A stomach virus, often called the “stomach flu,” is an infection of your intestines caused by a virus. Its medical name is viral gastroenteritis. Despite the nickname, it has nothing to do with influenza, which attacks your lungs and respiratory system. A stomach virus targets your digestive tract, causing watery diarrhea, nausea, vomiting, and abdominal cramps that typically last one to three days.
What Causes It
Several viruses can trigger gastroenteritis, but two are responsible for the vast majority of cases. Norovirus is the most common cause of foodborne illness worldwide and affects both children and adults. It spreads rapidly in confined spaces like cruise ships, dormitories, and nursing homes. Rotavirus is the leading cause of stomach virus illness in young children globally, usually spread when kids put contaminated fingers or objects in their mouths. A vaccine for rotavirus, given in two or three doses before 8 months of age, provides 85% to 98% protection against severe illness and prevents an estimated 40,000 to 50,000 hospitalizations among U.S. infants each year.
Symptoms in Adults and Children
The core symptoms are the same regardless of age: watery diarrhea, abdominal pain or cramping, nausea or vomiting, and sometimes fever. Most people feel the worst during the first day or two. Norovirus symptoms typically begin 12 to 48 hours after exposure and last one to three days.
The biggest difference between adults and children isn’t the symptoms themselves but how quickly dehydration sets in. Diarrhea is especially dangerous in newborns and infants, who can become severely dehydrated in just a day or two. In adults, dehydration develops more slowly, but it’s still the most common complication of any stomach virus.
Recognizing Dehydration
In adults, signs of dehydration include extreme thirst, dark-colored urine, urinating less than usual, dizziness or lightheadedness, and feeling unusually tired. You might also notice sunken eyes or cheeks. A simple test: if you pinch the skin on the back of your hand and it doesn’t flatten back to normal right away, you may be dehydrated.
In infants and young children, watch for no wet diapers for three hours or more, no tears when crying, a dry mouth, sunken eyes, and unusual listlessness. These signs warrant immediate medical attention. A dehydrated child can deteriorate within a day if untreated.
Stomach Virus vs. Food Poisoning
Both cause vomiting and diarrhea, so telling them apart can be tricky. The biggest clue is timing. A stomach virus has a 24 to 48 hour incubation period before symptoms start. Food poisoning hits much faster, typically two to six hours after eating contaminated food. Stomach viruses also tend to cause more “systemic” effects like fever and chills, though food poisoning can occasionally cause a low fever too.
If several people who ate the same meal get sick within hours, food poisoning is the likely culprit. If symptoms creep up a day or two later, or if family members fall ill one after another over several days, a virus is more probable.
How It Spreads
Stomach viruses are extremely contagious. They spread through direct contact with an infected person, contaminated food or water, and touching contaminated surfaces. What makes norovirus particularly difficult to contain is the length of its contagious window: you can still spread the virus for two weeks or more after you feel better. That means you can be back at work feeling fine and still passing the virus to others.
One important detail that surprises many people: alcohol-based hand sanitizer does not work well against norovirus. The CDC is clear that soap and water is the only effective way to remove it from your hands. You can use hand sanitizer as an extra step, but it is not a substitute for thorough handwashing.
Treatment and Recovery
There is no medication that kills a stomach virus. Treatment focuses on staying hydrated while your immune system clears the infection. Small, frequent sips of water, clear broths, or oral rehydration solutions work best, especially if you’re vomiting and can’t keep large amounts of fluid down. For infants, continue breast milk or formula as usual.
You may have heard of the BRAT diet (bananas, rice, applesauce, toast) as a go-to recovery plan. Current medical guidance no longer recommends it. Research shows that following a restricted diet does not help treat viral gastroenteritis. Once your appetite returns, you can go back to eating your normal diet, even if you still have some diarrhea. The same applies to children: give them what they normally eat as soon as they’re hungry again. Restricting food delays recovery without providing any benefit.
Warning Signs That Need Medical Attention
Most stomach virus cases resolve on their own within a few days. Adults should seek care if diarrhea lasts more than two days, if they’re having six or more loose stools a day, if they develop a high fever, or if they notice blood or black, tarry stools. A noticeable change in mental clarity, like unusual irritability or confusion, also warrants a doctor’s visit.
For children, the thresholds are lower. Any fever in an infant is a reason to call the doctor. Diarrhea lasting more than one day, frequent vomiting, signs of dehydration, or any change in alertness or energy in a child should be evaluated promptly.