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Outbreaks of norovirus are at their highest for five years, and have been hitting hospitals across the country. Nerys Hairon outlines how to prevent the spread of infection

Norovirus, which causes diarrhoea and vomiting, is sweeping the country and a number of hospital wards have been closed to new patients. The Royal College of GPs has urged patients with norovirus to stay at home, if possible for two days (48 hours) after the symptoms have gone. Doctors have also warned those affected to stay away from surgeries and hospitals.
Norovirus is the most common cause of infectious gastroenteritis in England and Wales (Health Protection Agency, 2008). It is estimated to affect between 600,000 and one million people in the UK each year (HPA, 2007a). The disease was historically known as ‘winter vomiting disease’ due to its seasonality and typical symptoms.
Although the illness is relatively mild, it can occur at any age because immunity to it does not last long.
Outbreaks are common in semi-closed environments such as hospitals, nursing homes, schools and cruise ships.

REPORTED CASES
The number of norovirus cases reported in 2007 was higher than in all other recent years, apart from 2002 (HPA, 2007b), which saw the most severe season recorded. This was associated with the emergence of a new antigenic virus type.
In 2007 the HPA received 1,325 norovirus laboratory reports from England and Wales in weeks 36–48 (early September to early December), compared with 685 in the
same period in 2006. There was a peak
of 1,845 during this period in 2002 (HPA, 2007b). However, these laboratory reports reflect only a tiny fraction (estimated at 1:1,500) of all infections in the community and hospitals, since most cases are
not reported.
The HPA urges caution in interpretation of the 2007 data, as the increased numbers may, in part, be a result of improved diagnostic capacity in regional laboratories. There is also thought to be increased awareness of the infection and symptoms among the public and doctors, so more cases are being identified.
More than three-quarters of all norovirus outbreaks reported to the HPA Centre for Infections occur in healthcare settings. The agency has previously estimated that, in epidemic seasons, noroviruses may cost the NHS more than £100m a year. The 2007 norovirus season started uncharacteristically early, with a greater number of cases nationally from the first week of November (HPA, 2007b).

THE VIRUS
Noroviruses are a group of viruses – in the past they have also been called ‘winter vomiting viruses’, ‘small round structured viruses’ or ‘Norwalk-like viruses’.
The virus is easily transmitted from one person to another. It can be transmitted by contact with an infected person, by consuming contaminated food or water or by contact with contaminated surfaces or objects.
The incubation period for norovirus is normally 24–48 hours (HPA, 2006). The illness is self-limiting and the symptoms last for 12–60 hours. They start with the sudden onset of nausea, followed by projectile vomiting and watery diarrhoea. Some patients may have a raised temperature, headaches and aching limbs. Most people make a full recovery within 1–2 days but some patients (usually the very young or elderly) may become very dehydrated and need hospital treatment. However, volunteer studies suggest that up to 30% of infections may be asymptomatic (Centers for Disease Control and Prevention, 2006). For a summary of clinical information on norovirus, see box below.
The HPA explains that norovirus often causes outbreaks because it is easily spread and is able to survive in the environment for many days.
As there are many different strains of norovirus and immunity is short-lived, outbreaks tend to affect over 50% of susceptible people (HPA, 2007a).

ADVICE TO PATIENTS
There is no specific treatment for norovirus apart from letting the illness run its course. The RCGP advises affected people to stay at home, take paracetamol and drink plenty of fluids. It also recommends that, if possible, patients should stay at home for two days (or 48 hours) after symptoms have ceased.
Good hygiene before and after contact with an infected person, including thorough handwashing, is important to prevent the spread of infection. Infected people should also avoid food preparation until 48 hours after symptoms have subsided (HPA, 2007a).
Very young children and elderly people should take extra care if they become infected, as dehydration is more common in these age groups.

PREVENTING FURTHER INFECTION
The HPA says that the most effective way to respond to an outbreak of norovirus is to disinfect contaminated areas, institute good hygiene measures and provide advice on food handling.
Healthcare settings tend to be particularly affected by outbreaks. Recent research found that the duration of outbreaks was reduced when control measures were implemented quickly in healthcare settings. These include closing wards to new admissions within four days of the start of the outbreak and implementing strict hygiene measures (HPA, 2007a).
In addition, a report by the Public Health Laboratory Service viral gastroenteritis working group reviewed the epidemiology of norovirus outbreaks and made detailed recommendations for their management in hospital settings (Chadwick et al, 2000). This article is available on the HPA’s website (www.hpa.org.uk).
The report said that by the time a norovirus outbreak has been recognised at ward level, most people in the area will have been exposed to the virus and infection control efforts must prioritise the prevention of spread of infection to other clinical areas. This involves containment of infected/exposed people (especially the prevention of patient and staff movements to other areas), hand hygiene and effective environmental decontamination.
The basic principles that underpin these recommendations will also apply to the management of some community-based institutional outbreaks.
Recommendations
Practitioners should implement the following control measures in affected clinical areas (Chadwick et al, 2000):

  • Cohort nurse or isolate symptomatic people;

  • Wear gloves and an apron for contact with an affected patient or environment;

  • Wash hands with soap and water after contact with an affected patient or environment, after removing gloves and apron (alcohol handrubs are ineffective against norovirus);

  • Remove exposed food such as fruit;

  • Consider the use of antiemetics for patients with vomiting;

  • Exclude affected staff from the ward immediately and for 48 hours after being symptom free;

  • Close the ward to prevent newly susceptible people from entering. Avoid transfers to unaffected departments or wards (unless medically urgent and after consultation with infection control staff);

  • Exclude non-essential personnel;

  • Caution visitors and emphasise hand hygiene;

  • Clean and disinfect vomit and faeces spillages promptly;

  • Increase the frequency of routine ward, bathroom and toilet cleaning;

  • Use freshly prepared 0.1% hypochlorite to disinfect hard surfaces after cleaning;

  • Do not reopen the ward until 72 hours after the last new case and 72 hours after uncontained vomiting and diarrhoea;

  • Thoroughly clean the ward and change bed curtains before reopening;

  • Clean carpets and soft furnishings with hot water and detergent, or steam clean. Vacuum cleaning is not recommended.

Chadwick et al’s (2000) study contains advice to prevent the spread of infection to unaffected areas, and an appendix provides information for staff. See www.hpa.org.uk.

References


Centers for Disease Control and Prevention (2006) Norovirus in Healthcare Facilities Fact Sheet. www.cdc.gov

Chadwick, P.R. et al (2000) Management of hospital outbreaks of gastroenteritis due to small round structured viruses. Journal of Hospital Infection; 45: 1, 1–10.

Health Protection Agency (2008) Norovirus (Norwalk-like Virus, Small Round Structured Virus/SRVS).
www.hpa.org.uk

Health Protection Agency (2007a) Norovirus – Frequently Asked Questions. www.hpa.org.uk

Health Protection Agency (2007b) Health Protection Report; 1: 51. London: HPA.

Health Protection Agency (2006) Clinical Information – Norovirus. www.hpa.org.uk

Norovirus-clinical summary

  • Incubation period: usually 24–48 hours.

  • Common clinical features: – vomiting; diarrhoea; fever.

  • Reservoir: gastrointestinal tract
    of humans.

  • Transmission: person-to-person by the faecal-oral route; risk of infection from aerosols of projectile vomit; environmental contamination, especially of toilets – gloves should be used by cleaners; contaminated food and water, especially bivalve molluscs.

  • Other relevant features: infectivity lasts for 48 hours after resolution of symptoms. The infective dose is extremely low.

Source: HPA (2006)

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