Home
Programs
Center for Infectious Diseases
Division of Communicable Disease Control
Norovirus Information for Local Health Departments

Norovirus

Jump to LHD Resources Information for Laboratories

Information for Local Health Departments

Norovirus is one of the leading causes of gastroenteritis and foodborne illness in the United States; an estimated 19 to 21 million illnesses occur each year. Norovirus infections result in over 100,000 hospitalizations annually, and are responsible for many more emergency department visits, especially among young children. The first norovirus outbreak was identified in Norwalk, Ohio in 1968.

Learn more about norovirus burden and trends in the U.S.

Noroviruses cause inflammation of the stomach and intestines, with most common symptoms including vomiting, diarrhea, and nausea. Noroviruses are very contagious and are transmitted through the fecal-oral route, i.e., accidental ingestion of food or drink contaminated with feces or vomit of someone who is infected. Noroviruses require only a small inoculum for infection, and can survive for weeks on surfaces and objects, so contaminated fomites and food vehicles play an important role in the spread of these viruses.

Norovirus shedding in stool peaks during the first 24-48 hours after onset of illness, but shedding can continue for weeks. Although norovirus infection can occur year-round, norovirus activity typically peaks between November and April. Outbreaks of norovirus commonly occur in settings where people are together in shared spaces such as restaurants, catered events, healthcare facilities, schools, childcare facilities, camps, shelters, correctional facilities, and cruise ships. Contaminated food and drinks can also cause outbreaks, either through contamination from infected food handlers or food contaminated at the source or during processing. Foods commonly implicated in norovirus outbreaks have included raw oysters and other shellfish, and fresh produce.

Identifying norovirus as the cause of an outbreak of gastrointestinal illness is key to implementing necessary control measures, removing potential sources, and preventing further transmission.

Learn more about current and previous norovirus outbreaks in the U.S.

Learn more about common settings of norovirus outbreaks

Key Points

Noroviruses are very contagious. Outbreaks are common and can spread very quickly, particularly in congregate settings, if not controlled.
Early identification of norovirus through collection and testing of clinical specimens is important for confirming and mitigating spread of disease and controlling outbreaks.
Both cleaning and disinfection are necessary to kill norovirus. Refer to EPA’s List G for disinfectant products to use against norovirus. Recommended cleaning measures for norovirus outbreaks in specific settings are available from CDPH and CDC.
Norovirus can spread through contaminated food and surfaces; it is important to thoroughly interview patients as soon as possible for accurate recall of possible exposures.
Outbreaks of norovirus are reportable to the LHD and CDPH per Title 17 (PDF). For information and guidance on reporting foodborne outbreaks, including norovirus, please see CDPH Foodborne Illnesses and Outbreaks Information for LHDs webpage.

Norovirus in California

In California, individual cases of norovirus illness are not reportable. However, healthcare providers are required to report all suspected outbreaks of acute gastroenteritis to the local health department (LHD) immediately by telephone (Title 17, Section 2500).

In addition to tracking outbreaks, norovirus activity in some communities is monitored by wastewater surveillance. Many California cities participate in WastewaterSCAN, a non-profit program that tests for several viruses in wastewater, including norovirus, at sites around the country.

For current data, see WastewaterSCAN Dashboard | About the Dashboard

Current disease surveillance methods rely on laboratory testing of clinical samples. In suspected outbreak settings, LHDs should attempt to collect stool specimens from three or more ill persons to confirm the viral etiology; a minimum of two norovirus-positive specimens from at least two different ill persons is needed to confirm outbreak etiology.

More information for laboratories

Norovirus Outbreak Reporting

Norovirus Outbreak Classifications: An outbreak of norovirus may be classified as “confirmed” or “suspected” depending on presence of compatible illness and laboratory detection of norovirus. Typical signs and symptoms of norovirus infection include vomiting, diarrhea, nausea, and abdominal pain.

Confirmed norovirus outbreak: The signs and symptoms of illness among people are consistent with norovirus infection; and norovirus is detected in laboratory specimens from two or more ill persons.
Suspected norovirus outbreak: The signs and symptoms of illness among people are consistent with norovirus infection; however, stool specimens were not collected, stool was not tested for norovirus, norovirus was detected in only one specimen, or norovirus was not detected at all.

