Norovirus (previously called Norwalk virus or winter vomiting bug) is a highly contagious calicivirus causing acute gastroenteritis — typically sudden onset of nausea, vomiting (often projectile), watery diarrhoea, abdominal cramps and low-grade fever lasting 24-72 hours in healthy adults. It is the most common cause of gastroenteritis globally (685 million cases/year) and the leading cause of food-borne disease outbreaks. Despite its brief illness in most healthy people, norovirus causes over 200,000 deaths annually — predominantly in elderly, immunocompromised and malnourished individuals.

How is norovirus spread?

Four main routes: Fecal-oral — ingesting contaminated food (shellfish — bivalves filter norovirus from contaminated water; raw produce; ready-to-eat foods handled by infected food workers) or water. Projectile vomiting aerosols — norovirus particles in vomit can be inhaled or land on surfaces up to 2 metres away. Contact transmission — touching contaminated surfaces then mouth. Person-to-person — through close contact with an infected person. The extremely low infectious dose (10-100 viral particles) means microscopic contamination is sufficient to cause infection.

Why is norovirus so hard to control in hospitals?

Hospital norovirus outbreaks are notoriously difficult to control because: the very low infectious dose means minimal contamination causes infection; norovirus is relatively resistant to alcohol-based hand gels (soap and water is more effective); environmental contamination is extensive after projectile vomiting; norovirus remains infectious on surfaces for days to weeks; staff and patients can be infectious before and after symptoms; and multiple transmission routes (direct, aerosol, surface) operate simultaneously. Ward closure, cohorting of affected patients, intensive cleaning with bleach, strict soap-and-water handwashing, and excluding symptomatic staff for 48 hours after symptoms resolve are the key control measures.

How is norovirus treated?

Treatment is supportive: oral rehydration with WHO/UNICEF ORS (or home fluids with salt and sugar) to replace lost fluids and electrolytes. IV fluids for severe dehydration. No antiviral treatment is approved for norovirus. Anti-emetics may help (but avoid in elderly — sedation risk). Rest and avoiding food until vomiting settles. Do not prepare food for others while symptomatic or for 48 hours after recovery.

Is norovirus the same as stomach flu?

The term "stomach flu" or "stomach bug" is commonly used but medically inaccurate — influenza (flu) is a respiratory virus with no gut manifestations. What is commonly called "stomach flu" is viral gastroenteritis, most often caused by norovirus (and rotavirus in young children, adenovirus in older children, astrovirus). Norovirus is the dominant cause of gastroenteritis in all age groups globally.

How does GMJ News cover norovirus?

GMJ News covers WHO norovirus data, hospital outbreak control, cruise ship outbreak response, alcohol gel vs soap-and-water efficacy, mRNA vaccine development, and foodborne prevention. Norovirus is the most common cause of healthcare-associated gastrointestinal illness — directly relevant to PHIG's hospital infection control programme and accreditation standards.

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Norovirus

GMJ News knowledge hub · last reviewed September 2026 · Georgian Medical Journal

Summary Statistics Glossary GMJ news FAQ Documents Organizations Research

Norovirus — a highly contagious Calicivirus — causes an estimated 685 million gastroenteritis cases per year globally (including 200 million in children under 5) and over 200,000 deaths annually, making it the single most common cause of gastroenteritis worldwide and the most common cause of food-borne disease outbreaks globally (WHO). Norovirus is notorious for hospital and cruise ship outbreaks — its extremely low infectious dose (10-100 viral particles), stability on surfaces, resistance to many disinfectants, and multiple transmission routes (fecal-oral, vomit aerosols, contaminated food) make containment exceptionally challenging. No vaccine is approved, though lipid nanoparticle mRNA vaccines are in clinical trials.

Key messages

685 million cases — #1 cause of gastroenteritis globally

Norovirus causes 685 million gastroenteritis cases and over 200,000 deaths per year globally — the most common cause of gastroenteritis worldwide and the leading cause of food-borne disease outbreaks globally (WHO).

