Norovirus, often called the "winter vomiting bug" or "stomach flu," is making headlines again as wastewater surveillance data shows the highly contagious virus spreading at elevated levels across much of the United States. Despite its nickname, norovirus is not related to influenza — it is a completely different virus that attacks the gastrointestinal system, causing sudden and often violent bouts of vomiting, diarrhea, and stomach cramps. With an estimated 19 to 21 million illnesses occurring annually in the U.S. alone, understanding what norovirus is, how it spreads, and how to protect yourself has never been more important.
What Exactly Is Norovirus?
Norovirus is a highly contagious virus that causes acute gastroenteritis — an inflammation of the stomach and intestines. Despite being commonly referred to as the "stomach flu," norovirus has no relation to the influenza virus, which causes respiratory illness. The confusion stems from the similar timing of outbreaks, as both tend to peak during the winter months.
According to the Centers for Disease Control and Prevention (CDC), norovirus is the leading cause of vomiting and diarrhea as well as foodborne illness in the United States. People of all ages can get infected, and because there are many different types of norovirus, you can get sick with it multiple times throughout your life. Infection with one type does not necessarily protect you against others.
One of the reasons norovirus is so notorious is its incredible contagiousness. "Very few norovirus particles are needed to infect a person. Other viruses need much more exposure," explains Dr. Scott Roberts, a Yale Medicine infectious diseases expert. In fact, it only takes as few as 10 virus particles to cause illness — a tiny amount compared to other pathogens.
How the Vomiting Bug Spreads
Norovirus spreads very easily and quickly through multiple routes. You can catch it through direct contact with someone who is infected — such as caring for them, sharing food or utensils, or eating food they handled. You can also contract it by consuming contaminated food or water, or by touching contaminated surfaces and then putting your unwashed fingers in your mouth.
The virus is shed in both stool and vomit in massive quantities. "People who are sick with it can release billions of virus particles," notes the University of Rochester Medical Center. A particularly challenging aspect of norovirus is that infected individuals can start spreading the virus before they even feel sick, and they can continue to spread it for two weeks or more after recovering.
Unlike respiratory viruses such as COVID-19 or influenza, norovirus is not transmitted through the air via coughing or sneezing. As Dr. Roberts explains, "This is not a respiratory disease, so you cannot transmit norovirus via coughing or sneezing, and masking and good ventilation won't work for protection." The virus spreads through the fecal-oral route, meaning tiny particles of infected stool or vomit enter another person's mouth.
Outbreaks are most common in settings where people are in close quarters, including schools, daycare centers, nursing homes, cruise ships, and restaurants. The CDC reports that there are approximately 2,500 norovirus outbreaks every year in the United States.
Norovirus Symptoms: What to Expect
Symptoms of norovirus usually develop suddenly, typically appearing 12 to 48 hours after exposure. The most common symptoms include diarrhea, vomiting, nausea, and stomach pain. Some people may also experience fever, headache, and body aches.
A hallmark of norovirus that distinguishes it from other stomach bugs is the intensity of the vomiting. "Some people only complain of diarrhea or vomiting, but a hallmark of norovirus is intense vomiting compared to other stomach bugs," reports NBC News. The onset can feel abrupt — one moment you feel fine, and the next you are experiencing severe gastrointestinal distress.
For most healthy individuals, norovirus illness resolves on its own within 1 to 3 days. However, the intense vomiting and diarrhea can lead to dehydration, which is the primary concern — especially for young children, older adults, and people with weakened immune systems. Signs of dehydration include decreased urination, dry mouth and throat, feeling dizzy when standing up, crying with few or no tears, and unusual sleepiness or fussiness in children.
Why Norovirus Is Surging: The GII.17 Variant
Current outbreaks are being driven in part by a newer variant of the virus called GII.17. During the 2024-2025 season, this strain caused about 75% of norovirus outbreaks in the United States, surpassing the previously dominant GII.4 strain that had been circulating for decades. The concern with GII.17 is not that it is inherently more dangerous, but that fewer people have partial immunity to it, allowing it to spread more easily through the population.
"The newer variant isn't more contagious in and of itself," explains Dr. Linda Yancey, an infectious disease specialist at Memorial Hermann in Houston. "It can spread more easily because fewer people have partial immunity to it, so they will get sick and spread the virus."
Wastewater surveillance has proven to be a crucial tool for tracking norovirus outbreaks, since most people who get sick do not visit a healthcare provider or get tested. According to WastewaterSCAN, an academic monitoring program run by Stanford and Emory Universities, norovirus concentrations have been trending upward, with levels currently categorized as "high" in many regions of the country.
