What
is Norwalk virus infection?
Norwalk virus infection is an intestinal illness that often occurs
in outbreaks. According to the Centers for Disease Control and Prevention,
it is estimated that over 180,000 people get the virus in the United
States each year. Norwalk and Norwalk-like viruses are increasingly
being recognized as leading causes of foodborne disease in the United
States. Infected people usually recover in 2 to 3 days without serious
or long-term health effects.
What is the infectious agent that
causes Norwalk virus infection?
Norwalk virus infection is caused by the Norwalk virus. The virus
was first identified in 1972 after an outbreak of gastrointestinal
illness in Norwalk, Ohio. Later, other viruses with similar features
were described and called Norwalk-like viruses. These have since
been classified as members of the calicivirus family.
Where is Norwalk virus found?
Norwalk and Norwalk-like viruses are found worldwide. Humans are
the only known hosts. The viruses are passed in the stool of infected
persons.
How do people get Norwalk virus infection?
People get Norwalk virus infection by swallowing food or water
that has been contaminated with stool from an infected person.
Outbreaks in the United States are often linked to eating raw
shellfish, especially oysters and clams. Shellfish become contaminated
via stool from sick food handlers or from raw sewage dumped overboard
by recreational and/or commercial boaters. Contaminated water,
ice, eggs, salad ingredients, and ready-to-eat foods are other
sources of infection.
Who is at risk for Norwalk virus infection?
Anyone can get Norwalk virus infection, but it may be more common
in adults and older children.
What are the signs and symptoms of Norwalk
virus infection?
- Nausea
- Vomiting
- Diarrhea
- Stomach cramps
- Severe illness or hospitalization is uncommon. Infected persons
usually recover in 2 to 3 days without serious or long-term
health effects.
How soon after exposure do symptoms appear?
Symptoms usually appear in 1 to 2 days after swallowing contaminated
food or water.
How is Norwalk virus infection diagnosed?
Laboratory diagnosis is difficult. Diagnosis is often based on
the combination of symptoms and the short time of illness.
What is the treatment for Norwalk
virus infection?
No specific treatment is available. Persons who are severely dehydrated
might need rehydration therapy.
How common is Norwalk virus infection?
Norwalk and Norwalk-like viruses are increasingly being recognized
as leading causes of foodborne disease in the United States. However,
since no routine diagnostic test is available, the true prevalence
is not known. Norwalk and Norwalk-like viruses have been linked
to outbreaks of intestinal illness on cruise ships and in communities,
camps, schools, institutions, and families.
Many oyster-related outbreaks of intestinal illness linked to
Norwalk-like viruses have been reported in Louisiana, Florida,
Maryland, and other states where oyster harvesting is common.
In 1993, 73 people in Louisiana and about 130 others in the United
States who ate oysters from Louisiana became ill. A malfunctioning
sewage system was the cause of an outbreak in 1996. An outbreak
in 1997 was linked to sewage from oyster-harvesting boats.
How can Norwalk virus be prevented?
- Wash hands with soap and warm water after toilet visits and
before preparing or eating food.
- Cook all shellfish thoroughly before eating.
- Wash raw vegetables before eating.
- Dispose of sewage in a sanitary manner.
- Food handlers with symptoms of Norwalk-like illness should
not prepare or touch food.
This fact sheet is for information only and is not meant to be
used for self-diagnosis or as a substitute for consultation with
a health-care provider. If you have any questions about the disease
described above, consult a health-care provider or you can contact
the Health Services Agency Public Health Communicable Disease
Program at (209) 558-5678.
Adapted from information from:
Association of State and Territorial Directors of Health Promotion
and Public Health Education
Ohio State University Family and Consumer Sciences
The Centers for Disease Control and Prevention
Iowa State University Extension Food Safety Project |
