Norovirus introduction routes into nursing homes and risk factors for spread: a systematic review and meta-analysis of observational studies

Impact of the COVID-19 pandemic on norovirus circulation in Germany

Human norovirus is a major cause of viral gastroenteritis in all age groups. The virus is constantly and rapidly changing, allowing mutations and recombination events to create great diversity of circulating viruses. With the start of the COVID-19 pandemic in 2020, a wide range of public health measures were introduced worldwide to control human-to-human transmission of SARS-CoV-2. In Germany, control measures such as distance rules, contact restrictions, personal protection equipment as well as intensive hand hygiene were introduced. To better understand the effect of the measures to control the COVID-19 pandemic on incidence and the molecular epidemiological dynamics of norovirus outbreaks in Germany, we analyzed national notification data between July 2017 and December 2022 and characterized norovirus sequences circulating between January 2018 and December 2022. Compared to a reference period before the pandemic, the incidence of notified norovirus gastroenteritis decreased by 89.7% to 9.6 per 100,000 during the 2020/2021 norovirus season, corresponding to an incidence rate ratio (IRR) of 0.10. Samples from 539 outbreaks were genotyped in two regions of the viral genome from pre-pandemic (January 2018 to February 2020) and samples from 208 outbreaks during pandemic time period (March 2020 to December 2022). As expected, norovirus outbreaks were mainly found in child care facilities and nursing homes. In total, 36 genotypes were detected in the study period. A high proportion of recombinant strains (86%) was found in patients, the proportion of detected recombinant viruses did not vary between the pre-pandemic and pandemic phase. The proportion of the predominant recombinant strain GII.4 Sydney[P16] was unchanged before pandemic and during pandemic at 37.5%. The diversity of most common genotypes in nursing homes and child care facilities showed a different proportion of genotypes causing outbreaks. In nursing homes as well as in child care facilities GII.4 Sydney[P16] was predominant during the whole study period. Compared to the nursing homes, a greater variety of genotypes at the expense of GII.4 Sydney[P16] was detected in child care facilities. Furthermore, the overall proportion of recombinant strain GII.3[P12] increased during the pandemic, due to outbreaks in child care facilities. The COVID-19 pandemic had a high impact on the occurrence of sporadic cases and norovirus outbreaks in Germany, leading to a near suppression of the typical norovirus winter season following the start of the pandemic. The number of norovirus-associated outbreak samples sent to the Consultant Laboratory dropped by 63% during the pandemic. We could not identify a clear influence on circulating norovirus genotypes. The dominance of GII.4 Sydney recombinant strains was independent from the pandemic. Further studies are needed to follow up on the diversity of less predominant genotypes to see if the pandemic could have acted as a bottleneck to the spread of previously minoritized genotypes like GII.3[P12].

The impact of COVID-19 pandemic on the incidence of acute gastroenteritis outbreaks in Catalonia (Spain)

We carried out a retrospective study of acute gastroenteritis (AGE) outbreaks reported between 1 January 2015 and 31 December 2021 in Catalonia (Spain) to compare the incidence from 2015 to 2019 with that observed from 2020 to 2021. We observed a higher incidence rate of outbreaks during the prepandemic period (16.89 outbreaks/1,000,000 person-years) than during the pandemic period (6.96 outbreaks/1,000,000 person-years) (rate ratio (RR) 0.41; 95% confidence interval (CI) 0.34 to 0.51). According to the aetiology of the outbreak, those of viral aetiology decreased from 7.82 to 3.38 outbreaks/1,000,000 person-years (RR 2.31; 95% CI 1.72 to 3.12), and those of bacterial aetiology decreased from 5.01 to 2.78 outbreaks/1,000,000 person-years (RR 1.80; 95% CI 1.29 to 2.52). There was a great reduction in AGE outbreaks in Catalonia. This reduction may have been due to the effect of the nonpharmaceutical measures applied to reduce the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), but the collapse of the healthcare system and epidemiological surveillance services may also have had a strong influence.

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.

Enablement of nursing home residents in infection prevention during general practitioner visits: A qualitative study

Introduction

Hand hygiene measures are essential to protect nursing home residents against nosocomial infections. Evidence on the prevention of nosocomial infections for nursing home residents by general practitioners during their medical visits in nursing homes or how they enable nursing home residents to perform hand hygiene measures is lacking. This study aimed to explore hand hygiene behaviors of general practitioners in nursing homes, their attitudes toward infection prevention measures, and the enablement of nursing home residents in performing hand hygiene measures.

Materials and methods

Semi-structured interviews were conducted with general practitioners and nursing home residents in Germany. Interviews were audio-recorded and transcribed. Data were analyzed using thematic content analysis.

Results

Overall, 12 general practitioners and 12 nursing home residents participated in the study. The general practitioners expressed the fact that the possibilities for practicing hand hygiene differ in individual nursing homes. For nursing home residents, the availability of hand rub solutions was limited. Instructions for residents on hand disinfection from general practitioners was not described. Due to the lack of enablement, the residents’ knowledge on how to correctly perform hand hygiene was low, although some of the nursing home residents have experience with multidrug-resistant organisms. The nursing home residents varied in their needs for active participation and enablement during the general practitioners visit.

Conclusion

Nursing home residents require continuous enablement by their general practitioners to maintain adequate hand hygiene. Therefore, general practitioners should consider the different needs of nursing home residents to ensure adequate individual hand hygiene and safety for the residents. Existing guidelines for infection prevention and control do not adequately cover the nursing home care setting for the enablement of residents to enquire about hand hygiene.