Recent data from the CDC's NoroSTAT program recorded 1,194 outbreaks between August 1 and early May of the current season. While this is lower than the 2,534 outbreaks recorded during the same period the previous year, experts caution that numbers are within the expected range for this time of year, and activity is likely to continue.
Effective Prevention Strategies
Preventing norovirus requires specific measures, as many common hygiene practices are not effective against this tough virus. Here is what works according to the CDC and infectious disease experts:
Wash your hands thoroughly with soap and water. This is the single most important prevention measure. Hand sanitizer alone does not work well against norovirus because the virus is encased in a protein shell that is resistant to alcohol. You should wash for at least 20 seconds, especially after using the bathroom, changing diapers, and before preparing or eating food.
Cook shellfish thoroughly and wash fruits and vegetables. Oysters and other filter-feeding shellfish can concentrate norovirus from contaminated water. Consuming raw or undercooked shellfish is a known risk factor for infection.
Clean and disinfect contaminated surfaces. Use EPA-registered disinfectants specifically labeled to kill norovirus. Standard cleaning may not be sufficient.
Wash laundry in hot water. If someone in your household is sick, handle soiled laundry carefully and wash items in hot water.
Stay home when sick. Do not prepare food or care for others while you are ill. The CDC recommends staying home for at least 48 hours after symptoms stop, as you can continue to shed the virus even after feeling better.
Treatment: What to Do If You Catch It
There is no specific antiviral medication for norovirus. Antibiotics are ineffective because norovirus is a virus, not a bacteria. Treatment focuses on managing symptoms and preventing dehydration.
The most important step is to drink plenty of fluids to replace what is lost through vomiting and diarrhea. Water is a good choice, but oral rehydration solutions available at pharmacies are most effective at replacing essential minerals and nutrients. Sports drinks may help with mild dehydration but may not fully replace what the body needs. Avoid fruit juices and fizzy drinks, as they can make diarrhea worse.
The NHS recommends staying home, getting plenty of rest, and drinking lots of fluids — taking small sips if you feel nauseous. Eating when you feel able to is fine, but it may help to avoid fatty or spicy foods. Over-the-counter pain relievers like paracetamol (acetaminophen) can help with discomfort, but children under 12 should not be given medication to stop diarrhea, and aspirin should never be given to children under 16.
Most people recover within a few days without medical intervention. However, if signs of severe dehydration develop — such as not urinating for 8 hours, feeling dizzy when standing, or being unable to keep fluids down — medical attention should be sought. Young children, older adults, and those with compromised immune systems are at highest risk for severe illness and may require intravenous fluids.
Current Status: Where Things Stand Now
As of late spring 2025, norovirus levels across the United States remain elevated, with wastewater data showing "high" concentrations in many regions. The Northeast has seen particular increases. A notable outbreak occurred among hikers on the Pacific Crest Trail in Southern California, highlighting how easily the virus spreads in group settings and outdoor communities.
While the current season's outbreak numbers are within historical averages and lower than last year's severe season — which was the worst since before the COVID-19 pandemic — experts caution that norovirus activity remains unpredictable. "Time will tell how bad it will get. Now is the time to be vigilant. I expect things to get worse before they get better," says Dr. Roberts.
What Happens Next: The Road Ahead
Looking forward, health officials are monitoring several factors that could influence norovirus activity. The continued circulation of the GII.17 variant means that population immunity remains relatively low, which could sustain transmission even outside the typical winter peak. Climate factors, including extreme heat that drives people indoors, and increased travel may also contribute to ongoing spread.
Researchers continue to work on norovirus vaccine development, though no vaccine is currently available. For now, prevention remains the best defense. As one expert put it, norovirus is one of the most contagious known illnesses — comparable to measles — with infected individuals spreading the virus to an average of seven other people. Understanding the virus and taking appropriate precautions is essential for staying healthy.
Key Takeaways: Everything You Need to Know
- Norovirus is a highly contagious virus that causes sudden vomiting, diarrhea, and stomach cramps — it is not the same as influenza.
- Symptoms typically appear 12-48 hours after exposure and last 1-3 days for most people.
- The virus spreads through direct contact, contaminated food and water, and touching contaminated surfaces.
- A newer variant called GII.17 is driving current outbreaks because many people lack immunity to it.
- Hand sanitizer does not kill norovirus — wash hands thoroughly with soap and water.
- There is no specific treatment; the main goal is preventing dehydration by drinking plenty of fluids.
- Stay home for at least 48 hours after symptoms end to avoid spreading the virus to others.
