What Is the Norovirus?

Illustration of norovirus

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Norovirus is the number one cause of gastroenteritis (the stomach flu) in the United States. It is a highly contagious virus that causes inflammation in the stomach and intestines. This leads to symptoms like abdominal cramping, vomiting, and watery diarrhea. Treatment of norovirus usually only involves drinking lots of fluids to prevent dehydration, though hospitalization for aggressive intravenous (through the vein) fluid replacement is required in severe cases.

norovirus
Verywell / Jessica Olah

Norovirus Symptoms

Symptoms of norovirus generally begin about 12 to 48 hours after exposure to the virus particles (which are not visible to the naked eye). The symptoms can last anywhere from 12 to 60 hours and include one or more of the following:

  • Cramping/stomach pain
  • Watery diarrhea (more common in adults)
  • Vomiting (more common in children)
  • Nausea
  • Fever
  • Headache
  • Body aches

The most common complication of norovirus is dehydration. If you are unable to keep even small amounts of fluid down or have had very severe diarrhea (or both), you may be dehydrated.

Symptoms of dehydration may include:

  • Dry mouth
  • Increased thirst
  • A decrease in urination and/or increased urine concentration (dark yellow color)
  • Headache
  • Fast heart rate
  • Weakness or unusual fatigue
  • Feeling dizzy or lightheaded when standing up

Additional signs of dehydration in infants and young children include:

  • Crying with few or no tears
  • Unusual sleepiness or fussiness

Severe dehydration may require medical treatment such as IV fluids or medications to help stop the vomiting. If you think you might be dehydrated due to vomiting or diarrhea, it's important to seek medical attention right away.

Causes

Norovirus is considered a foodborne illness because the virus can easily contaminate food and water sources. In fact, the majority of norovirus outbreaks occur in restaurants where an infected preparer or server handles food or serving items with their bare hands.

Raw fruits and vegetables or undercooked foods may also become contaminated with the norovirus. Another potential source is shellfish from water that is contaminated with the norovirus.

Lastly, sharing food or eating utensils with someone who is infected with the norovirus may spread the infection, as can touching objects that contain norovirus particles and then touching your mouth, nose, and/or eyes.

Like the flu and many other viral infections, people typically don't develop immunity to norovirus and can become infected more than once.

How Contagious Is Norovirus?

Norovirus is extremely contagious. It can be so even before a person starts showing symptoms and for as long as two weeks after they start to feel better. That said, norovirus is most contagious while a person is sick and during the first three days after symptoms subside.

Risk Factors

Norovirus sickens 21 million people a year and leads to approximately 800 deaths. Anyone can get it, but some people are at greater risk than others.

It is commonly responsible for outbreaks in crowded settings, so those who frequent places such as the following are at increased risk:

  • Hospitals
  • Nursing homes
  • Daycare centers
  • Schools
  • Military training centers
  • Resorts
  • Cruise ships

Those at highest risk are infants, young children, and older adults. These groups have immune systems that aren't as strong as those of older children or adults who are otherwise healthy, making it more difficult to recover from norovirus symptoms.

Besides this, people with a weak immune system who are infected with the norovirus—like those who have undergone an organ transplant or those with leukemia or HIV infection—are more likely to experience a more severe or prolonged case.

Diagnosis

The diagnosis of norovirus is generally made through a medical history and physical examination.

Medical History

During a medical history, your doctor will inquire about your specific symptoms, especially with regard to those related to dehydration.

Your doctor may also inquire about the specifics of your diarrhea, like whether it is watery versus bloody, or whether you have experienced a high fever. Answers to these questions can help sway your doctor away or toward a diagnosis of norovirus.

Physical Exam

During the physical exam, your doctor will inspect your abdomen, listen to bowel sounds with a stethoscope, percuss (tap on) your abdomen, and lastly, press gently on different areas of your abdomen to feel for masses, enlarged organs, or tenderness.

The abdominal part of the physical exam is important for ruling out more serious causes of abdominal pain such as:

In addition to evaluating your abdomen, your doctor will also take note of your vitals and check for signs of dehydration, like a dry mouth or poor skin turgor.

Laboratory Test

Less commonly, a test called the real-time reverse transcription-polymerase chain reaction (RT-qPCR) test may be used to diagnose norovirus. This assay detects the genetic material (RNA) of the virus and can be performed on stool, vomitus, food, water, and environmental specimens.

The RT-aPCR test is not commonly done because of the short course of the infection. It may be used if there is a large public outbreak or if a person has a weakened immune system (e.g., due to leukemia or organ transplant).

