Norwalk Virus Infection

 

• Norwalk virus infection is an intestinal illness that often occurs in outbreaks.
• Norwalk and Norwalk-like viruses are increasingly being recognized as leading causes of foodborne disease in the United States.
• The viruses are passed in the stool of infected persons. People get infected by swallowing stool-contaminated food or water. Outbreaks in the United States are often linked to raw oysters.
• Infected people usually recover in 2 to 3 days without serious or long-term health effects.
• To prevent Norwalk virus infection: 1) wash hands with soap and warm water after toilet visits and before preparing or eating food; 2) cook all shellfish thoroughly before eating; 3) wash raw vegetables before eating; and 4) dispose of sewage in a sanitary manner.

 

What is Norwalk virus infection?

Norwalk virus infection is an intestinal illness that often occurs in outbreaks.

 

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 questions about the disease described above, consult a health-care provider.