• Also Known As:
  • Norwalk virus
  • Winter vomiting bug
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What is Norovirus?

Norovirus is a virus that causes an infection of the digestive tract. The infection usually causes gastroenteritis, irritation of the stomach and intestines, and is sometimes thought of as a “stomach bug” or, incorrectly, as “stomach flu.” The most common signs and symptoms include the sudden onset of stomach pain, nausea, vomiting, and diarrhea.

Norovirus is highly contagious and is typically spread through ingestion of contaminated food or liquids, close contact with infected individuals, or by touching contaminated surfaces. People can be contagious and spread the illness for much longer than they are sick because norovirus is present in stool even before they develop signs and symptoms and can stay in stool for at least two weeks after they feel better.

The Centers for Disease Control and Prevention (CDC) estimates that norovirus sickens 20 million people in the U.S. each year. It is the most common cause of food poisoning in the United States. It is also the most common cause of acute diarrhea in healthy adults.

Norovirus can spread rapidly and cause outbreaks in places such as daycare centers, college dorms, nursing homes, cruise ships, schools, and other places where food is served and people are in close quarters. Individuals living or staying in these settings are at higher risk for catching norovirus. Eating or drinking at a place where food and liquid handling is unsanitary is also a common cause of norovirus infection.

Anyone can be infected with norovirus, and most people recover in a few days. However, young children, the elderly, and people with underlying conditions or weakened immune systems can develop severe signs and symptoms and serious complications such as dehydration and, without treatment, possibly death. Once infected with norovirus, you do not become immune and can be infected multiple times in a lifetime.


About Norovirus

Signs and Symptoms

Individuals usually develop norovirus signs and symptoms 12 to 48 hours after being exposed to the virus. Symptoms typically last for one to three days. Common norovirus signs and symptoms include:

  • Diarrhea
  • Nausea
  • Vomiting
  • Stomach Pain
  • Fever
  • Headache
  • Body aches

Since norovirus infection can cause diarrhea and/or vomiting several times a day, it can lead to dehydration. Signs and symptoms of dehydration can include dry mouth, less frequent urination, and dizziness. This complication can be dangerous for young children, the elderly, and people who have underlying illnesses.


Norovirus is typically diagnosed clinically, by evaluating the individual’s signs and symptoms, the severity of the symptoms, their duration, and what the individual has eaten recently.

Laboratory testing is typically not performed unless an individual is at higher risk for complications from an infection or if the symptoms:

  • Are severe and/or persist beyond a few days
  • Are thought to be caused by a different condition with similar symptoms
  • Appear to be part of a larger outbreak

If an outbreak is suspected by public health authorities, testing may be performed to determine whether norovirus or another microbe is causing the illnesses. Testing may be done to track cases and their locations, as well as to manage and contain outbreaks. (For more on this, read about public health testing for food and waterborne illnesses.)

People with severe illness or those at greater risk for complications may have their stool sample analyzed with the following tests to diagnose norovirus and rule out other types of infections:

  • Gastrointestinal pathogens panel – looks for multiple types of disease-causing (pathogenic) gastrointestinal microbes in a stool sample
  • Individual molecular tests (reverse transcriptase polymerase chain reaction, RT-PCR) – look specifically for norovirus RNA in a stool sample. Molecular tests are the preferred test for diagnosing norovirus infection.
  • Stool culture – detects several commonly encountered bacterial pathogens, such as Salmonella or Shigella, which could cause symptoms similar to norovirus
  • Stool white blood cells (WBC) – the presence of WBCs in stool may indicate a more severe infection with bacteria or some parasites. WBCs are not typically present in the stool in the case of norovirus infection.
  • O&P (Ova and Parasite) exam – may be done to rule out an infection with parasites that may cause symptoms similar to norovirus, especially if someone has been traveling internationally
  • Fecal occult blood test (FOBT) – ordered to help diagnose some infectious diseases that cause bloody diarrhea. Occult blood is absent in stool with a norovirus infection.

Other general tests may be performed if someone appears extremely ill, including if the person has a high fever or is very dehydrated:

  • Blood culture – sometimes ordered to detect or rule out bacterial infections that have spread into the blood (septicemia)
  • Electrolytes or Basic Metabolic Panel – used to monitor for sodium and potassium and acid-base imbalances to ensure proper organ function in people with severe dehydration
  • Complete blood count (CBC) – sometimes ordered to look for increased white blood cells as a sign of bacterial infection


Norovirus is highly contagious. To prevent norovirus infection:

  • Wash hands thoroughly and often, especially after using the restroom or handling diapers and before handling or eating food for yourself or others
  • Avoid contaminated food and water, or food prepared by someone who has, or recently had, norovirus symptoms
  • Wash fruits and vegetables, and cook seafood thoroughly

Individuals with norovirus are most contagious during their illness and during the first few days after recovering. The virus can remain in the stool for at least two weeks. Individuals who have had recent norovirus infections can help prevent spreading the virus by:

  • Disinfecting virus-contaminated areas with a chlorine bleach solution
  • Staying home from work, and other activities, especially if they involve food handling. Norovirus can be contagious for at least two weeks after symptoms resolve.
  • Keeping sick children at home
  • Avoiding travel until signs and symptoms have ended, and continue to use good handwashing



As with many food and waterborne illnesses, norovirus rarely requires treatment beyond supportive care that involves drinking plenty of fluids and getting enough rest. The symptoms usually resolves within a few days in people who are otherwise healthy.

Since norovirus is not a type of bacteria, antibiotics are not effective in treating the infection.

Anti-diarrheal medication may be recommended for people over age 65. In cases involving severe symptoms and significant dehydration, intravenous fluids and hospitalization may be required.

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