What is the appropriate initial management of acute gastroenteritis in an otherwise healthy adult presenting with sudden onset vomiting and watery diarrhea of less than seven days duration?

Acute Gastroenteritis in Otherwise Healthy Adults

Initial Management Strategy

For an otherwise healthy adult with sudden onset vomiting and watery diarrhea, begin immediate oral rehydration with low-osmolarity oral rehydration solution (ORS) using small, frequent volumes of 5–10 mL every 1–2 minutes, continue normal diet without restriction, and avoid antimotility agents until adequately hydrated. 1

Rehydration Protocol

Oral Rehydration Solution Administration

• Use commercially available low-osmolarity ORS (containing 75–90 mEq/L sodium) as first-line therapy for mild-to-moderate dehydration 1
• Administer 5–10 mL every 1–2 minutes using a spoon, medicine cup, or syringe—never allow rapid drinking from a cup or bottle, as this triggers vomiting and falsely suggests ORT failure 1
• Replace ongoing losses with approximately 10 mL/kg for each watery stool and 2 mL/kg for each vomiting episode 1
• Success rates exceed 90% when the small-volume, slow-administration technique is used correctly 1

Hydration Assessment

• Evaluate hydration status through skin turgor, mucous membrane moisture, capillary refill time, mental status, and vital signs 1
• Reassess after 2–4 hours; if dehydration persists, recalculate deficit and restart ORS 1

When to Escalate to IV Therapy

• Reserve intravenous rehydration for severe dehydration (≥10% fluid deficit), shock, altered mental status, failure of oral rehydration despite proper technique, or ileus 1
• 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 normal diet immediately during or after rehydration—do not withhold food or enforce fasting 1
• Early refeeding reduces illness severity and duration 1
• Recommended foods include starches (rice, potatoes, noodles), cereals, yogurt, fruits, and vegetables 1
• Avoid soft drinks, undiluted fruit juice, sports drinks, high-fat foods, and caffeinated beverages, as these worsen diarrhea through osmotic effects and altered motility 1

Pharmacological Considerations

Antimotility Agents

• Loperamide may be used in immunocompetent adults with acute watery diarrhea only after adequate hydration: initial dose 4 mg, then 2 mg after each loose stool, maximum 16 mg/day 2, 3
• Never use loperamide in bloody diarrhea, high fever, or suspected inflammatory/invasive diarrhea due to risk of toxic megacolon 2
• Loperamide is absolutely contraindicated in patients under 18 years of age 3

Antiemetics

• Ondansetron may reduce vomiting and facilitate oral rehydration in adults with significant nausea, though evidence is strongest in pediatric populations 1, 4

Antibiotics

• Routine antibiotics are not indicated because viral pathogens cause approximately 70% of acute gastroenteritis cases 1, 5
• Consider empirical antibiotics only when:
  • Bloody diarrhea with high fever and systemic toxicity (suggesting Shigella, Salmonella, Campylobacter) 1
  • Watery diarrhea persisting >5–7 days 1, 5
  • Recent foreign travel or known outbreak exposure 1
  • Immunocompromised status 5
• Fluoroquinolones or azithromycin are typical first-line choices when bacterial etiology is suspected 2

Agents to Avoid

• Do not use adsorbents (kaolin-pectin), antisecretory drugs, or toxin binders—they lack proven efficacy in reducing diarrhea volume or duration 1
• Avoid metoclopramide, as it is a prokinetic that accelerates transit and is counterproductive in diarrheal illness 1

Red Flags Requiring Immediate Medical Evaluation

• Bloody stools with high fever indicate possible bacterial dysentery and risk of hemolytic uremic syndrome 1
• Severe dehydration signs: altered consciousness, prolonged skin tenting (>2 seconds), cool extremities, poor capillary refill, rapid deep breathing 1
• Persistent tachycardia or hypotension despite initial fluid resuscitation 1
• Intractable vomiting despite antiemetics and proper ORS technique 1
• Absent bowel sounds (absolute contraindication to oral rehydration) 1

Hospitalization Criteria

• Severe dehydration (≥10% fluid deficit) or clinical shock 1
• Failure of oral rehydration therapy despite correct technique 1
• Altered mental status or severe lethargy 1
• Bloody diarrhea with fever and systemic toxicity requiring monitoring for complications 1
• Significant comorbidities or immunocompromised state 1
• Elderly patients (≥65 years) warrant lower threshold for admission due to higher morbidity and mortality risk 1

Common Pitfalls to Avoid

• Do not delay rehydration while awaiting diagnostic testing—initiate ORS immediately based on clinical assessment 1
• Do not use sports drinks, apple juice, or soft drinks as primary rehydration fluids; they lack appropriate electrolyte balance and may worsen diarrhea 1
• Do not withhold food during or after rehydration; early refeeding improves outcomes 1
• Do not give loperamide before adequate hydration or in the presence of bloody diarrhea, high fever, or systemic toxicity 2, 3
• Stool cultures are rarely needed for typical watery diarrhea in immunocompetent adults; reserve for bloody diarrhea, prolonged symptoms (>5–7 days), or suspected outbreak 1, 5

Infection Control

• Practice rigorous hand hygiene after toilet use, before food preparation, and before eating 1
• Separate ill persons from well persons until at least 2 days after symptom resolution 1
• Clean and disinfect contaminated surfaces promptly 1