A 55-year-old adult presents with nausea, vomiting followed by watery diarrhea; what is the most likely diagnosis and recommended management?

Acute Viral Gastroenteritis: Most Likely Diagnosis and Management

This 55-year-old patient most likely has acute viral gastroenteritis, and the primary treatment is oral rehydration solution (ORS), NOT empiric antibiotics or antimotility agents. 1

Most Likely Diagnosis

Viral gastroenteritis is the most common cause of acute nausea, vomiting followed by watery diarrhea in immunocompetent adults. 1, 2, 3

• Norovirus is the most frequent culprit, particularly during cold seasons, with an incubation period of 12-48 hours followed by vomiting, watery diarrhea, abdominal pain, myalgia, and low-grade fever. 1
• The illness is typically self-limiting, lasting 12-72 hours in immunocompetent hosts. 1
• Rotavirus is another common viral cause, with symptoms lasting 4-7 days. 1

Initial Assessment

Evaluate for dehydration severity by assessing: 1, 4

• Skin turgor and mucous membrane moisture
• Mental status changes
• Tachycardia and orthostatic hypotension
• Capillary refill time

Red flags requiring further investigation include: 1, 2, 3

• High fever (>38.5°C)
• Bloody or mucoid stools
• Severe abdominal pain
• Symptoms persisting >3 days
• Immunocompromised status
• Recent hospitalization or antibiotic use

Primary Management: Rehydration

Oral rehydration solution (ORS) is the cornerstone of treatment for mild to moderate dehydration. 1, 4, 5

Rehydration Protocol:

• For mild to moderate dehydration: Administer reduced osmolarity ORS at 50-100 mL/kg over 3-4 hours. 1
• For adults (≥30 kg): Give 2-4 L of ORS during initial rehydration phase. 1
• Replace ongoing losses: 120-240 mL ORS for each diarrheal stool or vomiting episode, up to ~2 L/day ad libitum. 1
• For severe dehydration or inability to tolerate oral intake: Use intravenous isotonic fluids (lactated Ringer's or normal saline). 6
• Nasogastric ORS administration may be considered if oral intake is not tolerated but patient is not severely dehydrated. 1

Nutritional Management

Resume age-appropriate diet immediately after rehydration is completed or during rehydration. 1, 4, 5

• Early refeeding reduces illness severity and duration. 5
• Provide easily digestible foods like starches, cereals, and cooked vegetables. 6
• Avoid foods high in simple sugars and caffeinated beverages, as they worsen diarrhea through osmotic effects. 5

Antiemetic Therapy

Ondansetron (4-8 mg PO every 8 hours as needed) may be given to facilitate oral rehydration when vomiting is significant. 5, 7

• This helps control vomiting and allows transition to oral intake. 6
• Correction of dehydration itself often reduces vomiting frequency. 6

When Antibiotics Are NOT Indicated

Empiric antimicrobial therapy is NOT recommended for acute watery diarrhea without recent international travel in immunocompetent adults. 1

• The evidence shows only a 1-day shorter illness on average with empiric antibiotics, which does not justify the risks. 1
• In the absence of inflammatory signs (high fever, bloody stools, severe abdominal pain), viral infection is significantly more likely, making antibiotics ineffective and potentially harmful. 1
• Antimicrobial treatment should be modified or discontinued when a viral etiology is confirmed. 1

Exceptions for Antibiotic Consideration:

• Immunocompromised patients or ill-appearing young infants. 1
• Bloody diarrhea with fever and systemic toxicity. 5
• Suspected bacterial dysentery (Shigella, Campylobacter, Salmonella). 1

Antimotility Agents: Use With Extreme Caution

Loperamide should be avoided in this presentation until viral gastroenteritis is confirmed and inflammatory causes are excluded. 5, 2

• Never use in children <18 years due to risk of serious adverse events. 5
• Contraindicated in bloody diarrhea, high fever, or suspected inflammatory bacterial infection. 2
• If used in confirmed watery diarrhea: 4 mg PO initially, then 2 mg after each loose stool (maximum 16 mg/day). 5
• Critical pitfall: Antimotility agents can mask worsening symptoms and delay recognition of complications like severe dehydration or secondary bacterial infection. 4

Adjunctive Therapies

Probiotics may be offered to reduce symptom severity and duration in immunocompetent patients. 4, 2

Infection Control

Implement strict infection control measures: 5

• Proper hand hygiene after toilet use and before food preparation
• Use gloves and gowns when caring for patients with diarrhea
• Clean and disinfect contaminated surfaces promptly
• Norovirus requires only 10-100 viral particles for transmission and spreads via contact with excretions, even aerosols. 1

Common Pitfalls to Avoid

• Never use antimotility or antispasmodic agents as monotherapy without ensuring adequate hydration first. 4
• Do not prescribe empiric antibiotics for uncomplicated acute watery diarrhea, as this promotes resistance and provides minimal benefit. 1
• Avoid inadequate fluid resuscitation, which can lead to worsening dehydration and shock. 6
• Do not delay rehydration while pursuing extensive diagnostic workup in typical presentations. 2, 3

When to Pursue Further Diagnostic Testing

Reserve diagnostic investigation for: 2, 3

• Severe dehydration or illness
• Persistent fever
• Bloody or mucoid stools
• Immunosuppression
• Suspected nosocomial infection or outbreak
• Symptoms persisting >7 days