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

OR 1: During norovirus outbreaks, undertake continuous risk assessment to establish which good practice points need to be introduced to minimize transmission.

OR 2: Provide staff with sufficient information and training so they are able to recognize and act quickly when a norovirus outbreak occurs.

HIS commissioned the authors to undertake this Working Party Report. The authors are members of the participating societies mentioned in Section Acknowledgements.

The views expressed in this publication are those of the authors. They have been endorsed by HIS, IPS and BIA, and approved following a consultation with external stakeholders (see online supplementary material, Part C).

This Working Party Report contains recommendations which aim to minimize the risk of norovirus transmission in health and care settings. The Working Party recommendations represent examples of good practice; they have been developed systematically through a multi-professional group based on published evidence and professional experience. These recommendations may be used in the development of local protocols for all health, care and social settings. It is also recognized that some other closed and semi-closed settings may benefit from these guidelines.

The previous guidelines relating to this topic were published in 2012 []. During this time, there have been some improvements in how norovirus is handled in different settings, and some technologies (i.e. molecular testing and some disinfection devices) have become more available. Additionally, there is now more evidence that immunocompromised and immunosuppressed individuals may suffer from chronic infections and may require different management. These guidelines fill a clinical gap by providing up-to-date recommendations on what actions need to be taken by health and care facilities to minimize the risk of norovirus transmission and prevent the outbreaks.

The main purpose of these guidelines is to inform IPC practitioners about the current UK policy and best available options for preventing and controlling norovirus outbreaks in health, care and social settings. These guidelines also highlight current gaps in knowledge, which will help to direct future areas of research.

These guidelines were developed with hospitals and other closed and semi-closed facilities in the health, care and social settings, including, but not limited to, hospices, nursing homes and residential homes. The guidelines are suitable for patients of all age groups. While the focus of these guidelines is health and care facilities, the Working Party acknowledge that some of these recommendations may also be relevant in other institutions such as prisons or day care centres.

Topics for these guidelines were derived from stakeholder meetings and were designed in accordance with the Population Intervention Comparison Outcomes framework (Appendix 1, see online supplementary material). In the preparation of these recommendations, systematic searches and systematic reviews of published literature were undertaken. Evidence was assessed for methodological quality and clinical applicability according to NICE protocols [].

The Working Party included academic and medical experts, virologists and microbiologists, clinical scientists, infection control practitioners, systematic reviewers and two lay member representatives.

Any healthcare practitioner can use these guidelines and adapt them for local use. Users should include clinical medical, nursing and estates staff. Healthcare IPC teams should use these guidelines to develop local policies and to aid their decision-making process during norovirus outbreaks. The available reported studies were predominantly conducted in hospital and nursing home settings. The Working Party believes that while many sections of these guidelines are particularly relevant to these facilities, some evidence and recommendations can be extrapolated to other institutions [e.g. sections on environment and equipment decontamination, use of personal protective equipment (PPE), and options for management of infected individuals].

Each section comprises an introduction, a summary of evidence with levels (known as evidence statements), a summary of the Working Party’s discussions, and the recommendations graded according to the available evidence.

The guidelines will be reviewed at least every 4 years and updated if change(s) are necessary, or if evidence emerges that requires a change in practice.

The primary aim of these guidelines is to provide advice on all aspects relating to the IPC of norovirus. The secondary aim is to identify the areas in need of further research to inform future norovirus guidelines.

The guidelines can be used to inform local protocols for preventing norovirus transmission and managing patients infected with norovirus. They also provide a framework for clinical audit and quality improvement initiatives. In addition, future research priorities identified by these guidelines will allow researchers to refine their applications to funding bodies.

It is anticipated that cost would be incurred by any facility affected by norovirus outbreaks; thus, the recommendations set in these guidelines aim to reduce the impact of these outbreaks by minimizing the number of individuals affected and reducing the duration of the outbreaks. The Working Party believes that, while additional cost would be incurred during an outbreak, failure to implement the recommendations early would result in greater cost both in terms of economics and quality of life. For the topics where recommendations aim to prevent the outbreaks from occurring, there is no anticipated additional cost unless existing practice falls below the currently accepted standard.

Regular audit remains an important part of any guideline implementation. Audit is effective only when the results are fed back to staff and when there is a clear plan for their implementation. Many organizations have already developed their local policies and audit measures, which may need to be updated following the publication of these new guidelines. The Working Party suggests that the following aspects should be audited:

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  Compliance with informing IPC team promptly if an outbreak is suspected.
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  Compliance with the introduced control measures (e.g. transmission-based precautions, handwashing, appropriate use of PPE, appropriate environmental cleaning, decontamination of equipment, compliance with guidelines for appropriate laundry handling).
• •
  Compliance with informing the receiving unit/facility and the ambulance/transport service that a patient is confirmed/suspected to be infected with norovirus.
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  Compliance with case surveillance during the outbreak.

