What stool studies should be ordered for a patient with diarrhea for 5 days?

Stool Studies for a Patient with Diarrhea for 5 Days

For a patient with diarrhea for 5 days, stool testing should be performed for Salmonella, Shigella, Campylobacter, Yersinia, C. difficile, and Shiga toxin-producing E. coli (STEC) if the diarrhea is accompanied by fever, bloody or mucoid stools, severe abdominal cramping or tenderness, or signs of sepsis.

Initial Assessment Considerations

When evaluating a patient with diarrhea for 5 days, consider these key factors to guide testing:

Clinical Features That Warrant Testing

• Presence of fever
• Bloody or mucoid stools
• Severe abdominal cramping
• Abdominal tenderness
• Signs of sepsis
• Immunocompromised state

Specimen Collection

• The optimal specimen is a diarrheal stool sample (one that takes the shape of the container)
• If a timely diarrheal sample cannot be collected, a rectal swab may be used for bacterial infections 1
• A single diarrheal stool specimen is sufficient for C. difficile toxin detection

Recommended Stool Studies Algorithm

1. Basic Testing Panel (for most patients with concerning features)

• Stool culture for Salmonella, Shigella, Campylobacter, and Yersinia
• C. difficile toxin testing
• STEC testing (O157 by culture and non-O157 by Shiga toxin or genomic assays) 1

2. Additional Testing Based on Specific Risk Factors

For patients with travel history or specific exposures:

• Vibrio species testing if:
  • Large volume rice water stools
  • Exposure to salty/brackish waters
  • Consumption of raw/undercooked shellfish
  • Travel to cholera-endemic regions within 3 days prior to onset 1

For immunocompromised patients:

• Broader testing including viral studies and examination for parasites
• For HIV/AIDS patients: additional testing for Cryptosporidium, Cyclospora, Cystoisospora, microsporidia, Mycobacterium avium complex, and cytomegalovirus 1

For patients with persistent abdominal pain:

• Test for Yersinia enterocolitica, especially in:
  • School-aged children with right lower quadrant pain
  • Patients with fever at epidemiologic risk for yersiniosis
  • Infants with direct/indirect exposure to raw/undercooked pork products 1

3. When to Test for Parasites

• Test for Giardia in all patients with chronic diarrhea (strong recommendation) 1
• For other parasites (besides Giardia), testing is not recommended without travel history to or recent immigration from high-risk areas 1
• For travelers with diarrhea lasting ≥14 days, evaluate for intestinal parasitic infections 1

4. When to Test for C. difficile

• Test for C. difficile if:
  • History of antimicrobial use in the preceding 8-12 weeks
  • Healthcare-associated diarrhea
  • Age >2 years with persistent diarrhea without other etiology 1

Special Considerations

Hospitalized Patients

• For patients who develop diarrhea after 72 hours of hospitalization:
  • Avoid routine stool cultures and ova/parasite testing (low yield) 2, 3
  • Focus on C. difficile testing, which has much higher yield in nosocomial diarrhea 3

Blood Cultures

• Obtain blood cultures if:
  • Patient is <3 months of age
  • Signs of septicemia or enteric fever
  • Systemic manifestations of infection
  • Immunocompromised state
  • High-risk conditions (e.g., hemolytic anemia)
  • Travel to/contact with travelers from enteric fever-endemic areas 1

Common Pitfalls to Avoid

1. Overordering tests: Avoid ordering comprehensive stool studies for all patients with diarrhea. Target testing based on clinical presentation and risk factors.

2. Ignoring the "3-day rule": For hospitalized patients with diarrhea developing after 3 days of admission, routine stool cultures have very low yield; focus on C. difficile testing instead 1.

3. Missing C. difficile: Remember that some patients with C. difficile infection may present with ileus, toxic megacolon, or leukocytosis without diarrhea, especially in postoperative settings 1.

4. Inadequate specimen collection: Ensure proper collection of diarrheal stool samples that take the shape of the container for optimal diagnostic yield 1.

5. Overlooking molecular testing interpretation: Consider that multiple-pathogen nucleic acid amplification tests detect DNA and not necessarily viable organisms 1.