Norovirus

Written by Stephanie Watson, Matt McMillen
Medically Reviewed by Dan Brennan, MD and Jabeen Begum, MD on February 07, 2025
9 min read

Norovirus is thought to be the most common cause of acute gastroenteritis (inflammation of your stomach and intestines leading to diarrhea and vomiting) around the world. It spreads easily through food and drink. In older people, young children, and those with chronic illnesses or weakened immune systems, the symptoms can be severe. Symptoms such as diarrhea and vomiting can increase your risk of dehydration, which could be life-threatening.

Norovirus was originally called the Norwalk virus after the town of Norwalk, Ohio. That’s where the first confirmed outbreak happened in 1968.

According to the CDC, noroviruses trigger about 19 to 21 million cases of acute gastroenteritis in the U.S. per year and send more than 465,000 people (most of them young children) to the emergency room. They also cause more than half of all foodborne disease outbreaks each year. About 900 people die from norovirus annually. Most of these deaths occur in people aged 65 or older. Although it can strike year-round, norovirus is more common in the winter. People sometimes call it the winter vomiting bug or stomach flu. It’s also called food poisoning because the viruses can be transmitted through contaminated food. Contaminated food isn’t always the reason, though.

There are different types of norovirus, all belonging to the same family called Caliciviridae, and each causes gastroenteritis. Experts divide noroviruses into 10 genogroups, which are further divided into nearly 50 different genotypes based on their genetic makeup. According to the CDC, GII.4 is the genotype that causes the most norovirus cases around the world. It’s further divided into what are called variants, each with unique gene mutations. These include GII.4 Sydney, GII.4 New Orleans, and GII.4 Hong Kong.

“GII.4 strains are often responsible for seasonal epidemics and widespread outbreaks, especially in places such as cruise ships, nursing homes, and schools,” says Harish Moorjani, MD, an infectious diseases specialist at Phelps Hospital in Sleepy Hollow, NY.

Another strain, called GII.17, has become more common in the U.S. in recent years. Nearly three-quarters of the recent outbreaks have been linked to it, possibly because few people have built a strong immunity to this strain.

Typical norovirus symptoms include nausea, vomiting (more often in children), watery diarrhea (more often in adults), and stomach cramps.

Other norovirus symptoms include:

  • Low-grade fever
  • Chills
  • Headache
  • Muscle ache
  • Fatigue

Most of these symptoms aren’t serious, but diarrhea and vomiting can remove a lot of the fluid your body needs. This could lead to dehydration. Children and older adults are most likely to experience dehydration, along with malnutrition from not getting enough nutrients.

Norovirus incubation period

If you get infected with the norovirus, you won’t show symptoms right away. That’s because it takes time for the virus to spread in your body. This is called the norovirus incubation period, which lasts 12-48 hours. So if you get infected, you’ll probably go from feeling completely healthy to very sick within a day or two after exposure.

“One of the most important factors is the host’s immune status,” says Priya Soni, MD, a pediatric infectious diseases specialist at Cedars-Sinai in Los Angeles, CA. People with weaker immune systems (such as babies, older adults, and those with certain health conditions) might take longer to show symptoms because the virus spreads more slowly in their bodies. On the other hand, some people may get sick faster if their immune system struggles to fight the virus early on.

Once your immune system recognizes an infection, it gets active and starts to fight it. This triggers inflammation as well as the symptoms that you’ll notice. The strength of your immune system can affect how mild or severe your symptoms are.

“Someone with a strong immune system may have a shorter incubation period and may have milder symptoms,” says Moorjani.

Norovirus without vomiting

Though a common symptom, vomiting doesn’t always happen with the norovirus.

“The severity and range of symptoms can vary based on factors like age, immune system status, and how much of the virus was ingested (taken in),” says Moorjani. “Children, older adults, and those with weakened immune systems are more likely to have vomiting and severe symptoms.”

Your norovirus symptoms likely will last one to three days, says Moorjani. However, even after your norovirus symptoms clear up and you feel better, you can still spread the virus to others.

How long are you contagious with norovirus?

“People are most contagious in the first 48 hours of illness,” says Moorjani. However, he adds, you can remain contagious for up to two weeks after your norovirus symptoms have passed. This means you could get other people sick during this period, though the virus usually gets less and less infectious over time.

“It’s crucial to continue practicing good hygiene, especially handwashing, even after feeling better,” says Moorjani.

In most cases, you can return to work or school after you’ve been symptom-free for 48 hours. Food service workers are generally urged to wait 72 hours before they handle food.

Norovirus isn’t related to the flu, which is an infection of the respiratory system that triggers fever, chills, aches, and pains. In fact, there’s no such thing as stomach flu.

People become infected when they eat or drink contaminated foods and beverages. Raw or undercooked oysters and raw fruits and vegetables have been linked to some outbreaks.

Noroviruses thrive in close quarters, such as restaurants, day care centers, and nursing homes, because they are hardy and highly contagious. They can survive extreme temperatures in water and on surfaces. 

How is norovirus spread?

Once someone is infected from contaminated food, the virus can quickly spread through shared food or utensils, handshakes, or close contact. It can live on surfaces for up to two weeks.

Is norovirus airborne?

When someone with the virus vomits, it can spread through the air and infect surfaces. It can stay airborne for up to two hours. The virus also spreads through poop, meaning someone who doesn’t thoroughly wash their hands after using the bathroom can pass it along. Dirty diapers can also contain norovirus.

The spread can be hard to control because it’s contagious even before norovirus symptoms appear. In other words, you can spread the virus before you know you’re sick.

