Norovirus is a small, non-enveloped RNA virus that causes acute gastroenteritis: vomiting, diarrhea, stomach cramps, and sometimes low-grade fever, lasting 1 to 3 days. CDC estimates 19 to 21 million US cases per year, making it the most common cause of foodborne illness outbreaks in the country. Severe disease and dehydration risk concentrate in young children, adults over 65, and immunocompromised people. The infectious dose is brutally low. A 2008 human challenge study by Atmar et al. found ID50 around 18 viral particles for the GI.1 Norwalk strain, which puts norovirus in a different class from most pathogens you encounter day to day.

That low infectious dose plus environmental hardiness plus prolific shedding (a sick person can release billions of particles per gram of stool) is what makes norovirus rip through cruise ships, schools, daycares, and households. Standard alcohol-based hand sanitizer has minimal effect. Most household disinfectants don't work either. Stopping a household outbreak takes deliberate technique, and most people get parts of it wrong. Norovirus precautions sit alongside the rest of the infection prevention toolkit, with disinfectant chemistry and hand hygiene doing more work than masks for this pathogen.

Key Takeaways

What is norovirus and why is it so contagious?

Norovirus is a non-enveloped RNA virus that causes acute gastroenteritis with sudden vomiting and diarrhea. It spreads through tiny doses, survives on surfaces and in food for days to weeks, resists most household cleaners, and infected people shed enormous viral loads in vomit and stool. The Atmar et al. 2008 human challenge study estimated an ID50 around 18 viral particles for the GI.1 Norwalk strain, against shedding of billions of particles per gram of stool.

Non-enveloped means norovirus has no lipid membrane. Alcohol-based sanitizers and many quaternary ammonium cleaners work by disrupting that lipid envelope, which is why they crush enveloped viruses like flu, COVID, and RSV but barely touch norovirus. Bleach, hydrogen peroxide at the right concentration, and physical removal with soap and water are what work.

Different genotypes circulate in any given year. The dominant US strain in recent winters has been GII.4 Sydney and its descendants. Infection produces only short-lived protection, often less than a year, and protection is largely strain-specific, which is why people can catch norovirus repeatedly. A vaccine candidate from Moderna entered phase 3 trials in 2024 but is not yet approved.

How does norovirus spread?

Norovirus spreads through fecal-oral transmission via contaminated food, contaminated water, surfaces touched after the bathroom, person-to-person contact, and aerosols generated during vomiting. The infectious dose is so low that any break in hand hygiene can transmit. A single contaminated food handler can infect dozens at a buffet, and a vomiting episode can leave airborne particles that contaminate a room.

Foodborne outbreaks are the largest category. Raw oysters, leafy greens, and any cold prepared food (sandwiches, salads, deli platters) handled by an asymptomatic shedder are classic vehicles. The 2024 US outbreak data continued the multi-decade trend of leafy greens and shellfish leading reported sources, per CDC's National Outbreak Reporting System.

Surfaces matter more for norovirus than for most viruses. Doorknobs, faucet handles, remote controls, phones, and bathroom fixtures all pick up viral particles from poorly washed hands. Norovirus survives on stainless steel and plastic for at least 2 weeks. Our foodborne disease outbreaks post covers the broader picture of contamination paths.

What disinfectants actually work against norovirus?

Bleach at 1,000 to 5,000 ppm sodium hypochlorite with at least 5 minutes of contact time is the EPA and CDC reference standard. Hydrogen peroxide-based cleaners on EPA's List G also work. Alcohol, quaternary ammonium compounds (the common kitchen sanitizers), and most "kills 99.9% of germs" labels do not include norovirus in their tested pathogens.

Mixing bleach correctly: 5 tablespoons of regular 5.25% household bleach per gallon of water gives roughly 1,000 ppm, which is the minimum for hard non-porous surfaces with no visible soiling. For surfaces with vomit or stool, scale to 5,000 ppm (about 25 tablespoons per gallon) and clean visible contamination first with disposable paper towels.

