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This page is about microbiologic aspects of the organism(s).  For clinical aspects of the disease, see Norovirus infection.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]


Norovirus is the cause of norovirus infection. Noroviruses (genus Norovirus) are a group of related, single-stranded RNA, nonenveloped viruses that cause acute gastroenteritis in humans. Noroviruses belong to the family Caliciviridae.


Common Causes

Norovirus is transmitted through person-to-person contact, food and water. Genotype GII.4 is mostly contact transmitted. Non-GII.4 genotypes such as GI.3, GI.6, GI.7, GII.3, GII.6 and GII.12 are mostly food-borne. Genogroup GI strains are more often transmitted through water. This is due to their higher stability in water compared to other strains of the virus.[1][2]

Norovirus is among top ranks of food-borne viruses, globally[3]. Transmission could occur in different stages of pre- and post-production of the food products. For instance, shellfish can be contaminated with fecal discharge in the water[4], fresh and frozen berries could be contaminated through water contaminated by sewage or contact during harvesting. Viral outbreaks through food-borne transmission can lead to a mixture of the viral strain and increased risk of genetic recombination. Studies show that about 7% of the foodborne outbreaks have a common source[5].

Less Common Causes

Norovirus also has a nosocomial transition, causing a major burden for health care services[6]. Immunocompromised patients may develop numerous norovirus variations due to the chronic infection. This intra-host viral variation may lead to the appearance of variants not similar to any of the ones of previous outbreaks, thus can escape the herd immunity.[7][1]

To date, animal norovirus strains have not been reported to infect human population, but there has been evidence of intra-species transmission. Human norovirus has been detected in the stools of pigs, cattle and dogs.[1]


  1. 1.0 1.1 1.2 de Graaf M, van Beek J, Koopmans MP (2016). "Human norovirus transmission and evolution in a changing world". Nat Rev Microbiol. 14 (7): 421–33. doi:10.1038/nrmicro.2016.48. PMID 27211790.
  2. Lysén M, Thorhagen M, Brytting M, Hjertqvist M, Andersson Y, Hedlund KO (2009). "Genetic diversity among food-borne and waterborne norovirus strains causing outbreaks in Sweden". J Clin Microbiol. 47 (8): 2411–8. doi:10.1128/JCM.02168-08. PMC 2725682. PMID 19494060.
  3. Havelaar AH, Kirk MD, Torgerson PR, Gibb HJ, Hald T, Lake RJ; et al. (2015). "World Health Organization Global Estimates and Regional Comparisons of the Burden of Foodborne Disease in 2010". PLoS Med. 12 (12): e1001923. doi:10.1371/journal.pmed.1001923. PMC 4668832. PMID 26633896.
  4. Le Guyader FS, Atmar RL, Le Pendu J (2012). "Transmission of viruses through shellfish: when specific ligands come into play". Curr Opin Virol. 2 (1): 103–10. doi:10.1016/j.coviro.2011.10.029. PMC 3839110. PMID 22440973.
  5. Verhoef L, Kouyos RD, Vennema H, Kroneman A, Siebenga J, van Pelt W; et al. (2011). "An integrated approach to identifying international foodborne norovirus outbreaks". Emerg Infect Dis. 17 (3): 412–8. doi:10.3201/eid1703.100979. PMC 3166008. PMID 21392431.
  6. Ahmed SM, Hall AJ, Robinson AE, Verhoef L, Premkumar P, Parashar UD; et al. (2014). "Global prevalence of norovirus in cases of gastroenteritis: a systematic review and meta-analysis". Lancet Infect Dis. 14 (8): 725–730. doi:10.1016/S1473-3099(14)70767-4. PMID 24981041.
  7. Debbink K, Lindesmith LC, Ferris MT, Swanstrom J, Beltramello M, Corti D; et al. (2014). "Within-host evolution results in antigenically distinct GII.4 noroviruses". J Virol. 88 (13): 7244–55. doi:10.1128/JVI.00203-14. PMC 4054459. PMID 24648459.

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