Gastroenteritis is an inflammation of the lining of your stomach and intestines, and it’s one of the most common acute illnesses adults experience. It causes diarrhea, vomiting, or both, and most cases resolve on their own within a few days. While people often call it the “stomach flu,” it has nothing to do with influenza.
What Causes Gastroenteritis
Viruses are the most frequent culprit. Norovirus is the leading cause of vomiting and diarrhea from acute gastroenteritis among people of all ages in the United States, and it’s responsible for about 1 in 5 cases of acute gastroenteritis worldwide. It’s also behind 58% of foodborne illness in the U.S., making it the top cause of food poisoning.
Bacteria account for a smaller but often more severe share of cases. Campylobacter is one of the most common causes of bacterial diarrheal illness, and Salmonella is another frequent offender. You pick up bacterial gastroenteritis from undercooked meat, contaminated water, or contact with infected animals. Parasites, certain medications, and chemical contaminants in food or water can also trigger it.
When the cause is something you ate or drank, whether viral, bacterial, parasitic, or chemical, the illness is classified as food poisoning. The distinction matters mainly because bacterial and parasitic infections sometimes need targeted treatment, while viral gastroenteritis does not.
Symptoms and How Long They Last
The hallmark symptoms are watery diarrhea, nausea, vomiting, and stomach cramps. Many people also feel feverish, achy, and generally wiped out. Viral gastroenteritis tends to come on suddenly and resolve within one to three days, though some cases drag on longer.
Bacterial infections often produce more intense symptoms. Campylobacter, for example, typically causes diarrhea (sometimes bloody), fever, stomach cramps, and nausea. Symptoms usually start two to five days after exposure and last about a week. Bloody diarrhea is a key signal that bacteria, rather than a virus, may be involved.
Dehydration: The Main Risk
The illness itself is rarely dangerous for otherwise healthy adults. The real threat is dehydration from losing fluids faster than you replace them. Signs to watch for include dark urine, dry mouth, dizziness when standing, and producing very little urine. Older adults and people with chronic health conditions are at higher risk because their bodies have less reserve to handle rapid fluid loss.
Replacing lost fluids and electrolytes is the single most important thing you can do. Water alone isn’t ideal because it doesn’t replace the sodium and potassium you’re losing. Oral rehydration solutions, available at most pharmacies and grocery stores, are designed to optimize fluid absorption in the gut by pairing sodium with glucose at a ratio that helps your intestines pull water back in efficiently. Sports drinks are a second-choice option since they contain more sugar and less sodium than your body needs, but they’re better than plain water if a rehydration solution isn’t available. Clear broths and diluted fruit juices also help.
Take small, frequent sips rather than gulping large amounts, especially if you’re still vomiting. Your stomach tolerates small volumes much better during the acute phase.
What to Eat During Recovery
You may have heard of the BRAT diet (bananas, rice, applesauce, toast) as the go-to recommendation. Current evidence doesn’t support restricting your diet this way. The National Institute of Diabetes and Digestive and Kidney Diseases states that research shows following a restricted diet does not help treat viral gastroenteritis, and most experts no longer recommend fasting or eating only bland foods.
The practical advice is simpler: when your appetite comes back, return to your normal diet, even if you still have some diarrhea. Your intestines recover faster with regular nutrition. That said, many people naturally gravitate toward plainer foods because rich, fatty, or heavily spiced meals just don’t sound appealing when your gut is irritated. Follow your instincts, but don’t feel you need to limit yourself to crackers and rice.
Over-the-Counter Medications
Anti-diarrheal medications can reduce the frequency of loose stools and make the illness more manageable. The most common option works by slowing intestinal movement, giving your gut more time to absorb water. For acute diarrhea, the typical approach is two tablets or capsules after the first loose bowel movement, then one after each subsequent episode, up to a daily maximum.
There are important limits. You should not use anti-diarrheal medication for more than two days for acute diarrhea unless a doctor advises otherwise. These medications should be avoided entirely if you have bloody diarrhea or a high fever, both of which suggest an infection your body may need to clear rather than slow down. If diarrhea doesn’t improve after two days or a fever develops, that’s a signal to get medical input.
Warning Signs That Need Attention
Most adults recover at home without complications. But certain symptoms suggest something more serious is going on:
- Vomiting lasting more than two days
- Diarrhea persisting more than several days
- Bloody diarrhea
- Fever above 102°F (39°C)
Any of these warrants a call to your doctor or a visit to urgent care. Bloody stool in particular can indicate a bacterial infection like Campylobacter or Salmonella that may need testing and, in some cases, antibiotics. Prolonged vomiting that prevents you from keeping any fluids down is the fastest route to dangerous dehydration.
How It Spreads and How to Prevent It
Norovirus is notoriously contagious. It spreads through direct contact with an infected person, contaminated food or water, and contaminated surfaces. The virus can survive on countertops, doorknobs, and other hard surfaces for days.
Handwashing is the most effective prevention. Use soap and water rather than alcohol-based hand sanitizer, since norovirus is resistant to many sanitizers. Wash thoroughly for at least 20 seconds, especially after using the bathroom, changing diapers, and before preparing food.
If someone in your household is sick, disinfect surfaces with a chlorine bleach solution: 5 to 25 tablespoons of standard household bleach (5% to 8% concentration) per gallon of water, according to CDC guidelines. This is significantly stronger than typical household cleaning concentrations because norovirus is hardy. You can also use EPA-registered disinfectants specifically labeled as effective against norovirus. Wash contaminated clothing and linens on the hottest setting and dry them thoroughly.
For bacterial gastroenteritis, safe food handling is your best defense. Cook meat to recommended internal temperatures, keep raw and cooked foods separate, refrigerate leftovers promptly, and be cautious with unpasteurized dairy and untreated water when traveling.