SYNONYM OR CROSS REFERENCE: Norwalk virus, Norwalk-like virus, winter vomiting disease, acute nonbacterial gastroenteritis, acute diarrhoeal illness, Southampton virus, Desert Shield virus, Cruise Ship virus, Snow Mountain virus, Mexico virus, White River Lordsdale virus, Camberwell virus, Toronto virus, Hawaii virus Footnote 1-3
CHARACTERISTICS: Noroviruses are a group of viruses belonging to the Norovirus genus and the Caliciviridae familyFootnote 14. Based on the sequence of the major capsid protein, these viruses are further divided into 6 genogroups (GI-GVI), consisting of numerous genotypesFootnote 15 . GI, GII and GIV are the only genogroups known to infect humans. GIII infect cattle; GV infect miceFootnote 16. Porcine noroviruses belong to GII, although porcine and human noroviruses belong to different genotypes within GII Footnote 17. GII is the most prevalent Norovirus genotype circulating in humans populations, accounting for more than 95% of all infections Footnote 15. Noroviruses are slightly smaller than other viruses in the Caliciviridae family, with a diameter of approximately 27 nmFootnote 5. The edges of the virus, when viewed by electron microscopy, are not well defined. The virus is round, non-enveloped, and has single-stranded, positive-sense, polyadenylated RNAFootnote 1Footnote 2. Norovirus recombination and antigenic drift results in replacement of circulating dominant viruses every 2-3 years, with the new variants able to re-infect hosts immune to previous virusesFootnote 15.
PATHOGENICITY: Norovirus infection causes acute gastroenteritis, characterized by rapid onset of nausea, vomiting, diarrhea, abdominal cramps, abdominal pain, mucus in stool, malaise, headache, and fever Footnote 1Footnote 5. The infection is usually resolved within 12 to 60 hours, although it can last longer in elderly, young children or immunocompromised individuals1-3Footnote 5, and these groups are at greatest risk for mortality and increased morbidity Footnote 1. Up to 30% of Norovirus infections are asymptomatic, however, these individuals are able to transmit the virusFootnote 16.
EPIDEMIOLOGY: Worldwide distribution. Noroviruses infect humans of all ages. Most outbreaks occur in hospitals, nursing homes, dining locations, schools, daycare centres, and vacation venues Footnote 1Footnote 4. Outbreaks occur throughout the year, but have a distinct winter seasonality Footnote 1. Because of persistence of Norovirus in the environment, outbreaks can last a long time and have been reported to last over 3 months Footnote 1. Noroviruses are responsible for 60-95% of outbreaks of nonbacterial acute infectious diarrhea Footnote 1.
HOST RANGE: Humans, pigs, cattle, miceFootnote 17.
INFECTIOUS DOSE: Less than 10 virions Footnote 2.
MODE OF TRANSMISSION: Norovirus transmission is usually person to person through the fecal-oral route Footnote 6. It can also be transmitted through the environment, contaminated surfaces, food, water, fomites, and aerosols Footnote 4Footnote 6.
INCUBATION PERIOD: Onset of symptoms usually takes 15-48 hours from the time of infection Footnote 2.
COMMUNICABILITY: Individuals can spread virus particles without showing symptoms of disease Footnote 2. Those who have recovered from symptoms and those who are asymptomatic can shed infectious virus particles up to three weeks after exposure Footnote 2.
RESERVOIR: Shellfish, Humans Footnote 1
DRUG SUSCEPTIBILITY: No specific antivirals.
SUSCEPTIBILITY TO DISINFECTANTS: Formulation R-82 for 10 minutes, 5-10% sodium hypochlorite for 10-20 minutes, peracetic acid or glutaraldehyde for 5 minutes Footnote 1Footnote 2Footnote 7. Recurrent outbreaks on cruise ships and in tropical resorts have been related to improper decontamination proceduresFootnote 8Footnote 9.
