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Common Settings of Norovirus Outbreaks

Most outbreaks of norovirus illness happen when infected people spread the virus to others through direct contact, such as by caring for them or sharing food or eating utensils with them. Food, water, and surfaces contaminated with norovirus can also cause outbreaks.

Norovirus outbreaks have been reported in many settings, some of the most commonly reported outbreak settings are listed below.

Healthcare Facilities

The most commonly reported setting for norovirus outbreaks in the United States and other industrialized countries is healthcare facilities, including long-term care facilities and hospitals. Over half of all norovirus outbreaks reported in the United States occur in long-term care facilities.

The virus can be introduced into healthcare facilities by infected patients, staff, visitors, or contaminated foods. Outbreaks in these settings can sometimes last months. Norovirus illnesses can be more severe, occasionally even deadly, in patients in hospitals or long-term care facilities compared with healthy people.

Restaurants and at Catered Events

Norovirus is the leading cause of outbreaks from contaminated food in the United States. About 50% of all outbreaks of food-related illness are caused by norovirus. Most of these outbreaks occur in food service settings like restaurants. Infected food workers are frequently the source of outbreaks in food-service settings, often by touching ready-to-eat foods, such as raw fruits and vegetables, with their bare hands before serving them. However, any food served raw or handled after being cooked can get contaminated with norovirus.

Norovirus outbreaks can also occur from food that is contaminated at the source or on the farm, such as oysters harvested from contaminated water, or fruit and vegetables sprayed with contaminated water in the field.

Foods that are commonly involved in norovirus outbreaks include:

  • leafy greens (such as lettuce),
  • fresh fruits, and
  • shellfish (such as oysters).

Schools and Child Care Centers

Norovirus outbreaks also frequently occur in schools, child care centers, colleges, and universities. Norovirus outbreaks on school and university campuses have even led to campus closures. Close quarters, shared spaces, and shared surfaces make it easy for norovirus to spread in schools. Children are also less likely to practice proper hand washing habits.

Cruise Ships

Cruise ships account for a small percentage (1%) of reported norovirus outbreaks overall. However, norovirus is most often the cause of outbreaks of diarrheal disease on cruise ships (over 90%). Because norovirus is the cause of most diarrheal outbreaks on cruise ships, and these outbreaks frequently get media attention, some people call norovirus the “cruise ship virus.” Norovirus can be especially challenging to control on cruise ships because of the close living quarters, shared dining areas, and rapid turnover of passengers. When the ship docks, norovirus can be brought on board in contaminated food or water or by passengers who were infected while ashore. Repeated outbreaks on consecutive cruises may also result from infected crew or environmental contamination. This is because norovirus can persist on surfaces and is resistant to many common disinfectants.

Definition of a Norovirus Outbreak

An outbreak of norovirus is defined as an occurrence of two or more similar illnesses resulting from a common exposure that is either suspected or laboratory-confirmed to be caused by norovirus.

You can use the NORS Dashboard to learn about reports of outbreaks of foodborne, waterborne, and enteric (gastrointestinal) diseases spread by person-to-person contact, environmental contamination, animal contact, and more.

Infographic: Quick stats: U.S. outbreaks of diarrhea and vomiting, 2009-2013
Outbreaks in health care facilities accounted for almost 63% of the norovirus outbreaks reported through the National Outbreak Reporting System from 2009 through 2012. 22% of outbreaks occurred in restaurants or banquet facilities.  The remaining 15% of the reported outbreaks occurred in schools or day-care facilities, a private residence, or other settings.

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