If you have norovirus symptoms, your doctor can give you a stool (poop) test to confirm that you have the illness. But a diagnosis is usually made based only on symptoms.

When should you call your doctor?

Call your doctor if you still have norovirus symptoms after three days. Also, watch for symptoms of dehydration, which may require medical attention.

In rare cases, vomiting could mean something more serious than norovirus. If your vomit is green or yellow, that could be a sign of a bowel obstruction. See a doctor right away.

Like other viruses, noroviruses don’t respond to antibiotics, which are designed to kill bacteria. No antiviral drug can treat norovirus, but in healthy people, norovirus symptoms should go away on their own within one to three days.

Norovirus treatment focuses on managing your symptoms. You should:

  • Drink plenty of liquids, especially liquids that contain electrolytes.
  • Get as much rest as possible.
  • Eat soft, bland foods.

Soni says the virus can’t cross the placenta, the organ that delivers oxygen and nutrients to your growing baby. That means it won’t directly affect your baby. But it can cause harm in other ways.

“It still can have impacts if a mother has severe dehydration from the illness,” says Soni.

If you become dehydrated due to norovirus, she says, your body becomes less able to absorb nutrients from the foods you eat. That means fewer nutrients will reach your baby. This can cause intrauterine growth restriction (IUGR), in which your baby doesn’t grow to a normal size. Your baby may need frequent monitoring during your pregnancy and you may need to deliver your baby early.

“It is very important to stay on top of your hydration if you’re pregnant and become infected with this virus,” says Soni.

Most people don’t have any long-term problems from the virus. Infection can lead to dehydration, especially in children, older people, and those with weakened immune systems.

Symptoms of dehydration include:

  • Dizziness when standing
  • Dry mouth
  • Peeing less
  • Unusual sleepiness
  • Fussiness or crying with few to no tears
  • Drowsiness
  • Sluggishness

To avoid dehydration, drink plenty of liquids, especially water and juices. Give children an oral rehydration solution, such as Pedialyte, to replace lost fluids and electrolytes. Avoid sugary drinks, which can make diarrhea worse. Also, avoid alcohol and caffeinated drinks, which can dehydrate you.

In case of severe dehydration, contact your doctor. Severe dehydration is sometimes treated with IV fluids.

Good hygiene is the key to avoiding a norovirus infection, especially when you’re close to a lot of other people.

  • Wash your hands often with soap and water for at least 20 seconds, especially after you go to the bathroom, change a baby’s diaper, or before you prepare or eat food. Alcohol-based cleansers aren’t as effective as soap and water.
  • Carefully throw away any infected items (such as dirty diapers).
  • Wash raw fruits and vegetables thoroughly. Cook oysters and other shellfish before eating them.
  • Clean and disinfect surfaces with a mixture of detergent and chlorine bleach after someone is sick.
  • If you’re traveling to areas with a high risk of norovirus infection, try to eat only cooked foods and drink only hot or carbonated beverages. Avoid food sold by unlicensed street vendors.

If you’ve already been infected:

  • Try to quarantine. Stay home from work. Children should stay home from school or child care.
  • Wash your hands often with soap and water for at least 20 seconds.
  • Avoid handling food and items other people will eat or touch. Disinfect contaminated surfaces.
  • Handle vomit and poop carefully. Wear disposable gloves and soak up material with disposable towels. Place soiled items in plastic bags and put them in the trash. Remove and wash clothes and linens that may be contaminated.
  • Avoid traveling until two to three days after your norovirus symptoms are gone.

Norovirus vaccine

Right now, no vaccine exists for the norovirus. However, that may change. Researchers have begun the final stages of testing a vaccine that may prevent the virus. Results from this study could be available soon. But many challenges exist.

“The virus is tricky to target because of the high number of different strains,” says Moorjani. “A vaccine, if developed, is more likely to reduce severity of symptoms and prevent some infections rather than providing complete protection. It may offer protection against some common strains, but it would likely need to cover multiple strains to be truly effective, considering the diversity of the virus.”

How long does norovirus live on surfaces?

“Norovirus is quite resilient and can survive on dry surfaces for up to two weeks,” says Soni, who points out that it lives the longest on nonporous surfaces, such as stainless steel or plastic.

Norovirus spreads easily and quickly. To minimize exposure and infection: 

  • Wash your hands often with soap and water for at least 20 seconds.
  • Avoid raw or undercooked oysters. 
  • Thoroughly wash raw fruits and vegetables.

How do norovirus and rotavirus differ?

Both viruses infect your gastrointestinal system and cause similar symptoms, such as nausea, vomiting, and diarrhea. However, they differ in a few important ways. Compared to norovirus, rotavirus more commonly affects children, and its symptoms typically last longer — about three to eight days. You can be vaccinated against rotavirus, but there’s no vaccine yet against norovirus.

Is it possible to get norovirus twice?

Yes, says Moorjani. “Having norovirus can provide some immunity to the specific strain you were infected with, but it is short-lived, lasting only a few months or so. Since there are many different strains, having immunity to one strain doesn’t protect you from others.”

Is there any season when norovirus infection is at its peak?

You can get norovirus at any time during the year, but most outbreaks occur in colder months, from November to April. One major reason is that people tend to gather indoors more during colder months, especially during the holiday season.

Do hand sanitizers kill norovirus?

According to the CDC, hand sanitizers don’t work effectively against norovirus. So, thoroughly wash your hands with soap and water. This offers the best protection. If you do use hand sanitizer, do so after washing your hands.