Gastroenteritis (Viral)

Viral gastroenteritis is a self-limited syndrome of rapid-onset nausea, vomiting, watery (non-bloody, non-mucoid) diarrhea, and cramping abdominal pain caused most commonly by norovirus, rotavirus, sapovirus, astrovirus, and enteric adenovirus. [1] It is the most common cause of acute nausea and vomiting and accounts for the majority of acute diarrheal illness in developed countries. [2-3] The cornerstone of management is oral rehydration and early refeeding; antibiotics are not indicated. [1][3]

• Onset and timeline: Abrupt onset typically 24–48 hours after exposure; preformed toxin food poisoning has a shorter incubation (2–7 hours) [4]
• Symptom characterization: Watery, non-bloody, non-mucoid diarrhea; nausea and vomiting (often predominant); diffuse crampy abdominal pain; malaise [1]
• Volume assessment: Quantify oral intake, urine output, number of emesis/diarrheal episodes, last void
• Exposures: Sick contacts, daycare/institutional setting, cruise ship, recent food (shellfish, salad bars, buffets), contaminated water [5]
• Important negatives: Absence of bloody stool, high fever, severe focal abdominal pain, and tenesmus makes viral etiology more likely [3-4]
• Medications: Recent antibiotics (C. difficile risk), PPIs, chemotherapy, laxatives [4]
• Travel history: International travel raises concern for bacterial/parasitic causes [3]

• Bloody or mucoid stools → suggests inflammatory/invasive bacterial pathogen [3]
• High fever ≥38.5°C (101.3°F) → suggests bacterial etiology or systemic infection [4]
• Signs of severe dehydration: altered mental status, syncope, oliguria, sunken eyes, poor skin turgor [4][6]
• Severe abdominal pain or peritoneal signs (especially age >50) → workup for surgical abdomen [4]
• Symptoms >7 days → consider non-viral or parasitic etiology [3]
• Immunocompromised patient → risk of severe, prolonged, or opportunistic infection (CMV, Cryptosporidium) [1]
• Extremes of age (infants <3 months, elderly ≥65) → higher risk of dehydration and complications [3][7]

• Oral rehydration solution (ORS): First-line therapy; low-osmolar solutions (200–250 mOsm/L) preferred [1][3]
• Ondansetron: Safe and effective for recalcitrant vomiting to facilitate oral rehydration; may be used in patients >4 years; may increase stool volume [1][7]
• Loperamide (adults only): 4 mg initial dose, then 2 mg after each unformed stool (max 8 mg/day for ≤48 hours); reduces stool frequency in acute watery diarrhea [4][8]
• Bismuth subsalicylate: Mildly effective antisecretory; safe alternative when loperamide is contraindicated [3][8]
• Loperamide + simethicone: Combination provides faster relief of diarrhea and gas-related discomfort [3]

Contraindicated/Avoid

• Loperamide in bloody/inflammatory diarrhea (risk of toxic megacolon), febrile dysentery, and children <18 years per IDSA guidelines [7]
• Loperamide contraindicated in children <2 years (respiratory depression risk) [9]
• Bismuth subsalicylate in children <12 years (Reye syndrome risk) [9]
• Antibiotics are not indicated for viral gastroenteritis [5]

• Early refeeding (within 4–6 hours of rehydration) shortens illness duration and improves nutritional outcomes [1][3]
• Age-appropriate regular diet is recommended; no evidence supports the traditional BRAT diet over a normal diet [3]
• Avoid: High-sugar beverages (juice, soda), caffeine, alcohol, and high-fat foods acutely, as these can worsen osmotic diarrhea
• Lactose-containing foods may transiently worsen diarrhea due to transient lactase deficiency but routine avoidance is not universally recommended
• Hydration: Frequent small sips of ORS; commercial formulations (Pedialyte 250 mOsm/L) or homemade solutions [1]

