The stomach bug, known medically as viral gastroenteritis, is an infection of the intestines caused by a virus. It’s not actually related to influenza despite being called the “stomach flu.” The hallmark symptoms are watery diarrhea, vomiting, and nausea, and most people recover fully within one to three days without any specific treatment.
What Causes It
Several viruses can trigger the stomach bug, but norovirus is by far the most common culprit. It affects people of all ages and is especially likely to tear through groups in confined spaces like cruise ships, dorms, and daycare centers. Symptoms typically appear 12 to 48 hours after exposure and last one to three days.
Rotavirus is the leading cause in young children worldwide, usually spreading when kids put contaminated fingers or objects in their mouths. Its symptoms take about two days to show up and can last three to eight days, which is notably longer than norovirus. Vaccines now prevent most rotavirus infections in children. Two less common viruses, adenovirus and astrovirus, primarily affect infants and young children but can occasionally hit adults. Adenovirus infections tend to linger the longest, sometimes up to two weeks.
Symptoms and What to Expect
Diarrhea is the dominant symptom, often watery and frequent. Vomiting and nausea usually accompany it, especially in the first 24 hours. Many people also develop a low fever, chills, stomach cramps, and body aches. You might feel completely wiped out even after the vomiting stops.
The worst of it typically hits within the first day or two. Most people with norovirus start feeling better within 48 hours. Rotavirus tends to drag on longer, particularly in young children, with symptoms persisting up to a week. During recovery, mild nausea and fatigue can linger for a few days after the acute phase passes.
Stomach Bug vs. Food Poisoning
These two get confused constantly because the symptoms overlap. The biggest clue is timing. Food poisoning hits fast, usually within two to six hours of eating contaminated food. The stomach bug has a longer incubation period of 24 to 48 hours, so you often can’t pinpoint when you were exposed.
The stomach bug also tends to produce more whole-body effects like fever, chills, and muscle aches. Food poisoning is more likely to be intense vomiting and diarrhea without as much systemic misery. Both cause watery diarrhea that can occasionally be bloody, but if you’re running a fever and everyone in your household is getting sick one after another, a virus is the more likely explanation.
How It Spreads
The stomach bug is extremely contagious. It spreads through direct contact with an infected person, touching contaminated surfaces, or eating contaminated food or water. Norovirus in particular is notoriously hardy. Tiny amounts of the virus (as few as 18 viral particles) are enough to cause infection, and an infected person sheds billions of them.
One important detail many people miss: you remain contagious even after you feel better. Viral shedding continues for days after symptoms resolve, which is why outbreaks spread so easily in families and workplaces. Returning to normal activities too soon, especially preparing food for others, is one of the main ways the virus keeps circulating.
Why Dehydration Is the Real Danger
The virus itself is rarely dangerous for otherwise healthy adults. The real risk is dehydration from losing so much fluid through vomiting and diarrhea. This is especially serious for infants, young children, and older adults, whose bodies have less margin for fluid loss.
Signs of dehydration to watch for include dry mouth, dark urine, dizziness when standing, and producing few or no tears when crying (in children). In infants, a sunken soft spot on the head and going six or more hours without a wet diaper are warning signs. Severe dehydration, marked by confusion, rapid heartbeat, or inability to keep any fluids down, requires emergency medical attention.
Staying Hydrated During the Illness
The single most important thing you can do is replace lost fluids. For adults, this means taking small, frequent sips of water, broth, or an electrolyte drink. Gulping large amounts at once often triggers more vomiting, so slow and steady works better.
For children, oral rehydration solutions are the gold standard. As a general guideline, children under 22 pounds should get about 2 to 4 ounces of rehydration solution after each episode of vomiting or diarrhea. Children over that weight need 4 to 8 ounces per episode. The goal is to replace roughly what’s being lost. If a child is mildly to moderately dehydrated, giving rehydration fluid steadily over two to four hours can usually correct the deficit without a trip to the emergency room.
What to Eat While Recovering
You’ve probably heard of the BRAT diet: bananas, rice, applesauce, and toast. It’s a reasonable starting point for the first day or two, but you don’t need to restrict yourself to just those four foods. Brothy soups, oatmeal, boiled potatoes, crackers, and plain dry cereal are all gentle on a recovering stomach and equally easy to digest.
Once you can keep bland foods down, start adding more nutritious options like cooked carrots, sweet potatoes without skin, avocado, skinless chicken or turkey, fish, and eggs. Your body needs protein and nutrients to recover, so staying on plain toast longer than necessary actually slows the process. During the acute phase and for a few days after, avoid dairy products, fried or greasy foods, caffeine, alcohol, acidic foods like citrus and tomato sauce, spicy foods, and high-fiber foods like raw vegetables, nuts, seeds, and beans.
Prevention and Cleaning Up
Handwashing with soap and water is the single best defense against the stomach bug. This is one case where alcohol-based hand sanitizer falls short. Norovirus has a protein shell that makes it resistant to alcohol, so sanitizer alone won’t reliably kill it. Soap and water, scrubbed for at least 20 seconds, physically removes the virus from your hands.
If someone in your home is sick, cleaning contaminated surfaces requires more than a standard wipe-down. The CDC recommends a bleach solution of 5 to 25 tablespoons of household bleach per gallon of water, left on the surface for at least five minutes. Regular household cleaners won’t reliably kill norovirus. Wash contaminated clothing and linens on the hottest water setting available, and try to isolate the sick person’s bathroom if possible.
Rotavirus vaccination has dramatically reduced childhood cases in countries where it’s part of the routine immunization schedule. There’s no vaccine for norovirus yet, so hand hygiene and surface disinfection remain the primary tools for preventing outbreaks.