Lay materials and continuing professional development questions are available in the

• online supplementary material (Parts D and E).

The topics for these guidelines were derived from the initial discussions of the Working Party during the stakeholder meeting. To prepare these recommendations, the Working Party collectively reviewed relevant evidence from published peer-reviewed literature. Methods were followed in accordance with the NICE manual for conducting evidence syntheses [].

Three electronic databases (Medline, Embase, EMCare) were searched for articles published until January 2022. Additionally, the Food Science and Technology Abstracts database was searched until February 2021, but as it revealed no additional evidence, the searches were not updated to 2022. Search terms were constructed using relevant MeSH and free-text terms (Appendix 1, see online supplementary material). Reference lists of identified articles were scanned for additional studies, and forward reference searching (identifying articles which cite relevant articles) was performed. The searches were restricted to primary articles published in the English language.

The search results were downloaded to an Endnote database and screened for relevance. One of two reviewers (AB, GM) reviewed the titles, abstracts and full-text papers. As per NICE methodology, the second reviewer checked 5% of the excluded studies for discrepancies. If discrepancies were found, the second reviewer checked all excluded records. Any discrepancies were addressed by a third reviewer (PC). The guidelines included any controlled trials, cohort studies, interrupted time series (ITS) studies, case–control studies, cross-sectional studies, diagnostic accuracy studies (DAS) and controlled/uncontrolled before/after (CBA/UBA) studies. Due to the limited evidence available, outbreak studies were included. For data on the efficacy of disinfecting and sanitizing agents, laboratory studies were also included. For the question about environmental sampling, environmental surveys were used. Where evidence was lacking, excluded studies which provided additional information were also described in some sections, with the limitations of using this information clearly highlighted. The results of study selection and the list of excluded studies are available in Appendix 2 (see online supplementary material).

Included epidemiological studies were appraised for quality using checklists recommended in the NICE guideline development manual []. The quality checklists included:

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  Randomized controlled trials (RCTs): RoB_2.0 for RCT
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  Non-RCTs: ROBINS for non-RCTs and cohort studies
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  Cohort studies: ROBINS for non-RCTs and cohort studies
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  ITS studies: EPOC RoB for ITS and before/after studies
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  Case–control studies: CASP for case–control studies
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  Cross-sectional studies: JBI checklist for analytical cross-sectional studies
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  UBA studies: EPOC RoB for ITS and before/after studies
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  DAS: QUADAS-2 for diagnostic accuracy studies
• •
  Outbreak studies, case series and case studies: Institute of Health Economics checklist for case series.

Environmental surveys and laboratory studies were not appraised for quality as no checklists exist for these types of studies. Critical appraisal and data extraction were conducted by one reviewer and checked by another reviewer. The results of quality appraisal are available in Appendix 3 (see online supplementary material).

Data were extracted by one reviewer and checked/corrected by another reviewer. For each question cluster, the data from the included studies were extracted to create the study description, data extraction and summary of findings tables (Appendix 4, see online supplementary material). The list of the studies rejected at full-text stage, with a reason for this decision, is included in the excluded studies table (Appendix 2b, see online supplementary material). Due to limited evidence, most of the data were described narratively. Meta-analyses were only possible for DAS.

The strength of the evidence was defined by GRADE (Grading of Recommendations Assessment, Development and Evaluation) tables (Appendix 5, see online supplementary material) and using the ratings ‘high’, ‘moderate’, ‘low’ and ‘very low’ to construct the evidence statements, which reflected the Working Party’s confidence in the evidence. The strength of recommendation was adopted from GRADE and reflects the strength of each evidence statement. In instances where no evidence was identified from searches, the statement ‘No evidence was found in studies published so far’ indicates that no studies have assessed this as an outcome. Where there was no evidence or a paucity of evidence, expert-based recommendations were made by expert experience. All disagreements were resolved by discussions and voting by members of the Working Party during the meetings.

When writing the recommendations, the Working Party considered the following:

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  Who should act on these recommendations?
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  What are the potential harms and benefits of the intervention and any unintended consequences?
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  What is the efficacy and the effectiveness of each intervention?
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  Is it possible to stop another intervention because it has been superseded by the new recommendation?
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  What is the potential effect on health inequalities?
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  What is the cost effectiveness of the intervention, including staff resources and other economic concerns?
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  Can the recommended interventions be feasibly put into practice?

