Norovirus: Why It's the Most Common Cause of Food Poisoning

The CDC estimates that norovirus causes 19 to 21 million illnesses in the United States every year. That makes it the single most common cause of foodborne disease by sheer volume. It accounts for roughly 56% of all foodborne illness outbreaks with a known cause. And yet most people have never thought about how it actually spreads.

Most people think of it as the “stomach flu.” It isn’t a flu at all. And understanding how it actually moves through food explains why certain prevention steps matter so much.

What Norovirus Is (and Isn’t)

Norovirus is a virus, not a bacterium. This distinction changes everything about how it behaves.

Bacteria grow and multiply in food. Norovirus does not. It simply contaminates food and sits there. You don’t need a large bacterial colony to get sick. You need as few as 18 viral particles — a dose so small it’s essentially invisible and undetectable without lab equipment.

Because it doesn’t multiply in food, there’s no “safe” window where contaminated food becomes more or less risky over time. Once it’s there, it’s there.

Norovirus also doesn’t produce toxins. It infects the cells lining your small intestine, disrupting water and electrolyte absorption and triggering rapid gastric emptying — which is the medical description of what you experience as sudden, forceful vomiting.

Symptoms and Timeline

The onset is fast and unmistakable. Within 12 to 48 hours after exposure:

• Sudden nausea followed by vomiting (often the dominant symptom)
• Watery diarrhea
• Stomach cramping
• Low-grade fever, muscle aches, and headache in some cases

The illness lasts 1 to 3 days in otherwise healthy adults. Dehydration is the main risk. For elderly adults, young children, and people with compromised immune systems, dehydration can be serious enough to require hospitalization. The CDC attributes roughly 900 norovirus deaths per year in the US, primarily among the elderly.

How It Gets into Food

Norovirus has two main routes into the food supply.

The first is contaminated water. Shellfish, especially oysters, are filter feeders. A single oyster filters up to 50 gallons of water per day, concentrating whatever is in that water — including norovirus particles from sewage contamination — directly into their tissue. You can’t tell from looking at an oyster whether it came from contaminated water. The contamination is internal.

The second route is an infected food handler. This is the most common source of restaurant outbreaks. A person with norovirus (or who recently had it) handles food without adequate handwashing and transfers virus onto ready-to-eat items. A single infected worker contaminating a salad bar or sandwich station can cause dozens of illnesses.

Raw produce is another vehicle. Contaminated irrigation water, processing plant workers, or contaminated surfaces at any point in the supply chain can introduce norovirus onto fruits, vegetables, or leafy greens.

The Hand Sanitizer Gap

This is the thing most people get wrong. Alcohol-based hand sanitizers — the standard product found in most restaurants and public spaces — do not reliably kill norovirus.

The reason comes down to viral structure. Enveloped viruses like influenza have a lipid (fat) membrane around their protein coat. Alcohol dissolves that membrane and destroys the virus. Norovirus is a non-enveloped virus. It has no lipid membrane. Its outer protein shell is resistant to alcohol at the concentrations found in consumer hand sanitizers.

Soap and water works differently. The mechanical action of scrubbing for 20 seconds physically removes viral particles from skin and rinses them down the drain. Soap helps break the surface tension that keeps particles adhered to skin.

This is why food safety authorities recommend soap and water specifically, not “soap and water or hand sanitizer.” For norovirus, they’re not equivalent.

Does Cooking Kill It?

Yes. Norovirus is inactivated by sustained heat at 145°F (63°C) or above. Cooking food to proper temperatures destroys any norovirus in the food at the time of cooking.

The scenario that causes most restaurant illnesses isn’t undercooked food. It’s re-contamination after cooking. A fully cooked chicken dish, plated by a worker who hasn’t washed their hands since touching their face or using the bathroom, is a norovirus delivery vehicle. The cooking step was fine. The serving step wasn’t.

This is why policies requiring sick employees to stay home matter so much. No amount of cooking a completed meal eliminates the risk of contamination at the point of service.

Disinfection After an Outbreak

Standard kitchen cleaners and disinfectants often fall short against norovirus. The protein shell that resists alcohol also resists many commercial cleaning products not specifically rated for norovirus.

The CDC recommends chlorine bleach solutions at a concentration of 1,000 to 5,000 ppm (5 to 25 tablespoons of household bleach per gallon of water) for disinfecting surfaces after a norovirus illness. EPA-registered disinfectants specifically tested against norovirus are another option — look for “norovirus” on the product label’s list of pathogens.

Vomit and diarrhea from a norovirus patient can contain billions of viral particles. Clean up spills immediately with disposable gloves and paper towels, discard them directly into a sealed bag, and then disinfect the area.

The Cross-Contamination Picture

Norovirus follows the same cross-contamination pathways as bacterial pathogens — infected hands touching food, contaminated surfaces transferring to food, raw shellfish contaminating nearby prep surfaces. The cross-contamination article covers these pathways in detail.

The difference is the infectious dose. For Salmonella, you typically need thousands to millions of bacteria to establish infection. For norovirus, you need fewer than 20 particles. That changes the risk calculus of what counts as “adequate” cleanup.

The food safety fundamentals framework applies here, but with one adjustment for norovirus: hand sanitizer cannot replace handwashing. For everything else on that list — refrigeration, cook temperatures, clean surfaces — the same rules apply.