What is the most appropriate management for a pediatric patient with abdominal pain, gaseous distention, and foul-smelling watery diarrhea after exposure to contaminated water?

Management of Pediatric Waterborne Gastroenteritis

The most appropriate management is metronidazole (option C), as this clinical presentation—foul-smelling watery diarrhea with gaseous distention following contaminated water exposure during camping—is highly suggestive of Giardia lamblia infection, for which metronidazole is the treatment of choice. 1, 2

Clinical Reasoning

Why Metronidazole is Correct

• Giardia is the most common parasitic cause of waterborne diarrhea in the United States, particularly associated with contaminated water sources during camping or outdoor activities 2
• The characteristic foul-smelling, watery diarrhea with gaseous distention and abdominal pain strongly suggests Giardia infection rather than viral or typical bacterial gastroenteritis 3, 2
• Metronidazole is effective for treating Giardia and interrupting transmission, which is particularly important in pediatric patients 2

Why Clindamycin is Incorrect

• Clindamycin has no role in treating waterborne gastroenteritis and is not indicated for Giardia, bacterial causes of watery diarrhea, or viral gastroenteritis 1
• The IDSA explicitly states that empiric antimicrobial therapy is not recommended for most pediatric patients with acute watery diarrhea without recent international travel, except for immunocompromised patients, young infants who appear ill, and patients with clinical features of sepsis 1

Essential Concurrent Management

Rehydration Therapy (Primary Priority)

• Oral rehydration solution (ORS) remains the cornerstone of treatment regardless of the specific pathogen 4, 1
• Assess dehydration severity clinically: mild (3-5%), moderate (6-9%), or severe (≥10%) 4
• For moderate dehydration, administer 100 mL/kg ORS over 2-4 hours, and replace ongoing stool losses with 10 mL/kg of ORS for each diarrheal stool 4, 1
• Severe dehydration requires immediate IV rehydration with 20 mL/kg boluses of Ringer's lactate or normal saline until perfusion normalizes 4

Nutritional Management

• Continue age-appropriate diet immediately after rehydration is completed—early feeding improves outcomes 1
• Continue breastfeeding throughout the illness if applicable 1
• For bottle-fed infants, resume full-strength formula immediately upon rehydration 4

Critical Pitfalls to Avoid

• Do not delay rehydration while awaiting diagnostic test results or stool examination for ova and parasites 1
• Do not give antimotility agents (loperamide) to any pediatric patient with acute diarrhea 1
• Do not restrict diet during or after rehydration—this worsens outcomes 1
• While stool examination for ova and parasites should ideally be performed three times on alternate days to rule out parasitic disease with confidence 2, treatment for Giardia can be initiated based on clinical presentation when the history and symptoms are highly suggestive

Diagnostic Considerations

• Stool microbiological tests are not routinely needed when viral gastroenteritis is the likely diagnosis 5
• However, in this case with contaminated water exposure and characteristic foul-smelling diarrhea with gaseous distention, the clinical picture warrants treatment for Giardia 3, 2
• Multiplex antimicrobial testing is preferred over traditional stool cultures when testing is indicated 6