• GI: Nausea, vomiting, diarrhea frequency/character, abdominal pain location/quality, blood in stool, tenesmus
• Constitutional: Fever, malaise, myalgias, weight loss
• Neurologic: Dizziness, lightheadedness, syncope, confusion (dehydration markers)
• Urinary: Decreased urine output, dark urine
• Cardiopulmonary: Palpitations, chest pain (electrolyte-related), dyspnea
• Skin: Rash (consider viral exanthem, reactive arthritis)

• Sick contacts: Household members, coworkers, classmates with similar symptoms — secondary attack rates are 15% for norovirus and 28% for rotavirus within households [10]
• Institutional exposure: Nursing home, daycare, cruise ship, hospital — norovirus outbreaks are common in congregate settings [5]
• Food exposure: Shared meals, restaurant visits, raw shellfish consumption
• Family history: Generally not contributory for acute viral gastroenteritis; consider IBD if recurrent episodes
• Immunocompromised household members at risk for prolonged shedding and severe disease

• Age extremes: Children <5 years (highest incidence) and adults ≥65 years [1][11]
• Congregate living: Cruise ships, long-term care facilities, dormitories, military barracks [5]
• Foodborne exposure: Raw/undercooked shellfish, contaminated salad greens, food prepared by infected handlers [1]
• Contaminated water or inadequately treated drinking water [1]
• Seasonality: Peak in winter months in temperate climates ("winter vomiting disease") [1]
• Immunosuppression: HIV/AIDS, transplant recipients, chemotherapy — risk of prolonged/severe illness [1]
• Lack of rotavirus vaccination in children [7]
• Fomite exposure: Norovirus persists on environmental surfaces and can cause recurrent outbreaks [5]

Cannot-miss diagnoses

• Appendicitis / surgical abdomen — focal RLQ pain, peritoneal signs, fever
• Mesenteric ischemia — severe pain out of proportion to exam, age >50, atrial fibrillation
• Bowel obstruction — distension, obstipation, bilious vomiting
• Diabetic ketoacidosis — nausea/vomiting with hyperglycemia, Kussmaul breathing
• Hemolytic uremic syndrome — bloody diarrhea followed by AKI, thrombocytopenia (post-STEC)

Important alternative diagnoses

• Bacterial gastroenteritis (Salmonella, Campylobacter, Shigella, STEC) — fever, bloody/mucoid stool, more severe abdominal pain [3]
• C. difficile — recent antibiotics or hospitalization [12]
• Preformed toxin food poisoning (S. aureus, B. cereus) — onset <6 hours after suspect meal [1]
• Parasitic infection (Giardia, Cryptosporidium) — prolonged watery diarrhea, travel history [1]
• Medication-induced diarrhea — antibiotics, PPIs, metformin, colchicine, SSRIs
• Early IBD flare — recurrent episodes, weight loss, extraintestinal manifestations [3]
• Hepatitis A/E — nausea, vomiting, jaundice, transaminase elevation [1]

• Prior episodes of gastroenteritis and their frequency
• Immunocompromising conditions: HIV, transplant, chemotherapy, biologics
• Chronic kidney disease — higher risk from dehydration and electrolyte derangements
• Cardiac disease — less tolerance for volume depletion and electrolyte shifts
• Diabetes — risk of DKA with dehydration; medication adjustments may be needed (hold metformin, SGLT2 inhibitors)
• IBD — distinguish flare from superimposed infection
• Prior abdominal surgery — adhesive obstruction can mimic gastroenteritis
• Rotavirus vaccination status in children [7]

Vital signs

• Tachycardia, orthostatic hypotension → dehydration
• Fever — low-grade is common; high/persistent fever suggests non-viral cause [1]