LHDs Participating in CalREDIE

LHDs not Participating in CalREDIE

Foodborne Transmission*

Create an outbreak report in CalREDIE by creating a “GI, Foodborne” outbreak and completing the “Foodborne OB” tab.

Complete the CDPH Foodborne Disease Outbreak Report Form (CDPH 8567)(PDF), and submit the completed reports to CDPH.

Other (e.g., person-to-person) or Unknown Mode of Transmission

Create an outbreak report in CalREDIE by creating a “GI, Other/Unknown” outbreak and completing the “Outbreak Report” and “Other Outbreak” tabs.

(form in development)

*Guidelines for completing the CDPH Foodborne Disease Outbreak Report (PDF) are available in the CalREDIE Document Repository. CDPH Infectious Diseases Branch (IDB) staff review foodborne disease outbreak reports and enter the reports into the U.S. Centers for Disease Control and Prevention (CDC) National Outbreak Reporting System (NORS).

Learn more about CDC reporting systems and surveillance for norovirus

For questions about norovirus outbreak investigations and reporting, please contact CDPH IDB.

Norovirus Control and Prevention

Because noroviruses are highly contagious, LHDs may need to restrict the activities of persons with norovirus infection from certain work or communal activities (such as food handling, health care, or day care) for at least 48 hours after symptoms have resolved. Other control measures vary by setting but may also include:

Grouping or cohorting ill persons from well persons, especially if exclusion from a setting is not an option
Enhanced disinfection, especially for outbreaks in congregate settings

CDPH IDB can provide assistance in determining appropriate control measures in outbreak situations. Awareness of local, state, and federal foodborne outbreak notifications and advisories can also help investigation, control, and prevention of foodborne outbreaks of norovirus. All patients involved with an outbreak should be educated regarding disease transmission and appropriate infection control measures; frequent handwashing and disinfection of surfaces is crucial.

Learn more about when and how to clean and disinfect a facility

Resources for LHDs by Setting

Healthcare Settings

Summary of CDC Recommendations

Evacuation Centers and Shelters

Schools and Childcare Centers

CDPH Norovirus Toolkit for School and Childcare Center Outbreaks (2.5MB, PDF)
CDPH Sample Linelist for School Outbreaks (Excel)
Best Practices for Cleaning, Sanitizing, and Disinfecting at Schools (video) – California Department of Pesticide Regulation
CDC Preventing Spread of Infections in K–12 Schools
CDC How to Clean and Disinfect Early Care and Education Settings

Camps, Camping, and Hiking

Additional Resources

Foodborne Outbreaks

Communications

Outbreak Reporting and Surveillance

Information for Laboratories

Norovirus is a genus that belongs to the family Caliciviridae. Noroviruses are subdivided into 10 genogroups and nearly 48 norovirus genotypes.

Because individual cases of norovirus are not reportable, and symptoms alone cannot distinguish norovirus from other gastroenteric viruses, current disease surveillance methods rely on laboratory testing of clinical samples from suspected viral gastroenteritis outbreaks and wastewater. The CDPH Viral and Rickettsial Disease Laboratory (VRDL) and select California public health laboratories can perform genetic sequencing on norovirus-positive specimens to determine genotype and relatedness to other circulating strains. The information provided by these tests can help CDPH and LHDs identify sources of outbreaks and implement infection control measures to prevent the spread of illnesses.

VRDL is part of CaliciNet which is the national norovirus outbreak surveillance network of federal, state, and local public health laboratories in the United States. Participating public health laboratories submit data, including genetic sequences of norovirus strains and epidemiological data from norovirus outbreaks, to the CaliciNet database. Submitted norovirus strains can be compared with other norovirus strains in the database, helping the CDC link outbreaks to a common source, monitor norovirus strains that are circulating, and identify newly emerging norovirus strains.

For questions about norovirus testing and CaliciNet, contact VRDL.

Resources for Public Health Laboratories

CaliciNet

Page Last Updated :

To Top

What’s New

Administrative

Diseases and Conditions

Family Health

Health and Safety

Health Facilities

Personal Health and Prevention

Licensing, Certification and Other Credentials

Person Interested In