The highly contagious norovirus is spreading quickly across the country as the year comes to a close thanks to a surging variant.
Why it matters: The new norovirus outbreaks come as the flu, whooping cough, measles and COVID have all seen spikes nationwide.
- Sickness from norovirus, often referred to as the "winter vomiting disease" or "winter vomiting bug," could require medical attention or even hospitalization for immunocompromised people, the elderly and children.
Driving the news: Cases of the norovirus have picked up in California in recent weeks as a new subvariant — GII.17 — has caused a batch of cases, per the Los Angeles Times.
- The San Francisco and Los Angeles areas specifically saw massive climbs in cases, officials told LAT.
- This comes as Michigan, New Jersey and North Carolina have seen an uptick in cases, too.
- Cases have reportedly been surging in Texas, Oklahoma, Colorado, Alabama, Montana and Wyoming, per data from Epic Research, which collects data from health systems that share anonymous patient data.
By the numbers: For the week ending on Dec. 9, the national positivity rate was at 9.9%, per the Centers for Disease Control and Prevention.
- It has since climbed to 12.11% for the week ending on Dec. 13.
Read more below to learn about the norovirus.
What does norovirus do to you?
In general, the norovirus is a contagious disease that causes extreme cases of vomiting and diarrhea because of inflammation of the stomach and intestines, per the CDC.
- It is one of the top causes of vomiting and diarrhea, the CDC says, and has gained the nickname "extreme vomiting disease."
What to know about norovirus variant GII.17
Norovirus isn't uncommon, with roughly 20 million people contracting the norovirus every year, per Scientific American.
- Outbreaks — rose from less than 10% during the 2022–23 season to 75% during the 2024–25 season, the CDC says.
- In December 2024, the U.S. saw a record-breaking month for norovirus cases, with test positivity spiking almost 25%.
- This year, cases began surging in the fall.
The rise in norovirus cases over the last two years has been widely attributed to a new variant — GII.17.
- The GII.17 previously circulated at low levels for decades before the recent spike, per the American Association for the Advancement of Science, and has since taken over as the top variant in the U.S.
In the 2022-23 season, the previous top variant, GII.4, accounted for nearly 49% of all outbreaks, while GII.17 accounted for 7.5%, according to CDC data.
- The following year, GII.17 rose to 75.4% and GII.4 outbreaks declined to 10.7%, per CDC.
Norovirus, COVID and the flu
Two other major illnesses are still swirling about during the holiday season.
- COVID cases are surging nationwide, with 31 states seeing infections grow or likely growing, per the CDC data.
- Many of these cases are being driven by the XFG Stratus variant.
Experts around the world have warned of a new flu outbreak, with a surge in cases in Europe, already disrupting hospitals.
- Many cases have been attributed to a new flu strain, a version of H3N2, that emerged over the summer.
Common norovirus symptoms to watch for
Symptoms for the "winter vomiting bug" begin anywhere within 12 to 48 hours of contracting the illness, per the CDC.
The most common symptoms include:
- Diarrhea.
- Vomiting.
- Nausea.
- Stomach pain.
- Dehydration (which is caused by extreme vomiting and diarrhea).
It's possible one could develop a fever or body aches from the norovirus, though that remains uncommon.
What should you do if you catch the norovirus?
There isn't a specific treatment for the norovirus, but symptoms typically end within one to three days, per the Cleveland Clinic.
Health officials recommend drinking liquids and electrolytes to stay hydrated.
- Bland foods can help manage symptoms, too.
How to stop the spread of norovirus
Most health officials recommend proper handwashing to avoid spreading the sickness, the CDC says.
- Cleaning surfaces and disinfecting areas can similarly help stop the spread.
- Hand sanitizer won't stop the spread, either, the CDC says. It's better to wash your hands thoroughly.
Anyone who catches the norovirus may want to avoid preparing food for a few days to limit the spread, per the CDC.
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