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

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

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

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

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

Norovirus Outbreaks in Long-term Care Facilities in the United States, 2009-2018: A Decade of Surveillance

BACKGROUND

In the United States, norovirus is the leading cause of healthcare-associated gastroenteritis outbreaks. To inform prevention efforts, we describe the epidemiology of norovirus outbreaks in long-term care facilities (LTCFs).

METHODS

The Centers for Disease Control and Prevention (CDC) collect epidemiologic and laboratory data on norovirus outbreaks from US health departments through the National Outbreak Reporting System (NORS) and CaliciNet. Reports from both systems were merged, and norovirus outbreaks in nursing homes, assisted living, and other LTCFs occurring in 2009-2018 were analyzed. Data from the Centers for Medicare and Medicaid Services and the National Center for Health Statistics were used to estimate state LTCF counts.

RESULTS

During 2009-2018, 50 states, Washington D.C., and Puerto Rico reported 13 092 norovirus outbreaks and 416 284 outbreak-associated cases in LTCFs. Participation in NORS and CaliciNet increased from 2009 to 2014 and median reporting of LTCF norovirus outbreaks stabilized at 4.1 outbreaks per 100 LTCFs (interquartile range [IQR]: 1.0-7.1) annually since 2014. Most outbreaks were spread via person-to-person transmission (90.4%), and 75% occurred during December-March. Genogroup was reported for 7292 outbreaks with 862 (11.8%) positive for GI and 6370 (87.3%) for GII. Among 4425 GII outbreaks with typing data, 3618 (81.8%) were GII.4. LTCF residents had higher attack rates than staff (median 29.0% vs 10.9%; P < .001). For every 1000 cases, there were 21.6 hospitalizations and 2.3 deaths.

CONCLUSIONS

LTCFs have a high burden of norovirus outbreaks. Most LTCF norovirus outbreaks occurred during winter months and were spread person-to-person. Outbreak surveillance can inform development of interventions for this vulnerable population, such as vaccines targeting GII.4 norovirus strains.

A Methodological Quality Evaluation of Meta-Analyses on Nursing Home Research: Overview and Suggestions for Future Directions

(1) Background: The nursing home (NH) research field lacks quality reporting about meta-analyses (MAs), and most gradings of MA evidence are biased on analyzing the effectiveness of independent variables in randomized control trials. (2) Objectives: This study aimed to perform a critical methodological review of MAs in the NH research field. (3) Methods: We searched the articles from four databases (PubMed, MEDLINE, CINAHL, and PsycINFO) until 15th January 2021. We reviewed a total of 41 published review articles in the NH research field. (4) Results: The studies primarily fell into the following categories: medicine (17/41), nursing (7/41), and psychiatry or psychology (6/41); 36.6% of the reviewed studies did not use any validated MA guidelines. The lowest correctly reported PRISMA 2000 guideline item was protocol and registration (14.6%), and more than 50% of articles did not report risk of bias. Moreover, 78.0% of studies did not describe missing reports of effect size formula. (5) Discussion: NH researchers must follow appropriate and updated guidelines for their MAs in order to provide validated reviews, as well as consider statistical issues such as the complexity of interventions, proper grouping, and scientific effect-size calculations to improve the quality of their study. Future quality review studies should investigate more diverse studies.

Assessment of Food and Waterborne Viral Outbreaks by Using Field Epidemiologic, Modern Laboratory and Statistical Methods-Lessons Learnt from Seven Major Norovirus Outbreaks in Finland

Seven major food- and waterborne norovirus outbreaks in Western Finland during 2014–2018 were re-analysed. The aim was to assess the effectiveness of outbreak investigation tools and evaluate the Kaplan criteria. We summarised epidemiological and microbiological findings from seven outbreaks. To evaluate the Kaplan criteria, a one-stage meta-analysis of data from seven cohort studies was performed. The case was defined as a person attending an implicated function with diarrhoea, vomiting or two other symptoms. Altogether, 22% (386/1794) of persons met the case definition. Overall adjusted, 73% of norovirus patients were vomiting, the mean incubation period was 44 h (4 h to 4 days) and the median duration of illness was 46 h. As vomiting was a more common symptom in children (96%, 143/149) and diarrhoea among the elderly (92%, 24/26), symptom and age presentation should drive hypothesis formulation. The Kaplan criteria were useful in initial outbreak assessments prior to faecal results. Rapid food control inspections enabled evidence-based, public-health-driven risk assessments. This led to probability-based vehicle identification and aided in resolving the outbreak event mechanism rather than implementing potentially ineffective, large-scale public health actions such as the withdrawal of extensive food lots. Asymptomatic food handlers should be ideally withdrawn from high-risk work for five days instead of the current two days. Food and environmental samples often remain negative with norovirus, highlighting the importance of research collaborations. Electronic questionnaire and open-source novel statistical programmes provided time and resource savings. The public health approach proved useful within the environmental health area with shoe leather field epidemiology, combined with statistical analysis and mathematical reasoning.

