Norovirus (Stomach Flu) Cases Are Surging: 3 Things to Know

Norovirus, the most common cause of “viral stomach flu,” is on the rise in the United States. Norovirus infections cause acute gastroenteritis—a stomach bug with cramps, diarrhea, vomiting, and other symptoms.

There were 91 suspected or confirmed norovirus outbreaks reported in the United States in the first week of December, according to the Centers for Disease Control and Prevention (CDC), exceeding the number of outbreaks during the same week in any year since 2012.

No one can say for sure why norovirus is spiking even higher now. But there are many subtypes of the virus, and one possible reason could be that a strain called GII.17—which was once uncommon here, so fewer people have a strong immunity to it—has become increasingly dominant in the U.S. In recent months, seven out of 10 norovirus outbreaks in this country are linked to this strain.

Norovirus outbreaks are most common between November and April—when an estimated 19 million to 21 million people get sick from the virus each year, which is why it has been nicknamed "the winter vomiting bug."

“Norovirus classically increases in the winter months for many reasons, but the major one is that everyone is congregating indoors, especially with the holidays,” says Scott Roberts, MD, a Yale Medicine infectious diseases expert. Another factor is its high transmissibility. “Very few norovirus particles are needed to infect a person. Other viruses need much more exposure,” he says.

Norovirus also spreads differently than respiratory diseases, including influenza (the flu) and COVID-19. “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,” says Dr. Roberts.

The main means of transmission is exposure to contaminated food, water, or surfaces, so the most important preventive strategies include disinfecting surfaces, heating food to sizzling temperatures, washing clothes in hot water, and washing hands frequently (that means soap and water, since hand sanitizer doesn’t work well against norovirus—more on that below).

We asked Dr. Roberts to share what you need to know about norovirus.

Although norovirus is also called the stomach flu, it’s not related to influenza, and the flu shot won’t prevent an infection or lessen the symptoms if you get it. It’s a virus that causes inflammation of the stomach and/or intestines, leading to acute gastroenteritis that comes on suddenly. The symptoms most commonly include abdominal cramps, diarrhea, nausea, and vomiting, but it can also cause body aches, chills, fever, headaches, and tiredness.

Infections typically happen when particles of the virus are transmitted through the fecal-oral route, meaning fecal matter that contains the virus somehow gets into a person’s mouth. This is why preventive hygiene is so important—it can happen when you are in direct contact, such as shaking hands with an infected person, or if you have indirect contact, such as when you consume a food or drink, use utensils, or touch a light switch or doorknob that has been contaminated and then touch your mouth.

“A person who has been sick with norovirus sheds billions of virus particles in their stool or vomit,” Dr. Roberts says. “And it only takes an exposure of as few as 10 particles for an individual to develop an infection.” What’s more, while people are most contagious when they are sick and a few days after their symptoms subside, they can still spread the virus for two weeks or more afterward, he adds.

“Norovirus is very hardy in the environment and can survive on surfaces for a prolonged period of time—more than most pathogens,” he says. “A single contact with a contaminated object or surface could lead to an infection.”

The virus can contaminate food and drink as well, and causes 58% of foodborne illnesses in the U.S., according to the CDC. People can be infected by eating raw shellfish, especially oysters, in which viral particles in contaminated water concentrate in the gut. This is borne out in recalls—in 2024, the Food and Drug Administration (FDA) issued several recalls of oysters found to be contaminated with norovirus. Among other foods that have been linked to norovirus food poisoning are leafy greens and fresh fruits, which may have been handled by food workers who were infected or sprayed with contaminated waters in the field.

While a norovirus outbreak can occur anywhere, it is especially common in places where people are in close contact, such as schools and nursing homes. It can also be a major problem on cruise ships, where multiple outbreaks were reported in the last year.

Proper handwashing is key to preventing a norovirus infection. That means washing hands frequently with soap and water, especially before eating or handling food, before giving or taking medicine, and after using the toilet or changing a diaper.

Hand sanitizers don’t work well for this virus. “Norovirus has a capsule around the virus that protects it against most routine disinfectants, such as alcohol-based, hand-sanitizing gels,” Dr. Roberts says. But vigorous washing with plain soap and water for 20 seconds creates friction that better washes away the viral particles.

Other prevention strategies from the CDC include:

• Wash all fruits and vegetables carefully under running water, without soap or special produce washes, even if you intend to peel them. Scrub firm vegetables like cucumbers with a clean produce brush. Dry produce with a clean cloth or paper towel.
• If you are preparing oysters and other shellfish to eat, cook them thoroughly to an internal temperature of at least 145°F.
• Perform routine cleaning and sanitizing of kitchen utensils, cutting boards, counters, and surfaces, especially after handling shellfish. Disinfect them using a chlorine bleach solution with a concentration of 1,000 to 5,000 ppm (5 to 25 tablespoons of household bleach [5% to 8%] per gallon of water) or use an EPA-registered disinfecting product against norovirus. Leave bleach disinfectant on the affected area for at least 5 minutes. This is also a good step to take if norovirus has infected anyone in your family.
• While cleaning or disinfecting, wear rubber or disposable gloves. Wipe the entire area with paper towels and throw them in a plastic trash bag.
• Wash clothes and linens that may have been exposed with detergent and hot water at the maximum available cycle length, and then machine dry them at the highest heat setting.

There is no medication that specifically treats norovirus—antibiotics treat bacterial diseases, such as bacterial pneumonia, and don’t help with viruses.

But it may help to know what to expect if you get sick. People develop symptoms within 12 to 48 hours of exposure to norovirus. Fatigue is common, so rest is important. Diarrhea and vomiting cause the body to lose fluids, so you’ll need to hydrate—in addition to water, try ice chips, fruit juice with water, broth, and low-calorie sports drinks (but avoid caffeinated and sugary drinks). If your urine is pale yellow—and not dark—that’s a sign that the body is getting enough fluids.

Once you can tolerate clear liquids without vomiting, try small meals of bland foods—bananas, rice, applesauce, and toast (known as the BRAT diet) are a good start. Avoid foods that could make diarrhea worse, such as milk and milk products, and high-fat foods like pizza. You should be able to resume a normal diet within a day or two.

Young children, older adults, and/or those who are immunocompromised, face a higher risk for complications than others. Each year, there are 900 norovirus-related deaths, mostly among adults ages 65 years and older. The biggest complication is dehydration, and anyone experiencing severe dehydration—with symptoms including light-headedness, confusion, and passing out—should seek medical care right away, since this complication may require hospitalization and treatment with intravenous fluids.

Mild dehydration can cause such symptoms as a decrease in urination, a dry mouth and throat, dizziness when standing, lack of tears, and unusual sleepiness. It can be treated with oral rehydration fluids that can be purchased over the counter without a prescription; these will also replace lost electrolytes (important minerals for the body, such as sodium and potassium).

It can take young children, older adults, and people who are infected when they were already sick with something else longer than usual to recover from norovirus. But most people get better within one to three days.