Norovirus spreads mainly through the fecal-oral route, meaning tiny particles of feces or vomit from an infected person get into your mouth. This can happen directly from another person, through contaminated food or water, or by touching contaminated surfaces. The virus is extraordinarily contagious: as few as 18 viral particles can cause an infection, which is why it tears through households, cruise ships, and restaurants so quickly.
Person-to-Person Contact
The most common way to catch norovirus is from someone who already has it. When a person with norovirus vomits, tiny droplets spray into the air and can land on nearby surfaces or directly in another person’s mouth. This aerosolization is one reason the virus spreads so fast in close quarters like dorm rooms or shared hotel bathrooms. Even something as simple as caring for a sick child or cleaning up after someone who vomited can expose you if you touch your face afterward.
You’re most at risk of catching it from someone who is actively symptomatic, especially while they’re vomiting. But infected people remain contagious well beyond the point where they feel better. Viral shedding peaks 2 to 5 days after infection and continues for an average of 4 weeks. That means someone who had symptoms over the weekend can still spread the virus at work the following week, even though they feel fine.
Adding to the problem, roughly 7% of people infected with norovirus never develop symptoms at all. During outbreaks, that number climbs to around 18%. These asymptomatic carriers still shed the virus in their stool and can pass it to others without ever knowing they’re infected.
Contaminated Food
Norovirus is the leading cause of foodborne illness outbreaks, and the foods most commonly involved are leafy greens like lettuce, fresh fruits, and shellfish (especially oysters). Contamination happens in two main ways: at the source or during preparation.
At the source, oysters filter large volumes of water as they feed. If that water contains sewage, the virus concentrates inside the shellfish. Fruits and vegetables can be contaminated if they’re irrigated or rinsed with water carrying the virus. This type of contamination is harder to control because the food arrives already carrying the pathogen, and cooking is the only reliable way to neutralize it.
More frequently, though, contamination happens in kitchens. Infected food workers are the most common source of restaurant and catering outbreaks. A worker who doesn’t wash their hands thoroughly after using the bathroom can transfer the virus to anything they touch, particularly ready-to-eat foods like salads, sandwiches, or sliced fruit that won’t be cooked before serving. Because the infectious dose is so incredibly low, even a trace amount of contamination is enough.
Contaminated Surfaces
Norovirus is remarkably durable outside the body. On hard surfaces at room temperature, it can survive for 21 to 28 days in a dried state. On carpets, the virus has been found to remain viable for up to 12 days even with regular vacuuming. This means a countertop, doorknob, light switch, or toilet handle contaminated by someone with norovirus can be a source of infection for weeks if it’s not properly disinfected.
The cycle works like this: an infected person touches a surface, you touch that same surface, then you touch your mouth, nose, or eat something with your hands. In shared living spaces, this is one of the hardest transmission routes to break because surfaces look clean even when they’re carrying millions of viral particles.
How Quickly Symptoms Appear
After exposure, symptoms typically show up within 12 to 48 hours. The illness usually starts suddenly with nausea, vomiting, watery diarrhea, and stomach cramps. Most people recover within 1 to 3 days, but as noted above, they continue shedding the virus in their stool for weeks afterward. This gap between feeling better and actually being non-contagious is a major driver of ongoing spread.
Why Standard Cleaning Doesn’t Work
One of the reasons norovirus is so persistent is that the usual methods people rely on to kill germs don’t work well against it. Alcohol-based hand sanitizers are not effective at neutralizing norovirus. They can be used as a supplement, but they are not a substitute for washing your hands with soap and water, which physically removes the virus rather than trying to chemically destroy it.
For surfaces, regular household cleaners are not enough. You need a bleach solution, specifically 5 to 25 tablespoons of standard household bleach (5% to 8% concentration) per gallon of water. Alternatively, look for EPA-registered disinfectants specifically labeled as effective against norovirus. Pay particular attention to bathrooms, kitchen surfaces, and any area where vomiting or diarrhea occurred. If someone in your home is sick, disinfect high-touch surfaces like faucet handles, refrigerator doors, and remote controls daily.
Reducing Your Risk
Thorough handwashing is the single most effective defense. Wash with soap and running water for at least 20 seconds, particularly after using the bathroom, changing diapers, and before preparing or eating food. This applies even if you feel perfectly healthy, since asymptomatic carriers are common.
When it comes to food, wash fruits and vegetables thoroughly, and cook shellfish to an internal temperature high enough to kill the virus (steaming oysters until the shells open is not sufficient). If someone in your household is sick, they should avoid preparing food for others not just during their illness but for at least two days after symptoms resolve, and ideally longer given how long shedding continues.
Contaminated laundry, including sheets, towels, and clothing, should be handled carefully. Wear gloves if possible, wash items on the longest available cycle with hot water, and machine dry them. Avoid shaking out soiled linens, which can aerosolize viral particles into the room.