Viral gastroenteritis is an infection of the intestines caused by a virus, leading to watery diarrhea, vomiting, stomach cramps, and sometimes fever. Often called the “stomach flu” (though it has nothing to do with influenza), it affects 19 to 21 million people in the United States each year from norovirus alone. Most cases resolve on their own within a few days, but dehydration is the main risk, especially for young children and older adults.
Which Viruses Cause It
Four viruses account for the vast majority of cases. Norovirus is the biggest one, responsible for about 50% of all viral gastroenteritis cases worldwide and more than 90% of outbreak-related cases. It hits people of all ages and is the reason behind most of those fast-moving stomach bugs that tear through cruise ships, schools, and nursing homes.
Rotavirus was historically the leading cause of severe diarrheal illness in infants and young children. Since the introduction of the rotavirus vaccine, its impact has dropped dramatically in countries with high vaccination rates, but it still causes an estimated 215,000 deaths per year globally, mostly in young children in lower-income countries. Adenovirus and astrovirus together account for roughly 2% to 9% of cases and primarily affect infants and young children, though adults can get them too.
How It Spreads
The primary route is fecal-oral transmission, which sounds alarming but happens more easily than you might expect. Microscopic particles of stool or vomit from an infected person end up on hands, surfaces, food, or water. From there, the virus reaches your mouth through direct contact, contaminated meals, or even tiny airborne droplets released when someone nearby vomits.
Specific ways this plays out in real life: an infected food handler touches your meal with bare hands, contaminated water irrigates produce in the field, a sick child touches a doorknob that you later touch before eating. Shellfish, particularly oysters, can harbor the virus when harvested from contaminated water. These viruses are also remarkably stable on surfaces, which is why outbreaks spread so efficiently in shared spaces like daycare centers, dormitories, and restaurants.
Symptoms and Timeline
The time between exposure and symptoms varies by virus. Norovirus is the fastest, with symptoms appearing 12 to 48 hours after contact. Rotavirus takes about 2 days. Adenovirus has a longer window of 3 to 10 days, and astrovirus typically shows up after 4 to 5 days.
Once symptoms start, expect some combination of watery diarrhea, nausea, vomiting, stomach cramps, and possibly a low-grade fever. The duration also depends on the virus:
- Norovirus: 1 to 3 days
- Rotavirus: 3 to 8 days
- Adenovirus: 1 to 2 weeks
- Astrovirus: 1 to 4 days
Norovirus tends to hit hard and fast, with intense vomiting that can come on suddenly. Rotavirus illness generally lasts longer and is more likely to cause significant dehydration in small children. Adenovirus infections can drag on for up to two weeks, which often catches people off guard.
Dehydration: The Real Danger
The virus itself isn’t usually life-threatening in otherwise healthy people. The danger comes from losing too much fluid through vomiting and diarrhea. In adults, early signs of dehydration include intense thirst, dark-colored urine, dry mouth, urinating less than usual, fatigue, and dizziness. These are your body’s signals to increase fluid intake aggressively.
In infants and young children, the warning signs look different. Watch for a dry mouth and tongue, crying without tears, no wet diapers for three hours or more, sunken-looking eyes, unusual sleepiness, and irritability. Children dehydrate faster than adults because of their smaller body size, so these signs can progress quickly.
Severe dehydration is a medical emergency. Signs include confusion, fainting, rapid heartbeat, rapid breathing, and little to no urination. Norovirus alone accounts for roughly 109,000 hospitalizations per year in the U.S., and dehydration is the primary reason people end up needing that level of care.
Treatment and Recovery
There is no antiviral medication for gastroenteritis. Treatment centers on replacing lost fluids and electrolytes while the virus runs its course. For most people, this means drinking plenty of water, broth, or an oral rehydration solution. These solutions contain a balanced mix of salts, sugars, and water that your intestines can absorb even during active illness. You can find them over the counter at most pharmacies.
Small, frequent sips work better than gulping large amounts, especially if vomiting is ongoing. Ice chips or popsicles can help when keeping liquids down feels difficult. Avoid sugary drinks like soda and undiluted fruit juice, which can actually worsen diarrhea by pulling more water into the intestines.
One outdated piece of advice worth correcting: the BRAT diet (bananas, rice, applesauce, and toast) was long recommended during recovery, but the CDC has noted that it’s unnecessarily restrictive and provides suboptimal nutrition for a recovering gut. Withholding food for more than 24 hours is also inappropriate and can lead to malnutrition, particularly in children. Current guidance recommends returning to a normal, age-appropriate diet as quickly as possible after rehydration. Complex carbohydrates, lean meats, yogurt, fruits, and vegetables are all fine. Early feeding actually shortens illness duration and improves nutritional outcomes.
How to Prevent It
Handwashing is the single most effective defense. Wash with soap and water for at least 20 seconds, particularly after using the bathroom, changing diapers, and before preparing or eating food. Alcohol-based hand sanitizers are less effective against norovirus than soap and water, so don’t rely on them as your only method.
When someone in your household is sick, cleaning contaminated surfaces matters. Standard household cleaners may not be enough. The CDC recommends a chlorine bleach solution of 5 to 25 tablespoons of household bleach (5% to 8% concentration) per gallon of water, left on the surface for at least five minutes. You can also use an EPA-registered disinfectant specifically labeled as effective against norovirus. Wash any contaminated clothing or linens promptly, using the longest available wash cycle.
For children, the rotavirus vaccine has been a major public health success. Modeling studies in Asia projected that widespread vaccination could prevent more than 710,000 hospitalizations and 35,000 deaths, representing a roughly 49% reduction in rotavirus-related hospitalizations. In the U.S. and other countries with high vaccine uptake, rotavirus has gone from the leading cause of severe infant diarrhea to a relatively uncommon one. There is currently no vaccine available for norovirus.
If you’re sick, avoid preparing food for others and try to stay home for at least two days after symptoms resolve. You can still shed the virus for days after feeling better, so continued handwashing during that window helps protect the people around you.