Norovirus is a highly contagious virus that causes acute gastroenteritis, leading to vomiting and diarrhea in millions of people annually in the United States1 . Each year, norovirus results in approximately 19 to 21 million illnesses and about 2,500 reported outbreaks, with the highest incidence occurring from November to April1 2. After a notable decline during the COVID-19 pandemic, norovirus outbreaks have surged back to levels seen before the pandemic, raising concerns about public health and infection control3 4.
💡 Did You Know?
Data on suspected and confirmed norovirus outbreaks reported to CDC by participating state health departments are updated monthly. NoroSTAT data helps assess current and past norovirus activity and the impact of emerging genotypes16 .
Understanding Norovirus Contagion
Norovirus is the leading cause of acute gastroenteritis outbreaks across all age groups in the United States5 . It is responsible for the majority of foodborne illness outbreaks, accounting for nearly 60% of such cases annually2 . The virus causes symptoms such as vomiting, diarrhea, abdominal cramps, nausea, and sometimes fever or body aches6 7. These symptoms typically appear 12 to 48 hours after exposure and usually last one to three days7 .
The virus is highly infectious, with only a few viral particles needed to cause infection. A person infected with norovirus can shed billions of virus particles in their stool or vomit, and exposure to as few as 10 particles can lead to illness7 . Norovirus spreads primarily through the fecal-oral route, which includes:
- Direct person-to-person contact, such as caring for someone who is sick or sharing utensils8 9.
- Consumption of contaminated food or water, especially uncooked or raw items like oysters, leafy greens, and fresh fruits9 .
- Contact with contaminated environmental surfaces, where the virus can survive for prolonged periods8 10.
Norovirus is not airborne but can be transmitted through aerosolized particles from vomit or diarrhea, which contaminate surfaces and facilitate spread8 11. The virus's unencapsulated structure contributes to its resilience, allowing it to survive harsh environmental conditions and resist many common disinfectants8 10.
Norovirus outbreaks have returned to pre-pandemic levels as COVID-19 restrictions eased, with recent weeks showing outbreak counts higher than any since 2012. The virus spreads mainly through contaminated food, surfaces, and direct contact, emphasizing the importance of handwashing and environmental cleaning. Vulnerable groups, including young children and older adults, remain at high risk for severe illness and complications1 47.
Outbreaks most commonly occur in settings where people gather closely, such as long-term care facilities, restaurants, schools, hospitals, and cruise ships11 9. Long-term care facilities are the most frequent setting, accounting for over half of reported outbreaks12 9. Children under five and adults over 65 are particularly vulnerable to severe illness and complications like dehydration1 2.
The median basic reproduction number (R0) of norovirus is approximately 2.75, indicating that each infected person can spread the virus to nearly three others on average13 . This high transmissibility contributes to rapid outbreak growth, especially in crowded or enclosed environments13 .
“A person who has been sick with norovirus sheds billions of virus particles in their stool or vomit, and it only takes an exposure of as few as 10 particles for an individual to develop an infection.”
— Scott Roberts, MD, Yale Medicine7
| Setting | Percentage of Norovirus Outbreaks9 |
|---|---|
| Long-term care facilities | Over 50% |
| Restaurants | Significant proportion |
| Schools and childcare | Common |
| Hospitals | Frequent |
| Cruise ships | Over 90% of diarrheal outbreaks on ships but only ~1% of total outbreaks |
| Sources: 9 | |
How COVID Precautions Reduced Spread
During the COVID-19 pandemic, widespread adoption of non-pharmaceutical interventions (NPIs) such as social distancing, enhanced hand hygiene, mask-wearing, and stay-at-home orders led to a dramatic decline in norovirus outbreaks14 12. These measures, initially aimed at reducing SARS-CoV-2 transmission, also effectively interrupted the spread of norovirus and other enteric pathogens14 .
Data from the Norovirus Sentinel Testing and Tracking (NoroSTAT) network illustrate this trend clearly. NoroSTAT is a collaborative surveillance system involving select U.S. state health departments and the CDC, which collects epidemiologic and laboratory data on norovirus outbreaks6 12. The number of reported outbreaks dropped from 1,056 during the 2019–2020 surveillance year to just 343 in 2020–2021, coinciding with the peak of COVID-19 restrictions12 . As restrictions eased, outbreaks rebounded to 992 in 2021–2022, nearly triple the previous year’s count, approaching pre-pandemic levels12 3.
The reduction in norovirus outbreaks during the pandemic was largely due to:
- Increased handwashing with soap and water, which is more effective against norovirus than alcohol-based hand sanitizers14 810.
- Social distancing and reduced social gatherings, limiting close contact and person-to-person transmission14 .
- Staying home when sick, reducing opportunities to spread the virus in communal settings14 8.
Norovirus transmission occurs mainly through contact with contaminated surfaces or direct contact with infected individuals, not through airborne spread8 15. The virus’s ability to survive on surfaces for extended periods makes environmental cleaning critical to controlling outbreaks8 10.
Norovirus transmission can be prevented by thorough handwashing and proper cleaning and disinfection of contaminated surfaces3 .
“The only way to prevent norovirus is by careful handwashing and disinfecting. When handling contaminated objects or surfaces, wear disposable gloves. Wash soiled clothes and linens immediately in hot water. Frequently clean surfaces and objects that the sick person has touched using either a chlorine bleach solution with at least 5.25% bleach or a product approved by the EPA for norovirus.”
— Public health guidance10
Preventing Future Norovirus Cases
Despite norovirus’s high contagiousness and environmental resilience, good hygiene and public health practices remain the cornerstone of prevention12 8. The virus’s ability to survive on surfaces and its low infectious dose make controlling outbreaks challenging, especially in high-risk settings like healthcare facilities, schools, and restaurants8 9.
Key prevention strategies include:
- Washing hands thoroughly with soap and water for at least 20 seconds, especially after using the bathroom and before eating or preparing food8 2.
- Avoiding food preparation and close contact with others for at least 48 hours after symptoms resolve, as viral shedding can continue during this period3 2.
- Cleaning and disinfecting contaminated surfaces promptly using chlorine bleach solutions or EPA-approved disinfectants effective against norovirus10 .
- Washing fruits and vegetables under running water and cooking shellfish thoroughly to an internal temperature of at least 145ºF to reduce foodborne transmission2 9.
- Encouraging sick individuals to stay home from work, school, or childcare to prevent spreading the virus8 2.
“Norovirus classically increases in the winter months for many reasons, but the major one is that everyone is congregating indoors, especially with the holidays.”
— Scott Roberts, MD, Yale Medicine7
| Prevention Measure | Importance and Notes |
|---|---|
| Handwashing with soap and water | Most effective; hand sanitizers are less effective8 10 |
| Surface disinfection | Use bleach or EPA-approved products10 |
| Food safety practices | Wash produce; cook shellfish thoroughly2 9 |
| Staying home when sick | Prevents person-to-person spread8 2 |
| Avoiding food preparation post-illness | At least 48 hours after symptoms end3 |
Currently, there is no licensed norovirus vaccine available, although vaccine development is underway17 . Challenges to vaccine creation include the virus’s frequent mutation, genetic diversity, and the lack of a robust laboratory cultivation system17 . Advances in molecular epidemiology and genetic research may facilitate future vaccine breakthroughs17 .
Until a vaccine becomes available, public health efforts must focus on education and adherence to hygiene practices, especially during the peak norovirus season from November to April12 8. These measures are particularly crucial for vulnerable populations such as young children, older adults, and those in communal living environments1 2.
