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