Download Norwalk Virus

Norwalk Virus
Presentation to
Board of Public Health
Duxbury, Massachusetts
March 20, 2003
David Brumley, MD, MBA
Sources: Centers for Disease Control
The Merck Manual*
*Copyright © 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002 Merck & Co., Inc., Whitehouse Station, NJ, USA. All rights
reserved.
Noroviruses
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Norwalk-like viruses (NLVs)
Caliciviruses (because they belong to the virus family Caliciviridae)
Small round structured viruses.
History
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Noroviruses are named after the original strain “Norwalk virus,”
which caused an outbreak of gastroenteritis in a school in Norwalk,
Ohio, in 1968.
Epidemiology
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Occurs year-round
Outbreaks of norovirus gastroenteritis have taken place in
restaurants, cruise ships, nursing homes, hospitals, schools,
banquet halls, summer camps, and family dinners.
CDC estimates that 23 million cases of acute gastroenteritis are
due to norovirus infection.
It is estimated that as many as half of all food-related outbreaks
of illness may be caused by norovirus.
Waterborne outbreaks of norovirus disease in community
settings have often been caused by sewage contamination of
wells and recreational water.
Sites of Infection
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Among the 232 outbreaks of norovirus illness reported to CDC
from July 1997 to June 2000,
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57% were foodborne
16% were due to person-to-person spread
3% were waterborne
Common settings for outbreaks
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restaurants and catered meals (36%)
nursing homes (23%)
schools (13%)
vacation settings or cruise ships (10%)
Transmission
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Noroviruses are found in the stool or vomit of infected people.
become infected with the virus in several ways, including:
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eating food or drinking liquids that are contaminated with norovirus;
touching surfaces or objects contaminated with norovirus, and then
placing their hand in their mouth;
having direct contact with another person who is infected and
showing symptoms (for example, when caring for someone with
illness, or sharing foods or eating utensils with someone who is ill).
The virus is very contagious and can spread rapidly throughout
nursing home and day care environments.
Transmission
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Both stool and vomit are infectious.
It is thought that as few as 10 viral particles may be sufficient to
infect an individual.
Particular care should be taken with young children in diapers who
may have diarrhea.
People infected with norovirus are contagious from the moment
they begin feeling ill to at least 3 days after recovery.
Some people may be contagious for as long as 2 weeks after
recovery
Asymptomatic infection may occur in as many as 30% of
infections,
Symptoms
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Typically nausea, vomiting, diarrhea, and some stomach cramping.
People who are sick with norovirus illness can often vomit violently,
without warning, and the vomit is infectious.
Sometimes low-grade fever, chills, headache, muscle aches, and
a general sense of tiredness.
Often begins suddenly, and the infected person may feel very sick.
Usually brief, with symptoms lasting only about 1 or 2 days.
Course of Illness
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Symptoms of norovirus illness usually begin about 24 to 48
hours after ingestion of the virus, but they can appear as early
as 12 hours after exposure.
There are many different strains of norovirus, which makes it
difficult for a person’s body to develop long-lasting immunity
Norovirus illness can recur throughout a person’s lifetime
Some people are more likely to become infected and develop
more severe illness than others due to genetic factors.
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People of O blood group are at greatest risk for severe infection.
Diagnosis
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Norovirus can often be found in stool samples of infected
persons by using special tests.
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best made from stool specimens taken within 48 to 72 hours after
onset of symptoms
Blood tests looking for antibodies against norovirus are also
performed, when the stool tests are inconclusive or were not
done.
Sequencing of noroviruses found in clinical samples has helped
in conducting epidemiologic investigations by linking cases to
each other and to a common source and by differentiating
outbreaks that were mistakenly connected.
Treatment
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No antiviral medication that works against norovirus
No vaccine to prevent infection
Norovirus infection cannot be treated with antibiotics.
Treatment is supportive with fluids for dehydration (oral or
intravenous)
Prognosis
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Usually not serious, although people may feel very sick and
vomit many times a day
Most people get better within 1 or 2 days
No long-term health effects related to their illness.
Can become dehydrated and may need medical attention
No evidence to suggest that an infected person can become a
long-term carrier of norovirus.
Prevention
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Resistant to environmental challenge.
– They are able to survive freezing, and temperatures as high as
60°C,
– Have even been associated with illness after being steamed in
shellfish.
– Can survive in up to 10 ppm chlorine, well in excess of levels
routinely present in public water systems.
Prevention
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Frequently wash your hands, especially after toilet visits and
changing diapers and before eating or preparing food.
Carefully wash fruits and vegetables, and steam oysters before
eating them.
Thoroughly clean and disinfect contaminated surfaces
immediately after an episode of illness by using a bleach-based
household cleaner.
Immediately remove and wash clothing or linens that may be
contaminated with virus after an episode of illness (use hot
water and soap).
Flush or discard any vomitus and/or stool in the toilet and make
sure that the surrounding area is kept clean.
Prevention
(Food Handlers)
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Persons who are infected with norovirus should not prepare
food while they have symptoms and for 3 days after they
recover from their illness
Food and drinks can very easily become contaminated with
norovirus because the virus is so small and because it probably
takes fewer than 100 norovirus particles to make a person sick
Some foods can be contaminated with norovirus before being
delivered to a restaurant or store.
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Several outbreaks have been caused by the consumption of
oysters harvested from contaminated waters.
Other produce such as salads and frozen fruit may also be
contaminated at source.
Surveillance
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CDC currently does not conduct active surveillance to monitor
outbreaks of gastroenteritis caused by noroviruses.
Outbreaks are reported to CDC’s Viral Gastroenteritis Section,
Respiratory and Enteric Viruses Branch, Division of Viral and
Rickettsial Diseases, National Center for Infectious Diseases
(NCID)
CaliciNet is a database of norovirus sequences identified from
outbreaks of norovirus that can then help to determine links
between outbreaks.
Cruise Ship Outbreaks
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CDC investigated 21 reports of gastroenteritis aboard
17 cruise ships beginning January 1 through
December 2, 2002.
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9 were confirmed to be associated with noroviruses
3 were attributable to bacterial agents
9 were unknown etiology
For comparison, in 2002, CDC confirmed 26 landbased outbreaks of gastroenteritis attributable to
norovirus
Vessel Sanitation Program
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Currently, over 140 cruise ships participate in the program.
The inspection focuses on the following:
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The ship's water supply
The ship's spas and pools
The ship's food
The potential for contamination of food and water
The practices and personal hygiene of employees
The general cleanliness and physical condition of the ship
The ship's training programs in general environmental and public health
practices
Inspection scores and reports are published on the VSP website
www2.cdc.gov/nceh/vsp/vspmain.asp.
Scores are also published every month in the Summary of Sanitation
Inspections of International Cruise Ships, commonly referred to as
the green sheet.