Norovirus outbreaks in long-term care facilities in Catalonia from 2017 to 2018

Norovirus is the leading cause of outbreaks of acute viral gastroenteritis. We carried out this study to investigate outbreaks in long-term care facilities reported in 2017 and 2018 in Catalonia (Spain). The characteristics of the centers, exposed persons and the genogroups responsible were analyzed. Viral loads were estimated. The attack rate (AR) of the outbreaks studied, and the rate ratio (RR) and the odds ratio (OR) and their 95% confidence intervals as measures of association were calculated. The mean cycle thresholds were compared using the t-test for independent means. We included 30 outbreaks (4631 exposed people). The global AR was 25.93%. The RR of residents vs. staff was 2.28 (95% CI 2.0–2.6). The RR between AR in residents with total or severe dependence vs. residents with moderate, low or no-dependence was 1.23 (95% CI 1.05–1.45). The AR were higher in smaller centers than in larger ones (38.47% vs. 19.25% and RR 2; 95% CI 1.82–2.2). GII was responsible for 70% of outbreaks. No association was found between the genogroup and presenting symptoms (OR 0.96; 95% CI 0.41–2.26). Viral loads were higher in symptomatic than in asymptomatic patients (p = 0.001).

Healthcare-associated foodborne outbreaks in high-income countries: a literature review and surveillance study, 16 OECD countries, 2001 to 2019

BackgroundHealthcare-associated foodborne outbreaks (HA-FBO) may have severe consequences, especially in vulnerable groups.AimThe aim was to describe the current state of HA-FBO and propose public health recommendations for prevention.MethodsWe searched PubMed, the Outbreak Database (Charité, University Medicine Berlin), and hand-searched reference lists for HA-FBO with outbreak onset between 2001 and 2018 from Organisation for Economic Co-operation and Development (OECD) countries and HA-FBO (2012-2018) from the German surveillance system. Additionally, data from the European Food Safety Authority were analysed.ResultsThe literature search retrieved 57 HA-FBO from 16 OECD countries, primarily in the US (n = 11), Germany (n = 11) and the United Kingdom (n = 9). In addition, 28 HA-FBO were retrieved from the German surveillance system. Based on the number of outbreaks, the top three pathogens associated with the overall 85 HA-FBO were Salmonella (n = 24), norovirus (n = 22) and Listeria monocytogenes (n = 19). Based on the number of deaths, L. monocytogenes was the main pathogen causing HA-FBO. Frequently reported implicated foods were 'mixed foods' (n = 16), 'vegetables and fruits' (n = 15) and 'meat and meat products' (n = 10). Consumption of high-risk food by vulnerable patients, inadequate time-temperature control, insufficient kitchen hygiene and food hygiene and carriers of pathogens among food handlers were reported as reasons for HA-FBO.ConclusionTo prevent HA-FBO, the supply of high-risk food to vulnerable people should be avoided. Well working outbreak surveillance facilitates early detection and requires close interdisciplinary collaboration and exchange of information between hospitals, food safety and public health authorities.

Understanding the Importance of Contact Heterogeneity and Variable Infectiousness in the Dynamics of a Large Norovirus Outbreak

BACKGROUND

Large norovirus (NoV) outbreaks are explosive in nature and vary widely in final size and duration, suggesting that superspreading combined with heterogeneous contact may explain these dynamics. Modeling tools that can capture heterogeneity in infectiousness and contact are important for NoV outbreak prevention and control, yet they remain limited.

METHODS

Data from a large NoV outbreak at a Dutch scout jamboree, which resulted in illness among 326 (of 4500 total) individuals from 7 separate camps, were used to examine the contributions of individual variation in infectiousness and clustered contact patterns to the transmission dynamics. A Bayesian hierarchical model of heterogeneous, clustered outbreak transmission was applied to represent (1) between-individual heterogeneity in infectiousness and (2) heterogeneous patterns of contact.

RESULTS

We found wide heterogeneity in infectiousness across individuals, suggestive of superspreading. Nearly 50% of individual infectiousness was concentrated in the individual's subcamp of residence, with the remainder distributed over other subcamps. This suggests a source-and-sink dynamic in which subcamps with greater average infectiousness fed cases to those with a lower transmission rate. Although the per capita transmission rate within camps was significantly greater than that between camps, the large pool of susceptible individuals across camps enabled similar numbers of secondary cases generated between versus within camps.

CONCLUSIONS

The consideration of clustered transmission and heterogeneous infectiousness is important for understanding NoV transmission dynamics. Models including these mechanisms may be useful for providing early warning and guiding outbreak response.

Infection Control Citations in Nursing Homes: Compliance and Geographic Variability

Objectives

To report the initial compliance with new infection control regulations and geographic disparities in nursing homes (NHs) in the United States.

Design

Retrospective cohort study from November 27, 2017 to November 27, 2019.

Setting and Participants

In total, 14,894 NHs in the continental United States comprising 26,201 inspections and 176,841 deficiencies.

Methods

We measured the cumulative incidence of receiving F880: Infection Prevention and Control deficiencies, geographic variability of F880 citations across the United States, and the scope and severity of the infection control deficiencies.

Results

A total of 6164 NHs (41%) in the continental United States received 1 deficiency for F880, and 2300 NHs (15%) were cited more than once during the 2-year period. Geographic variation was evident for F880 deficiencies, ranging from 20% of NHs in North Carolina to 79% of NHs in West Virginia. Between 0% (Vermont) and 33% (Michigan) of states’ NHs were cited multiple times over 2 years. Facilities receiving 2 or more F880 deficiencies were more reliant on Medicaid, for-profit, and served more acute residents. Infection Prevention and Control deficiencies were of similar severity but of greater scope in NHs that were cited multiple times.

