Noroviruses are a group of viruses that cause the "stomach flu," or gastroenteritis. Norovirus was recently approved as the official name for the group of viruses sometimes described as "Norwalk-like viruses" (NLV). Other names that have been used include caliciviruses (Caliciviridae) and small round structured viruses.

Viruses are different from bacteria and parasites, some of which can cause illnesses similar to norovirus infection. Like all viral infections, noroviruses are not affected by treatment with antibiotics, and cannot grow outside of a person's body.

Symptoms of Illness Caused by Norovirus

Symptoms of norovirus illness include:

• Nausea
• Vomiting
• Diarrhea
• Some stomach cramping

Sometimes, people experience:

• Low-grade fever
• Chills
• Headache
• Muscle aches
• General sense of tiredness (fatigue)

Norovirus illness often begins suddenly, and the infected person may feel very sick. Symptoms usually begin about 24 to 48 hours after ingestion of the virus, but can appear as early as 12 hours after exposure. Symptoms usually last for about 1 or 2 days, with vomiting many times a day. In general, children experience more vomiting than adults.

People who get ill from norovirus have no long-term health effects related to their illness.

However, sometimes infected persons are unable to drink enough liquids and experience dehydration that may need special medical attention. This is usually a problem seen among the very young, the elderly, and the persons with weakened immune systems.

How Do People Become Infected with Noroviruses?

Noroviruses are found in the stool or vomit of infected people. People can become infected in various 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

People working in daycare centers or nursing homes should pay special attention to children and residents who have norovirus illness. Norovirus is very contagious and can spread rapidly throughout such environments.

Norovirus can spread easily from person to person. 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. It is particularly important to maintain good hand-washing and other hygienic practices, even after they have recently recovered from norovirus illness. Particular care should be taken with young children in diapers who may have diarrhea.

Who can get a norovirus infection?

Anyone can become infected with norovirus and its many strains. Because there are many strains of the virus, it is difficult for a person's body to develop long-lasting immunity, meaning that the norovirus illness can recur throughout a person's lifetime. Genetic factors can also make people more or less susceptible to being infected and developing a more severe form of the illness.

Treating 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, since antibiotics fight against 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, such as oral rehydration fluids (ORF), juice, or water to prevent dehydration. Sports drinks do not replace the nutrients and minerals lost during norovirus illness.

Preventing Norovirus

The following guidelines are recommended for preventing Norovirus:

• Frequently wash your hands, especially after toilet visits and 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, using hot water and soap, wash clothing or linens that may be contaminated with norovirus after an episode of illness
• Flush or discard any vomit 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 three days after they recover from their illness. Food that may have been contaminated by an ill person should be disposed of properly.