Microbiology · Other RNA viruses
Norovirus !
- Virus
- Non-enveloped (naked)
- Contact
- Exam priority: medium
A highly contagious virus that causes sudden vomiting and diarrhoea. It drives outbreaks on cruise ships and in hospitals, schools and restaurants.
Updated 2026-11-01
Also called: Norwalk virus
At a glance
- Shape
- Icosahedral with cup-shaped depressions
- Genome
- Single-stranded, positive-sense RNA
- Envelope
- Non-enveloped (naked)
- Family
- Caliciviridae, genus Norovirus
- Size
- About 27 to 40 nm
Morphology
- Naked capsid very resistant to the environment, alcohol and freezing
- Several genogroups; GII.4 causes most outbreaks
Transmission
- Faecal-oral and through vomit particles
- Food handled by an infected person; raw shellfish (oysters)
- Contaminated surfaces
- A very low infectious dose: a few particles are enough
- Shedding continues for two weeks or more after recovery
Reservoir: Humans
Isolation precautions
What the care team adds to standard precautions.
- Contact
- Gown and gloves; dedicated equipment. For C. difficile, soap-and-water hand washing.
Virulence factors
- Binds histo-blood group antigens on gut epithelium; some non-secretors are resistant
- Disrupts small-intestine villi and gastric emptying
- Short-lived immunity and many variants: frequent reinfection
Diseases it causes
- Acute gastroenteritis with explosive vomiting and diarrhoea, in outbreaks at all ages Acute (viral) gastroenteritis →
Clinical picture
- Onset 12 to 48 hours after exposure
- Vomiting, watery diarrhoea, nausea and abdominal pain; sometimes fever and myalgia
- Lasts 1 to 3 days
- Risk of dehydration in young children, older adults and the chronically ill
Diagnosis
- Clinical and epidemiological diagnosis in an outbreak
- RT-PCR on stool or gastrointestinal panels
Treatment
Oral or intravenous rehydration according to severity. There is no approved antiviral or vaccine; antibiotics do not help.
Drug class only; doses and regimens are set by the clinician from the current guideline.
Prevention
- Handwashing with soap and water (alcohol gel works less well)
- Surface disinfection with hypochlorite (bleach)
- Keeping ill food handlers off work until 48 hours after symptoms end
- Cooking shellfish thoroughly
- Contact precautions in hospital
Test yourself
Think of the answer, then tap the question to see it.
Why is alcohol gel not enough against norovirus?
It is a non-enveloped virus that resists alcohol; soap and water plus bleach disinfection are advised.
What is the most common cause of gastroenteritis outbreaks on cruise ships and in hospitals?
Norovirus.
How soon after exposure does norovirus illness begin?
Within 12 to 48 hours.
Related
Related conditions
← Back to the group: Other RNA viruses
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: About Norovirus (CDC, 2025); Appendix A: Type and Duration of Precautions Recommended for Selected Infections and Conditions (CDC, 2024).
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Representative model, for educational purposes only.