Focused exam

• General: Ill-appearing, listless (severe); alert and well-appearing (mild)
• Mucous membranes: Dry or tacky → dehydration
• Eyes: Sunken (especially children) [6]
• Skin turgor: Decreased; capillary refill >2 seconds in children
• Abdomen: Diffuse mild tenderness without rebound or guarding; hyperactive bowel sounds. Focal tenderness, rigidity, or peritoneal signs → surgical evaluation
• Rectal exam: Assess for occult blood if inflammatory cause suspected [4]
• Neurologic: Altered sensorium suggests severe dehydration or alternative diagnosis

Dehydration assessment scales: The Clinical Dehydration Scale (CDS) in children uses general appearance, eyes, mucous membranes, and tears to grade severity. [6][13]

Most cases require no laboratory testing. [1][12]

When indicated (moderate-severe illness, high-risk patients):

• BMP/CMP: Electrolytes (hyponatremia, hypokalemia), BUN/Cr (pre-renal azotemia, AKI), glucose, bicarbonate [1][3]
• Expected findings: Metabolic alkalosis (predominant vomiting) or hyperchloremic non-anion gap metabolic acidosis (predominant diarrhea); elevated BUN:Cr ratio; lactic acidosis if hypovolemic [1][14]
• CBC: Leukocytosis may suggest bacterial etiology; thrombocytopenia raises concern for HUS [7]
• Lactate: If concern for sepsis or significant hypovolemia

Stool testing — reserve for

• Bloody, mucoid, or febrile diarrhea
• Immunocompromised patients
• Symptoms ≥7 days
• Suspected outbreak (food handlers, institutional settings)
• Infants <3 months [1][3][12]
• Multiplex PCR (e.g., BioFire FilmArray GI Panel) is preferred over culture when testing is indicated [3][15]

• Imaging is generally unnecessary for uncomplicated viral gastroenteritis
• Abdominal X-ray or CT abdomen/pelvis if concern for obstruction, perforation, appendicitis, or ischemia
• CT with IV contrast is the study of choice when surgical pathology is suspected
• Ultrasound may be useful in pediatric patients to evaluate for appendicitis or intussusception

• Clinical Dehydration Scale (CDS): Validated 4-item tool for children (general appearance, eyes, mucous membranes, tears) — scores 0 (none), 1–4 (some), 5–8 (moderate-severe) [13]
• Point-of-care ultrasound (POCUS): IVC collapsibility for volume assessment in adults
• Stool multiplex PCR panels: Detect 22 pathogens (bacterial, viral, parasitic) with results in ~60 minutes; useful for outbreak investigation and infection control [16]
• Rapid norovirus PCR (e.g., Xpert Norovirus): Sensitivity 92–100%, specificity 93–100%, results in 90 minutes [1]

• Not routinely indicated for uncomplicated viral gastroenteritis
• Obtain ECG when:
  • Severe dehydration with electrolyte abnormalities suspected
  • Elderly patients or those with cardiac comorbidities
  • Palpitations, chest pain, or syncope
• Findings to recognize:
  • Hypokalemia: Flattened T waves, U waves, ST depression, prolonged QT, risk of torsades de pointes [17]
  • Hyperkalemia (less common): Peaked T waves, widened QRS, sine wave pattern [17]
  • Hypomagnesemia: Prolonged QT, torsades de pointes [17]
  • Sinus tachycardia from dehydration/hypovolemia

Viral gastroenteritis presents as acute-onset watery, non-bloody diarrhea with nausea/vomiting, typically self-limited within 1–3 days. [1] Norovirus is the most common cause in all age groups in the post-rotavirus vaccine era, responsible for ~18% of global acute gastroenteritis cases. [1][5] Globally, rotavirus remains the leading cause of diarrheal deaths, followed by norovirus. [18]

Severity stratification

• Mild: Tolerating oral fluids, no dehydration signs, <6 stools/day
• Moderate: Some dehydration, frequent vomiting limiting oral intake, 6–10 stools/day
• Severe: Signs of significant dehydration or shock, inability to tolerate oral fluids, altered mental status

Complications: Dehydration (most common), electrolyte disturbances (hyponatremia in 16% of hospitalized children with moderate-severe dehydration), AKI, metabolic acidosis, and rarely seizures in children. [6][19]

