January 17, 2003

The Norwalk virus – what MGHers should know

With the recent influx of occurrences of Norwalk or Norwalk-like infections, there has been an increased concern and many questions about the virus. Below are some helpful facts about the Norwalk virus compiled by the MGH Infection Control Department.

How do people get Norwalk virus infection?
Norwalk virus infection is an intestinal illness that often occurs in outbreaks. People contract Norwalk virus infection by swallowing food or water that has been contaminated with stool from an infected person. Outbreaks in the United States often are linked to eating raw shellfish, especially oysters and clams. Shellfish become contaminated by 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 and stomach cramps are symptoms. Severe illness or hospitalization is uncommon.

How soon after exposure do symptoms appear?
Symptoms usually appear in one to two 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.

Can the infection be prevented?
To help prevent Norwalk virus infection, individuals should wash hands with soap and warm water after toilet visits and before preparing or eating food. All shellfish should be cooked thoroughly before eating. Raw vegetables should be washed before eating. Sewage should be disposed of in a sanitary manner. Food handlers with symptoms of Norwalk-like illness should not prepare or touch food. Infected people usually recover in two to three days without serious or long-term health effects.

For more information, call the MGH Infection Control Department at (617) 726-2036.