What is the appropriate management for an otherwise healthy adult presenting with acute gastroenteritis?

Management of Acute Gastroenteritis in Otherwise Healthy Adults

Oral rehydration solution (ORS) is the first-line treatment for mild to moderate dehydration in otherwise healthy adults with acute gastroenteritis, with intravenous fluids reserved only for severe dehydration, shock, or failure of oral rehydration. 1

Initial Assessment and Hydration Status

Evaluate dehydration severity through specific clinical signs rather than waiting for laboratory confirmation 1:

• Mild dehydration (3-5% fluid deficit): Slightly dry mucous membranes, normal vital signs, adequate urine output 1
• Moderate dehydration (6-9% fluid deficit): Dry mucous membranes, loss of skin turgor, tachycardia, decreased urine output 1
• Severe dehydration (≥10% fluid deficit): Altered mental status, prolonged capillary refill, hypotension, minimal or no urine output 1

The most accurate assessment is acute weight change if baseline weight is known, though this is rarely available in practice 1.

Rehydration Protocol

Oral Rehydration (First-Line for Mild-Moderate Dehydration)

For moderate dehydration, administer 100 mL/kg ORS over 2-4 hours, then replace ongoing losses with 10 mL/kg for each watery stool and 2 mL/kg for each vomiting episode. 1

• Use low-osmolarity ORS formulations rather than sports drinks or juices, which can worsen diarrhea through osmotic effects 1
• If vomiting is present, start with small volumes (5-10 mL every 1-2 minutes) and gradually increase as tolerated 1
• Reassess hydration status after 2-4 hours; if still dehydrated, reestimate deficit and restart rehydration 1

Intravenous Rehydration (Reserved for Specific Indications)

Reserve IV fluids for patients with 1:

• Severe dehydration (≥10% fluid deficit)
• Shock or altered mental status
• Failure of oral rehydration therapy
• Intractable vomiting despite antiemetics
• Ileus (absent bowel sounds)

Use isotonic fluids (lactated Ringer's or normal saline) until pulse, perfusion, and mental status normalize, then transition to ORS 1.

Nutritional Management

• Resume age-appropriate diet immediately during or after rehydration begins—do not fast or restrict diet. 1
• Early refeeding reduces illness severity and duration 1
• Avoid foods high in simple sugars (soft drinks, undiluted apple juice) as they exacerbate diarrhea through osmotic effects 1
• Limit or avoid caffeine, as it stimulates intestinal motility and worsens diarrhea 1

Pharmacological Management

Antiemetics

Ondansetron may be given to adults after adequate hydration is achieved to facilitate oral rehydration when vomiting is significant. 2, 3

• Ondansetron is adjunctive only—not a substitute for proper rehydration 3
• Avoid ondansetron in patients with bloody diarrhea, fever suggesting bacterial infection, or suspected inflammatory diarrhea 2, 3
• Exercise caution in patients with cardiac conditions or those taking QT-prolonging medications (Class IA/III antiarrhythmics, certain antipsychotics, antibiotics like moxifloxacin) due to risk of arrhythmias 3, 4

Antimotility Agents

Loperamide may be given to immunocompetent adults with acute watery diarrhea once adequately hydrated. 1

However, critical contraindications include 1, 4:

• Bloody diarrhea or fever (suggests invasive bacterial infection)
• Suspected C. difficile infection
• Recent antibiotic use
• Patients taking multiple CYP3A4 or CYP2C8 inhibitors (increases loperamide exposure 12.6-fold with combined itraconazole and gemfibrozil) 4
• Elderly patients on QT-prolonging medications 4

Do not use loperamide as first-line therapy—proper rehydration takes priority. 1

Probiotics

Probiotics (particularly Lactobacillus GG and Saccharomyces boulardii) may reduce symptom severity and duration in adults 1, 5.

Antimicrobials

Antimicrobial therapy has limited usefulness since viral agents cause most acute gastroenteritis. 1

Consider antibiotics only in specific situations 1, 6:

• Bloody diarrhea with fever and systemic toxicity
• Recent antibiotic use (test for C. difficile)
• Recent travel to developing countries
• Immunodeficiency
• Severe symptoms with confirmed bacterial pathogen

Infection Control

• Practice rigorous hand hygiene after toilet use, before eating, and after handling soiled items 1
• Use gloves and gowns when caring for ill persons 1
• Clean and disinfect contaminated surfaces promptly 1
• Isolate ill persons until at least 2 days after symptom resolution 1

Indications for Hospitalization

Admit patients with 1:

• Severe dehydration (≥10% fluid deficit) or signs of shock
• Failure of oral rehydration therapy
• Altered mental status
• Intractable vomiting despite antiemetics
• Persistent tachycardia or hypotension despite initial fluid resuscitation
• Bloody diarrhea with fever and systemic toxicity (concern for hemolytic uremic syndrome with enterohemorrhagic E. coli)
• Significant comorbidities (elderly ≥65 years, immunocompromised, severe cardiac/renal disease)

Critical Pitfalls to Avoid

• Do not delay rehydration while awaiting diagnostic testing—begin ORS immediately 1
• Do not use sports drinks or apple juice as primary rehydration solutions for moderate-severe dehydration 1
• Do not give antimotility agents in bloody diarrhea or suspected bacterial infection 1, 4
• Do not unnecessarily restrict diet—resume normal eating immediately 1
• Do not use adsorbents, antisecretory drugs, or toxin binders—they lack efficacy 1
• Do not underestimate dehydration in elderly patients, who may not manifest classic signs and have higher mortality risk 1

Monitoring and Follow-Up

• Monitor vital signs, urine output, and clinical hydration markers every 2-4 hours during active rehydration 1
• Discharge when patient tolerates oral intake, produces adequate urine, and is clinically rehydrated 1
• Provide clear instructions on continuing ORS at home to replace ongoing losses 1
• Advise return if symptoms worsen, bloody stools develop, high fever occurs, or signs of dehydration recur 1