Initial stabilization

• [1][3]

Rehydration strategy by severity: [1]

• Minimal/no dehydration: Ad lib oral fluids; ORS as tolerated; half-strength apple juice is acceptable in children with mild illness [13]
• Mild-moderate dehydration: ORS 50–100 mL/kg over 3–4 hours; frequent small sips; reassess frequently
• Severe dehydration/shock: IV isotonic crystalloid (NS or LR) bolus 20 mL/kg; transition to oral rehydration once stabilized [6]

Pharmacotherapy (adults)

• Ondansetron 4–8 mg PO/IV/ODT for vomiting (facilitates oral rehydration)
• Loperamide 4 mg initially, then 2 mg after each unformed stool (max 8 mg/day × 48 hours) for watery diarrhea only [4]
• Bismuth subsalicylate 525 mg PO q30–60 min (max 8 doses/24 hours) as alternative [8]

Pharmacotherapy (children)

• Ondansetron ODT 0.15 mg/kg (max 4 mg) × 1 dose to facilitate oral rehydration in children >4 years [1][7]
• Avoid loperamide in children <18 years per IDSA [7]
• Zinc supplementation recommended in low-income settings [20]

Refeeding: Resume age-appropriate regular diet within 4–6 hours of rehydration. [1][3]

Discharge criteria

• Tolerating oral fluids without recurrent vomiting
• Adequate urine output
• No signs of significant dehydration
• Reliable follow-up and ability to return if worsening
• Caregiver able to monitor (pediatric patients)

Admission criteria

• Severe dehydration unresponsive to oral/IV rehydration in ED
• Inability to tolerate oral fluids despite antiemetics
• Hemodynamic instability or signs of shock
• Significant electrolyte abnormalities requiring correction
• Infants <3 months with dehydration
• Immunocompromised with severe symptoms
• Concern for alternative surgical diagnosis

Observation: Consider for patients with moderate dehydration requiring IV fluids who may improve with a few hours of rehydration and reassessment. [13]

Specialist consultation

• Surgery if peritoneal signs or concern for surgical abdomen
• GI if prolonged symptoms (>7 days), suspected IBD, or immunocompromised with refractory disease
• Infectious disease for immunocompromised patients with severe or prolonged illness

Follow-up timing

• Most patients recover within 1–3 days [1]
• PCP follow-up in 2–3 days if symptoms persist; sooner for high-risk patients (elderly, infants, immunocompromised)

Return precautions — instruct patients to return immediately for:

• Inability to keep down any fluids for >12–24 hours
• Bloody or black stools
• High fever (>101.3°F / 38.5°C)
• Severe abdominal pain or distension
• Decreased urination, no tears (children), dizziness/lightheadedness
• Confusion or lethargy
• Symptoms worsening after initial improvement or lasting >7 days

Patient counseling

• Hand hygiene is the most effective prevention measure; alcohol-based sanitizers have limited efficacy against norovirus (soap and water preferred) [5]
• Contagion period: Patients remain infectious for ≥48 hours after symptom resolution; food handlers should not return to work until 48 hours symptom-free [5]
• Environmental decontamination: Norovirus persists on surfaces; clean with bleach-based solutions [5]
• Rotavirus vaccination for eligible infants [7]

The following algorithm from the AAFP provides a practical framework for evaluating and managing acute diarrhea in the ED and primary care settings:

1. Viral Gastroenteritis. — Flynn TG, Olortegui MP, Kosek MN. Lancet. 2024.

2. Evaluation and Treatment of Nausea and Vomiting in Adults. — Johns T, Lawrence E. American Family Physician. 2024.

3. Acute Diarrhea in Adults. — Meisenheimer ES, Epstein C, Thiel D. American Family Physician. 2022.

4. Acute Infectious Diarrhea in Immunocompetent Adults. — DuPont HL. The New England Journal of Medicine. 2014.

5. Norovirus. — Sara A. Mirza and Jan Vinjé CDC Yellow Book. 2025.

6. Balanced Crystalloid Solutions Versus 0.9% Saline for Treating Acute Diarrhoea and Severe Dehydration in Children. — Florez ID, Sierra J, Pérez-Gaxiola G. The Cochrane Database of Systematic Reviews. 2023.

