What Is Norovirus? Symptoms, Causes, Diagnosis, Treatment, and Prevention

Norovirus is a highly contagious virus that causes more than half of all foodborne illnesses in the United States. (1) It’s also the leading cause in the United States of a type of stomach illness called acute gastroenteritis (inflammation of the stomach and intestines), which causes vomiting and diarrhea. (1)

Norovirus can spread from person to person through contaminated food or water, or when a person touches a contaminated surface and transfers the virus to their mouth.

While norovirus is commonly known as stomach flu, it is not, in fact, related to the seasonal flu, which is caused by the influenza virus; and it is not related to the virus that causes COVID-19. Other names for norovirus include “food poisoning” and a “stomach bug.” (2)

The symptoms of acute gastroenteritis from norovirus typically develop 12 to 48 hours after catching the virus and last for about one to three days. (2) Some of the most common symptoms include:

• Diarrhea
• Stomach pain
• Nausea and vomiting
• Fever
• Headache
• Body aches

Diarrhea and vomiting can also cause some people to become dehydrated, especially younger children, older adults, and people who have other illnesses. The symptoms of dehydration include:

• Decreased urination
• Dry mouth
• Dry throat
• Dizziness when standing up
• Crying and fussiness in children

It’s also possible to have norovirus but not show any signs of symptoms of the illness. (3)

Norovirus is found in the feces and vomit of people who’ve been infected by the virus. People get norovirus by accidentally ingesting tiny amounts of these feces or vomit, which can be found on unwashed food, in contaminated water, or on a contaminated surface.

People with the infection can release billions of norovirus particles, but it only takes a small amount of those particles to make someone sick. (4)

In particular, norovirus can be transmitted by:

• Eating food or drinking liquids that are contaminated with norovirus (for example, food that’s grown in contaminated water)
• Touching an object or surface that’s been contaminated with norovirus, then touching your mouth
• Having direct contact — such as sharing food or utensils — with a person who has norovirus
• Drinking contaminated water from a well or from a pool that isn’t properly cleaned

More than half of all norovirus outbreaks in the United States occur in long-term care facilities. Outbreaks also occur in hospitals, restaurants, and at catered events. About 1 percent of all reported norovirus outbreaks occur on cruise ships. (5)

A doctor can usually diagnose norovirus based on a person’s symptoms.

Norovirus can also be detected in a stool sample. If you have an underlying health issue or weakened immune system, your doctor may want to order a stool test.

Prognosis of Norovirus

Most people will recover from norovirus without needing any treatment, but older adults, small children, and people with underlying medical conditions can be more susceptible to dehydration, and may therefore require medical treatment or even a hospital stay.

Norovirus usually lasts from one to three days.

Although the symptoms usually only last for a few days, people are contagious for much longer. Some people can keep shedding the virus in their feces for weeks — or even months, if you have underlying conditions — after recovering from the infection. (2)

Because there are many different types of norovirus, you can get sick from it many times. Some people might develop an immunity to some types of norovirus, but it’s not clear how long their immunity lasts.

A person’s susceptibility to norovirus is partly determined by their genetics. (6)

There’s no specific treatment for a norovirus infection. If you have an infection, the best course of action is to rest and drink plenty of fluids to prevent dehydration.

Sports drinks or other fluids that don’t have caffeine or alcohol in them may help with mild dehydration, but your best bet is to buy over-the-counter oral rehydration fluids.

If you aren’t able to drink enough liquid, or are more severely dehydrated, you may need to be given fluids intravenously, in a hospital.

Medication Options

There are no specific medicines that treat norovirus.

Antibiotics don’t work against norovirus because they only fight bacteria, not viruses. (7)

Alternative and Complementary Therapies

If you’re struggling to keep food down, you might try eating bland foods, including: (2)

• Soup
• Bananas
• Potatoes
• Rice
• Crackers

Prevention of Norovirus

Norovirus is highly contagious, so it’s important to prevent the spread of the infection by following good hygiene practices. Some steps to take include:

• Washing your hands with soap and water, especially after going to the bathroom or changing diapers (hand sanitizer isn’t a substitute for hand-washing, since alcohol is not as effective a shield against norovirus particles) (8)
• Washing fruits and vegetables thoroughly before eating them
• Cooking seafood (such as oysters or other shellfish) thoroughly
• Cleaning and disinfecting contaminated surfaces (with a bleach-based household cleaner)
• Washing laundry thoroughly and handling soiled items (such as from vomit) with rubber or disposable gloves
• Refraining from preparing food for others if you’re sick

Most people will recover from norovirus in a few days.

Some people, however, are more at risk for severe dehydration from norovirus, especially pregnant women or people who are older or have weakened immune systems. (2)

Norovirus is responsible for 58 percent of all foodborne illnesses in the United States, according to the U.S. Centers for Disease Control and Prevention (CDC). There are approximately 2,500 norovirus outbreaks each year, most of them occurring from November to April. (1)

According to the CDC, each year in the United States, norovirus causes an average of: (1)

• 19 to 21 million cases of acute gastroenteritis
• 2,270,000 outpatient visits (these are mostly young children)
• 465,000 emergency room visits (mostly young children)
• 109,000 hospitalizations
• 900 deaths

Norovirus is the most common cause of foodborne illness in the United States, but it’s not the only cause. The other most common causes include:

• Salmonella
• Clostridium perfringens
• Campylobacter
• Staphylococcus aureus

Favorite Organizations for Essential Information

For more information about norovirus, visit the following websites:

Centers for Disease Control and Prevention (CDC)

Learn more about norovirus and other leading causes of foodborne illnesses — including how to prevent infection — at the CDC’s website.

National Foundation for Infectious Diseases (NFID)

The NFID is a nonprofit organization that’s committed to educating the public about infectious diseases.