Noroviruses are a group of related RNA (ribonucleic acid) viruses that cause acute viral gastroenteritis (also known as the "
stomach flu"). Norovirus was recently approved as the official genus name for the group of viruses provisionally described as "Norwalk-like viruses" (NLV). Noroviruses are part of the genus
Norovirus and the family
Caliciviridae.
How Did Norovirus Get Its Name?
Noroviruses are named after the original strain, "Norwalk virus," which caused an outbreak of gastroenteritis in a school in Norwalk, Ohio, in 1968. Currently, there are at least four norovirus genogroups (GI, GII, GIII, and GIV), which, in turn, are divided into at least 20 genetic clusters.
Several other names have been used for noroviruses in the past, including:
- Norwalk-like viruses (NLVs)
- Caliciviruses (because they belong to the virus family Caliciviridae)
- Small round structured viruses, or SRSVs (because of their appearance).
Norovirus in the Environment
Noroviruses are relatively resistant to environmental challenge: they can survive freezing, temperatures as high as 140°F (60°C), and have even been associated with illness after being steamed in shellfish. Moreover, noroviruses can survive in up to 10 ppm chlorine, well in excess of levels routinely present in public water systems.
Illnesses Caused by Norovirus
Illnesses caused by norovirus infections have several names, including:
- Stomach flu. This "stomach flu" is not related to the flu (or influenza), which is a respiratory illness caused by influenza virus.
- Viral gastroenteritis. The most common name for illness caused by norovirus. Gastroenteritis refers to an inflammation of the stomach and intestines.
- Acute gastroenteritis.
- Non-bacterial gastroenteritis.
- Food poisoning (although there are other causes of food poisoning).
- Calicivirus infection.
Noroviruses are not related to bacteria and parasites that can cause gastrointestinal illnesses. Norovirus is not a "new" virus, but interest in it is growing as more is learned about how frequently noroviruses cause illness in people.
Transmission of Norovirus
Noroviruses are highly contagious and can spread easily from person to person. Noroviruses are found in the stool or vomit of infected people.
Norovirus transmission can happen in one of several ways, including:
- Eating food or drinking liquids that are contaminated with norovirus
- Touching surfaces or objects contaminated with norovirus and then putting your hands in your mouth
- Having direct contact with another person who is infected and showing symptoms (for example, when caring for someone with the illness or sharing foods or eating utensils with someone who is ill).
People infected with norovirus are usually 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 hand washing and other hygienic practices after they have recently recovered from norovirus illness.
Incubation Period for Norovirus
When a person becomes infected with a norovirus, the virus begins to multiply within the small intestine. After approximately 1 to 2 days,
norovirus gastroenteritis symptoms can appear. This period between the
norovirus transmission and the start of symptoms is the "
norovirus incubation period." In some cases, the norovirus gastroenteritis incubation period can be as short as 12 hours after exposure.
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