The California Department of Public Health (CDPH) is alerting healthcare providers about elevated norovirus activity throughout California and nationwide.
Norovirus activity has been elevated throughout the United States, with sustained increases observed in wastewater concentrations at many sites in California, since mid-January 2023. The U.S. Centers for Disease Control and Prevention (CDC) reports steadily increasing norovirus test percent positivity and numerous outbreaks have been reported throughout the U.S.
Wastewater monitoring in California by the Stanford Sewer Coronavirus Alert Network (SCAN) and WastewaterSCAN programs have shown similar rising trends of norovirus concentrations detected in wastewater monitoring sites throughout the state, with large increases since mid-January. To date, the trends at many California sites have not yet decreased to previous low levels, suggesting continued elevated norovirus disease activity in many areas.
Since February 1, 2023, at least 25 outbreaks of norovirus in California have been confirmed by laboratory testing, likely reflecting hundreds of illnesses in the state.
This included several outbreaks in long-term care facilities, and at least one elementary school outbreak, which required closure for control. However, gastrointestinal outbreaks are often not confirmed by laboratory testing, so the true number of norovirus outbreaks likely well exceeds those confirmed by laboratory testing.
CDPH reminds healthcare providers to report all outbreaks of acute gastroenteritis, including suspected outbreaks of norovirus, to the local health department (LHD).
After an incubation period of 12–72 hours, norovirus infection presents with an abrupt onset of nausea, vomiting, watery diarrhea, and abdominal pain. Most illnesses are self-limited and typically last 48 to 72 hours. Dehydration can occur and illness may be severe in older adults, infants, and immunocompromised persons.
Norovirus infections are most communicable during the acute stage of the disease, but infected persons can continue to shed the virus for two to three weeks, even after clinical recovery. Transmission requires only a very small viral inoculum.
Norovirus is highly transmissible and can readily spread from person to person, through contaminated food or drink, contaminated surfaces, or through direct contact. Norovirus survives readily in the environment and is relatively resistant to common disinfectants. Therefore, norovirus can spread easily, particularly in closed and crowded settings, and can be challenging to control.
Reporting and Surveillance
Confirmed and suspected outbreaks of norovirus are reportable to public health authorities per the California Code of Regulations (CCR) Title 17 § 2500 (PDF). However, because individual cases of norovirus are not reportable, current disease surveillance methods rely on laboratory testing of clinical samples from suspected viral gastroenteritis outbreaks and monitoring of wastewater data.
Laboratory testing confirms the diagnosis of norovirus infection, as symptoms of norovirus alone cannot distinguish it from other gastroenteric viruses (such as rotavirus, sapovirus, astrovirus, and adenovirus) or bacterial causes (such as Salmonella).
Laboratory confirmation is especially useful in the setting of a suspected outbreak as genotyping can help determine if other illnesses or outbreaks are linked. Testing could also be useful in immunocompromised patients, or those with severe or persistent symptoms.
In suspected viral gastroenteritis outbreak settings, local health departments (LHDs) attempt to collect stool specimens from three or more ill persons to confirm the viral etiology. The CDPH Viral and Rickettsial Diseases Laboratory (VRDL) and select California public health laboratories (PHLs) can perform genetic sequencing on positive norovirus 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.
In addition to tracking outbreaks, norovirus activity in the community is reflected by wastewater surveillance. Many California cities participate in WastewaterSCAN, a national network of sites that monitor levels of several viruses in wastewater, including norovirus. Monitoring of norovirus levels in wastewater is also conducted by the Stanford Sewer Coronavirus Alert Network.
Prevention and Control
Norovirus is very contagious and the virus can survive for weeks on surfaces and objects. The infection can spread quickly in settings such as schools and childcare centers, congregate living settings, healthcare facilities, and cruise ships.
Contact and standard precautions are recommended when interacting with patients with suspected or confirmed norovirus infection. The most important action is handwashing with soap and water for at least 20 seconds before and after contact with each patient (hand sanitizers are typically not effective against norovirus). In addition, gloves and gowns should be worn to reduce the likelihood of exposure to infectious vomitus or fecal material when caring for patients.
If there is an anticipated risk of splashes to the face during the care of patients, particularly among those who are vomiting, surgical or procedure masks and eye protection or a full face shield should also be used.
Thorough cleaning and disinfection of examination rooms, bathrooms, and other “high touch" surface areas while using personal protective equipment such as gloves, gowns, and masks should be performed after a patient with confirmed or suspected norovirus infection has been seen. Disinfectants with activity against norovirus should be used for cleaning. If such disinfectants are not available, a bleach solution should be used.
Other recommended control measures vary by setting, but typically include:
- Exclusion of ill people from school, work, and other communal activities for at least 48 hours after symptoms have resolved; and
- Grouping or cohorting of ill and well persons (i.e., keeping ill and well persons apart), especially if exclusion from the setting is not an option.
The CDPH norovirus webpage includes links to numerous tools and resources for responding to norovirus in common outbreak settings:
For questions regarding norovirus, contact your LHD.