Bleach loses potency over time and breaks down faster in heat. Keep it in the original opaque container, replace any bottle older than 12 months, and mix the working solution fresh each time. The contact time matters. Wiping bleach on and off in 30 seconds doesn't kill norovirus. Spray the solution on, leave it visibly wet for 5 to 10 minutes, then wipe.

How to disinfect a home after a norovirus exposure

Follow the 6-step procedure embedded as structured data on this page (gloves and mask, paper-towel removal of contamination, bleach at correct concentration, 5-minute minimum contact, hot-water laundry, hand washing). Do this any time someone vomits or has diarrhea on a surface, and again as a routine clean of high-touch points each day during illness in the household.

A few real-world pitfalls. Carpets and upholstery are difficult because bleach damages fabric. EPA-registered hydrogen peroxide cleaners (List G) are the better option for porous surfaces. Steam cleaning at sustained 70°C+ also works but takes longer. Soft toys and cloth items go straight in the laundry on hot. Anything that can't be cleaned reliably should be discarded.

Phones, remote controls, and doorknobs are the usually-missed surfaces. Wipe them with a disinfectant safe for electronics, or a cloth lightly dampened with hydrogen peroxide solution for screens. Toilets, faucet handles, and the floor around the toilet need full bleach treatment after every illness episode in that bathroom. The home isolation guide covers room layout for ongoing illness.

How do you stop it spreading inside a household?

Pick one bathroom for the sick person, mask both the patient and caregiver during direct care, dedicate cleaning supplies and laundry to the sick room, and continue strict precautions for at least 48 hours after symptoms stop. Do not let the recovered person handle food for anyone else for at least 3 days, and ideally 7. Viral shedding outlasts symptoms by days to weeks.

Isolation in shared spaces is the hardest part. If you only have one bathroom, the sick person uses it, then the surfaces get bleach-cleaned before anyone else enters. Toothbrushes go in separate cups. Towels are not shared, and the sick person's towels go in the wash on hot daily. Soap-and-water hand hygiene every time anyone leaves the bathroom is the single most useful intervention.

Children and elderly household members are the highest priority for protection because they dehydrate fastest. Push fluids on the sick person (oral rehydration solution beats water or sports drinks) and watch for signs of severe dehydration: dark urine, dizziness on standing, lethargy. Most norovirus illness resolves at home, but hospitalization for IV fluids is appropriate when oral intake fails.

FAQ

How long is norovirus contagious after symptoms stop?

People remain measurably contagious for at least 48 hours after vomiting and diarrhea stop, and viral shedding can continue for up to 2 weeks at lower levels. The 48-hour minimum is why food handlers, healthcare workers, and childcare staff are excluded from work for that long after recovery. Hand hygiene matters for the full shedding window.

Why doesn't hand sanitizer work against norovirus?

Norovirus is non-enveloped, meaning it has no lipid membrane. Alcohol-based sanitizers work primarily by disrupting that envelope. Without it, alcohol has minimal effect on viral structure. Soap and water for 20 seconds physically removes the virus from skin even without inactivating it. CDC recommends soap-and-water as the only reliable option during norovirus outbreaks.

Can you get norovirus more than once?

Yes, repeatedly. Immunity from natural infection is short and largely strain-specific. Different norovirus genotypes circulate each season, and reinfection within the same year is possible. People with blood type O appear slightly more susceptible than other types. There is no licensed vaccine yet, though candidates are in late-stage trials.

Should you go to the hospital for norovirus?

Most cases resolve at home in 1 to 3 days with oral rehydration. Seek emergency care for signs of severe dehydration (no urine for 8+ hours, dizziness, confusion), inability to keep fluids down for more than 24 hours, blood in stool or vomit, or in any infant under 1 year with persistent vomiting. Older adults and immunocompromised people have lower thresholds for medical care.

Can you cook norovirus out of food?

Norovirus is heat-stable up to about 60°C. Standard cooking temperatures (above 70°C internal) inactivate it, but warm food kept at intermediate temperatures stays infectious. Steaming oysters until shells open is not enough. Cold prepared foods, salads, and lightly cooked items are the highest-risk vehicles. CDC tracks oyster-related outbreaks each year as a recurring source.