Norovirus is a highly contagious stomach bug that causes sudden vomiting and diarrhea, typically lasting one to three days. It belongs to the Caliciviridae family and carries a small RNA genome, which mutates frequently enough to produce new strains every few years. That constant shape-shifting is one reason norovirus remains the leading cause of acute gastroenteritis worldwide, responsible for over 70,000 hospitalizations and roughly 800 deaths in the United States each year.
Why Norovirus Spreads So Easily
Norovirus is remarkably efficient at infecting people. As few as 18 viral particles can cause illness, while a single gram of stool from an infected person can contain billions of infectious doses. That extreme mismatch between what it takes to get sick and how much virus a sick person produces is the core reason outbreaks move so fast through households, cruise ships, schools, and nursing homes.
The virus spreads through several routes. The most common is the fecal-oral route: microscopic particles of stool or vomit from an infected person end up in someone else’s mouth. That can happen through direct contact, contaminated food, shared surfaces, or contaminated water. Aerosolized vomit plays a surprisingly important role. When a person with norovirus vomits, tiny droplets spray through the air, land on nearby surfaces or food, and can even enter another person’s mouth directly. This is why a single vomiting episode in a shared space like a restaurant or dormitory can trigger a wave of new infections.
Food becomes contaminated when an infected person handles it with bare hands, when it sits on a contaminated surface, or when it’s grown or harvested in contaminated water. Oysters are a well-known example because they filter large volumes of water and concentrate the virus. Drinking water and recreational water can also carry norovirus when sewage systems fail or when an infected person vomits or has diarrhea in the water.
Symptoms and Timeline
Symptoms hit fast. The incubation period is 12 to 48 hours after exposure, and the onset is abrupt. The hallmark signs are nausea, vomiting, watery diarrhea, and stomach cramps. Some people develop a low-grade fever and muscle aches. The diarrhea is typically non-bloody.
Most healthy adults and children recover fully within one to three days without medical treatment. The illness feels miserable but resolves on its own. The main risk during that window is dehydration from fluid loss through vomiting and diarrhea, especially in young children and older adults who may not be able to replace fluids quickly enough.
Who Faces Serious Risk
People of all ages get norovirus, but the virus hits hardest at the extremes of age and in those with weakened immune systems. Older adults face the greatest danger. Some studies show a 30-day mortality rate of 7% for older patients with community-acquired norovirus infection. Newborns are also vulnerable to serious complications. People with compromised immune systems experience higher rates of complications, more severe illness, and can continue shedding the virus for weeks or months without showing symptoms, silently spreading it to others.
Dehydration is the primary cause of hospitalization and death. For most people, drinking enough fluids to replace what’s lost is sufficient. But for vulnerable groups, the rapid fluid loss can become dangerous quickly.
Why You Can Get It More Than Once
Unlike some viruses that grant lasting immunity after a single infection, norovirus offers only temporary protection. After recovering, your immune system recognizes the strain that infected you, but that protection fades over time. Worse, it provides limited defense against different strains. Research has shown that people recently infected with one strain are susceptible to a different strain much sooner than they are to the same one.
The virus also evolves to dodge population immunity. The most common group of noroviruses, known as GII.4, produces new variants every few years that are different enough to slip past antibodies built up from earlier infections. This is similar to how flu strains shift over time, and it’s a major reason norovirus continues to cause widespread outbreaks year after year.
Prevention That Actually Works
There is no vaccine for norovirus, so prevention comes down to hygiene and environmental cleaning. The single most important step is washing your hands thoroughly with soap and water, especially after using the bathroom, changing diapers, and before preparing food. Alcohol-based hand sanitizers do not work well against norovirus. You can use them as a supplement, but they are not a substitute for soap and water. This is one of the most common mistakes people make during outbreaks.
When cleaning up after someone who’s been sick, surfaces need to be disinfected with a bleach-based cleaner. Standard household cleaners may not be strong enough. The CDC recommends a chlorine bleach solution for hard surfaces where vomit or diarrhea has contacted. Contaminated laundry should be handled carefully (avoiding shaking it, which can aerosolize particles) and washed on the longest, hottest cycle available.
If someone in your household is infected, try to isolate them from food preparation areas. Fruits and vegetables should be rinsed thoroughly, and shellfish should be cooked to an internal temperature high enough to inactivate the virus. Because the virus can survive on surfaces for days, wiping down commonly touched objects like doorknobs, light switches, and toilet handles is critical during and after an illness.
Viral Shedding After Recovery
One of the trickiest things about norovirus is that people continue to shed the virus in their stool well after they feel better. While symptoms resolve in one to three days, viral particles can remain in stool for two weeks or longer. People with weakened immune systems may shed the virus for months. This means someone who feels completely healthy can still contaminate food or surfaces if they aren’t careful about hand hygiene. It’s a major driver of secondary infections within families and institutional settings like hospitals and long-term care facilities.