A highly contagious stomach virus is spreading rapidly across the U.S. as Americans prepare for holiday travel and gatherings.
Norovirus — often called the winter vomiting disease — has been climbing steadily since mid-October, particularly in Louisiana, Michigan, and Indiana, according to WastewaterSCAN, a monitoring program run by Stanford and Emory universities.
According to WastewaterSCAN's scientific program manager, Amanda Bidwell, norovirus concentrations in wastewater have jumped 69% nationwide since October, placing overall U.S. activity in the program's "high" category.
Levels are especially elevated in the Northeast and Midwest. While the virus is circulating widely, activity remains below last year's unusually large spike, driven by the GII.17 strain.
Between August and November 2024, the CDC recorded 235 norovirus outbreaks; during the same period this year, the number stands at 153.
Bidwell cautioned that it is too early to know how severe the rest of the season will be, but said the virus follows a consistent annual pattern from November through April.
The CDC tracks norovirus through voluntary reporting from labs and health departments but does not monitor via wastewater, which may cause official numbers to lag behind actual infections.
According to Bidwell, wastewater is an "unbiased way of looking at what is happening in a community."
For more than three decades, most outbreaks were tied to a strain known as GII.4. But in 2024, roughly 75% of cases were linked to the GII.17 variant, which has grown more common globally.
Scientists say the shift could be due to viral mutations, changes in population immunity, or both. Some experts believe last year's outsized spread occurred because many Americans had little immunity to the newer GII.17 variant.
Norovirus is one of the most contagious human infections, responsible for nearly 20 million U.S. cases every year and more than half of all foodborne illnesses.
It spreads through microscopic particles of vomit or fecal matter, contaminated food or water, and contact with infected surfaces.
Symptoms typically appear within 12 to 48 hours and include vomiting, diarrhea, stomach pain, fever, and body aches, according to the Mayo Clinic.
Vulnerable groups — including older adults, young children, and those with weakened immune systems — face increased risk of dehydration and complications.
Even after recovery, an infected person can continue shedding the virus for more than two weeks.
Norovirus is also extremely resilient, surviving high temperatures and resisting many common disinfectants, including alcohol-based hand sanitizers.
The CDC recommends frequent handwashing with soap, bleaching contaminated surfaces, washing soiled items in hot water, and thoroughly rinsing produce. Shellfish should be fully cooked to reduce risk.
There is no specific treatment beyond hydration, though Moderna is conducting a Phase 3 trial for a potential norovirus vaccine.
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