Norovirus

norovirus molecule

What Is Norovirus?

Norovirus is thought to be the most common cause of acute gastroenteritis (diarrhea and vomiting illness) around the world. It spreads easily through food and drink and can have a big impact on people's health.

Norovirus was originally called the Norwalk virus, after the town of Norwalk, OH, where the first confirmed outbreak happened in 1972.

On average, noroviruses cause 19 million to 21 million cases of acute gastroenteritis in the U.S. per year and send more than 450,000 people to the emergency room, according to the CDC. They cause more than half of all foodborne disease outbreaks each year. There are many types of noroviruses, and exposure to one type may not protect you from the others.

Although norovirus can strike year-round, it’s more common in the winter. People sometimes call it the “winter vomiting bug.” Noroviruses also are sometimes called food poisoning, because they can be transmitted through contaminated food. They aren't always the result of food contamination, though.

Norovirus Symptoms

If you come down with a norovirus infection, you'll probably go from feeling completely healthy to absolutely miserable within a day or two after being exposed. Typical symptoms include nausea, vomiting (more often in children), watery diarrhea (more often in adults), and stomach cramps.

Other norovirus symptoms include:

Most of these symptoms aren't serious, but diarrhea and vomiting can deplete your body of the fluid it needs, and you can become dehydrated. Children and the elderly are most susceptible to dehydration, as well as malnutrition from not getting enough nutrients.

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

How long is norovirus contagious?

It’s possible to shed the virus for up to 8 weeks. This means there’s a chance you could make other people sick. It usually gets less and less infectious over time.

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

When should you call your doctor?

Call your doctor’s office if you still have symptoms after 3 days. Also, watch for symptoms of dehydration, which may also require a doctor’s 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.

Norovirus vs. Stomach Flu

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

Norovirus Causes and Risk Factors

People become infected with noroviruses when they eat or drink contaminated foods and beverages. Raw or undercooked oysters and raw fruits and vegetables have been blamed in some outbreaks. You can also get infected if you touch an object or surface that has been infected with the virus and then touch your nose, mouth, or eyes.

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

Once someone is infected from contaminated food, the virus can quickly pass from person to person through shared food or utensils, by shaking hands, or through other close contact.

When someone with the virus vomits, the virus can spread through the air and contaminate surfaces. The virus also spreads through feces, meaning someone who doesn’t thoroughly wash their hands after using the bathroom can pass it along. Dirty diapers can also harbor norovirus.

Young children, the elderly, and people who have weakened immune systems are particularly more vulnerable to noroviruses. The spread can be hard to control because it's contagious before symptoms appear. In other words, you can spread the virus before you know you’re sick.

Norovirus Diagnosis

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

Norovirus Treatment

Noroviruses, like other viruses, don't respond to antibiotics, which are designed to kill bacteria. No antiviral drug can treat norovirus, but in healthy people, the illness should go away on its own within 1 to 3 days.

Norovirus Complications

Most people don't have any long-term problems from the virus.

Norovirus 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
  • Listlessness
  • Lethargy

To prevent dehydration, make sure to 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, as well as alcohol and caffeinated beverages, which can dehydrate you further.

If severe dehydration develops, contact your doctor. Severe dehydration is sometimes treated with intravenous (IV) fluids.

Norovirus Prevention

Good hygiene is the key to preventing 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 going to the bathroom or changing a baby's diaper, and before you prepare or eat food. Alcohol-based cleansers are not as effective as soap and water.
  • Carefully throw away any contaminated 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 have norovirus, don't prepare food for at least 2 to 3 days after you feel better. Try not to eat food that has been prepared by someone else who is sick.

WebMD Medical Reference Reviewed by Hansa D. Bhargava, MD on August 10, 2020

Sources

SOURCES:

Edward Gaydos, DO, pediatrician, Cleveland Clinic.

CDC: "Norovirus: Clinical Overview," “Burden of Norovirus Illness in the U.S.”

San Francisco Department of Public Health: "Norovirus."

Mesa County Valley School District 51. 

Los Angeles Fire Department. 

USA Today: "Norwegian Joy cruise passengers fall ill with possible norovirus."

CDC: "About Norovirus: Overview."

KidsHealth: "Stomach Flu."

University of Maryland: "Viral Gastroenteritis (Stomach Flu)."

Mayo Clinic: "Viral Gastroenteritis (Stomach Flu)."

University of Michigan: "Gastroenteritis in Adults and Older Children."

Mayo Clinic: “Norovirus Infection.”

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