Viral gastroenteritis (stomach flu) is a contagious infection of the stomach and intestines that causes watery diarrhea, nausea, vomiting, cramps, and sometimes fever. It spreads through close contact with infected people or contaminated food, water, and surfaces. Most cases improve in 1–3 days, but dehydration can be dangerous, especially in children and older adults. For stomach flu (viral gastroenteritis), see your primary care doctor (or a pediatrician for kids), and go to urgent care/ER if you can’t keep fluids down or show signs of dehydration.

Most healthy adults recover at home in 1–3 days (sometimes longer), but dehydration can become serious, especially for infants, older adults, and people with weakened immune systems.

What is viral gastroenteritis?

Viral gastroenteritis is inflammation of the stomach and intestines caused by a virus. Despite the nickname “stomach flu,” it is not influenza. Influenza affects the respiratory system (nose, throat, lungs), while gastroenteritis affects the digestive tract.

Common symptoms of stomach flu

People can experience different combinations of symptoms. The most common include:

• Watery diarrhea (often non-bloody)
• Nausea and vomiting
• Stomach cramps or abdominal pain
• Low-grade fever
• Body aches, fatigue, headache

How fast do symptoms start?

Symptoms often begin within 12–72 hours after exposure (timing depends on the virus).

How long does stomach flu last?

Most people feel significantly better in 1–3 days, though symptoms can last longer in some cases (especially in kids or if dehydration develops).

Red flags: When to see a doctor

Use these as “don’t wait” signs.

Adults: get medical care urgently if you have:

• Can’t keep liquids down for 24 hours
• Diarrhea or vomiting lasting more than 2 days
• Signs of dehydration: very dark urine, little/no urination, dizziness, fainting, severe weakness
• Blood in stool or black/tarry stool
• Vomiting blood
• Severe or worsening abdominal pain
• High fever (or fever that doesn’t improve)

Babies & children: call a pediatric provider right away if:

• Fewer wet diapers, very dry mouth, no tears, or unusual sleepiness
• Persistent vomiting or can’t keep fluids down
• Bloody diarrhea
• Severe stomach pain, extreme irritability, or lethargy
• Fever in a young infant (especially under 3 months) should be evaluated quickly

Emergency warning signs (any age): confusion, fainting, inability to wake/stay awake, severe dehydration, severe abdominal pain.

For viral gastroenteritis (stomach flu), the right doctor depends on severity and who the patient is:

• Most adults: start with a Primary Care doctor (Family Medicine or Internal Medicine). They can confirm it’s likely viral, rule out red flags, and guide hydration/meds.
• If you need same-day care: Urgent Care is appropriate for moderate symptoms, dehydration concerns, or if you’re not improving after 48–72 hours.
• Children/babies: see a Pediatrician (or pediatric urgent care).
• Severe dehydration or danger signs: go to the Emergency Room (ER) (they can give IV fluids, labs, and imaging if needed).
• If symptoms keep coming back, last >1–2 weeks, or there’s blood in stool / unexplained weight loss: see a Gastroenterologist (GI) for deeper evaluation (and to rule out non-viral causes).
• If you’re immunocompromised (chemo, transplant meds, advanced HIV, etc.) and you get significant symptoms: contact your primary doctor right away, they may involve Infectious Disease if needed.

Go to urgent care/ER now if any of these apply: you can’t keep fluids down, you’re very dizzy/fainting, you have very dark urine or aren’t peeing, severe belly pain, blood in vomit or stool, or signs of dehydration in a child (few wet diapers, no tears, unusual sleepiness).

What causes viral gastroenteritis?

You can catch stomach flu by:

• Being in close contact with someone infected
• Eating or drinking contaminated food or water
• Touching contaminated surfaces and then touching your mouth (very common)

Most common viruses

• Norovirus: the most common cause in many communities; spreads fast in families, schools, cruise ships, workplaces
• Rotavirus: more common in infants/young children (vaccination reduces severe cases)
• Other viruses can also cause gastroenteritis depending on location and season.

Is stomach flu contagious?

Yes—very. Many stomach viruses spread easily because:

• Only a small amount of virus can cause illness
• People can spread it before they feel fully sick and sometimes after symptoms improve
• Virus particles can stay on surfaces if not cleaned properly

Tip: If one person in the household is sick, treat it like a “containment situation” for 48–72 hours.

Treatment: what to do at home

There’s no “cure” antibiotic for viral gastroenteritis. The goal is hydration + symptom control + preventing complications.

1) Hydrate early (most important)

• Take small sips every 2–5 minutes if nausea is strong
• Use oral rehydration solution if diarrhea/vomiting is frequent (best balance of water + electrolytes)
• If vomiting: pause 10–15 minutes, then restart with tiny sips

Avoid: alcohol, very sugary drinks, and large amounts of juice (can worsen diarrhea).

2) Eat gently when ready

Start with easy foods and small portions:

• broth, toast, rice, bananas, applesauce, potatoes, crackers
• then add lean proteins and normal foods as tolerated

3) Rest + protect your stomach

• Rest helps recovery
• Avoid heavy, greasy, spicy foods until you’re improving

4) Medicines (use thoughtfully)

Some over-the-counter options may help certain adults, but avoid anti-diarrheal medication if you have fever, blood in stool, severe belly pain, or concern for bacterial infection. When in doubt, check with a clinician.

Dehydration: the main complication

Dehydration is the most common reason people need urgent care. Watch for:

• dry mouth
• very dark urine
• urinating much less
• dizziness, weakness
• in children: fewer wet diapers, no tears, sunken eyes, unusual sleepiness

If dehydration signs appear, it’s safer to get evaluated sooner rather than later.

Prevention (how to stop spread)

Handwashing beats sanitizer for stomach viruses

• Wash with soap and water for 20 seconds, especially after bathroom use and before eating or cooking.

Separate personal items

• Don’t share utensils, cups, towels, or toothbrushes while someone is sick.

Disinfect high-touch surfaces

• Clean bathroom surfaces, doorknobs, counters, and faucets daily during illness (and after symptoms stop).

Laundry safety

• Handle soiled bedding/clothes carefully; wash hot if possible and wash hands afterward.

Food safety

• Rinse produce, cook seafood thoroughly, and avoid preparing food for others while sick.

FAQ

How can I tell if it’s stomach flu or food poisoning?
They can feel identical early on. Stomach flu often spreads through close contact and may come with a known exposure (family member sick). Food poisoning may be linked to a shared meal. Bloody stool, high fever, severe pain, or symptoms lasting more than a few days should be evaluated.

How long is stomach flu contagious?
Many people are most contagious while actively vomiting/with diarrhea, but some viruses can spread for days after symptoms improve. Be extra strict with handwashing and surface cleaning for at least 48 hours after you feel better.

Can stomach flu cause fever?
Yes, low-grade fever can happen. High or persistent fever is a reason to get medical advice, especially with severe pain or bloody stool.

What should I drink with stomach flu?
Small, frequent sips of water, broth, and oral rehydration solutions are best. If symptoms are heavy, oral rehydration solution is usually more effective than sports drinks.

What should I eat with stomach flu?
Start bland and simple (toast, rice, bananas, broth). Return to normal foods gradually as nausea and diarrhea improve.

Why is my diarrhea watery but not bloody?
Watery non-bloody diarrhea is common with viral gastroenteritis. Blood in stool is more concerning for bacterial infection or other causes and should be evaluated.

When should I go to urgent care for stomach flu?
Go if you can’t keep liquids down, have dehydration symptoms, blood in stool/vomit, severe belly pain, or symptoms that don’t improve after 48–72 hours.