Responding to Norovirus Outbreaks

Key points

  • Prompt investigation and reporting are critical for identifying the cause of norovirus outbreaks and the primary way the virus spread.
  • Timely collection of appropriate specimens is important for rapid response.
Food safety inspectors examining food from gorcery store.

Typical responsibilities during an outbreak

Public health workers have several responsibilities during a norovirus outbreak.

State, local, & territorial health departments:

  • Serve as the lead agencies in most investigations of norovirus outbreaks.
  • Interview patients, collect stool specimens, and sometimes perform diagnostic testing.
Keep Reading: Laboratory Testing for Norovirus

CDC helps investigate and control norovirus outbreaks by:

  • Providing epidemiologic consultation and tools.
  • Testing specimens and genotyping those samples that test positive for norovirus.
  • Coordinating multi-state outbreak investigations as needed.

Food regulatory agencies (FDA, USDA, & state authorities):

  • Collaborate with health departments when a link between contaminated food and illness is identified.
  • Perform food testing for specific foods, such as shellfish and produce.
  • Coordinate recalls of foods involved in outbreaks.

Using clinical and epidemiologic criteria

When it is not possible to get laboratory confirmation of norovirus, health departments can use clinical and epidemiologic criteria. These can help determine if the outbreak was likely caused by norovirus (suspected norovirus outbreaks).

Kaplan's criteria

The original criteria proposed by Kaplan et al. are:

  1. A mean (or median) illness duration of 12 to 60 hours
  2. A mean (or median) incubation period of 24 to 48 hours
  3. More than 50% of people with vomiting
  4. No enteric bacteria found

When all four criteria are present, it is very likely that the outbreak was caused by norovirus. However, about 30% of norovirus outbreaks do not meet these criteria. If the criteria are not met, it does not mean that the outbreak was not caused by norovirus.

Lively's criteria

An alternate set of clinical criteria proposed by Lively et al. have been identified that are more sensitive for norovirus.

  1. A greater proportion of cases with vomiting than with fever
  2. Bloody diarrhea in less than 10% of cases
  3. Vomiting in greater than 25% of cases

The Lively criteria and more often available during outbreak investigations than the Kaplan criteria.

Resources

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Content Source:
National Center for Immunization and Respiratory Diseases; Division of Viral Diseases