Extremely infectious — 10-100 viral particles

Norovirus requires as few as 10-100 viral particles to cause infection — one of the lowest infectious doses of any pathogen. This extraordinary infectivity, combined with environmental stability, explains its propensity for explosive outbreaks.

Hospital and cruise ship outbreaks

Norovirus is notorious for explosive institutional outbreaks in hospitals, care homes, cruise ships, restaurants and schools. Vomiting patients produce aerosols that can infect people within 2 metres. Ward closure is often required to control hospital outbreaks.

Self-limiting in healthy adults — dangerous in elderly

In healthy adults and older children, norovirus gastroenteritis is typically self-limiting (24-72 hours). In elderly patients, especially in care homes, and in immunocompromised patients, norovirus can cause severe prolonged diarrhoea, dehydration and death.

No vaccine approved — difficult to develop

No norovirus vaccine is approved. Vaccine development is challenged by: the lack of a cell culture system; many distinct genotypes (GI, GII with multiple subtypes — GII.4 causes approximately 50-70% of outbreaks); short-lived immunity (no long-lasting immunity from natural infection); and the difficulty of measuring protective immunity.

ORS and infection control — the only interventions

Treatment: oral rehydration. Prevention: scrupulous hand hygiene (soap and water — alcohol gel is less effective against norovirus than against many other pathogens); surface disinfection with bleach; avoiding food preparation when ill; 48-hour exclusion after symptoms resolve.

Key statistics

685M

gastroenteritis cases/year globally

WHO

200K+

norovirus deaths/year (predominantly elderly in LMICs)

WHO

cause of gastroenteritis globally (all ages) and food-borne outbreaks

WHO

10-100

viral particles sufficient to cause infection (extremely low)

WHO

24-72hr

typical illness duration in healthy adults

WHO

approved norovirus vaccines

WHO 2024

Norovirus outbreak settings — % of reported outbreaks by exposure setting (CDC/WHO)

Source: WHO/CDC. Restaurants and care facilities account for most food-borne outbreaks; hospitals for nosocomial clusters.

Glossary of key terms

Norovirus (Calicivirus)
WHOA non-enveloped positive-sense RNA virus — family Caliciviridae, genus Norovirus. Classified into genogroups (GI, GII, GIV infect humans); multiple genotypes within each genogroup. GII.4 is the dominant genotype causing approximately 50-70% of outbreaks globally. Extremely stable — survives 60°C for 30 minutes, chlorinated water up to 10ppm, and surfaces for days to weeks.

Explosive vomiting
WHO/ClinicalProjectile vomiting — a hallmark of norovirus gastroenteritis — generates contaminated aerosols that can infect others within 2 metres. In hospital wards, a single vomiting patient can initiate a ward-wide outbreak. This aerial spread is why norovirus is so difficult to contain in institutional settings even with good hygiene.

Herd immunity and norovirus
WHO/ResearchNatural norovirus infection generates short-lived immunity (approximately 6-24 months) to specific strains — not cross-protective against all norovirus strains. This means reinfection is common throughout life. The lack of durable, cross-protective immunity makes vaccine development challenging.

FUT2 gene (Secretor status)
ResearchApproximately 20% of people are non-secretors — they lack the FUT2 gene encoding the enzyme that places histo-blood group antigens (HBGA) on gastrointestinal mucosa. Non-secretors are naturally resistant to most GII norovirus strains (which use HBGA as a receptor). This provides a natural protection that has genetic population significance.

Bleach for norovirus disinfection
WHO/Infection controlNorovirus is resistant to many common disinfectants, including alcohol-based hand gels at standard concentrations (60-70% ethanol — less effective than for bacteria). Key disinfection agents: 1,000-5,000 ppm sodium hypochlorite (household bleach diluted 1:10 to 1:50) for environmental surfaces. Soap and water handwashing (physical removal of virus) is more effective than alcohol gel for norovirus.

mRNA norovirus vaccine (Moderna)
Research/Phase 2An mRNA vaccine encoding the VP1 capsid protein of the dominant GII.4 genotype — in Phase 2 clinical trials as of 2024. Challenge study data (administering norovirus to healthy volunteers after vaccination) showed approximately 79% protection against infection and 84% against moderate/severe disease.