Key learning points:
- Healthcare environments are vulnerable to outbreaks of norovirus throughout the year but particularly in the winter months
- Norovirus is easily spread through contact with those already infected or through contact with contaminated equipment and surfaces
- Washing hands thoroughly with soap and water can help prevent the spread of norovirus
Each winter healthcare environments and other places where people group together in high numbers are vulnerable to outbreaks of norovirus. The norovirus causes a very unpleasant infection with symptoms including vomiting and diarrhoea. For most people the infection lasts about 24 to 48 hours without complication, but in those with an underlying medical condition it can be serious and, on occasion, fatal.1 The seasonal arrival of this unwanted guest has become an annual event, so how can we limit the spread of norovirus?
How common is norovirus infection?
Norovirus infections can occur throughout the year but are especially common during the winter months. As the levels of infection increase in the community it becomes more likely that an outbreak will happen in the healthcare setting. The laboratory reports of norovirus infection in Scotland are published weekly by Health Protection Scotland (http://www.hps.scot.nhs.uk) and represent a valuable resource when assessing trends in infection prevalence over the years. The seasonality of norovirus infection is clearly shown in the NHS Scotland data, with the highest reports of norovirus in the winter months, but we do not yet know why this is the case. The burden of infection in healthcare settings also varies annually with some years being worse than others – for example there was a relatively high burden of norovirus outbreaks during the winter 2012-2013 whereas the following winter season was less severe. Outbreaks of norovirus in the acute hospital setting may result in wards being closed to admissions, reduced bed availability and increases in staff sick leave,2 resulting in greater pressures on healthcare staff.
How is norovirus spread?
In healthcare settings multiple introductions of norovirus may occur throughout the season with a number of different noroviruses circulating and causing infection at the same time.3 Norovirus can be spread in a number of different ways.
Person-to-person transmission is probably most common. Researchers have shown that people experimentally infected with norovirus may shed the virus in their faeces for more than a month – long after the symptoms of infection have passed,4 but it is unclear if they are still infectious past the symptomatic phase. In addition not all people with norovirus show active infection but may still shed the virus.4 Norovirus may also be present in the saliva of infected people for 10 to 15 days from the onset of symptoms.5
The environment may also have an important role to play as it can quickly become heavily contaminated with norovirus during outbreaks. For example, an environmental investigation of ward areas in the hospital setting has shown that norovirus spreads far and wide - contaminating surfaces, medical equipment and reaching far from the source of the outbreak, with the virus detected even after cleaning.3 Some examples of the areas contaminated included those near to the patient including beds, lockers, tables and call bells, medical equipment including blood pressure machines, intravenous pump and thermometers, hand hygiene equipment and non-clinical areas including nurses' station computers, telephones, and notes trolleys.3 What causes such high levels of contamination is unclear but it may be spread via contaminated hands, as most of the areas found contaminated are areas likely to have been touched either by healthcare workers or patients. Experiments in the laboratory setting have shown that hands contaminated with norovirus can readily transfer the virus to multiple surfaces.6
There is also the possibility that norovirus spreads through the air, perhaps when people vomit. In 1994 Caul proposed that vomiting could give rise to infectious aerosols:7 Airborne transmission was implicated in a norovirus outbreak on a tour bus in the early 1990s;8 a reusable grocery bag, perhaps contaminated through airborne spread of norovirus, was implicated in an outbreak in a sports team in 2010;9 but the most quoted example of possible airborne norovirus is the work by Marks et al which suggested that airborne transmission of norovirus was the cause of an outbreak in a hotel in 1998.10 What is unfortunate is that none of these studies were undertaken in the healthcare setting and while they do provide evidence for the airborne spread of norovirus they are not based on direct detection of the virus in the air, but rather by implication.
We have seen that norovirus outbreaks are a major issue for the healthcare sector and that there are probably multiple routes of transmission: person-to-person spread, the healthcare environment and perhaps the air. So how do we minimise the spread of this pathogen most effectively? Clearly standard infection control precautions play a major role, as does effective cleaning and disinfection. However, hand hygiene is probably one of the most effective measures against the spread of norovirus.