Conclusions and Implications

As the coronavirus disease 2019 pandemic challenges hospitals with an increased surge of patients from the community, NHs will be asked to accept convalescing patients who were previously infected with the virus. NHs will need to rely on infection control practices to mitigate the effects of the virus in their facilities. Particular attention to NHs that have fared poorly with repeat infection control practices deficiencies might be a good first step to improving care overall and preventing downstream morbidity and mortality among the highest-risk patients.

Epidemiology of 2017 influenza outbreaks in nine Australian Aged care facilities

Background

The 2017 A/H3N2 influenza season was the most severe season since the 2009 influenza pandemic. There were over 591 influenza outbreaks in institutions across the state of New South Wales (NSW) in Australia.

Aim

To describe the epidemiology of influenza outbreaks in nine Sydney aged care facilities in 2017.

Methods

Study data were collected from nine Sydney aged care facilities for 2017 influenza season. Descriptive epidemiological analysis was conducted.

Results

From the nine sites included, with a total of 716 residents, four sites reported laboratory‐confirmed influenza outbreaks during the study period, with an attack rate in residents ranging from 6% to 29%. The outbreaks resulted in lockdowns in two facilities and hospitalisation of seven residents. No deaths were reported as a result of influenza infection. Influenza A was the most common influenza type reported across the facilities. The duration of outbreak lasted for 1‐4 weeks varied by site.

Conclusion

The 2017 season was a severe influenza season recorded in Australia. About half of the facilities studied experienced outbreaks of influenza, with a high attack rate among residents. Infection prevention and control measures and outbreak management plans are crucial for aged care facilities, including vaccination of staff and visitors to prevent outbreaks among the vulnerable residents.

Norovirus in health care and implications for the immunocompromised host

PURPOSE OF REVIEW

The majority of norovirus outbreaks in the United States occur in healthcare facilities. With the growing population of immunocompromised hosts who are in frequent contact with healthcare facilities, norovirus is not only a threat to hospitals and nursing homes but also to these individuals. This review summarizes the impact of norovirus infection on healthcare facilities and immunocompromised hosts.

RECENT FINDINGS

The natural history of norovirus infection in immunocompromised individuals remains poorly understood. Although host immune responses play a critical role in reducing duration of viral shedding and viral load in norovirus-infected individuals, why some immunocompromised patients spontaneously recover while others develop a chronic and protracted course of illness remains unclear. Norovirus outbreaks occur in healthcare facilities because the virus is highly contagious, resistant to disinfection and efficiently transmitted. The use of real-time metagenomic next-generation sequencing and phylogenetic analyses has provided valuable information on transmission patterns in complex hospital-associated norovirus outbreaks. The development of human intestinal enteroid cultures enables the determination of effectiveness of disinfectants against human noroviruses, circumventing the validity questions with surrogate virus models due to differences in susceptibility to inactivation and disinfectants.

SUMMARY

Metagenomics next-generation sequencing can enhance our understanding of norovirus transmission and lead to more timely mitigation strategies to curb norovirus outbreaks in healthcare facilities. With new in-vitro cultivation methods for human noroviruses, candidate vaccines and effective antivirals could be available in the near future.

Transmission routes of rare seasonal diseases: the case of norovirus infections

Norovirus (NoV) is the most commonly recognized cause of acute gastroenteritis, with over a million cases globally per year. While usually self-limiting, NoV poses a substantial economic burden because it is highly contagious and there are multiple transmission routes. Infection occurs through inhalation of vomitus; faecal-oral spread; and food, water and environmental contamination. While the incidence of the disease is predictably seasonal, much less is known about the relative contribution of the various exposure pathways in causing disease. Additionally, asymptomatic excretion and viral shedding make forecasting disease burden difficult. We develop a novel stochastic dynamic network model to investigate the contributions of different transmission pathways in multiple coupled social networks representing schools, hospitals, care-homes and family households in a community setting. We analyse how the networks impact on transmission. We used ward-level demographic data from Northumberland, UK to create a simulation cohort. We compared the results with extant data on NoV cases from the IID2 study. Connectivity across the simulated cohort was high. Cases of NoV showed marked seasonality, peaking in early winter and declining through the summer. For the first time, we show that fomites and food appear to be the most important exposure routes in determining the population burden of disease. This article is part of the theme issue 'Modelling infectious disease outbreaks in humans, animals and plants: epidemic forecasting and control'. This theme issue is linked with the earlier issue 'Modelling infectious disease outbreaks in humans, animals and plants: approaches and important themes'.

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.

What proportion of care home outbreaks are caused by norovirus? An analysis of viral causes of gastroenteritis outbreaks in care homes, North East England, 2016-2018

BACKGROUND

Outbreaks of infectious gastroenteritis are common in care homes for the elderly. Norovirus can cause these outbreaks, but diagnosis is frequently based solely on clinical characteristics. Our objective in this study was to describe the epidemiology of norovirus and other gastrointestinal pathogens in these settings.

METHODS

We analysed surveillance data from gastroenteritis outbreaks reported in North East England between 04 July 2016 to 01 July 2018. Stool samples taken during these outbreaks were tested for a range of viral and bacterial pathogens. We described the epidemiology of these outbreaks and explored the characteristics of norovirus outbreaks versus from other viral causes using multivariable logistic regression.

RESULTS

From the 566 care home gastroenteritis outbreaks in this study, we found that norovirus was the pathogen most frequently isolated. Norovirus was detected in 64% of outbreaks with a pathogen identified. Sapovirus was found in 13%; rotavirus in 11%. We found that norovirus outbreaks were associated with higher attack rates (aOR 1.03, 95% CI 1.01-1.05) and fewer cases sampled (aOR 0.74, 95% CI 0.60-0.91), compared to outbreaks caused by other viral pathogens.

