Norovirus is a highly contagious virus that infects the lining of your intestines, causing sudden vomiting and diarrhea. It’s the leading cause of foodborne illness in the United States, responsible for an estimated 19 to 21 million infections every year. Often called the “stomach flu” or “stomach bug,” norovirus has nothing to do with influenza. It’s a distinct virus with some remarkable traits that make it exceptionally good at spreading.
How Norovirus Spreads
Norovirus is one of the most infectious pathogens known. An estimated dose as low as 18 viral particles can cause a full infection, which is an almost impossibly small number. For comparison, a single drop of stool from an infected person contains billions of viral particles. This extreme infectivity explains why norovirus tears through households, cruise ships, nursing homes, and schools so quickly.
The virus spreads through direct contact with an infected person, contaminated food or water, and contaminated surfaces. Touching a doorknob or countertop that someone with norovirus touched hours (or even days) earlier, then touching your mouth, is enough. In laboratory studies, norovirus remained detectable on airplane cabin surfaces like plastic tray tables, leather seats, and seat belts for the entire 30-day study period. That kind of environmental durability is a major reason outbreaks are hard to contain.
A person sheds the virus most heavily while symptomatic, but can continue spreading it for days or even weeks after feeling better.
Symptoms and Timeline
Symptoms typically hit between 12 and 48 hours after exposure. The onset is often abrupt: you may feel fine one hour and be vomiting the next. The hallmark symptoms are nausea, vomiting, watery diarrhea, and stomach cramps. Some people also develop a low-grade fever, headache, body aches, and fatigue.
The acute illness usually lasts one to three days. Most healthy adults recover fully without treatment. The main risk is dehydration, especially in young children, older adults, and people with weakened immune systems, who may need medical attention for fluid replacement. Vomiting and diarrhea together can drain the body’s fluids quickly, so steady sipping of water or an oral rehydration solution matters.
Why It’s So Hard to Kill
Norovirus lacks an outer fatty envelope, which is the feature that makes many other viruses vulnerable to alcohol. Most alcohol-based hand sanitizers work by dissolving that lipid coating. Since norovirus doesn’t have one, standard hand sanitizer is far less effective against it. Research shows that ethanol can damage the virus’s protein shell but leaves its genetic material intact, meaning the virus can still potentially cause infection.
Soap and water is the recommended hand hygiene method during a norovirus outbreak. The mechanical action of rubbing and rinsing physically removes viral particles from your skin, even if it doesn’t chemically destroy them.
For surfaces, regular household cleaners often aren’t enough. A bleach solution at a concentration of at least 1,000 parts per million of sodium hypochlorite (roughly 5 tablespoons of standard household bleach per gallon of water), prepared fresh daily, is the standard recommendation for disinfecting contaminated areas. That concentration reliably reduces norovirus on surfaces by more than 99.9%.
Peak Season and Who’s at Risk
Norovirus outbreaks happen year-round, but the peak season runs from November through April in the United States. During those months, the virus causes roughly 109,000 hospitalizations annually. Anyone can get norovirus, and unlike some infections, having it once does not give you lasting immunity. The virus comes in many genetically distinct strains, and protection from one strain doesn’t reliably extend to others. Most people will have norovirus multiple times throughout their lives.
Children under five and adults over 65 face the highest risk of severe dehydration and hospitalization. People with compromised immune systems can experience prolonged illness lasting weeks or months rather than the typical few days.
How Norovirus Is Diagnosed
Most norovirus infections are diagnosed based on symptoms alone, especially during known outbreaks. When lab confirmation is needed, the preferred method is a molecular test that detects the virus’s genetic material in stool or vomit samples. These tests are extremely sensitive, picking up as few as 10 to 100 copies of the virus.
Rapid antigen tests that deliver faster results do exist, but they miss 25% to 50% of true infections. They’re sometimes used as a first screening step during outbreaks, but a negative result on a rapid test should be followed up with the more sensitive molecular test before ruling norovirus out.
Treatment
There is no antiviral medication for norovirus. Treatment focuses entirely on replacing lost fluids and electrolytes. For most people, that means drinking plenty of water, broth, or oral rehydration solutions and resting until the illness passes. Severe dehydration, particularly in very young children or elderly adults, sometimes requires intravenous fluids in a medical setting.
Anti-nausea and anti-diarrheal medications can help manage symptoms but don’t shorten the course of the illness. The virus simply has to run its course while your immune system clears it.
How to Protect Yourself
Wash your hands thoroughly with soap and water, especially after using the bathroom, changing diapers, and before preparing or eating food. This is one of the few infections where hand sanitizer is genuinely not a good substitute.
During an active outbreak in your household, clean contaminated surfaces immediately with a fresh bleach solution. Wash soiled laundry at the highest temperature the fabric allows and dry it on high heat. If someone in your home is sick, try to designate a separate bathroom for them if possible, and avoid sharing towels or utensils.
With food, thoroughly wash fruits and vegetables, cook shellfish to an internal temperature of at least 145°F, and avoid preparing food for others while you’re symptomatic and for at least two days after symptoms stop.
Vaccines on the Horizon
No approved vaccine for norovirus currently exists, but one candidate is in a large Phase 3 clinical trial involving nearly 38,000 participants. The vaccine uses mRNA technology, the same platform behind recent COVID-19 vaccines, and targets the most common norovirus strains. If the trial demonstrates safety and efficacy, it could become the first norovirus vaccine available to adults.