What are noroviruses?

Noroviruses are a group of viruses that cause “stomach flu,” or gastroenteritis (GAS-tro-en-ter-I-tis), in people. Norovirus is also commonly known as Norwalk or the “cruise ship virus."

What are the symptoms of illness caused by noroviruses?

Symptoms usually include nausea, vomiting, diarrhea, and some stomach cramping. Sometimes people also have low-grade fever, chills, headache, muscle aches, and a general sense of tiredness.

The illness often begins suddenly, and the infected person may feel very sick. The illness is usually brief, with symptoms lasting from 12 hours to 5 days. In general, children experience more vomiting than adults. Most people with norovirus illness experience both diarrhea and vomiting.

How serious is norovirus disease?

It's usually not serious, although people may feel very sick and vomit many times a day. Most people get better within 1-2 days, and they have no long-term health effects related to the norovirus. However, sometimes people become dehydrated due to vomiting and diarrhea and may need special medical attention.

Children and infants, the elderly, and people with weakened immune systems are more likely to experience dehydration, hospitalization, and complications, including death.

How do people become infected with noroviruses?

These viruses are very contagious and can spread rapidly. Noroviruses are found in the stool or vomit of infected people. They can be passed directly to other people or to the environment (handrails, walls, toys, tables, countertops) where other people pick it up. People can become infected with the virus in several ways, including:

  • Eating food or drinking liquids that are contaminated;
  • Touching contaminated surfaces or objects and then placing their hand in their mouth; and
  • Having direct contact with another person who is infected and showing symptoms (for example, caring for someone who is ill or sharing foods or eating utensils with someone who is ill).

When do symptoms begin?

Symptoms usually begin about 24-48 hours after ingestion of the virus, but they can appear as early as 12 hours after exposure.

How long are people contagious?

People infected with norovirus are contagious from the moment they begin feeling ill to at least 3 days after recovery. Some people may be contagious for as long as 2 weeks after recovery. So it's very important for infected people to use good handwashing and other hygienic practices and not to prepare food while contagious.

What’s the best way to prevent spreading norovirus to family, friends, and community?

  • Stay home when you have symptoms.
  • Use a separate bathroom if possible and wash your hands thoroughly after each episode of illness.
  • Thoroughly clean and disinfect contaminated surfaces immediately after an episode of illness by using a bleach solution as described below.
  • Immediately remove and wash clothing or linens that may be contaminated. Handle soiled linens and clothes as little as possible and with minimum agitation to prevent microbial contamination of the air and people.
  • Close toilet lids while flushing. This may help cut down on virus being projected into the air in tiny droplets of water.
  • Do not prepare food while you have symptoms and for 3 days after recovery. Dispose of food that may have become contaminated. People in occupations that, by their nature, can easily spread illness (such as food handlers, daycare providers, and health-care providers) should stay home for 48-72 hours after symptoms stop.

Can norovirus infections be prevented?

Yes. You can decrease your chance of coming in contact with noroviruses by following these preventive steps:

  • Wash your hands often, especially after using the toilet and changing diapers and before eating or preparing food.
  • Carefully wash fruits and vegetables and steam oysters before eating them.

What is an effective cleaner and disinfectant?

Chlorine is the most effective way to kill noroviruses. Use chlorine bleach from a new bottle in the following concentrations for these surfaces:

  • Stainless steel and items that have had contact with food or mouth: Soak 10-20 minutes in a solution of 5 tablespoons bleach to 1 gallon water.
  • Nonporous surfaces (tile floors, countertops, sinks, toilets): Soak 10-20 minutes in 1/3 cup bleach to 1 gallon water.
  • Porous surfaces (wooden floors, carpets): Soak 10-20 minutes in 1 and 2/3 cups bleach to 1 gallon water.
  • Carpets: Pick up visible organic debris with absorbent material and discard in a plastic bag. Steam clean at 158 degrees Fahrenheit for 5 minutes or 212 degrees for 1 minute.
  • Textiles (linens, clothing): Remove visible organic debris with absorbent material and discard in a plastic bag. Keep contaminated and uncontaminated clothes separate. Minimize disruption of soiled linens and laundry to minimize aerosols. Wash in a pre-wash cycle, then use a regular wash cycle with detergent and dry separately from contaminated clothing at a temperature greater than 170 degrees.

How do I protect myself when using chlorine bleach?

Chlorine bleach is corrosive. It can irritate skin, eyes, upper and lower respiratory tract, and all mucosal tissue. Take these precautions when working with it.

  • Never mix bleach with other cleaners, disinfectants, or other chemicals.
  • Prepare bleach solution in a well-ventilated area.
  • Do not use a spray bottle to apply a bleach solution.
  • Use disposable gloves, mask, eye protection, and protective clothing, especially when working with more concentrated bleach solutions.

More About Noroviruses

Frequently Asked Questions(PDF, 120KB)

Preventing & Controlling Noroviruses in Child-Care Facilities(PDF, 197KB)

Preventing & Controlling Noroviruses in Long-Term Care Facilities(PDF, 176KB)

Norovirus Information for Food Handlers(PDF, 163KB)

Norovirus Website of Centers for Disease Control & Prevention