to-passenger contacts, but crew can act as a reservoir of infection from cruise to cruise. This is the first quantification of the relative roles of environmental and direct transmission of norovirus. While environmental transmission has the potential to maintain a sustained series of outbreaks aboard a cruise ship in the absence of strict sanitation practices, direct transmission dominates. We find that intensive promotion of good hand washing practices may prevent outbreaks. Isolation of ill passengers and cleaning are beneficial, but appear to be less efficacious at outbreak control.

Environmental Surveillance for Noroviruses in Selected South African Wastewaters 2015-2016: Emergence of the Novel GII.17

Norovirus (NoV) GII.4 is the predominant genotype associated with gastroenteritis pandemics and new strains emerge every 2-3 years. Between 2008 and 2011, environmental studies in South Africa (SA) reported NoVs in 63% of the sewage-polluted river water samples. The aim of this study was to assess whether wastewater samples could be used for routine surveillance of NoVs, including GII.4 variants. From April 2015 to March 2016, raw sewage and effluent water samples were collected monthly from five wastewater treatment plants in SA. A total of 108 samples were screened for NoV GI and GII using real-time RT-qPCR. Overall 72.2% (78/108) of samples tested positive for NoVs with 4.6% (5/108) GI, 31.5% (34/108) GII and 36.1% (39/108) GI + GII strains being detected. Norovirus concentrations ranged from 1.02 × 10² to 3.41 × 10⁶ genome copies/litre for GI and 5.00 × 10³ to 1.31 × 10⁶ genome copies/litre for GII. Sixteen NoV genotypes (GI.2, GI.3, GI.4, GI.5, GI.6, GII.2, GII.3, GII.4, GII.7, GII.9, GII.10, GII.14, GII.16, GII.17, GII.20, and GII.21) were identified. Norovirus GII.2 and GII.17 co-dominated and the majority of GII.17 strains clustered with the novel Kawasaki 2014 variant. Sewage surveillance facilitated detection of Kawasaki 2014 in SA, which to date has not been detected with surveillance in children with gastroenteritis <5 years of age. Combined surveillance in the clinical setting and environment appears to be a valuable strategy to monitor emergence of NoV strains in countries that lack NoV outbreak surveillance.

Norovirus transmission dynamics: a modelling review

Norovirus is one of the leading causes of viral gastroenteritis worldwide and responsible for substantial morbidity, mortality and healthcare costs. To further understanding of the epidemiology and control of norovirus, there has been much recent interest in describing the transmission dynamics of norovirus through mathematical models. In this study, we review the current modelling approaches for norovirus transmission. We examine the data and methods used to estimate these models that vary structurally and parametrically between different epidemiological contexts. Many of the existing studies at population level have focused on the same case notification dataset, whereas models from outbreak settings are highly specific and difficult to generalise. In this review, we explore the consistency in the description of norovirus transmission dynamics and the robustness of parameter estimates between studies. In particular, we find that there is considerable variability in estimates of key parameters such as the basic reproduction number, which may mean that the effort required to control norovirus at the population level may currently be underestimated.

Incorporating social contact data in spatio-temporal models for infectious disease spread

Routine public health surveillance of notifiable infectious diseases gives rise to weekly counts of reported cases-possibly stratified by region and/or age group. We investigate how an age-structured social contact matrix can be incorporated into a spatio-temporal endemic-epidemic model for infectious disease counts. To illustrate the approach, we analyze the spread of norovirus gastroenteritis over six age groups within the 12 districts of Berlin, 2011-2015, using contact data from the POLYMOD study. The proposed age-structured model outperforms alternative scenarios with homogeneous or no mixing between age groups. An extended contact model suggests a power transformation of the survey-based contact matrix toward more within-group transmission.

High prevalence of GII norovirus in hospitalized children with acute diarrhea, in Beijing

This study was addressed to the relationship between norovirus and acute diarrhea in hospitalized children, including hospital-acquired infection (HAI) and community-acquired infection (CAI) in a children's hospital in Beijing. RT-PCR was used to detect norovirus in stool specimen, followed by sequence analysis for PCR products. From 2010 to 2013, a total of 1248 specimens, including 661 from the HAI group and 587 from the CAI group were tested for norovirus. Norovirus were detected in 380 of 1248 (30.4%) diarrheal specimens. The positive rate for norovirus detection was higher in children within HAI group than CAI group (35.3%, 232/661 vs. 25.6%, 148/587), and the difference was significant (X² = 14.35, P<0.05). For age distribution, the highest positivity rates of norovirus were in age of 0–5 months for HAI group and 12–23 months for CAI group. In the study, 262 amplicons of the VP1 region from norovirus-positive specimens were sequenced, which showed GII.3 and GII.4 norovirus were the most common genotypes detected in 50.0% (n = 131) and 48.9% (n = 128) of the positive specimens, respectively. Regarding the wards distribution, GII.3 norovirus was mainly detected in ward for neonatal diseases (36/85 in HAI group; 19/46 in CAI group), GII.4 norovirus was mainly detected in ward for respiratory and digestive diseases (21/85 in HAI group; 15/33 in CAI group). Conclusion: The data elaborated the importance of norovirus in hospital associated infectious diarrhea. The prevalence of norovirus is higher from HAI group than CAI group, and the norovirus from the patients in CAI group could be the source of infection in HAI group.