The wording of the evidence statements and the recommendations reflected the strength of the evidence and its classification. The following criteria were used:

• •
  ‘Offer’, ‘measure’, ‘advise’, ‘refer’, ‘use’ or similar wording was used if the Working Party believed that most practitioners/commissioners/service users would choose an intervention if they were presented with the same evidence: this usually means that the benefits outweigh harms, and that the intervention is cost effective. This reflects a strong recommendation for the intervention. If there was a legal duty, or if not following a recommendation may have serious consequences, the word ‘must’ was used.
• •
  ‘Do not offer’ or similar wording was used if the Working Party believed that harms outweighed the benefits or if an intervention was not likely to be cost effective. This reflected a strong recommendation against the intervention. If there was a legal duty, or if not following a recommendation may have serious consequences, the words ‘must not’ were used.
• •
  ‘Consider’ was used if the Working Party believed that the evidence did not support a strong recommendation, but that the intervention may have been beneficial in some circumstances. This reflected a conditional recommendation for the intervention.
• •
  The ‘do not offer, unless…’ or similar recommendation was made if the Working Party believed that the evidence did not support a strong recommendation, and that the intervention was not likely to be beneficial, but could be used in some circumstances, for instance if no other options were available. This reflected a conditional recommendation against the intervention.
• •
  Good practice points were made when there was no evidence to support the recommendation, but the Working Party considered that the intervention was essential or beneficial to good clinical practice.

Feedback on draft guidelines was received from the participating organizations and through consultation with relevant stakeholders. The draft report and standard comments form were placed on the HIS website for 4 weeks. The availability of the draft was advertised via e-mail and social media. Stakeholders were invited to comment on format, content, local applicability, patient acceptability and recommendations. The Working Party reviewed stakeholder comments, and agreed revisions collectively (see online supplementary material, Part C). All reviews received from individuals with a conflict of interest or those who did not provide a declaration were excluded.

There are inherent properties in building, ward and room design which can either have a primary effect on transmission or a secondary effect by modifying behaviour. Ensuring a layout with appropriate ventilation and minimizing horizontal surfaces are thought to decrease transmission. In addition, using materials which are easy to clean, and installing no-touch devices for operating doors or lights may help to reduce environmental transmission. Both the number of handwash stations and their positioning encourages appropriate hand hygiene. Hospital design should include sufficient side rooms with en-suite bathrooms for suspected and confirmed infectious cases. These are recommended not only in ward settings but also in assessment areas such as accident and emergency (A&E) departments and medical assessment units. In a ward setting, an assessment about the needs of the population being cared for is needed to help determine the correct ratio of side rooms. This would allow for balancing the benefits of side rooms (infection control) against the harms of individual rooms (increased risk of falls, unmet social need in long-stay patients). Flexibility in design, both on the ward/unit and at hospital level, may be important so that the institutions have the ability to adjust side room capacity depending on need at the time. It is generally accepted that multi-occupancy rooms carry a higher risk of transmission between the occupants. Previous UK guidelines [] recommended that every opportunity should be taken within plans for new builds and refurbishment/renovation to maximize the ability to control outbreaks, and these should include adequate provision of single-occupancy rooms and bays with doors. However, this recommendation was not based on the published evidence which explored whether and how the building design contributes to the initiation and progression of norovirus outbreaks, and whether adapting the building design could help to prevent or control outbreaks.

