1. Foodborne Norovirus Outbreaks
Dr. Aron Hall
Epidemiologist specializing in norovirus
Centers for Disease Control and Prevention
Based on the article
Epidemiology of Foodborne Norovirus Outbreaks,
United States, 2001–2008
Aron J. Hall, Valerie G. Eisenbart, Amy Lehman Etingüe, L. Hannah Gould, Ben A. Lopman, and Umesh D. Parashar
Emerging Infectious Diseases
October 2012
National Center for Emerging and Zoonotic Infectious Diseases
Emerging Infectious Diseases

2. What are noroviruses?
Noroviruses are a diverse group of viruses in the family Caliciviridae.
They are named after the original Norwalk virus that caused an outbreak of gastroenteritis in a school in Norwalk, Ohio, in 1968.
Currently, 5 groups of noroviruses are recognized. Three of them can affect humans.
>25 different types of norovirus strains have been identified within these groups and new strains continue to emerge.
Because there are so many different types of noroviruses, people can get infected many times during their lifetime.
It is possible to develop immunity to specific types, but we don’t know how long that immunity lasts.

3. What are the signs and symptoms of infection with a norovirus?
Signs and symptoms include:
Acute gastroenteritis (inflammation of the stomach and intestines)
diarrhea, vomiting, nausea, stomach pain
Fever, body aches, fatigue
Dehydration (because of having diarrhea and vomiting many times per day)
Less urination
Dry mouth or throat
Dizziness
When someone gets infected with norovirus, they may say they have ‘food poisoning’ or ‘stomach flu’.
Food poisoning can be caused by noroviruses, but other germs and chemicals can also cause food poisoning.

4. Are noroviruses dangerous?
Most people with norovirus illness get better in 1-3 days.
Some people may get severely dehydrated, especially young children, the elderly, and people with weakened immune systems.
Each year, norovirus causes about 70,000 hospitalizations and 800 deaths, mostly in young children and the elderly.

5. How are noroviruses spread?
People with norovirus illness shed billions of virus particles in their stool and vomit.
People can get infected by:
eating food or drinking liquids contaminated with norovirus
touching surfaces or objects that have norovirus on them then putting fingers in mouth
having direct contact with someone infected with norovirus
caring for, or sharing food, drinks, or eating utensils with an infected person

6. How are noroviruses spread? (cont.)
Food handlers, such as those in restaurants, can spread norovirus to others when they are ill.
They can easily contaminate the food and drinks that they touch.
People who consume these food or drinks can get infected and sick, leading to a norovirus outbreak.
About 50% of all outbreaks of food-related illness are caused by norovirus. In many of these cases, sick food handlers were involved in spreading the virus.

7. How big of an issue is foodborne norovirus outbreaks in the United States?
Noroviruses are the leading cause of outbreaks from contaminated food in the United States.
In our study, we found that:
On average one foodborne norovirus outbreak was reported every day in the United States.
These outbreaks resulted in over 10,000 illnesses, 1,200 healthcare provider visits, 150 hospitalizations, and 1 death each year.

8. Why are noroviruses a big issue?
Noroviruses are a public health problem.
They are highly contagious.
People with norovirus illness shed billions of virus particles in their stool and vomit, but it only takes a very small amount of them (<100 particles) to make someone sick.
They spread easily and quickly, especially in closed places like daycare settings, nursing homes, schools, and cruise ships.
They are hard to get rid of because they:
stay on objects and surfaces and still infect people after days or weeks
survive both freezing and heating (although not thorough cooking) and even some disinfectants
They are constantly evolving.
difficult to develop a vaccine

9. What food items are more likely to contain norovirus?
Foods commonly involved in norovirus outbreaks include:
Raw or undercooked foods, such as leafy greens, fresh fruits, or shellfish.
Any food served raw or handled after being cooked can get contaminated with noroviruses.
Fresh produce may be handled at several different points, including harvesting, processing, and preparing, before it is eaten.
Water used to irrigate crops can cause norovirus contamination, which will persist on raw food.
Raw or undercooked shellfish, like oysters, can be problematic when they are harvested from contaminated water.
Ready-to-eat foods, like sandwiches and salads.
It is often hard to determine the specific food that caused an outbreak because noroviruses spread in many ways.
In our study, the specific food source for over half of the foodborne norovirus outbreaks was never identified.

10. How can future norovirus outbreaks be prevented in the food industry?
First, focus on food handler.
We found that infected food handlers were the source of 53% of foodborne norovirus outbreaks.
They possibly contributed to 82% of outbreaks.
Most outbreaks were caused by food in restaurants contaminated during preparation.
Food handlers should:
always practice good hand hygiene
avoid touching foods with bare hands
stay out of the kitchen and not handle or prepare food when they are sick
Second, consider protecting food before it reaches the kitchen.
Some outbreaks caused by shellfish and produce were likely contaminated during production.
Using safe water for growing and irrigation can help prevent food from getting contaminated at the source.

11. Is there a vaccine for norovirus?
Currently, no vaccine is available to protect against norovirus, but research is being done in this area.

12. What should people do to avoid getting foodborne norovirus?
First, always wash your hands carefully with soap and water after using toilet and changing diapers and before eating, preparing, or handling food.
Second, wash your fruits and vegetables thoroughly, and cook oysters and other shellfish thoroughly before eating them.
Third, do not handle or prepare food for others when you are sick.
Fourth, clean and disinfect contaminated surfaces after throwing up or having diarrhea.
Finally, wash any soiled laundry thoroughly after throwing up or having diarrhea.
More information, visit CDC’s norovirus website at

13. Thank you to all authors
Aron J. Hall, Valerie G. Eisenbart, Amy Lehman Etingüe, L. Hannah Gould, Ben A. Lopman, and Umesh D. Parashar
For more information, please contact:
Emerging Infectious Diseases
Centers for Disease Control and Prevention
1600 Clifton Road NE, Mailstop D61, Atlanta, GA , USA
Telephone: /Fax:
Web:
The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention.
National Center for Emerging and Zoonotic Infectious Diseases
Emerging Infectious Diseases