What is the role of fecal calprotectin in diagnosing and managing Shiga toxin 2 (Stx2) Escherichia coli (E. coli) infections?

Fecal Calprotectin Has No Role in Diagnosing or Managing Shiga Toxin 2 E. coli Infections

Fecal calprotectin is not recommended for the diagnosis or management of Shiga toxin-producing E. coli (STEC) infections, including Stx2-producing strains. The established diagnostic approach relies on direct detection of Shiga toxin or the genes encoding it, combined with bacterial culture for E. coli O157:H7 1.

Recommended Diagnostic Approach for STEC

Primary Testing Strategy

All stool specimens from patients with acute community-acquired diarrhea should be simultaneously cultured for E. coli O157:H7 AND tested with an assay that detects Shiga toxins 1. This dual approach is critical because:

• Culture alone misses non-O157 STEC strains that may produce Shiga toxin 2, which are associated with higher risk of hemolytic uremic syndrome (HUS) 1
• Toxin detection alone does not allow for bacterial isolation, which is essential for outbreak detection and public health surveillance 1
• Stx2-producing strains are more virulent than Stx1-producing strains and carry increased risk of both bloody diarrhea and HUS 1

Testing Indications

The Infectious Diseases Society of America and CDC recommend STEC testing for 1:

• All patients with acute community-acquired diarrhea, regardless of:

  • Patient age (not just children) 1
  • Season of the year 1
  • Presence or absence of visible blood in stool 1
  • Presence or absence of fever 1

• Specific high-risk presentations including 1:

  • Fever with diarrhea
  • Bloody or mucoid stools
  • Severe abdominal cramping or tenderness
  • Signs of sepsis

Timing of Specimen Collection

Collect stool specimens as early as possible after diarrhea onset, ideally within the first week of illness 1. Bacteria and toxin genes may be difficult or impossible to detect after 1 week, and Shiga toxin genes can be lost by the bacteria over time 1.

Why Fecal Calprotectin Is Not Used

Fecal calprotectin is a nonspecific marker of intestinal inflammation that does not:

• Distinguish STEC from other causes of inflammatory diarrhea
• Identify the specific toxin type (Stx1 vs. Stx2)
• Provide bacterial isolates for serotyping or outbreak investigation
• Meet the diagnostic requirements outlined in established guidelines 1

Clinical Management Implications

Critical Management Principle

Early identification of Stx2-producing STEC is essential because antibiotics are absolutely contraindicated 2, 3. Antibiotic use increases the risk of HUS by inducing bacterial lysis and increasing Shiga toxin release 2.

Cornerstone of Treatment

Aggressive intravenous volume expansion is the primary therapeutic intervention that reduces morbidity and mortality 2. Early volume expansion during the diarrhea phase (before HUS develops) significantly reduces the risk of oligoanuric renal failure in children who subsequently develop HUS 1, 2.

Monitoring for Complications

Approximately 8% of patients with O157 STEC infection develop HUS, characterized by thrombocytopenia, hemolytic anemia, and renal failure 1, 2. Monitor for 2:

• Complete blood count for thrombocytopenia and hemolytic anemia
• Renal function (creatinine, blood urea nitrogen)
• Urine output for early HUS detection

Common Pitfalls to Avoid

• Do not rely on selective testing criteria such as visible blood in stool, patient age, or season—this misses many infections 1
• Do not use white blood cell presence in stool as a criterion for STEC testing, as it is neither sensitive nor specific 1
• Do not delay testing—specimens should be collected and tested as early as possible in the illness course 1
• Do not administer antibiotics once STEC is suspected or confirmed, particularly for Stx2-producing strains 2, 3
• Do not use fecal calprotectin as a substitute for direct Shiga toxin detection and bacterial culture 1