[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Other RNA viruses](https://durgical.com/en/microbiology/groups/other-rna-viruses/) › Norovirus

[Microbiology](https://durgical.com/en/microbiology/) · [Other RNA viruses](https://durgical.com/en/microbiology/groups/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

## Key points

- Non-enveloped positive-sense calicivirus
- Leading cause of gastroenteritis outbreaks at all ages
- Very low infectious dose
- Resists alcohol: wash with soap and water and disinfect with bleach
- Contact precautions

## 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 →](https://durgical.com/en/conditions/acute-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

## Memory aid

Norovirus says "no" to alcohol gel: beat it with soap, water and bleach.

## 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.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/microbiology/norovirus/)

## Related

- [Rotavirus](https://durgical.com/en/microbiology/rotavirus/)

## Related conditions

- [Acute (viral) gastroenteritis](https://durgical.com/en/conditions/acute-gastroenteritis/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

**Contact**
Gown and gloves; dedicated equipment. For C. difficile, soap-and-water hand washing.

**Droplet**
Surgical mask within about a metre; single room.

**Airborne**
N95 respirator and a negative-pressure room.

[← Back to the group: Other RNA viruses](https://durgical.com/en/microbiology/groups/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](https://www.cdc.gov/norovirus/about/index.html) (CDC, 2025); [Appendix A: Type and Duration of Precautions Recommended for Selected Infections and Conditions](https://www.cdc.gov/infection-control/hcp/isolation-precautions/appendix-a-type-duration.html) (CDC, 2024).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/microbiology/norovirus/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/norovirus/