As the holiday season approaches, a nasty, highly contagious virus is spreading across the country—and it's not. flu or COVID-19.
Norovirus, also called “winter vomitingAccording to WastewaterSCAN dataacademic program at Stanford University in partnership with Emory University.
As of Nov. 21, Amanda Bidwell, WastewaterSCAN's science program manager, reported that norovirus concentrations in wastewater have increased nationwide by 69% since October.
“We are now in the high category for norovirus nationally,” she said. According to wastewater data.
Rates are currently lower compared to last year's surge, which was in the vast majority of cases caused according to experts, the GII.17 variant, which may have mutated and become more infectious. There were 235 norovirus outbreaks reported between August and November 2024, according to the Centers for Disease Control and Prevention.
During the same period this year, there were 153 outbreaks.
It's unclear whether the same incidence rate will continue in 2026, but outbreaks are expected to continue to rise, Bidwell said.
“We have three years of data that show we have a strong seasonal pattern,” she said. “But I can’t say right now how big that peak will be.”
A CDC spokesperson said the agency closely monitors the norovirus season, which is most common from November to April.
The CDC tracks norovirus through voluntary reporting from clinical laboratories and health departments, but does not currently track the presence of norovirus in wastewater, which may be why its tracking does not match WastewaterScan data. People can get sick but not see a doctor.
Bidwell said wastewater is “an unbiased way to look at what's going on in society.”
Here's what you need to know about norovirus and how it's spreading this year.
Norovirus variant becomes increasingly dominant
For over 30 years, One strain has predominated in norovirus outbreaksGII.4. There were outbreaks last year in the vast majority of cases caused variant GII.17, which accounts for about 75% of outbreaks.
The GII.17 strain has become more common in several countries, including the United States, in the 2020s. The increase in GII.17 may explain why the peaks in 2024 and the spread this year began earlier, in October, rather than in winter.
Dr. Robert Atmar, a professor at Baylor College of Medicine's School of Medicine, said a combination of factors may have led to GII.17's dominance.
“Two possibilities are that something in the virus changed to make it more infectious, or that there was a change in the population to which a large proportion were susceptible,” he said. “And it's probably a combination of both. But whether that continues this year, I think that's one of the biggest questions in our scientific community.”
Dr. Craig Wilen, assistant professor of laboratory medicine and immunobiology at Yale University, said GII.17 may not actually be more contagious, but many people likely have less immunity to the new variant.
“It's likely that GII.17 was so effective in infecting so many people last year because we had significantly less immunity to the virus because it was quite different from the viruses we had previously been infected with.”
It's hard to say how this year's norovirus season will pan out.
Atmar said either variant has a “50/50 chance” of dominating this year, but does not expect the same level of disease as last year due to “increased immunity.”
Norovirus symptoms
Norovirus is very contagiousthe disease is only human. Norovirus outbreaks can happen anywhere and cause 20 million infections per year. It is responsible for more than half of the foodborne illnesses in the United States each year.
It is spread from person to person through vomit or droplets of feces that end up in a person's mouth. It can also be spread by contact with contaminated food, water or surfaces.
main symptoms are diarrhea and vomiting, which is why they got the name “two bucket disease” Other symptoms include fever, abdominal pain and body aches.
Symptoms such as vomiting and diarrhea may require medical attention for older adults, young children and people with weakened immune systems, according to the WHO. Mayo Clinic.
Symptoms usually appear 12 to 48 hours after infection and last several days. Someone can still spread the virus for more than two weeks, even after symptoms have gone away.
How to protect yourself from norovirus
Norovirus is notoriously difficult to kill. It is difficult to wash off and can withstand temperatures up to 145°F. Many scientists call this “ideal pathogen“
Wilen said norovirus is “very stable in the environment.”
“It is highly contagious. Traditional ethanol-based hand sanitizers do not work as well against this virus as they do against other viruses,” said the Yale assistant professor.
In order to kill norovirusThe CDC recommends washing your hands thoroughly with soap, treating contaminated areas with diluted bleach, and washing contaminated clothing with hot water and detergent. Wearing gloves and discarding them after cleaning increases protection.
Fruits and vegetables should be washed thoroughly, and properly cooked oysters and shellfish can also reduce the risk of infection, says the Centers for Disease Control and Prevention (CDC).
There is no specific treatment for norovirus, but rehydration is key to replacing lost fluids.
Although there is currently no vaccine for norovirus, Moderna Phase 3 Trial Begins.
