Norovirus, also known as the winter vomiting bug, is a common cause of sickness, diarrhea, and gastroenteritis.
According to the Centers for Disease Control and Prevention (CDC), norovirus causes gastroenteritis in 19–21 million people per year in the United States. The virus is also responsible for 56,000–71,000 annual hospitalizations and 570–800 deaths in the U.S. every year.
Although norovirus more commonly causes infection during the winter months, it can affect people at any time of the year.
People sometimes incorrectly refer to a norovirus infection as “stomach flu.” The medical term is gastroenteritis, and it does not have a connection with the flu, which is a respiratory infection.
In this article, we define the symptoms and causes of norovirus and explain how to treat and prevent infection.
Norovirus is a member of the Caliciviridae family of viruses. These viruses are responsible for about 90% of viral gastroenteritis outbreaks and close to 50% of cases across the world.
Norovirus spreads in the feces and vomit of people and animals with the infection. People can contract the virus by:
- consuming contaminated foods
- drinking contaminated water
- touching their mouth with the same hand that they just used to touch someone who has norovirus or a contaminated surface
It can be difficult to eliminate noroviruses because they can survive in hot and cold temperatures, and they are resistant to many disinfectants.
Noroviruses continually undergo genetic changes. For this reason, humans tend to develop a norovirus infection more than once during their lifetime, although the symptoms are usually less severe each time.
Typically, the first symptom of norovirus is nausea.
Other common symptoms include:
- stomach pain
- abdominal cramps
- watery or loose diarrhea
- feeling unwell and lethargic
- fever and chills, which are usually mild
- body aches
During the brief period when symptoms are present, people can feel very ill and vomit many times a day, often violently and without warning.
The CDC note that signs and symptoms usually last 1–3 days and appear between 12 and 48 hours after the initial infection. In some cases, diarrhea may last longer than 3 days.
It is important to note that once the symptoms have resolved, the virus can still spread through the stool and vomit for 2 weeks.
No specific therapy exists for noroviral gastroenteritis. Instead, doctors aim to prevent dehydration and control symptoms.
Fasting will not speed up recovery. People with norovirus should eat a light diet consisting of foods that are easy to digest, such as rice, bread, soups, and pasta. Infants with norovirus should continue to follow their regular diet.
A person will need to ensure that they replace the fluids that they lose through vomiting or diarrhea. Replacing fluids in very young children and older adults is especially crucial, as people in these age groups are particularly susceptible to dehydration that comes on very rapidly.
Some people may find it beneficial to take oral rehydration fluids. Examples of available products include Infalyte, Kao Lectrolyte, Naturalyte, Oralyte, and Pedialyte.
Dehydration can be sudden and, for some people, life threatening. People with dehydration who are not able to drink enough liquids may need to receive fluids intravenously.
The following risk factors may increase a person’s likelihood of becoming infected with the norovirus:
- having a weakened immune system, for example, people who have undergone an organ transplant and individuals living with HIV
- living in a household whose members do not correctly observe food hygiene practices
- living with a child who attends a child care center or preschool
- staying in a hotel, cruise ship, or vacation resort where many people congregate
- living in a closed or semi-closed community, such as a nursing home, hospital, or retirement center
After a norovirus infection, people have temporary immunity from further infection, although this usually only lasts for about 2–3 years.
The Department of Health and Human Services suggest that the following are the most common causes of human norovirus infections:
- contaminated foods
- ready-to-eat foods, such as salads, ice, cookies, fruit, and sandwiches, that a worker with a norovirus infection has handled
- any food that contains particles of the feces or vomit of a person with norovirus
According to the CDC, about 70% of foodborne norovirus infection outbreaks occur due to the direct contamination of food by a handler with norovirus immediately before its consumption.
Outbreaks have often had links to cold food, including salads, sandwiches, and bakery products.
Authorities have also implicated liquid food items, such as salad dressing and cake icing, as outbreak causes.
Sometimes, oysters from contaminated waters have taken the blame for widespread gastroenteritis outbreaks.
Sewage contamination of wells and recreational water has also caused waterborne outbreaks of norovirus infection in community settings.
The best way to prevent the spread of foodborne noroviruses is to practice proper food handling. Good hand hygiene and food cleaning are important for preventing the transmission of norovirus.
Noroviruses can survive freezing temperatures, as well as those as high as 140°F or 60°C. Some people may even develop an infection after eating steamed shellfish. Noroviruses can also survive in up to 10 parts per million of chlorine, levels that are much higher than those available in current public water systems.
Despite these survival features, experts say that relatively simple personal and food hygiene measures can significantly reduce the foodborne transmission of noroviruses.
The following steps can reduce a person’s risk of norovirus infection:
- Handwashing: Washing the hands frequently and thoroughly with soap and warm water can reduce the risk of infection, especially after going to the bathroom or changing a diaper and before preparing meals.
- Cleaning surfaces: People should preferably clean with a bleach-based household cleaner. When possible, they should let the bleach remain on the surface for about 10 minutes. People with norovirus may often vomit violently, without warning. They should clean any surfaces near the vomit promptly and thoroughly, as the vomit can be infectious.
- Avoiding risky foods: People should try to avoid shellfish that may have come from contaminated waters. They should also discard any foods that a person with norovirus may have prepared. People should thoroughly wash and scrub all fruits and vegetables.
- Removing infected feces and vomit: People need to ensure that they flush these away and clean the surrounding toilet area immediately with a bleach-based household cleaner.
- Washing clothing and bedclothes: If these items could have become contaminated, people should wash them with hot, soapy water.
- Keeping the toilet seat down: When flushing a toilet, people should keep the toilet seat down to prevent infectious microbes from entering the air.
- Staying at home: Avoiding public contact can reduce the spread of norovirus. This advice is particularly relevant for people who have norovirus and work in a job that requires them to handle food.
- Using disposable towels: People who are especially vulnerable to infection, such as those caring for an infected person, should use disposable paper towels rather than cloth ones to dry their hands. The virus can survive for some time on objects.
- Taking care when traveling: People who are traveling to a location with a less developed sanitation system should only use bottled water, even for brushing their teeth. It is also advisable to avoid buffets and uncooked foods.
Hospitals and other healthcare facilities also have a role to play in preventing transmission. They should focus on methods to limit the spread of the virus, such as isolating people with an infection.
In the vast majority of cases, a norovirus infection resolves itself within a few days and has no complications.
Less commonly, the following complications may occur:
Some people are unable to drink enough liquids to replace those that they lose through vomiting or diarrhea. They may become dehydrated and require special medical attention.
Young children, older adults, and individuals of any age who need a caregiver are especially vulnerable.