7. 2017 Infectious Diseases Society of America Clinical Practice Guidelines for the Diagnosis and Management of Infectious Diarrhea. — Shane AL, Mody RK, Crump JA, et al. Clinical Infectious Diseases : An Official Publication of the Infectious Diseases Society of America. 2017.

8. ACG Clinical Guideline: Diagnosis, Treatment, and Prevention of Acute Diarrheal Infections in Adults. — Riddle MS, DuPont HL, Connor BA. The American Journal of Gastroenterology. 2016.

9. Traveling Safely with Infants and Children. — Michelle Weinberg and Patrick W. Hickey CDC Yellow Book. 2025.

10. Community Burden and Transmission of Acute Gastroenteritis Caused by Norovirus and Rotavirus in the Netherlands (RotaFam): A Prospective Household-Based Cohort Study. — Quee FA, de Hoog MLA, Schuurman R, Bruijning-Verhagen P. The Lancet. Infectious Diseases. 2020.

11. Norovirus and Other Viral Causes of Medically Attended Acute Gastroenteritis Across the Age Spectrum: Results From the Medically Attended Acute Gastroenteritis Study in the United States. — Burke RM, Mattison CP, Marsh Z, et al. Clinical Infectious Diseases : An Official Publication of the Infectious Diseases Society of America. 2021.

12. Guide to Utilization of the Microbiology Laboratory for Diagnosis of Infectious Diseases: 2024 Update by the Infectious Diseases Society of America (IDSA) and the American Society for Microbiology (ASM). — Miller JM, Binnicker MJ, Campbell S, et al. Clinical Infectious Diseases : An Official Publication of the Infectious Diseases Society of America. 2024.

13. Gastroenteritis in Children. — Hartman S, Brown E, Loomis E, Russell HA. American Family Physician. 2019.

14. Integration of Acid–Base and Electrolyte Disorders. — Seifter JL. The New England Journal of Medicine. 2014.

15. FilmArray GI Panel in the Assessment of Acute Gastroenteritis. — Bryce C. American Family Physician. 2024.

16. Clinical Impact of Syndromic Molecular Point-of-Care Testing for Gastrointestinal Pathogens in Adults Hospitalised With Suspected Gastroenteritis (GastroPOC): A Pragmatic, Open-Label, Randomised Controlled Trial. — Brendish NJ, Beard KR, Malachira AK, et al. The Lancet. Infectious Diseases. 2023.

17. Electrocardiographic Manifestations: Electrolyte Abnormalities. — Diercks DB, Shumaik GM, Harrigan RA, Brady WJ, Chan TC. The Journal of Emergency Medicine. 2004.

18. Global, Regional, and National Age-Sex-Specific Burden of Diarrhoeal Diseases, Their Risk Factors, and Aetiologies, 1990-2021, for 204 Countries and Territories: A Systematic Analysis for the Global Burden of Disease Study 2021. — GBD 2021 Diarrhoeal Diseases Collaborators. The Lancet. Infectious Diseases. 2025.

19. The Incidence and Factors Associated With Dysnatremia in Children With Acute Gastritis/­Gastroenteritis. — Chaiyapak T, Sommai K, Banluetanyalak P, et al. Pediatrics International : Official Journal of the Japan Pediatric Society. 2024.

20. Comparison of Recommendations in Clinical Practice Guidelines for Acute Gastroenteritis in Children. — Lo Vecchio A, Dias JA, Berkley JA, et al. Journal of Pediatric Gastroenterology and Nutrition. 2016.