The transmissibility of noroviruses: Statistical modeling of outbreak events with known route of transmission in Japan

In Japan, the fraction of norovirus outbreaks attributable to human-to-human transmission has increased with time, and the timing of the increased fraction has coincided with the increase in the observed fraction of genogroup II genotype 4 (GII.4). The present study aimed to estimate the time-dependent changes in the transmissibility of noroviruses. The effective reproduction number (R_y), for year y, was estimated by analyzing the time series surveillance data for outbreak events from 2000 to 2016. R_y was estimated by using the fraction of outbreak events that were attributable to human-to-human transmission and by employing three different statistical models that are considered to mechanistically capture the possible data-generating process in different ways. The R_y estimates ranged from 0.14 to 4.15 in value, revealing an overall increasing trend (p<0.05 for all three models). The proportion of outbreaks caused by GII and GII.4 viruses among the total events also increased with time, and positive correlations were identified between transmissibility and these proportions. Parametric modeling of R_y indicated that the time-dependent patterns of R_y were better described by a step function plus linear trend rather than the step function alone that reflects the widespread use of reverse transcriptase PCR (RT-PCR) in and after 2007 for laboratory diagnosis. Accordingly, we conclude that norovirus transmissibility has increased over the past 16 years in Japan. The change is at least partially explained by the time-dependent domination of the contagious GII genogroup (e.g., GII.4), indicating that noroviruses better fitted to humans have selectively caused the human-to-human transmissions, thereby altering the epidemiology of this pathogen.

Norovirus Disease in Older Adults Living in Long-Term Care Facilities: Strategies for Management

Purpose of Review

Noroviruses are the most common cause of gastroenteritis outbreaks in long-term care facility (LTCFs). This review summarizes the most up-to-date knowledge on norovirus infection in LTCFs with the aim of identifying potential strategies for management.

Recent Findings

LTCF residents are at greater risk of norovirus infection. Early identification of norovirus infection and prompt initiation of appropriate supportive therapy are required to reduce morbidity and mortality. Measures to prevent outbreaks and reduce the risk of norovirus infection in LTCFs include timely diagnosis and implementation of infection control interventions to limit virus transmission.

Summary

Current guidelines for prevention and control are based on generic principles of infection control. Real-time reverse transcription-quantitative polymerase chain reaction assays have been the gold standard for the rapid and sensitive detection of noroviruses. With the recent breakthroughs of human norovirus in vitro culture, doors are now opened to evaluate the efficacy of environmental disinfectants and hand hygiene options. Additionally, development of licensed vaccines against noroviruses may provide another important tool for infection prevention among high-risk individuals.

A large outbreak of acute gastroenteritis caused by the human norovirus GII.17 strain at a university in Henan Province, China

Background

Human noroviruses are a major cause of viral gastroenteritis and are the main etiological agents of acute gastroenteritis outbreaks. An increasing number of outbreaks and sporadic cases of norovirus have been reported in China in recent years. There was a large acute gastroenteritis outbreak at a university in Henan Province, China in the past five years. We want to identify the source, transmission routes of the outbreak by epidemiological investigation and laboratory testing in order to provide the effective control measures.

Methods

The clinical cases were investigated, and analysed by descriptive epidemiological methods according to factors such as time, department, grade and so on. Samples were collected from clinical cases, healthy persons, the environment, water, and food at the university. These samples were tested for potential bacteria and viruses. The samples that tested positive for norovirus were selected for whole genome sequencing and the sequences were then analysed.

Results

From 4 March to 3 April 2015, a total of 753 acute diarrhoea cases were reported at the university; the attack rate was 3.29%. The epidemic curve showed two peaks, with the main peak occurring between 10 and 20 March, accounting for 85.26% of reported cases. The rates of norovirus detection in samples from confirmed cases, people without symptoms, and environmental samples were 32.72%, 17.39%, and 9.17%, respectively. The phylogenetic analysis showed that the norovirus belonged to the genotype GII.17.

Conclusions

This is the largest and most severe outbreak caused by genotype GII.17 norovirus in recent years in China. The GII.17 viruses displayed high epidemic activity and have become a dominant strain in China since the winter of 2014, having replaced the previously dominant GII.4 Sydney 2012 strain.

Electronic supplementary material

The online version of this article (doi:10.1186/s40249-017-0236-z) contains supplementary material, which is available to authorized users.

Re-assessing the total burden of norovirus circulating in the United Kingdom population

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Norovirus is the commonest cause of GI disease in the UK.

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Less stringent diagnostic threshold Increases previous estimate by 26%.

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Re-assessed estimate equates to burden of infection at 59 per 1000 person years.

The second Infectious Intestinal Diseases study (IID2) estimated the incidence of norovirus in the UK at 47/1000 population (three million cases annually). Clinically significant norovirus was defined using a cycle threshold (ct) value of <30; a more stringent cut-off than used in diagnostic laboratories. The low infectious dose of norovirus means asymptomatic individuals potentially contribute to ongoing transmission. Using a less stringent but diagnostically relevant threshold increases the estimation of the population burden of norovirus infection by around 26% to 59/1000 person years (95% CI 52.32–64.98), equating to 3.7 million norovirus infections annually (3.3–4.1 million). With possible vaccines on the horizon for norovirus, having a good estimate of the total burden of norovirus infection, as well as symptomatic disease will be useful in helping to guide vaccination policy when candidate vaccines become available.

Capturing norovirus transmission

Human norovirus is a leading cause of gastroenteritis and is efficiently transmitted between humans and around the globe. The burden of norovirus infections in the global community and in health-care settings warrant the availability of outbreak prevention strategies and control measures that are tailored to the pathogen, outbreak setting and population at risk. A better understanding of viral and host determinants of transmission would aid in developing and fine-tuning such efforts. Here, we describe mechanisms of transmission, available model systems for studying norovirus transmission and their strengths and weaknesses as well as future research strategies.