CONCLUSIONS

These results are important as they quantify the contribution of norovirus to gastroenteritis outbreaks in care homes. Given this evidence, we emphasize the importance of non-specific outbreak interventions that can affect the impact of all such outbreaks. We further recommend that these findings are used to inform the implementation strategies of any norovirus-specific interventions such as a norovirus vaccine.

Gastroenteritis and respiratory infection outbreaks in French nursing homes from 2007 to 2018: Morbidity and all-cause lethality according to the individual characteristics of residents

Background

Gastroenteritis (GE) and respiratory tract infection (RTI) outbreaks are a significant issue in nursing homes. This study aimed to describe GE and RTI outbreaks with infection and all-cause lethality rates according to the individual characteristics of nursing home residents.

Methods

Clinical and virological surveillance were conducted (2007 to 2018). Virus stratifications for the analysis were: outbreaks with positive norovirus or influenza identifications (respectively NoV+ or Flu+), episodes with no NoV or influenza identification or testing (respectively NoV- or Flu-). Associations between individual variables (sex, age, length of stay (LOS), autonomy status) and infection and lethality rates were tested with univariate and Mantel-Haenszel (MH) methods.

Results

61 GE outbreaks and 76 RTI oubreaks (total 137 outbreaks) were recorded involving respectively 4309 and 5862 residents. In univariate analysis, higher infection rates and age were associated in NoV+, NoV-, and Flu+ contexts, and lower infection rates were associated with longer stays (NoV+ and NoV-). In MH stratified analysis (virus, sex (female/male)) adjusted for LOS (<4 or ≥4 years), the odds of being infected remained significant among older residents (≥86 years): NoV+/male (Odds ratio (OR_MH): 1.64, 95% confidence interval (CI): 1.16–2.30) and Flu+/female and male (respectively OR_MH: 1.50, CI: 1.27–1.79 and 1.73, CI: 1.28–2.33). In univariate analysis, lower autonomy status (NoV+, Flu+ and Flu-) and increased age (Flu+) were associated with higher lethality. In MH adjusted analysis, significant OR_age adjusted for autonomy was: Flu+/ ≥86 years compared with <86 years, 1.97 (1.19–3.25) and OR_autonomy adjusted for age for the more autonomous group (compared with the less autonomous group) was: Flu+, 0.41 (0.24–0.69); Flu-, 0.42 (0.20, 0.90).

Conclusion

The residents of nursing homes are increasingly elderly and dependent. The specific infection and lethality risks according to these two factors indicate that surveillance and infection control measures are essential and of high priority.

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.

Estimating the burden of care home gastroenteritis outbreaks in England, 2014-2016

BACKGROUND

Outbreaks of infectious gastroenteritis in care homes are common, with norovirus a frequent cause. In England there is no co-ordinated national surveillance system. We aimed to estimate the burden of these outbreaks.

METHODS

Using a generalised linear mixed effects regression model we described the relationship between the observed number of care home outbreaks and covariates. Estimated model parameters were used to infer uplift in the number of outbreaks expected if all areas were subjected to enhanced surveillance. From this we then estimated the total burden of care home gastroenteritis outbreaks in this period.

RESULTS

We estimated a total of 14,146 care home gastroenteritis outbreaks in England during 2014-2016; this is 47% higher than the reported total and a rate of 32.4 outbreaks per 100 care homes per year. The median number of outbreaks from the model estimates was 31 (IQR 20-46) compared to 19 (IQR 12-34) reported from routine surveillance.

CONCLUSIONS

This estimated care home gastroenteritis burden in England indicates that current surveillance substantially underestimates the number of outbreaks, by almost half. Improving this surveillance could provide better epidemiological knowledge of the burden of norovirus to inform public health policy, particularly with the advent of norovirus vaccines.

The role of dependency in a norovirus outbreak in a nursing home

PURPOSE

The objectives of the epidemiological investigation were to describe factors associated with prolonged transmission of acute gastroenteritis in a nursing home during a norovirus outbreak.

METHODS

A retrospective cohort study was conducted among residents (N = 89) and staff members (N = 86) of the nursing home. Outbreak description was performed in both residents and staff members. Among residents, attack rates and relative risks and their 95% confidence interval (95% CI) associated with different identified risk factors including consumption of normal, mixed and choped meal, score of dependency were calculated. A multivariate logistic regression model was fitted to assess the independent association between risk factors and the occurrence of acute gastroenteritis over the entire outbreak duration. Environmental investigations and review of practices were carried out among staff.

RESULTS

Respectively 49/89 respondent residents (AR 58%) and 9/47 respondent staff members (AR 19%) reported gastrointestinal symptoms between September 17 and October 21, 2016. Norovirus type II was isolated in five stool samples. Residents with dependency score (Gir) below 4 were at higher risk of acute gastroenteritis [RR 2.1 (95% CI 1.1-4.1)] compared to those autonomous. It was the only identified risk factor. In addition, the review of practices in staff identified several breaks in the application of hygiene control standards including misuse of personal protective equipment (gloves were not changed between caring for different patients), inappropriate hand hygiene technique, and disinfection of environmental surfaces with an ineffective product on norovirus.

CONCLUSIONS

This episode reminds the importance of early recognition of acute gastroenteritis cases and the implementation of rigorous management measures in order to limit the spread of the epidemic in a highly vulnerable dependent population.