There was moderate evidence of risk associated with multi-occupancy rooms from one prospective cohort study [], one UBA study [], one case-control study [], one cross-sectional study [] and one outbreak study []. All studies reported that multi-occupancy rooms were associated with increased risk of norovirus transmission. One study [], which conducted surveillance in six hospitals in one NHS trust over a 3-month period during the norovirus season, reported that from a total of 20 outbreaks in the season, the majority [N=16 (80%), affecting a total of 44 patients] occurred in a hospital with Nightingale-style wards which only had 7% single-occupancy beds. This was also the only hospital which reported that staff were affected by norovirus. Of these 16 outbreaks, four (25%) were contained within one bay, 11 (69%) affected an entire ward, and one (6%) affected multiple wards. In contrast, the hospital with the highest number of single beds (46%) experienced two outbreaks (two patients in each), which were contained within the same bay. There were two additional outbreaks in two other hospitals (number of single beds not reported) which affected three and six patients, and there were two hospitals (number of single beds not reported) which did not experience any norovirus outbreaks during the 3-month study period. It is noteworthy that the data from laboratory testing showed that sporadic cases of norovirus were present in all hospitals throughout the study period. The authors concluded that outbreaks are more likely to occur, and are more difficult to control, in Nightingale-style wards. Another study [] compared the data for risk factors from index cases who started an outbreak to sporadic cases who did not infect others. The study was conducted during three norovirus winter seasons in hospitals. The authors reported that the number of patients in the room was the most prominent factor for outbreak occurrence, and that in the multi-variate analysis, the presence of each additional patient was associated with increased risk of outbreak occurrence [odds ratio (OR) 1.9, 95% confidence interval (CI) 1.3–2.6; P<0.01]. A similar study [], which was undertaken in hospitals over five norovirus seasons, reported that being cared for in a double room was not associated with increased risk of norovirus infection (OR 1.69, 95% CI 0.99–2.9; P=0.06). However, being in the same room with a roommate who had ongoing norovirus symptoms, or whose symptoms had resolved less than 48 h previously, was associated with increased risk. In the multi-variate analysis which was adjusted for age, colonization pressure and care in multi-occupancy rooms, having a roommate with norovirus symptoms was the only factor significantly associated with increased risk of infection (OR 25.2, 95% CI 7.8–81.6; P<0.01). The authors also mentioned that the risk of infection increased with exposure time (data not reported). One UBA study [] did not report data on norovirus infections, but mentioned that single-occupancy rooms were beneficial because they resulted in fewer ward closures (one in year 1 and four in year two after moving to a building with more single beds vs 21, 34 and 13 in the 3 years preceding the move) and fewer beds lost due to norovirus outbreaks (57 vs 172 beds lost per 100,000 bed-days, respectively). Finally, one study [], which reported an outbreak involving 173 cases, lasting 54 days in multiple wards in one hospital and costing £341,534, concluded that a Nightingale-style ward was one of the reasons why the outbreak continued and was difficult to control. This style of ward made some interventions ineffective and required specialist recommendations (e.g. ward closures were not effective, and entire floor closures were required as the wards shared some facilities such as kitchen, dining areas, toilets and handwashing stations). The authors also reported that barrier nursing in Nightingale-style wards was difficult, and that isolation or cohorting by bay was not always possible. It was also reported that reducing bed capacity to increase the space between beds was one of the successful interventions which eventually led to outbreak resolution.

There was weak evidence of benefit from one UBA study [] which assessed the effectiveness of installing bay doors in hospital wards. This was a quality improvement project which aimed to reduce the effect of the outbreaks. The authors reported that a number of different interventions were introduced, and the installation of the bay doors was the most important improvement. They stated that windows were also installed, so the patients could be seen from the nursing station, and their care was not compromised as a result of this conversion. Other interventions included more support from the IPC team, staff and patient cohorting (as opposed to staff restrictions and ward closures previously), and improved communication. The authors reported that the relative change in the ratio of confirmed hospital outbreaks to community outbreaks per month was 0.317 (95% CI 0.129–0.778; P=0.025) in the year after improvements took place compared with a year before the improvements. The median number of patients and staff affected remained the same (ratio of expected counts 1.080, 95% CI 0.85–1.370; P=0.517 for patients; 0.651, 95% CI 0.386–1.096; P=0.105 for staff), and the decreased incidence of outbreaks resulted in a decreased number of days of restricted admission (ratio of expected counts 0.742, 95% CI 0.558–0.987; P=0.041) and a decreased number of bed-days lost (ratio of expected counts 0.344, 95% CI 0.189–0.628; P=0.001).

There was weak evidence of benefit from one case–control study reported in two articles [,] which assessed the effect of partitions between beds on the risk of norovirus outbreaks in care homes for older people. The authors reported that the presence of partitions between beds was the only significant protective factor in a multi-variate analysis [relative risk (RR) 0.6, 95% CI 0.4–0.8; P=0.002].

1.1: No recommendation.

GPP 1.1: Perform risk assessment of the ward/unit ‘hierarchy of controls’ to establish the risk of norovirus transmission between patients.

GPP 1.2: Where risk of transmission is high, consider making small changes to the ward/unit layout (e.g. installing partitions, bay doors or including flexible designs). However, consider and risk assess any potential adverse effects of doing this (e.g. on ventilation systems).

GPP 1.3: Assess individual risk of norovirus infection to the patient and consider additional control measures for patients at the highest risk (i.e. those who are immunocompromised).

All services registered under the Health and Social Care Act 2008 are expected to have a policy for the control of outbreaks of communicable infections (governed in England by the Care Quality Commission). These are often developed through the IPC team. Outbreaks of norovirus can disrupt delivery of services to patients considerably. Closure of hospitals and care/nursing homes can have an indirect effect on other facilities. Thus, all facilities need to ensure minimal disruption to services by developing plans for use in outbreak situations. However, it is not clear what these plans should include, and how they impact on outbreak progression. Previous guidelines [] stated that organizations must develop systematic business continuity plans for use in outbreak situations, and that the plans should include actions for safe environments, staffing, information, surveillance, communications and leadership, although none of these recommendations were supported by relevant evidence from published literature.

