Acute Gastroenteritis: Symptoms, Causes, and Treatment

By The Tessan Editorial Team · July 19, 2026 · 7 min read

Also known as: Stomach flu, Stomach bug, Viral gastroenteritis, AGE

What Is Acute Gastroenteritis?

Acute gastroenteritis (AGE) is an acute inflammation of the stomach and intestines, usually infectious in origin and most often viral, causing diarrhea, vomiting, abdominal pain, and sometimes fever. According to the World Health Organization, diarrheal disease is the third leading cause of death in children 1 to 59 months of age, killing roughly 444,000 children under 5 each year. In the U.S., CDC researchers estimate that about 179 million episodes occur annually. Norovirus, the most common cause across the age spectrum, peaks during the winter in temperate climates.

Causes and Risk Factors

Viral agents:

• Norovirus: the most common cause of acute gastroenteritis across the age spectrum in the U.S., and the leading cause of outbreaks in people of all ages
• Rotavirus: the leading cause of severe gastroenteritis in children under 5, and the most common cause of diarrheal illness in U.S. children before routine vaccination began in 2006
• Enteric adenoviruses, astrovirus

Bacterial agents:

• Salmonella, Campylobacter, Yersinia: spread through contaminated food and water
• Enterotoxigenic E. coli, Clostridioides difficile (symptoms may begin during or within 2 weeks of antibiotic therapy)
• Staphylococcus aureus (preformed toxin): rapid-onset food poisoning, typically 30 minutes to 8 hours after eating, resolving within 24 hours

Parasitic agents: Giardia is the main parasite behind travelers’ diarrhea, followed by Cryptosporidium.

Risk factors: unwashed hands, contaminated water or food, group settings, travel, weakened immunity.

Symptoms

Symptoms appear quickly after exposure, most often within 4 to 48 hours:

• Diarrhea: loose or watery stools, three or more a day
• Nausea and vomiting (often predominant in viral forms)
• Abdominal pain (cramps, rumbling bowel sounds)
• Fever, which is one of the most common symptoms. A high fever (over 102°F) or bloody diarrhea is a sign to see a doctor
• Signs of dehydration (extreme thirst, dry mouth, urinating less than usual, dark-colored urine, feeling tired), the major complication to watch for

How long it lasts depends on the germ. Norovirus symptoms usually clear in 1 to 3 days, astrovirus in 1 to 4 days, rotavirus in 3 to 8 days, and enteric adenovirus can run 1 to 2 weeks. Common bacterial causes tend to run about as long: Salmonella usually lasts 4 to 7 days, and Campylobacter about a week. High fever, bloody diarrhea, protracted vomiting, or severe abdominal pain point to a cause other than a plain viral gastroenteritis.

Diagnosis

Acute viral gastroenteritis is a clinical diagnosis, in part because viral testing is not readily available in most clinics and emergency departments. Testing is reserved for certain situations:

• Stool testing for Salmonella, Shigella, Campylobacter, Yersinia, C. difficile, and Shiga toxin-producing E. coli: for diarrhea with fever, bloody or mucoid stools, severe abdominal cramping or tenderness, or signs of sepsis
• A broader panel of bacterial, viral, and parasitic agents: in the context of a possible outbreak, or in an immunocompromised patient
• C. difficile testing if diarrhea develops during or after antibiotic treatment
• Blood tests: significant dehydration can show up as hemoconcentration on a blood count and as electrolyte disturbances on a chemistry panel

Available Treatments

Management is mainly symptomatic.

Rehydration (the priority treatment):

• Oral rehydration solution (Pedialyte, Naturalyte, Infalyte, CeraLyte, or generic equivalents): reduced-osmolarity ORS is the first-line therapy for mild to moderate dehydration in infants, children, and adults
• Drink plenty of liquids (water, broth, oral rehydration solution)
• IV rehydration for those who are severely dehydrated or cannot keep oral fluids down

Diet:

• Resume an age-appropriate normal diet during or right after rehydration. You can most often go back to eating normally even if you still have diarrhea
• Easily tolerated choices: cereals, bread, potatoes, lean meats, plain yogurt, bananas, fresh apples, vegetables
• Avoid milk and dairy, caffeinated drinks, high-fat foods, and foods with a lot of simple sugars, since lactose digestion may stay impaired for a while after the gut lining is injured

Medications:

• Loperamide (Imodium): should not be given to children under 18, and should be avoided at any age with bloody diarrhea or diarrhea with fever, where it risks toxic megacolon. It is also not recommended for people aged 65 or older
• Antiemetics (ondansetron) to help keep oral rehydration down when vomiting is significant
• Probiotics (Lactobacillus rhamnosus GG, Saccharomyces boulardii): the Cochrane review restricted to large, low risk of bias trials found no difference from placebo, and its authors conclude the evidence does not support using probiotics to treat acute infectious diarrhea
• Antibiotics: not routine. They are reserved for severe illness, high fever, symptoms dragging past 7 days, high-risk patients, and C. difficile infection, where the causative antibiotic is stopped and targeted treatment started