Characterization of intra- and inter-host norovirus P2 genetic variability in linked individuals by amplicon sequencing

Noroviruses are the main cause of epidemics of acute gastroenteritis at a global scale. Although chronically infected immunocompromised individuals are regarded as potential reservoirs for the emergence of new viral variants, viral quasispecies distribution and evolution patterns in acute symptomatic and asymptomatic infections has not been extensively studied. Amplicons of 450 nts from the P2 coding capsid domain were studied using next-generation sequencing (454/GS-Junior) platform. Inter-host diversity between symptomatic and asymptomatic acutely infected individuals linked to the same outbreak as well as their viral intra-host diversity over time were characterized. With an average of 2848 reads per sample and a cutoff frequency of 0.1%, minor variant haplotypes were detected in 5 out of 8 specimens. Transmitted variants could not be confirmed in all infected individuals in one outbreak. The observed initial intra-host viral diversity in asymptomatically infected subjects was higher than in symptomatic ones. Viral quasispecies evolution over time within individuals was host-specific, with an average of 2.8 nt changes per day (0.0062 changes per nucleotide per day) in a given symptomatic case. Nucleotide polymorphisms were detected in 28 out of 450 analyzed nucleotide positions, 32.14% of which were synonymous and 67.86% were non-synonymous. Most observed amino acid changes emerged at or near blockade epitopes A, B, D and E. Our results suggest that acutely infected individuals, even in the absence of symptoms, which go underreported and may enhance transmission, may contribute to norovirus genetic variability and evolution.

Chronic sequelae and severe complications of norovirus infection: A systematic review of literature

Norovirus causes an estimated 18% of all cases of acute gastroenteritis worldwide and is found to be associated with mortality. To create a first overview of severe complications and chronic sequelae of norovirus infections, a systematic review of literature was performed. Of 3928 individual hits, 176 publications remained for data extraction. Study periods varied between 1974 and 2017, though strongly skewed towards the last decade (n = 122, 70%). Countries of studies were worldwide, though Africa, and Carribean, Central and South America were underrepresented. Strong evidence was found for chronic diarrhea in immunocompromised patients, affecting 9%-100% of investigated cohorts. The duration of chronic diarrhea varied from four weeks up to nine years, leading to either wasting, weight loss or failure to thrive in a third of the reported cases (224). Other complications with significant evidence were necrotizing enterocolitis (NEC) in preterm infants associated with norovirus infection (8 papers), and benign infantile convulsions with gastroenteritis (BICG; 19 papers). Studies on norovirus infection and inflammatory bowel disease (IBD) mostly concluded against this association (5 of 7). The remaining papers mentioned a large variety of possible sequelae or complications. Based on the available literature, chronic norovirus diarrhea is the major sequela of norovirus infection in primary immune deficient, oncologic and transplant patients. Norovirus infection - like other gastrointestinal pathogens - can cause a range of sequelae and complications, and should be considered in the differential diagnosis of these manifestations.

How timely closure can reduce outbreak duration: gastroenteritis in care homes in North West England, 2012-2016

Background

Data on outbreaks of infectious gastroenteritis in care homes have been collected using an internet-based surveillance system in North West England since 2012. We analysed the burden and characteristics of care home outbreaks to inform future public health decision-making.

Methods

We described characteristics of care homes and summary measures of the outbreaks such as attack rate, duration and pathogen identified. The primary analysis outcome was duration of closure following an outbreak. We used negative binomial regression to estimate Incidence Rate Ratios (IRR) and confidence intervals (CI) for each explanatory variable.

Results

We recorded 795 outbreaks from 379 care homes (37.1 outbreaks per 100 care homes per year). In total 11,568 cases, 75 hospitalisations and 29 deaths were reported. Closure within three days of the first case (IRR = 0.442, 95%CI 0.366–0.534) was significantly associated with reduced duration of closure. The total size of the home (IRR = 1.426, 95%CI = 1.275–1.595) and the total attack rate (IRR = 1.434, 95%CI = 1.257–1.595) were significantly associated with increased duration of closure.

Conclusions

Care homes that closed promptly had outbreaks of shorter duration. Care home providers, and those advising them on infection control, should aim to close homes quickly to prevent lengthy disruption to services.

Risk factors for hospital norovirus outbreaks: impact of vomiting, genotype, and multi-occupancy rooms

BACKGROUND

Norovirus is frequently introduced to the hospital and is a frequent cause of hospital outbreaks. Recognition of the factors that facilitate or impede norovirus transmission is an important step to effectively prevent hospital outbreaks.

AIM

To investigate risk factors for norovirus outbreaks in hospital settings.

METHODS

Clinical data, ward setting, and norovirus genotype were collected from all 65 norovirus-positive index cases in outbreaks and all 186 sporadic norovirus cases at 192 wards in southern Sweden during 2010-2012 in a nested case-control study. Uni- and multivariate statistical analyses were conducted.

FINDINGS

Outbreak was independently associated with the number of patients sharing a room with the norovirus case (odds ratio (OR): 1.9 per additional patient in the room; P < 0.01), vomiting (OR: 2.6; P = 0.04), age >80 years (OR: 3.2; P < 0.01), comorbidity (OR: 2.3; P = 0.05), and onset of symptoms after admission to the ward (OR: 3.5; P < 0.01) in the multivariate analysis. Infection with genotype GII.4 was found to be strongly associated with outbreak in the univariate analysis (OR: 5.7; P < 0.01). Moreover, associations between GII.4 and vomiting (OR: 2.5; P = 0.01) and old age (OR: 4.3: P < 0.01) were found.