Current guidelines state its importance. Public Health England states that healthcare workers should wash their hands with soap and water in accordance with the World Health Organization ‘five moments’ for hand hygiene, and should also encourage and help patients to wash their hands.11 Guidance from Health Protection Scotland is similar and states that alcohol-based hand rubs should not be used as a replacement for soap and water.12
The American guidelines (Centers for Disease Control and Prevention) ask healthcare workers to actively promote hand hygiene to staff, patients and visitors.13 There is a clear push towards the use of soap and water and this is because further research is needed into the effectiveness of alcohol based hand rubs in preventing the spread of norovirus, so at the moment their use related to norovirus is not recommended.13
Washing our hands in accordance with the ‘five moments’ will help reduce the spread of norovirus in many ways. Washing hands between visiting patients will help reduce transfer of the virus from one patient to another. If equipment or surfaces around the wards are contaminated with norovirus then washing hands before touching patients will help prevent further spread of the virus.
While norovirus spreads easily within the healthcare setting something as simple as washing your hands with soap and water can help prevent the spread of the infection to others.
1. Trivedi TK, Desai R, Hall AJ, Patel M, Parashar UD, Lopman BA. Clinical characteristics of norovirus-associated deaths: A systematic literature review. American Journal of Infection Control. 2013 7//;41(7):654-7.
2. Zingg WMD, Colombo CRNMPH, Jucker TRN, Bossart WP, Ruef CMD. Impact of an Outbreak of Norovirus Infection on Hospital Resources. Infection Control and Hospital Epidemiology. 2005;26(3):263-7.
3. Morter S, Bennet G, Fish J, Richards J, Allen DJ, Nawaz S, et al. Norovirus in the hospital setting: virus introduction and spread within the hospital environment. Journal of Hospital Infection. 2011 2//;77(2):106-12.
4. Atmar RL, Opekun AR, Gilger MA, Estes MK, Crawford SE, Neill FH, et al. Norwalk Virus Shedding after Experimental Human Infection. Emerging infectious diseases. 2008;14(10):1553-7. PubMed PMID: PMC2609865.
5. Kirby A, Dove W, Ashton L, Hopkins M, Cunliffe NA. Detection of norovirus in mouthwash samples from patients with acute gastroenteritis. Journal of Clinical Virology. 2010 8//;48(4):285-7.
6. Barker J, Vipond IB, Bloomfield SF. Effects of cleaning and
disinfection in reducing the spread of Norovirus contamination via environmental surfaces. Journal of Hospital Infection. 2004
7. Caul EO. Small round structured viruses: airborne transmission and hospital control. The Lancet. 1994 5/21/;343(8908):1240-2.
8. Chadwick PR, Walker M, Rees AE. Airborne transmission of a small round structured virus. The Lancet. 1994 1/15/;343(8890):171.
9. Repp KK, Keene WE. A Point-Source Norovirus Outbreak Caused by Exposure to Fomites. Journal of Infectious Diseases. 2012 June 1, 2012;205(11):1639-41.
10. Marks PJ, Vipond IB, Carlisle D, Deakin D, Fey RE, Caul EO. Evidence for airborne transmission of Norwalk-like virus (NLV) in a hotel restaurant. Epidemiology and Infection. 2000;124(3):481-7.
11. Norovirus Working Party. Guidelines for the management of norovirus outbreaks in acute and community health and social care settings. Public Health England, 2012.
12. Health protection Scotland. HPS Norovirus Outbreak Guidance Season 2014 - 2015: Preparedness, control measures & practical considerations for optimal patient safety and service continuation in hospitals. Glasgow, UK: Health Protection Scotland, 2014.
13. HICPAC Norovirus Gastroenteritis Guideline writing group. Guideline for the prevention and control of norovirus gastroenteritis outbreaks in healthcare settings. Atlanta, USA: Centers for Disease Control and Prevention, 2011.
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