Fecal Characteristics of E. coli Diarrhea
E. coli diarrhea typically presents as acute, often bloody diarrhea, though blood in the stool is NOT always present and should never be used to rule out infection. 1
Key Stool Characteristics
STEC (Shiga Toxin-Producing E. coli) - Most Clinically Important
Bloody diarrhea is the classic presentation, but this is misleading in practice:
- Both O157 and non-O157 STEC strains are frequently isolated from patients with NON-bloody diarrhea 1
- Approximately 8% progress to hemolytic uremic syndrome (HUS), making early recognition critical 1
- Severe abdominal cramping accompanies the diarrhea 2
White Blood Cells in Stool - Unreliable Marker
White blood cells are often but NOT always detected in STEC infections and should NOT be used as a criterion for testing 1. This is a critical pitfall—many clinicians inappropriately use absence of fecal leukocytes to exclude E. coli testing.
Other Diarrheagenic E. coli Pathotypes
The stool characteristics vary by pathotype 3, 4:
- EPEC (Enteropathogenic E. coli): Mostly acute, mild diarrhea lasting 6-13 days, though some patients experience severe diarrhea with 10-40 bowel movements per day or persistent/chronic diarrhea 3
- EAEC (Enteroaggregative E. coli): Most commonly identified subtype in surveillance data, often presents with mucous-like stool 5
- ETEC (Enterotoxigenic E. coli): Typically watery diarrhea
Clinical Presentation Patterns
Timing and Duration
- Acute diarrhea is the predominant pattern (0-13 days) 2
- Bacteria become difficult or impossible to detect after 1 week of illness 1
- Some strains cause persistent/chronic diarrhea, though this is uncommon 1
Age-Related Differences
- Children: More likely to have fever, vomiting, and abnormal serum sodium levels 3
- Adults: More often report abdominal pain and longer duration of diarrhea 3
- Highest incidence in children <5 years, but almost half of all STEC isolates come from persons >12 years 1
Associated Findings
- Leukocytosis occurs in 24% of symptomatic aEPEC infections 3
- Fever may or may not be present
- Severe abdominal cramping, particularly with STEC 2
Critical Testing Implications
All stool specimens from patients with acute community-acquired diarrhea should be tested for STEC regardless of:
- Presence or absence of blood in stool 1
- Patient age 1
- Season of the year 1
- Presence or absence of white blood cells 1
The absence of visible blood does NOT rule out STEC infection—this is the single most important clinical pitfall to avoid 1. Selective testing based on bloody stools results in many missed infections and delayed outbreak detection.