There was weak evidence of benefit from one UBA study [] and one outbreak report [] which assessed the effectiveness of preparedness for norovirus outbreaks on outbreak occurrence and the incidence of norovirus infection. One study [] used a Plan–Do–Study–Act cycle model for introducing nationwide activities before the outbreaks occurred, based on the evaluation of experience of norovirus outbreaks from a previous winter season. The ‘Plan’ phase included recommended actions that hospitals could undertake before and during the norovirus season, a norovirus season start alert, a norovirus outbreak tracker, assistance with media messaging, and specific guidance on escalation plans. The ‘Do’ phase involved the hospitals introducing these interventions within their settings. The ‘Study’ phase was monitoring of the norovirus outbreaks during the winter season, and the ‘Act’ phase was learning from the results and subsequent planning for the next season (data for the next season not reported). In total, 15 NHS boards from Scotland participated in the study. The authors reported that the number of wards closed due to norovirus outbreaks (a proxy measure for number of outbreaks) reduced from 759 in the year before the intervention to 307 in the year when preparedness was introduced. It was also reported that there were 15 sudden peaks in ward closures before the intervention and only six after the intervention at the peak of the norovirus season, and 53 wards were closed before the intervention and 25 wards were closed after the intervention. The authors also reported that preparedness enabled the hospitals to introduce the control measures early, and, in some instances, these measures were in place before the outbreak was confirmed. Another study [] reported two outbreaks which occurred in a geriatric rehabilitation hospital within 18 months of each other. The authors reported that both outbreaks were contained within one ward, but that the first outbreak involved more cases (41 vs 24 in the second outbreak). It was reported that due to previous experience and preparation, staff were able to act once they recognized a third case of norovirus, and were able to implement some control measures before an IPC nurse was informed. While the duration and number of patients affected were comparable in both outbreaks (16 vs 13 patients and 14 vs 16 days in the first and second outbreaks, respectively), the number of staff affected by the outbreak was reduced (21 vs 11 in the first and second outbreaks, respectively), and the ward reopened earlier after the second outbreak (data not reported) which resulted in less disruption to hospital activities for staff and patients.

No studies were found in the existing literature that assessed the cost of preparing for norovirus outbreak in any setting.

There was weak evidence of benefit from one UBA study [] which assessed the effect of preparedness for norovirus outbreaks in the healthcare setting on staff experience. The authors mentioned that all IPC teams participating in the study reported a positive experience during the season when preparedness was in place, and this was not limited to the reduced number of outbreaks. The IPC teams believed that with preparation, staff attitudes towards norovirus changed and there was better co-operation between IPC teams and ward managers during the outbreaks. The authors also reported that IPC teams commented on a previous season (data collected before the introduction of interventions) and all teams reported only negative experiences.

No studies were found in the existing literature that assessed the effect of preparing for norovirus outbreak on patient experience.

2.1: No recommendation.

GPP 2.1: Wherever possible, prepare staff for potential norovirus outbreaks by providing reminders, guidance, training and education so that staff are able to act quickly.

An increase of cases of norovirus in institutions usually reflects increased incidence of these infections in the community. Therefore, by minimizing the number of individuals being admitted, it may be possible to minimize secondary infection clusters in different institutions. Admission avoidance (also known as ‘hospital at home’), where active treatment is provided by healthcare professionals in the patient's home, may be a suitable alternative. This usually comprises treatment for a condition that otherwise would require acute hospital inpatient care. Different models of care currently exist in the UK, some of which do not require initial assessment in secondary care. These services often have the ability to perform hospital-level diagnostic tests (e.g. point-of-care blood and molecular testing) and provide interventions such as treatment with intravenous fluids. Previous guidelines [] recommended that the admission of unnecessary cases should be avoided and that, whenever possible, patients should be cared for at home. They also recommended that rapid risk assessment of an infected individual should be undertaken by a competent doctor to ensure patient safety is not compromised. Little is currently known about whether this strategy is clinically and cost effective, specifically whether it helps to prevent outbreaks of norovirus in institutions while still providing adequate care for infected individuals.

No studies were found in the existing literature that assessed the clinical benefit of avoiding admission or incarceration of individuals who are suspected or confirmed to be infected with norovirus in any setting.

No studies were found in the existing literature that assessed the cost benefit of avoiding admission or incarceration of individuals who are suspected or confirmed to be infected with norovirus in any setting.