CONCLUSION

This is the first study to investigate clinical, ward and genotype risk factors for norovirus hospital outbreaks. Recognition of these factors may help direct and prioritize infection control actions based on the outbreak risk. The results also suggest that the outbreak association with GII.4 partly may be explained by an enhanced ability to induce vomiting.

Identifying Potential Norovirus Epidemics in China via Internet Surveillance

Background

Norovirus is a common virus that causes acute gastroenteritis worldwide, but a monitoring system for norovirus is unavailable in China.

Objective

We aimed to identify norovirus epidemics through Internet surveillance and construct an appropriate model to predict potential norovirus infections.

Methods

The norovirus-related data of a selected outbreak in Jiaxing Municipality, Zhejiang Province of China, in 2014 were collected from immediate epidemiological investigation, and the Internet search volume, as indicated by the Baidu Index, was acquired from the Baidu search engine. All correlated search keywords in relation to norovirus were captured, screened, and composited to establish the composite Baidu Index at different time lags by Spearman rank correlation. The optimal model was chosen and possibly predicted maps in Zhejiang Province were presented by ArcGIS software.

Results

The combination of two vital keywords at a time lag of 1 day was ultimately identified as optimal (ρ=.924, P<.001). The exponential curve model was constructed to fit the trend of this epidemic, suggesting that a one-unit increase in the mean composite Baidu Index contributed to an increase of norovirus infections by 2.15 times during the outbreak. In addition to Jiaxing Municipality, Hangzhou Municipality might have had some potential epidemics in the study time from the predicted model.

Conclusions

Although there are limitations with early warning and unavoidable biases, Internet surveillance may be still useful for the monitoring of norovirus epidemics when a monitoring system is unavailable.

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.

Swab Sampling Method for the Detection of Human Norovirus on Surfaces

Human noroviruses are a leading cause of epidemic and sporadic gastroenteritis worldwide. Because most infections are either spread directly via the person-to-person route or indirectly through environmental surfaces or food, contaminated fomites and inanimate surfaces are important vehicles for the spread of the virus during norovirus outbreaks. We developed and evaluated a protocol using macrofoam swabs for the detection and typing of human noroviruses from hard surfaces. Compared with fiber-tipped swabs or antistatic wipes, macrofoam swabs allow virus recovery (range 1.2-33.6%) from toilet seat surfaces of up to 700 cm2. The protocol includes steps for the extraction of the virus from the swabs and further concentration of the viral RNA using spin columns. In total, 127 (58.5%) of 217 swab samples that had been collected from surfaces in cruise ships and long-term care facilities where norovirus gastroenteritis had been reported tested positive for GII norovirus by RT-qPCR. Of these 29 (22.8%) could be successfully genotyped. In conclusion, detection of norovirus on environmental surfaces using the protocol we developed may assist in determining the level of environmental contamination during outbreaks as well as detection of virus when clinical samples are not available; it may also facilitate monitoring of effectiveness of remediation strategies.

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.

Norovirus shedding among food and healthcare workers exposed to the virus in outbreak settings

BACKGROUND

Noroviruses (NoV) are highly contagious and the leading cause of nonbacterial outbreaks of gastroenteritis worldwide. Individuals who are infected asymptomatically may act as reservoirs and facilitate the transmission of NoV, but the likelihood of workers of becoming infected in outbreak settings has not been systematically studied.

OBJECTIVES

We evaluated the occurrence of norovirus infections among workers exposed to the virus in different outbreak settings.

STUDY DESIGN

We screened feces from food handlers and healthcare workers related with gastroenteritis outbreaks, and shedding concentrations over time were calculated from serial samples of infected individuals. Sequence analyses of the capsid P2 domain and region C were used to evaluate linkage between asymptomatic employees and outbreak cases.

RESULTS

Of all employees, 59.1% were positive for NoV, and more than 70% of them were asymptomatic. Asymptomatic infections were significantly more frequent in foodborne compared to person-to-person transmitted outbreaks; and in restaurants and hotels, compared to nursing homes and healthcare institutions. Mean viral loads were similar between symptomatic and asymptomatic individuals, starting at 7.51±1.80 and 6.49±1.93 log10 genome copies/g, respectively, and decreasing to 5.28±0.76 and 4.52±1.45 log10 genome copies/g after 19days.

CONCLUSIONS

The likelihood of becoming infected when a NoV outbreak occurs at the work place is high and similar between food handlers and healthcare workers, but asymptomatic infections are more frequently identified among food handlers. Since shed amounts of viruses in the absence of symptoms are also high, reinforcement of hygiene practices among workers is especially relevant to reduce the risk of virus secondary transmissions.

Acceptability of temporary suspension of visiting during norovirus outbreaks: investigating patient, visitor and public opinion

BACKGROUND

Noroviruses are a leading cause of outbreaks globally and the most common cause of service disruption due to ward closures. Temporary suspension of visiting (TSV) is increasingly a recommended public health measure to reduce exposure, transmission and impact during norovirus outbreaks; however, preventing patient-visitor contact may contravene the ethos of person-centred care, and public acceptability of this measure is not known.

AIM

To investigate the acceptability of TSV during norovirus outbreaks from the perspectives of patients, visitors and the wider public.

METHODS

Cross-sectional survey of patients (N = 153), visitors (N = 175) and the public (N = 224) in three diverse areas in Scotland. Health Belief Model constructs were applied to understand ratings of acceptability of TSV during norovirus outbreaks, and to determine associations between these levels and various predictor variables.