PHYSICAL INACTIVATION: Noroviruses are inactivated by temperatures of 71.3°C for 1 minute Footnote 10. It can survive at pH 2.7 for at least 3 hours Footnote 10. UV radiation may have intermediate effect Footnote 10.
SURVIVAL OUTSIDE HOST: Norwoviruses have a protein capsid protecting it from the environment Footnote 2. They can survive in seawater, groundwater, fresh water, soil, and inanimate surfaces for an unknown period of time. Norwalk virus cannot be cultivated under laboratory conditions as of yet. Feline calicivirus, another member of this family, with similar structure, can survive on glass surfaces for 21-28 days at room temperature and for longer periods at 4°C Footnote 11. At 37°C, feline calcinivirus survives over 24 hours Footnote 11.
SURVEILLANCE: Monitor for symptoms and confirm clinically Footnote 1. Viral RNA can be detected in stool samples using reverse transcription PCR Footnote 10. ELISA is also available for identifying noroviruses Footnote 3.
Note: All diagnostic methods are not necessarily available in all countries.
FIRST AID/TREATMENT: No specific therapy other than rest, oral rehydration and intravenous electrolyte replacement Footnote 2.
IMMUNIZATION: None Footnote 1
LABORATORY-ACQUIRED INFECTIONS: None reported as of 2010.
PRIMARY HAZARDS: Ingestion, exposure of mucous membranes to infective aerosols Footnote 6.
SPECIAL HAZARDS: None
RISK GROUP CLASSIFICATION: Risk Group 2 Footnote 12.
CONTAINMENT REQUIREMENTS: Containment Level 2 facilities, equipment, and operational practices for work involving infectious or potentially infectious materials, animals, or cultures.
PROTECTIVE CLOTHING: Lab coat. Gloves when direct skin contact with infected materials or animals is unavoidable. Eye protection must be used where there is a known or potential risk of exposure to splashes Footnote 13.
OTHER PRECAUTIONS: All procedures that may produce aerosols, or involve high concentrations or large volumes should be conducted in a biological safety cabinet (BSC). The use of needles, syringes, and other sharp objects should be strictly limited. Additional precautions should be considered with work involving animals or large scale activities Footnote 13.
SPILLS: Allow aerosols to settle and, wearing protective clothing, gently cover spill with paper towels and apply an appropriate disinfectant, starting at the perimeter and working towards the centre. Allow sufficient contact time before clean up Footnote 13.
DISPOSAL: Decontaminate all wastes that contain or have come in contact with the infectious organism by autoclave, chemical disinfection, gamma irradiation, or incineration before disposing Footnote 13.
STORAGE: The infectious agent should be stored in leak-proof containers that are appropriately labelled Footnote 13.
REGULATORY INFORMATION: The import, transport, and use of pathogens in Canada is regulated under many regulatory bodies, including the Public Health Agency of Canada, Health Canada, Canadian Food Inspection Agency, Environment Canada, and Transport Canada. Users are responsible for ensuring they are compliant with all relevant acts, regulations, guidelines, and standards.
UPDATED: March 2017
PREPARED BY: Centre for Biosecurity, Public Health Agency of Canada
Although the information, opinions and recommendations contained in this Pathogen Safety Data Sheet are compiled from sources believed to be reliable, we accept no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting from the use of the information. Newly discovered hazards are frequent and this information may not be completely up to date.
Copyright © Public Health Agency of Canada, 2017 Canada
International Committee on Taxonomy of Viruses (ICTV). Available online at http://ictvonline.org
White, P.A. (2014) Evolution of norovirus. Clinical Microbiology and Infection, 20(8):741-745.
Morillo, S.G.; Timenstsky, M. D. (2011) Norovirus: an overview. Revista da Associaçao Medica Brasileira, 57(4): 453-458.
Mattison, K.; Shukla, A.; Cook, A.; Pollari, F.; Friendship, R.; Kelton, D.; Bidawid, S.; Farber, J.M. (2007) Human Noroviruses in Swine and Cattle, Emerging Infectious Diseases 13(8): 1184-1188.