What is the best course of treatment for a 24-year-old active duty male with a 1-day history of nausea, vomiting, and diarrhea, who recently had a possible upper respiratory infection (URI) and presents with bilateral swollen tonsils, abdominal tenderness, and guarding, but is hemodynamically stable and afebrile?

Management of Acute Gastroenteritis with Abdominal Tenderness

This patient requires symptomatic treatment with oral rehydration, ondansetron for nausea/vomiting control, and close observation for 24-48 hours, but the bilateral lower quadrant tenderness with guarding warrants urgent surgical evaluation to exclude appendicitis or other acute abdominal pathology before attributing symptoms solely to gastroenteritis. 1

Critical Initial Assessment

The concerning feature here is bilateral lower quadrant tenderness with guarding in a patient with gastroenteritis symptoms. 1 This physical finding is atypical for uncomplicated viral gastroenteritis and raises concern for:

• Appendicitis (can present with diarrhea and vomiting in 10-20% of cases)
• Mesenteric adenitis (especially given recent URI symptoms)
• Inflammatory bowel disease (though less likely with acute 1-day onset)
• Infectious colitis requiring specific treatment

Key pitfall to avoid: Do not dismiss significant abdominal tenderness and guarding as simple gastroenteritis without excluding surgical pathology. 1

Immediate Management Steps

Hydration Assessment and Repletion

• Oral rehydration solution (ORS) is first-line therapy for mild to moderate dehydration, even in the presence of vomiting. 2
• The patient should receive ORS containing Na 90 mM, K 20 mM, Cl 80 mM, HCO₃ 30 mM, glucose 111 mM. 1
• Given hemodynamic stability and ability to tolerate oral intake, IV fluids are not immediately necessary unless ORS fails. 2

Antiemetic Therapy

• Ondansetron 4-8 mg orally or IV as needed is the recommended antiemetic for symptomatic relief in acute gastroenteritis. 1, 2
• This facilitates tolerance of oral rehydration and improves patient comfort. 3, 1
• Ondansetron may increase stool volume/diarrhea as a side effect, but this is acceptable given the benefit for nausea control. 3, 2

Antidiarrheal Considerations

Loperamide should NOT be used in this patient at present. 3, 1 The presence of abdominal tenderness and guarding raises concern for inflammatory or invasive diarrhea, where antimotility agents are contraindicated due to risk of toxic megacolon. 3

• Loperamide 4 mg initial dose, then 2 mg after each loose stool (maximum 16 mg/day) would only be appropriate if:
  • No fever develops 3, 1
  • No blood in stool 1
  • Abdominal examination normalizes 3
  • No signs of inflammatory diarrhea 3

When to Obtain Stool Studies

Stool studies are NOT routinely needed for acute diarrhea <14 days with no fever, no blood, and no severe systemic symptoms. 1 However, testing becomes indicated if:

• Fever develops 1
• Blood or pus appears in stool 1
• Severe abdominal pain persists or worsens 1
• Symptoms persist >7 days 1
• Recent antibiotic use (concern for C. difficile) 3
• Severe dehydration requiring hospitalization 1

The URI Connection and Mesenteric Adenitis

The recent 6-7 day URI with bilateral swollen tonsils (without exudates) suggests a viral upper respiratory infection. 1 This temporal relationship is important because:

• Mesenteric adenitis commonly follows viral URI and can cause significant abdominal pain with tenderness, mimicking appendicitis. 1
• Adenovirus and other respiratory viruses can cause both URI and gastroenteritis symptoms simultaneously. 1
• The bilateral nature of lower quadrant tenderness may favor mesenteric adenitis over appendicitis (which typically localizes to right lower quadrant). 1

Observation Protocol

Close monitoring over 24-48 hours is essential with serial abdominal examinations. 3, 1 The patient should be assessed for:

• Worsening peritoneal signs (increasing tenderness, rebound, rigidity) 3, 1
• Fever development (temperature >38°C) 1
• Persistent or worsening pain despite symptomatic treatment 1
• Signs of dehydration (orthostatic vital signs, decreased urine output) 1
• Bloody stools 1

If any of these develop, immediate surgical consultation and laboratory evaluation (CBC, CRP, electrolytes) are warranted. 3, 1

Dietary Management

• Early refeeding is recommended once vomiting is controlled with ondansetron. 3
• Small, frequent meals are better tolerated than large meals. 2
• The BRAT diet (bananas, rice, applesauce, toast) has limited supporting data but is not harmful. 3
• Avoid instructing the patient to refrain from solid food for 24 hours, as this does not provide clinical benefit. 3
• Continue normal diet as tolerated. 3

Special Consideration: COVID-19

Given the GI symptoms and recent URI, consider COVID-19 testing. 1 Up to 61% of COVID-19 outpatients experience GI symptoms, and GI symptoms can precede respiratory symptoms by several days. 1 If COVID-19 is suspected, the patient should self-quarantine until symptoms resolve. 1

Antibiotic Considerations

Antibiotics are NOT indicated for uncomplicated acute gastroenteritis in this immunocompetent patient. 3, 4 Antibiotic treatment does not improve outcomes in uncomplicated URI or acute diarrhea in previously healthy individuals. 4

Antibiotics would only be considered if:

• Stool studies identify a bacterial pathogen requiring treatment 3
• Surgical pathology is identified requiring perioperative coverage 3
• Severe systemic illness develops 3

Disposition Decision

This patient can be managed as outpatient IF:

• Abdominal examination improves or remains stable over 2-4 hours of observation 1
• Tolerates oral rehydration without persistent vomiting 1, 2
• No fever develops 1
• No peritoneal signs emerge 1
• Reliable for follow-up within 24 hours 1

Admission or surgical consultation is required IF:

• Peritoneal signs worsen or persist 3, 1
• Fever develops 1
• Unable to tolerate oral intake despite ondansetron 2
• Signs of severe dehydration 1
• Clinical deterioration 1

Return Precautions

The patient must return immediately for:

• Fever >38°C 1
• Worsening abdominal pain 1
• Blood in stool 1
• Persistent vomiting despite ondansetron 2
• Signs of dehydration (dizziness, decreased urination, dry mouth) 1
• Symptoms persisting >7 days 1