FINDINGS

The majority (84.6%) of respondents indicated that the possible benefits of TSV are greater than the possible disadvantages. Conversely, the majority (70%) of respondents disagreed that TSV 'is wrong as it ignores people's rights to have contact with family and friends'. The majority (81.6%) of respondents agreed that TSV would be more acceptable if exceptions were made for seriously ill or dying patients. Correlational analysis demonstrated that overall acceptability was positively related to perceived severity (r = 0.65), identified benefits (r = 0.54) and implementing additional communication strategies (r = 0.60); acceptability was negatively related to potential barriers (r = -0.49).

CONCLUSIONS

There is greater service user and public support for the use of TSV than concerns around impinging upon patients' rights to have visitors. TSV should be considered as an acceptable infection control measure that could be implemented consistently during norovirus outbreaks.

Vomiting as a Symptom and Transmission Risk in Norovirus Illness: Evidence from Human Challenge Studies

BACKGROUND

In the US, noroviruses are estimated to cause 21 million cases annually with economic losses reaching $2 billion. Outbreak investigations frequently implicate vomiting as a major transmission risk. However, little is known about the characteristics of vomiting as a symptom or the amount of virus present in emesis.

METHODOLOGY AND PRINCIPAL FINDINGS

Emesis samples and symptomology data were obtained from previous norovirus human challenge studies with GI.1 Norwalk virus, GII.2 Snow Mountain virus, and a pilot study with GII.1 Hawaii virus. Viral titers in emesis were determined using strain-specific quantitative RT-PCR. In all four studies, vomiting was common with 40-100% of infected subjects vomiting at least once. However, only 45% of subjects with vomiting also had diarrhea. Most of the emesis samples had detectable virus and the mean viral titers were 8.0 x 105 and 3.9 x 104 genomic equivalent copies (GEC)/ml for GI and GII viruses, respectively (p = 0.02). Sample pH was correlated with GII.2 Snow Mountain virus detection.

CONCLUSIONS AND SIGNIFICANCE

Half of all subjects with symptomatic infection experienced vomiting and the average subject shed 1.7 x 108 GEC in emesis. Unlike shedding through stool, vomiting is more likely to result in significant environmental contamination, leading to transmission through fomites and airborne droplets. This quantitative data will be critical for risk assessment studies to further understand norovirus transmission and develop effective control measures. The correlation between sample pH and virus detection is consistent with a single site of virus replication in the small intestine and stomach contents becoming contaminated by intestinal reflux. Additionally, the frequency of vomiting without concurrent diarrhea suggests that epidemiology studies that enroll subjects based on the presence of diarrhea may be significantly underestimating the true burden of norovirus disease.

Infectious Diarrhea: Norovirus and Clostridium difficile in Older Adults

Norovirus infection usually results in acute gastroenteritis, often with incapacitating nausea, vomiting, and diarrhea. It is highly contagious and resistant to eradication with alcohol-based hand sanitizer. Appropriate preventative and infection control measures can mitigate the morbidity and mortality associated with norovirus infection. Clostridium difficile infection is the leading cause of health care-associated diarrhea in the United States. Antibiotic use is by far the most common risk factor for C difficile colonization and infection. Appropriate preventive measures and judicious use of antibiotics can help mitigate the morbidity and mortality associated with C difficile infection.

Noroviruses on surfaces: detection, persistence, disinfection and role in environmental transmission

Human noroviruses (HuNoVs), the most common cause of infectious nonbacterial gastroenteritis and the cause of numerous foodborne and hospital outbreaks, are easily transmitted from person-to-person. HuNoVs may persist on surfaces for long periods of time and may be transferred via hands, foods, fomites and air. In this review, studies on methods for detecting HuNoVs on environmental surfaces, such as swabbing, are presented. The review also focuses on recent studies on the efficiency of disinfectants for inactivating HuNoV or its surrogates, such as murine norovirus, on environmental surfaces and hands. Although HuNoV is probably more resistant than MuNoV, this study data adds to the understanding of HuNoV transmission routes and selection of tools for the prevention of HuNoV gastroenteritis outbreaks.

The Where is Norovirus Control Lost (WINCL) Study: an enhanced surveillance project to identify norovirus index cases in care settings in the UK and Ireland

BACKGROUND

Norovirus outbreaks have a significant impact on all care settings; little is known about the index cases from whom these outbreaks initiate.

AIM

To identify and categorise norovirus outbreak index cases in care settings.

METHODS

A mixed-methods, multi-centre, prospective, enhanced surveillance study identified and categorised index cases in acute and non-acute care settings.

RESULTS

From 54 participating centres, 537 outbreaks were reported (November 2013 to April 2014): 383 (71.3%) in acute care facilities (ACF); 115 (21.4%) in residential or care homes (RCH) and 39 (7.3%) in other care settings (OCS). Index cases were identified in 424 (79%) outbreaks. Of the 245 index cases who were asymptomatic on admission and not transferred within/into the care setting, 123 (50%) had been an inpatient/resident for 4 days. Four themes emerged: missing the diagnosis, care service under pressure, delay in outbreak control measures and patient/resident location and proximity.

CONCLUSION

The true index case is commonly not identified as the cause of a norovirus outbreak with at least 50% of index cases being misclassified. Unrecognised norovirus cross-transmission occurs frequently suggesting that either Standard Infection Control Precautions (SICPs) are being insufficiently well applied, and or SICPs are themselves are insufficient to prevent outbreaks.