Recommended Stool Tests and Treatment for Diarrhea
For initial evaluation of diarrhea, stool testing should be performed for Salmonella, Shigella, Campylobacter, Yersinia, C. difficile, and STEC in patients with fever, bloody or mucoid stools, severe abdominal cramping or tenderness, or signs of sepsis. 1, 2
Initial Diagnostic Testing Based on Clinical Presentation
High-Risk Patients Requiring Testing
- Fever with diarrhea
- Bloody or mucoid stools
- Severe abdominal cramping or tenderness
- Signs of sepsis
- Immunocompromised patients
- Infants <3 months of age
- Patients with hemolytic anemia
- Recent travelers from endemic areas with febrile illness
- Suspected outbreak settings
Standard Initial Testing Panel
- Bacterial culture for Salmonella, Shigella, Campylobacter, and Yersinia 1, 2
- C. difficile testing (if healthcare exposure or recent antibiotics) 1, 2
- STEC testing - culture for O157:H7 on Sorbitol-MacConkey agar or chromogenic agar AND Shiga toxin detection for non-O157 STEC 1, 2
Additional Targeted Testing Based on Specific Presentations
- Vibrio species: Test if patient has large-volume rice-water stools or exposure to seafood/brackish waters 1
- Yersinia enterocolitica: Test if patient has persistent abdominal pain, especially school-aged children with right lower quadrant pain 1
- Parasitic testing: Consider for persistent diarrhea (>14 days), especially in travelers or immunocompromised patients 1
Treatment Approach Based on Cause
1. Bacterial Infections
- Non-severe, non-bloody diarrhea: Supportive care with fluid and electrolyte replacement
- Severe or bloody diarrhea:
- Targeted antimicrobial therapy based on identified pathogen
- Avoid antimotility agents in bloody diarrhea until STEC is ruled out
2. C. difficile Infection
- First-line treatment: Oral vancomycin 125 mg four times daily for 10 days 3
- Clinical success rates of approximately 81% can be expected 3
- Monitor for recurrence (occurs in 18-23% of cases) 3
3. Viral Gastroenteritis
- Supportive care with fluid and electrolyte replacement
- Antimotility agents may be used for symptom control in non-bloody diarrhea
4. Parasitic Infections
- Targeted antiparasitic therapy based on identified organism
- For Giardia: metronidazole or tinidazole 1
5. Non-specific/Uncomplicated Diarrhea
- Loperamide dosing for adults: Initial 4 mg (two capsules) followed by 2 mg after each loose stool, maximum 16 mg/day 4
- Loperamide for children 2-12 years: Age/weight-based dosing 4
- 2-5 years (13-20 kg): 1 mg three times daily
- 6-8 years (20-30 kg): 2 mg twice daily
- 8-12 years (>30 kg): 2 mg three times daily
Special Considerations
Immunocompromised Patients
- Broader testing recommended including:
Chronic Diarrhea (>14-30 days)
- Consider screening for:
Traveler's Diarrhea
- Testing not recommended in most uncomplicated cases 1
- For persistent diarrhea (>14 days), evaluate for parasitic infections 1
- Test for C. difficile if antimicrobial agents were used in preceding 8-12 weeks 1
Common Pitfalls and Caveats
Overreliance on stool cultures: Standard stool cultures have limited sensitivity (60-90%) and require 24-48 hours for results 6, 7
Failure to consider non-infectious causes: Most chronic diarrhea cases are non-infectious, with IBS/functional diarrhea being common causes 5
Inappropriate use of antimotility agents: Avoid in bloody diarrhea until STEC is ruled out due to risk of complications
Interpretation of molecular tests: Nucleic acid amplification tests detect DNA and not necessarily viable organisms; clinical correlation is essential 1, 8
Specimen collection timing: Fresh diarrheal stool is the optimal specimen, providing higher detection rates (49% vs. 9%) 2
Overlooking C. difficile in antibiotic-exposed patients: Always consider C. difficile testing in patients with recent antibiotic exposure or healthcare contact
Failure to distinguish between secretory and osmotic diarrhea: This distinction helps narrow differential diagnosis and guide treatment 9