Overview of Norovirus

A very contagious and common virus that causes vomiting and diarrhea

Sponge covered in germs
Norovirus germs can be very difficult to kill. Aerotoons/Getty Images

Norovirus is the number one cause of gastroenteritis, or "stomach flu," in the United States. It is a highly contagious virus that causes inflammation in the stomach and intestines. This inflammation leads to symptoms like abdominal cramping, vomiting, and watery diarrhea.

Norovirus is usually diagnosed at a doctor's office, through a medical history and physical examination. Laboratory testing is not usually indicated unless there is a public outbreak.

The treatment of norovirus is usually done at home and involves drinking lots of fluids to prevent dehydration. Doctors often recommend oral rehydration solutions to ensure ample hydration and reverse any potential electrolyte abnormalities. If severe dehydration occurs, hospitalization is required for aggressive intravenous (through the vein) fluid replacement.

Cause

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 food is handled by an infected food handler 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 (which are not visible to the naked eye), and then touching your mouth, nose, and/or eyes.

How Contagious Is Norovirus?

Norovirus is extremely contagious and is commonly responsible for outbreaks in crowded settings like hospitals, nursing homes, daycare centers, schools, military training centers, resorts, and cruise ships.

What may be surprising to you is that norovirus can be contagious before a person even 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.

Important Point

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

Who Is Most at Risk?

Norovirus sickens 21 million people a year and leads to approximately 800 deaths. Those at highest risk are infants, young children, and older adults. Both of 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 the symptoms.

Besides early or advanced age, 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 course.

Symptoms

Symptoms of norovirus generally begin about 12 to 48 hours after exposure to the virus particles, 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
  • Infants or young children may cry with few or no tears or be unusually sleepy or fussy

Important Point

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.

Diagnosis

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

Medical History

During the medical history, a doctor will inquire about a person's specific symptoms, especially with regards to symptoms of dehydration. If severely dehydrated, which is more common in children and older adults, hospitalization for intravenous (through the vein) fluids may be needed.

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 towards 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, called the 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., 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

Because it takes so little of the virus, to make someone sick, it is hard to prevent.

But there are things you can do to reduce your risk for contracting norovirus:

  • Wash Your Hands Frequently and Correctly. It is important to wash your hands with soap and water. Using hand sanitizer also may help, but it is not very effective at killing norovirus. Make sure you wash thoroughly for at least 20 seconds—the time it takes to sing the "Happy Birthday" song twice. 
  • Clean, Clean, Clean. When you have norovirus and you are vomiting, the last thing you will feel like doing is cleaning. But making sure you clean after vomiting or having diarrhea will get rid of the particles that spread the germs. Make sure you clean with a product that contains bleach or make your own bleach-based cleaner with bleach and water (about 1 cup of bleach to 1 gallon of water). Using products that don't contain bleach won't do any good, as they won't kill the virus. 
  • Do Laundry. Wash your clothes, bed linens, towels and anything else that has come into contact with you while you have been sick. Wash in hot water and dry in the dryer to ensure they are as clean as possible. 
  • Don't Prepare Food. If you are sick with norovirus or you have had symptoms of it in the past two days, don't prepare food for anyone else. The highly contagious virus is frequently spread through food when someone who has had it prepares food for others. Although washing your hands will help remove the germs, it takes so little of the virus to make someone else sick that it isn't worth the risk. If there is someone else in your home that can prepare food, make sure they do so while you are sick and recovering. 
  • Stay "Quarantined". Technically you aren't truly quarantined when you have norovirus, but staying away from other people will help protect them from getting sick. If you can, try to stay in your room and use only one bathroom when you are sick. Others who live in the house should try to stay away from the "sick room" until you have recovered - and cleaned. 

Family Members or Close Contacts of Someone With Norovirus

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

  • Wear Gloves. If you are caring for someone with norovirus, it's unlikely they will be up to cleaning. You may be the one cleaning most often and this can put you in direct contact with the virus you are trying to avoid. The best thing you can do to try to prevent yourself from getting it is to wear gloves every time you clean something. Whether it's the bathroom or laundry that your sick loved one has used, wearing gloves provides an extra barrier between you and the virus. While you wear the gloves, make sure you don't touch your nose, eyes or mouth with them and wash your hands as soon as you take them off. 
  • Stay Away. It sounds mean, but staying away from the person who is sick as much as possible will help protect you from getting it. Sleep in a different room, use a different bathroom and keep as much distance as possible to avoid spreading the illness around the house. 
  • Don't Share. You should have learned that sharing is important as a young child, but not this time. Sharing items that your sick spouse, child or roommate has used is a sure-fire way to get sick yourself. Even sharing the remote control for the TV could be bad news. If the person who is sick uses the remote and has the virus on her hands, then you use it and you get the virus on your hands as well. You may touch your mouth, nose or eyes without even realizing it and infect yourself that easily. 

Bottom Line

In the end, it is extremely difficult to avoid getting norovirus when someone in your house has it. But taking these steps certainly won't hurt, and they will reduce your chances of getting sick or spreading your illness to someone else. 

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, and 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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