Download Clear guidance crucial to norovirus control

Clinical Review
Forum
Clear guidance crucial
to norovirus control
In the second part a two-part series, Paul McKeown looks at the
transmission, clinical features and future of norovirus
Gastroenteritis or intestinal infectious disease (IID)
remains a major cause of morbidity and mortality in developing countries. Additionally, despite the major public
health advances that have improved beyond recognition the
quality of our food, water and sanitation since the 19th
century, they remain one of the most common illnesses in
developed countries.
Transmission of norovirus
Transmission of noroviruses can be by person-to-person,
environmental, foodborne and waterborne routes.
Person-to-person spread: This is the primary mode of transmission. Noroviruses may be spread from person-to-person
by the faecal-oral route and by vomiting (air-oral/mucous
membrane spread), probably by causing widespread aerosol
dissemination of virus particles, environmental contamination and subsequent indirect person-to-person spread. In
some settings, particularly hospitals, transmission via vomiting may be more important than the established faecal-oral
route of infection associated with other enteric pathogens.15
Environmental spread: Norovirus is known to be very
effective at spreading directly in the environment. This is
due to its ability to withstand drying, high temperatures and
routine disinfection.
Foodborne spread: Foods that are touched or handled
and are not subjected to further cooking (above 60OºC),
such as cold meats, salads or sandwiches are commonly
implicated in foodborne norovirus infection.16 Filter-feeding
bivalve molluscan shellfish such as oysters can harbour and
concentrate viruses if they are grown in water contaminated
with sewage.17,18
Waterborne spread: Water as a method of transmission
of norovirus has been monitored for some time in the US
by the Environmental Protection Agency. Outbreaks have
repeatedly been traced to contaminated drinking water
sources and recreational water.19,20 As well as water, ice is
being increasingly recognised as vehicles for transmission
of norovirus.21 In 2002, a large outbreak affecting almost
100 tourists from the Republic of Ireland and Northern Ireland was traced to ice prepared with contaminated water
in a number of skiing resorts in Andorra.22 Water is a very
effective vehicle of transmission because the infectious
dose is so tiny and the virus can pass through standard
filters and survive the levels of chlorine used
for drinking water antisepsis.19
Outbreaks
Noroviruses are extremely effective
outbreak pathogens; hardy, readily
propagated in the environment and having a tiny infectious
dose. They can survive for long periods on surfaces such as
door handles, worktops and furnishings.
Characteristically, the outbreaks noroviruses produce
occur against a constantly changing background of waxing
and waning activity. Extensive outbreaks were experienced
across the northern hemisphere in 2001-2002; a smaller
upsurge was seen in 2004-2005. That norovirus could
produce a global pandemic of gastroenteritis was first recognised in the extensive global upsurge in 1995-1996.23
As a result, they have been responsible for some quite
spectacular outbreaks. In Ireland, there have been a
number of outbreaks in hotels that have each resulted in
hundreds of cases of illness. In Japan in 1990, an outbreak resulted in more than 3,200 cases of illness among
schoolchildren.24
Outbreaks will occur wherever people congregate, and
have been reported in a variety of settings including: nursing homes, hospitals, cruise ships, aircraft and restaurants
and events with catered meals.19,22,25-27 Since it is a community infection, outbreaks in congregate settings such as
these are simply a reflection and a gauge of what is happening in the community.
In Ireland, in 2002, 90% of reported outbreaks of IID (representing more than 150 outbreaks) were either confirmed
or suspected as being caused by norovirus.28 Of these, about
70% occurred in hospitals and other healthcare settings. A
similar proportion of healthcare-associated outbreaks occur
in the UK and across the rest of Europe.29 Their management and control in any setting is challenging.
Outbreaks in hotels, aircraft and cruise liners are invariably very expensive, in terms of direct and indirect costs and
the potential damage to business. Outbreaks in hospitals
and other healthcare settings have the potential to seriously
disrupt the functioning of regional and even national health
systems. The management and control in such settings can be
extremely difficult.31,32 However, the situation is improving.
The size of outbreaks is one measure of how well spread
the outbreak pathogen is being contained. Over the past six
or more years in Ireland, the size of outbreaks in hospitals
and nursing homes has halved; a measure of how effectively
infection control and public health professionals are more
rapidly identifying and closing down outbreaks.
Pathogenesis
Information from volunteer studies has demonstrated that
susceptibility to noroviral infection varies between individuals, due in part to previous exposure to the virus and
FORUM April 2009 65
15. Novirus-OF/NH2* 1
26/03/2009 11:54:49
Forum
Clinical Review
to immunological status. Interestingly, noroviruses have
recently been shown to bind in preferential ways to a number
of histo-blood group antigens (complex carbohydrates found
on many different cell types, including gastrointestinal epithelial cells; three distinct antigens exist: A, B, and O). The
result of this is that people with blood group B are partially
protected against infections with genogroup 1, and that
people with blood group O are partially protected genogroup
2 viruses (responsible for most human disease).