No studies were found in the existing literature that assessed the effect of avoiding admission or incarceration of individuals who are suspected or confirmed to be infected with norovirus on patient satisfaction in any setting.

There was very weak evidence of risk from two outbreak studies [,] which reported the effect of allowing patients suspected or confirmed to be infected with norovirus to be admitted into hospital. One of these studies [] reported a prolonged outbreak which affected a total of 173 individuals and lasted 54 days. The authors reported that one of the reasons for the prolonged duration of the outbreak was the continuous admission of new cases from the community with a known ongoing epidemic of norovirus, which infected other individuals in hospital. The second study [] reported an outbreak in hospital which occurred after the admission of some symptomatic cases from a nursing home. The authors reported that the index case illness was initially mistakenly assumed to be due to foodborne salmonella, and this resulted in the hospital admitting patients without appropriate precautions. Subsequently, as a result of an outbreak in hospital, 28 cases became ill over the course of 18 days. The authors also mentioned that the outbreak in the nursing home met the Kaplan criteria, which would have helped in implementing the interventions earlier, and their report illustrates how admitting symptomatic cases with no IPC measures leads to outbreaks in hospitals.

3.1: No recommendation.

GPP 3.1: Where feasible, avoid admitting patients with suspected/confirmed norovirus and offer suitable supportive treatment (e.g. rehydration therapy) in the community.

Declaration of an outbreak requires careful balancing. On one hand, prompt declaration and an introduction of appropriate measures may help facilities to contain the outbreak quickly. On the other hand, this declaration can have a reputational and financial impact, and may lead to unnecessary service disruptions. Previous guidelines [] acknowledged that declaring an outbreak is needed but did not provide clear recommendations when this should occur. The guidelines also stated that outbreaks may not necessarily need laboratory confirmation, and the occurrence of multiple cases may not necessarily warrant the declaration of an outbreak. Additionally, the guidelines asserted that the outbreak declaration ‘can be tailored to suit the prevailing circumstances’. This, however, may be confusing for individual facilities, and clarity is needed regarding the definition of an outbreak and when an outbreak should be considered. This is especially important when IPC specialists are not readily available (e.g. in community settings). For these settings, a period of increased incidence rather than an outbreak can be declared, but there still needs to be a clear definition when this action should be triggered. Historically, Kaplan’s criteria [see Glossary (Part A of online supplementary material) for definition] were applied to declare a norovirus outbreak, although with molecular testing, which provides more rapid confirmation, these criteria may now have less clinical value. There also needs to be a clear recommendation for when an outbreak could be declared over. This also needs to be balanced carefully so that patient services can recommence but without the risk of the outbreak recurring.

There was weak evidence from one cross-sectional study [] which evaluated the effect of recognizing a norovirus outbreak and introducing interventions early. The study evaluated outbreaks which occurred in nursing homes during the norovirus season prospectively. The authors reported that in outbreaks in which control measures were in place within 3 days, there were significantly lower attack rates for staff (20% vs 33.4%; P=0.019) but no observed benefit for residents (35.9% vs 39.5%; P=NS), and early control measures did not influence the duration of the outbreaks (15.9 vs 18.5 days; P=NS).

There was inconsistent evidence from outbreak studies [,,, , , , , , , , , , , , , , , , , , ] which reported different triggers for recognizing outbreaks in healthcare settings. Fourteen studies [,, , , , , , , , , , , , ] reported that an outbreak was recognized when an increase in cases of gastroenteritis was observed, and the control measures were introduced before norovirus was confirmed as an aetiological agent. The duration of the outbreak before it was recognized varied from 0 days (day 1) to 6 weeks. These outbreaks affected between three and 355 cases (median 51 cases) and lasted between 5 days and 2 months (median 18 days). The study which reported that it took 6 weeks to recognize the outbreak [] reported the highest number of cases and the longest duration. The outbreak which was recognized on the first day [] involved three cases and lasted 7 days. One study [] reported that the outbreak was declared as soon as the first person (who was also later confirmed to be an index case) became ill with symptoms of gastroenteritis (day 1). This outbreak still affected a total of 60 cases and lasted 22 days. Two studies [,] reported that an outbreak was recognized when laboratory results confirmed norovirus as an infectious agent causing gastroenteritis in patients (days 5 [] and 2 []). These outbreaks were reported to affect 28 [] and 14 [] cases, lasting 8 [] and 14 [] days. One study [] reported that the outbreak was recognized when cases of gastroenteritis occurred on more than one ward (day 2), eventually affecting 42 cases and lasting 17 days. Two studies [,] reported that they recognized the outbreak after they became aware that the cases fit the Kaplan criteria for viral gastroenteritis (days 2 [] and 7 []). These studies were reported to affect 95 [] and 24/28 (nursing home/hospital) [] cases (in this study, the outbreak was reported to spread from a nursing home to a local hospital), and lasted 22 [] and 9/18 (nursing home/hospital) days []. Lastly, only one study [] reported that the institution failed to recognize an outbreak until the second wave of cases occurred (day 17). This outbreak affected 101 cases and lasted 44 days. None of the studies assessed the cost or patient/staff experience.