Treatment

The key treatment for the norovirus is to drink lots of fluids. While sports drinks may be all that is needed to rehydrate in adults and older children, oral rehydration solutions, like Pedialyte or Ceralyte, are better for replacing important nutrients and minerals lost through vomiting and/or diarrhea.

Occasionally, a norovirus infection will be bad enough to require medical treatment. Although there is no medication that can kill or cure the infection, there are medications, like Zofran (ondansetron), that can help stop or reduce vomiting so that you don't get dehydrated.

Some people may require intravenous fluid replacement in a hospital if they are showing signs of dehydration and cannot tolerate oral fluids.

Besides severe dehydration and/or an inability to keep fluids down, other indications for hospitalization may include:

  • Severe abdominal pain
  • Intractable vomiting
  • Prolonged symptoms (close to or more than one week)
  • Pregnancy
  • Older adults or infants
  • Individuals with a weakened immune system

Prevention

While it is not always possible to avoid foodborne illnesses like norovirus, as it takes so little of the virus to make someone sick, these three steps will significantly help reduce your everyday risk.

  • Wash your hands frequently and correctly: It is important to wash your hands with soap and water frequently throughout the day, especially after using the bathroom or before preparing food. Making a trip to the sink is ideal, as hand sanitizer cannot kill certain bugs, including norovirus. Make sure you wash thoroughly for at least 20 seconds—the time it takes to sing the "Happy Birthday" song twice. 
  • Avoid touching your mouth: Even with frequent and good handwashing, you may inadvertently touch a contaminated surface. By avoiding touching your mouth, you can prevent the transmission of tiny infectious particles into your body.
  • Routinely sanitize and clean: It's important to routinely sanitize your home and workspace, especially kitchens (including utensils and counters). Make sure you clean with a product that contains bleach or make your own bleach-based cleaner. Using products that don't contain bleach won't do any good, as they won't kill the virus.

When Close Contacts Have Norovirus

If you live in the same house with someone who has norovirus (or you suspect they do), and you don't yet have it, there are additional steps you can take to protect yourself.

  • When possible, stay away: It may not always be practical, but staying away from the person who is sick as much as possible will help protect you from getting sick too. Sleep in a different room, use a different bathroom, and keep as much distance as possible. 
  • Wear gloves: If you are caring for someone with norovirus, it's unlikely they will be up to cleaning. You may be the one doing this chore most often, which can put you in direct contact with the virus. The best thing you can do is wear gloves. When doing so, make sure you don't touch your nose, eyes, or mouth, and wash your hands as soon as you're done cleaning up.
  • Make sure laundry gets done: Wash clothes, bed linens, towels, and anything else that the sick person touches. Use hot water and dry items in the dryer using high heat to ensure they are as clean as possible. If laundry is soiled, handle it with rubber gloves and wash your hands after placing items in the washer.
  • Don't share: Sharing items that your sick spouse, child, or roommate has used is a sure way to get sick yourself. Even sharing the remote control for the TV could be bad news.
  • Don't let them prepare food: If someone is sick with norovirus, don't let them prepare food for you or anyone else, if possible. In fact, the Centers for Disease Control and Prevention (CDC) recommends the individual not prepare food for at least two days after symptoms stop.

A Word From Verywell

While becoming infected with norovirus is an unpleasant experience, be reassured that most people feel better within one to three days. In the meantime, continue being proactive about handwashing. If you do get infected, be sure to hydrate aggressively.

Lastly, on a more positive note, a norovirus vaccine is currently being investigated. This would be a much more effective and less arduous preventive strategy than the current one (infection control).

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Article Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Switaj TL, Winter KJ, Christensen SR. Diagnosis and Management of Foodborne Illness. Am Fam Physician. 2015 Sep 1;92(5):358-65.

  2. Centers for Disease Control and Prevention. (November 2019). How Norovirus Spreads.

  3. Robilotti E, Deresinski S, Pinsky BA. Norovirus. Clin Microbiol Rev. 2015 Jan;28(1):134-64. doi: 10.1128/CMR.00075-14

  4. Centers for Disease Control and Prevention, "Norovirus: Laboratory Diagnosis" 2018

  5. Centers for Disease Control and Prevention, "Preventing Norovirus" (2019)

  6. Lucero Y, Vidal R, O'Ryan G M. Norovirus vaccines under development. Vaccine. 2018 Aug 28;36(36):5435-41. doi: 10.1016/j.vaccine.2017.06.043

Additional Reading
  • Alexandraki I, Smetana GW. (2019). Acute viral gastroenteritis in adults. Aronson MD, ed. UpToDate. Waltham, MA: UpToDate Inc.