The virus produces histological changes in the epithelium of the small intestine within 24 hours with blunting of
jejunoileal villi. These will heal almost completely over the
following two to eight weeks.
Clinical features
Illness due to norovirus is characterised by acute, rapid
onset of nausea, vomiting, abdominal cramps and occasional diarrhoea. Vomiting is generally the principal
symptom (although it may be reduced or absent). It is usually of sudden onset and may be projectile, resulting in
widespread soiling.
Not uncommonly, the patient may experience sudden,
spontaneous projectile vomiting with little warning; so
sudden, in fact, that they may have insufficient time to reach
the lavatory. This is particularly true in the case of elderly
people or those with limited mobility. As a result, there can
be considerable public environmental soiling and significant
risk of more widespread dissemination of the virus.
As the projectile vomiting can be very forceful, the vomitus tends to become partially aerosolised; the resultant mist
being capable of wide distribution, an important consideration when cleaning and decontaminating affected area.
Prolonged diarrhoea can also be a feature, especially in
children.30 Recently in Ireland, cases in which diarrhoea
has been the sole gastrointestinal symptom have been
increasingly reported.31 The patient may complain of other
symptoms including headache, muscle aches, chills and
fever.32 As many as 30% of cases may be asymptomatic.
The incubation period generally ranges from 15 to 48 hours.
Prior to the advent of electron microscopy and RT-PCR, diagnosis of outbreaks was based on a series of clinical criteria
known as Kaplan’s Criteria33 which, with only slight revision,
is still used for early identification of a possible norovirus
outbreak. The illness is generally mild, lasting between one
and three days and in mild cases, a few hours.
Small amounts of clear fluids are all that is required in
treatment terms for the vast majority of cases; recovery is
usually rapid. If severe, the vomiting may result in dehydration, especially in the elderly and very young. Rarely,
disease may be extremely severe with prostration, marked
systemic upset, markedly reduced levels of consciousness
and disseminated intravascular coagulopathy.34 The period
of infectivity can be deceptively long; viral shedding can
continue for some time, perhaps several days, after full
recovery from noroviral infection. Moreover, outbreaks have
been associated with pre-symptomatic, symptomatic and
post-symptomatic food handlers.32
Control measures
Outbreaks due to norovirus are not eradicable, but they are
controllable. There is a large body of evidence that simple
interventions can minimise the spread of noroviruses:
Scrupulous handwashing: This is the most effective pre-
vention and control measures at minimising the spread of
norovirus infection.
Immediate cleaning and disinfection: Following an episode of vomiting or faecal soiling: since a single vomiting
individual can distribute viral particles across a wide area,
immediate cleaning and decontamination of the soiled area
is essential with particular attention being paid to those
areas touched by hands.
Isolation: Exclusion of ill staff from work or isolation of
groups of ill people (patients or residents of a nursing
home) as affected cohorts is necessary. Regardless of the
setting, these fundamental interventions form the basis of
control of outbreaks. Exclusion of ill staff for at least 48
hours after the last episode of vomiting or diarrhoea (given
the length of time noroviruses are shed following recovery)
and training of staff to rapidly seal off, clean and decontaminate the affected area, have been shown to be effective ways
of limiting spread.
In order to eradicate the virus from surfaces, it is necessary to use a strong (1:1000) hypochlorite solution on hard
surfaces. In order to decontaminate soft furnishings, steam
cleaning is required. There is a range of advice on minimising the impact of norovirus in various settings available on
the HPSC website www.ndsc.ie
Within healthcare settings, certain factors in hospitals
appear to contribute to promoting transmission of norovirus including: close patient contact; susceptible patients;
movement of patients and staff; hygiene (if sub-optimal);
and throughput of visitors and other staff.31 In healthcare
settings, an early, rapid response to an outbreak is the key
to its control. Having an agreed hospital/nursing home
outbreak plan in place is the best method for ensuring uniformity and effectiveness of response.31 Once an outbreak
is suspected, the prompt establishment of a control team to
oversee the management of the outbreak is essential.31
The future
Noroviruses, like all viruses, are evolving. Upsurges in
activity, as have been seen before, can be expected in the
future. Straightforward guidance with clear descriptions
of roles, responsibilities and interventions are crucial for
effective control of this infection. In order to decontaminate soiled areas, trials using various ‘fogging’ products
– antiviral disinfectants administered in a mist to mimic
the distribution of viruses during episodes of vomiting – are
underway. Initial results are moderately promising.
Vaccination is one of the most cost-effective approaches
to reducing the morbidity and mortality caused by microbial
agents, and as a result, extensive studies looking at the
feasibility of producing a norovirus vaccine have been conducted in several centres. Despite it being such a common
and generally mild condition, there may be a strong argument for targeted use of such a vaccine in certain settings.35
At the moment, however, vaccine development is still at a
very early stage.
Paul McKeown is a consultant in public health medicine with
the Health Protection Surveillance Centre
The first part of this article was published in the March
issue of Forum (2009; 26(3): 51-52).
References on request
66 FORUM April 2009
15. Novirus-OF/NH2* 2
26/03/2009 11:55:05