There was weak evidence from outbreak studies [, , , , , , , ] which reported different triggers for recognizing outbreaks outside healthcare settings. Seven studies [, , , , , , ] reported that an outbreak was recognized when an increase in cases of gastroenteritis was observed, and the control measures were introduced before norovirus was confirmed as an aetiological agent. The duration of the outbreak before it was recognized varied between 1 (day 2) and 5 days (day 6). These outbreaks affected between 15 and 427 cases (median 158 cases) and lasted between 5 and 22 days (median 13.5 days). One study [] reported that the outbreak was recognized when surveillance identified a large number of cases of gastroenteritis and triggered an alert. This outbreak affected 156 cases and lasted 17 days. None of the studies assessed the cost or patient/staff experience.

There was additional evidence from excluded studies which retrospectively evaluated the utility of clinical symptoms [,] or diagnostic tests [, , , ] for the detection of norovirus outbreaks. One study [] reported that, in comparison with polymerase chain reaction (PCR) testing, Kaplan’s criteria were 63.9% sensitive and 100% specific in distinguishing confirmed norovirus outbreaks from non-viral outbreaks. However, they also reported that only 3.3% of norovirus outbreak reports and 1.2% of non-viral outbreak reports provided sufficient clinical information for Kaplan’s criteria to be applied. Newly developed CART (classification and regression tree) modelling which assessed the proportion of cases with bloody stools, the proportion of cases with diarrhoea, the proportion of cases with fever, the proportion of cases with vomiting, the fever-to-vomiting ratio and the diarrhoea-to-vomiting ratio was 85.7% sensitive and 92.4% specific. It was also reported that 24.9% of norovirus outbreaks and 20.6% of non-viral outbreaks had sufficient data to apply the CART characteristics. Another study [] reported that Kaplan’s criteria were the most useful clinical criteria with sensitivity and specificity of 68% and 99%, respectively. They reported that the fever-to-vomiting and the diarrhoea-to-vomiting ratios were more sensitive but less specific, and therefore have less utility in recognizing norovirus outbreaks. However, it needs to be noted that both studies based their conclusions on published reports of resolved outbreaks, and it is not possible to determine whether these criteria would be sufficiently sensitive to recognize the outbreak early when only a small number of cases are affected. Four studies used PCR and enzyme immunoassays (EIA) to evaluate their ability to identify norovirus outbreaks. The study used two different EIA kits and assessed them for their utility to identify norovirus outbreaks. Two studies [,] concluded that EIA is less sensitive than PCR, and while the kits have some value in recognizing the outbreaks early, any gastroenteritis outbreak which tested negative by EIA should still be investigated by PCR for confirmation. Another study [] reported that obtaining at least one norovirus-positive sample by either EIA or PCR from a total of two to four submitted samples was sufficient to establish norovirus as a cause of an outbreak. However, they also reported that, in order to avoid false-negative results for an outbreak affecting under 10% of patients, at least three samples need to be submitted for testing with PCR and at least six samples for testing with EIA. The last study [] reported that if all outbreak specimens contained norovirus, there would be over 99% likelihood of identifying norovirus as a causative agent when at least three specimens are sent for testing with PCR and EIA. They also reported that testing more than five true-negative samples may result in false-positive results.

There was moderate evidence from 11 outbreak studies [,,,, , ,,,,,] which reported different triggers for declaring the end of outbreaks in healthcare settings. Three studies [,,] declared the end of an outbreak 5 days after the last case was identified, one study [] 5 days after the last symptoms occurred, one study [] 72 h after the last symptoms occurred, one study [] 2 days after the last symptoms occurred, one study [] 24 h after the last case was identified, three studies [,,] on the day the last case was identified, and one study [] when the number of cases started to decrease. None of the studies reported a second wave or any cases occurring after the outbreak was declared over, except in one outbreak [] where three new cases were identified which were transferred from elsewhere and represented a re-introduction rather than a continuing outbreak. None of the studies assessed the cost or patient/staff experience.

There was inconsistent evidence from three outbreak studies [,,] which reported different triggers for declaring the end of outbreaks in healthcare settings. One study [] reported that the end of the outbreak was declared a day after the last case was identified, and two studies [,] reported that the end of the outbreak was declared on the last day that cases were identified. None of the studies reported a second wave or any cases occurring after the outbreak, and none of the studies assessed the cost or patient/staff experience.