Prevention and Practical Tips

Prevention relies on simple hygiene measures:

• Wash hands thoroughly before eating and after using the toilet, lathering with soap for at least 20 seconds
• Cook food thoroughly. Poultry, all ground meats, and all stuffed meats should reach an internal temperature of 165°F, and seafood, steaks, chops, and roasts 145°F. Reheat leftovers to 165°F
• Refrigerate leftovers within 2 hours of serving, and keep the refrigerator below 40°F
• Wash raw fruits and vegetables, and keep raw foods separate from ready-to-eat foods
• When traveling: drink only beverages that are sealed, boiled, chlorine-treated, or otherwise known to be purified

Rotavirus vaccination: infants receive 2 or 3 doses depending on the vaccine (the monovalent vaccine from 6 to 24 weeks, the pentavalent from 6 to 32 weeks). A meta-analysis of observational studies put effectiveness against rotavirus hospitalization at 89% in high-income countries (95% CI 84 to 92%).

When Should You See a Doctor?

See a doctor right away for signs of dehydration, stools that are black and tarry or contain blood or pus, a high fever over 102°F, frequent vomiting or an inability to drink enough liquid or oral rehydration solution, six or more loose stools in a day, severe pain in the abdomen or rectum, or a change in mental state such as irritability or lack of energy.

Adults should also call for diarrhea lasting more than 2 days. For children, the thresholds are tighter: diarrhea lasting more than a day, any fever in an infant, or a high fever in an older child. Get help right away if the child is an infant, was born prematurely, or has other medical conditions, and likewise if the patient is immunocompromised, elderly, or medically fragile.

If in doubt, do not hesitate to consult a doctor quickly.

Sources

• CDC, Emerging Infectious Diseases: Acute Gastroenteritis Surveillance through the National Outbreak Reporting System, the estimate of 179 million AGE episodes a year in the U.S.
• CDC, Emerging Infectious Diseases: Incidence, Etiology, and Healthcare Utilization for Acute Gastroenteritis in the Community, United States, norovirus as the most common cause of AGE across the age spectrum
• CDC Yellow Book: Norovirus, norovirus winter peak and its role in outbreaks in people of all ages
• CDC Yellow Book: Travelers’ Diarrhea, Giardia and Cryptosporidium in travelers, safe beverages, and loperamide limits
• MedlinePlus: Viral gastroenteritis, incubation of 4 to 48 hours, the viruses involved, and foods that are usually tolerated
• NIDDK: Viral gastroenteritis, how long each virus lasts, dehydration signs, oral rehydration solutions, diet, foods to avoid, and when to seek care
• NIDDK: Symptoms and causes of lactose intolerance, infections that injure the small intestine reducing lactase
• StatPearls: Viral Gastroenteritis, viral predominance, the three-stools-a-day definition, clinical diagnosis, blood test findings, antiemetics, and loperamide in people 65 and older
• StatPearls: Bacterial Diarrhea, foodborne bacteria, Staphylococcus aureus preformed toxin onset, C. difficile timing, and antibiotic indications
• StatPearls: Rotavirus, rotavirus as the leading cause of severe gastroenteritis in children under 5, and the two vaccine schedules
• StatPearls: Pediatric Dehydration, oral rehydration for mild to moderate dehydration and IV fluids for severe dehydration or persistent vomiting
• MedlinePlus: Salmonella infections, duration of Salmonella illness
• MedlinePlus: Campylobacter infections, duration of Campylobacter illness
• MedlinePlus: Handwashing, hand hygiene guidance
• MedlinePlus: Food safety, safe cooking temperatures and refrigerating leftovers within 2 hours
• FDA: Refrigerator Thermometers, Cold Facts about Food Safety, keeping the refrigerator at 40°F or below
• CDC: Food Poisoning Symptoms, fever as a common symptom, and a fever over 102°F or bloody diarrhea as reasons to see a doctor
• Infectious Diseases Society of America (IDSA), Clinical Practice Guidelines for the Diagnosis and Management of Infectious Diarrhea, stool testing indications, oral rehydration as first-line therapy, early refeeding, loperamide, and antiemetics
• Cochrane review: Probiotics for treating acute infectious diarrhoea, evidence on probiotics
• Rotavirus vaccine population effectiveness, systematic review and meta-analysis, 89% effectiveness against hospitalization in high-income countries
• World Health Organization (WHO), global child mortality from diarrheal disease