Environmental Health and Safety

Norovirus FAQs

an electron micrograph of the Norovirus, CDC image ID 2172

What are noroviruses?

Noroviruses are a group of viruses that cause the “stomach flu,” or gastroenteritis (GAS-tro-en-ter-I-tis), in people. Several other names have been used for noroviruses, including:

  • Norwalk-like viruses (NLVs)
  • Caliciviruses (because they belong to the virus family Caliciviridae)
  • Viral gastroenteritis — the most common name for illness caused by norovirus
  • Acute gastroenteritis
  • Non-bacterial gastroenteritis
  • Food poisoning (although there are other causes of food poisoning)

Stomach flu — this “stomach flu” is not related to the flu (or influenza), which is a respiratory illness caused by influenza virus.

What are the symptoms of illness caused by noroviruses?

Symptoms may include nausea, vomiting, diarrhea, stomach cramps, headache, fever, chills, muscle aches, and a general sense of tiredness.

The illness often begins suddenly, and the infected person may feel very sick. In most people the illness is self-limiting with symptoms lasting for about 1 or 2 days. In general, children experience more vomiting than adults.

How serious is norovirus disease?

People may feel very sick and vomit many times a day, but most people get better within 1 or 2 days, and they have no long-term health effects related to their illness. However, sometimes people are unable to drink enough liquids to replace the liquids they lost because of vomiting and diarrhea. These persons can become dehydrated and may need special medical attention.

How do people become infected with noroviruses?

Noroviruses are found in the stool or vomit of infected people. People can become infected with the virus in several ways, including:

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

When do symptoms appear?

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

Are noroviruses contagious?

Noroviruses are very contagious and can spread easily from person to person. Both stool and vomit are infectious.

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. Therefore, it is particularly important for people to use good handwashing and other hygienic practices after they have recently recovered from norovirus illness.

Who gets norovirus infection?

Anyone can become infected with these viruses. There are many different strains of norovirus, which makes it difficult for a person’s body to develop long-lasting immunity. Therefore, norovirus illness can recur throughout a person’s lifetime. In addition, because of differences in genetic factors, some people are more likely to become infected and develop more severe illness than others.

What treatment is available for people with norovirus infection?

Currently, there is no antiviral medication that works against norovirus and there is no vaccine to prevent infection. Norovirus infection cannot be treated with antibiotics. This is because antibiotics work to fight bacteria and not viruses.

Norovirus illness is usually brief in healthy individuals. When people are ill with vomiting and diarrhea, they should drink plenty of fluids to prevent dehydration. Dehydration among young children, the elderly, the sick, can be common, and it is the most serious health effect that can result from norovirus infection. By drinking oral rehydration fluids (ORF), juice, or water, people can reduce their chance of becoming dehydrated. Sports drinks do not replace the nutrients and minerals lost during this illness.

Can norovirus infections be prevented?

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

  • Frequently wash your hands, especially using the toilet, after changing diapers and before eating or preparing food
  • Carefully wash fruits and vegetables, and steam oysters before eating them
  • Thoroughly clean and disinfect contaminated surfaces immediately after an episode of illness by using a bleach-based household cleaner
  • Immediately remove and wash clothing or linens that may be contaminated with virus after an episode of illness (use hot water and soap)
  • Do not eat raw meat. Always make sure meat is completely cooked
  • Do not let foods sit out for a long time. Keep cold foods cold and hot foods hot so bacteria will not grow in them
  • Refrigerate and freeze foods in shallow containers for complete cooling
  • Clean cutting boards and items used to prepare raw foods before using them again
  • Flush or discard any vomitus and/or stool in the toilet and make sure that the surrounding area is kept clean

Persons who are infected with norovirus should not prepare food while they have symptoms and for 3 days after they recover from their illness. Food that may have been contaminated by an ill person should be disposed of properly.

If you are camping or hiking and need to drink water from lakes, rivers, or streams, boil the water for one minute, treat it with chlorine or iodine, or use an iodine-based water filter system.

If you travel in developing countries, only drink bottled water or treat the water like you would when camping. Do not use ice made from untreated water and do not brush your teeth with tap water. If you eat fruit or vegetables make sure they have been peeled, cooked, or washed in water treated with chlorine or iodine. Do not eat foods if you are not sure that they are clean and safe.

The information in this FAQ was taken from the following sources:

Centers for Disease Control and Prevention (CDC) Norovirus
Texas Department of State Health Services (DSHS) — Infectious Disease Control Unit