4.1: No recommendation.

GPP 4.1: If an outbreak is suspected, consider introducing control measures (including transmission-based precautions) before laboratory results are available.

GPP 4.2: If a sporadic case of norovirus is identified, consider introducing control measures (including transmission-based precautions) to prevent an outbreak (for the next 72 h).

GPP 4.3: Whenever possible, maintain the control measures in place for 72 h after the last episode of vomiting or diarrhoea in the last known case before declaring the end of an outbreak.

Effective communication can mean different things to different people; therefore, by stating and recommending to whom and what to communicate could alter the course of the outbreak, potentially preventing further cases and shortening its duration. Consideration of what to communicate may depend on the role that individual has within the management of the outbreak. For example, bed managers or discharge co-ordinators may need different information than the Director of Public Health or Director of Adult Social Services. The start of an outbreak could mean that independent organizations may be required to inform regulatory bodies, which could lead to further independent investigations. Clear and precise communication may also be beneficial for friends and families whose loved ones are affected by the outbreak, as they may have concerns regarding their rehabilitation or deterioration. Previous guidelines [] did not make any specific recommendations about the communication at the start of an outbreak, but they did acknowledge that IPC teams should inform the managerial team of the facilities affected, as well as the local health protection organizations, and when the outbreak was declared. They also stated that control measures should be introduced at the same time. It is, however, not clear whether this action is necessary, especially if control measures have been put in place.

There was moderate evidence from 12 studies [,,,, , , , ,,,,] describing a total of 13 outbreaks, all in hospital settings, which stated that the outbreak was reported to a hospital IPC/epidemiology team. These outbreaks affected between three and 355 cases (median 25 cases), lasting from 5 days to more than 2 months (median 14 days). None of the studies specifically mentioned that reporting to the hospital team was beneficial for outbreak management; however, in all except one study, it was evident that the IPC/epidemiology team was responsible for outbreak investigation and providing advice about the control measures that needed to be implemented. Only in one outbreak [] was it reported that some (but not all) control measures were introduced before the hospital team was informed. Following the introduction of control measures, the outbreaks affected a further one to 51 cases (median eight cases, based on nine studies [,,,, , ,,,] reporting 10 outbreaks), lasting from 2 to 16 days (median 6 days, based on 10 studies [,,,, , ,,,,] reporting 11 outbreaks). None of these studies reported cost or patient/staff experience.

There was moderate evidence from 14 studies [,,, , ,,, , , ,,,,] describing a total of 15 outbreaks, occurring in hospitals [,,,,,], nursing homes [,,] or long-term care facilities (LTCFs) [,,,,,], which stated that the outbreak was reported to the local public health unit. Two of these studies [,] mentioned that this was done in addition to reporting to their own hospital IPC team. These outbreaks affected between 10 and 355 cases (median 74 cases), lasting from 8 days to more than 2 months (median 22 days). None of the studies specifically mentioned that reporting to the local public health unit was beneficial for the outbreak management; however, the unit was responsible for outbreak management in all except two studies. One of these studies [] mentioned that interventions were introduced as recommended by the hospital IPC team but the outbreak continued, which prompted the hospital to report the outbreak to the local authorities. The other study [] reported that assistance from the local health authority was needed for the first outbreak, but during the second outbreak, the recommendations from the IPC nurse in hospital were sufficient. There was also one study which mentioned that the local public health unit erroneously classified an outbreak as a foodborne outbreak due to salmonella, which delayed the introduction of interventions necessary for controlling a norovirus outbreak and resulted in the outbreak spreading to the local hospital. The authors reported that norovirus was recognized by the local authorities only when laboratory results became available, which was 1 day after the nurse in the nursing home realized that the outbreak fit the Kaplan criteria for viral aetiology and introduced appropriate control measures. Following introduction of the interventions, the outbreaks lasted from 3 to 59 days (median 14 days, based on 12 studies [,,,,, , , ,,,] reporting 13 outbreaks) and affected a further four to 98 cases (median 29 cases, based on 11 studies [,,,, , , ,,,] reporting 12 outbreaks). In addition to reporting to the local health authority, one study [] mentioned that they reported an outbreak, which occurred in a nursing home, to the emergency department in a local hospital to prevent transmission in the new setting. The authors reported that only one staff member became ill as a result of this communication. One study [] also mentioned that the above-mentioned outbreak, which was mistaken for salmonella, was reported to the national department of health. This, however, was to report an incident and not to seek advice in order to prevent further cases. None of these studies reported cost or patient/staff experience.