What is the treatment for bloody diarrhea caused by Escherichia coli (E. coli)?

Treatment for Bloody Diarrhea Caused by E. coli

For bloody diarrhea caused by E. coli, antibiotics are generally contraindicated when Shiga toxin-producing E. coli (STEC) is suspected or confirmed, as they significantly increase the risk of hemolytic uremic syndrome (HUS). 1, 2

Critical First Step: Identify if STEC is Involved

The most important initial action is determining whether the E. coli is a Shiga toxin-producing strain (STEC), particularly E. coli O157:H7 or other Shiga toxin 2-producing strains, because this fundamentally changes management. 1

Clinical features suggesting STEC infection include: 1

• Bloody diarrhea with abdominal tenderness
• Absence of fever at initial presentation (approximately 65% have WBC >10,000/µL but may be afebrile)
• Recent consumption of undercooked ground beef, leafy greens, or contaminated water 3

Immediate diagnostic testing should include: 1

• Stool testing for Shiga toxin (or genes encoding them)
• Culture to distinguish E. coli O157:H7 from other STEC
• If available, tests that differentiate Shiga toxin 1 from Shiga toxin 2 (toxin 2 is more potent and associated with higher HUS risk)

Treatment Algorithm

If STEC is Suspected or Confirmed: NO ANTIBIOTICS

The cornerstone of management is aggressive hydration, NOT antibiotics. 1, 2

• Intravenous fluid administration during the diarrhea phase reduces the risk of oligoanuric renal failure in patients who subsequently develop HUS 1
• Dehydration at admission is associated with increased need for dialysis in post-diarrheal HUS 1
• Oral rehydration solution (ORS) for mild-moderate dehydration; IV fluids for severe dehydration, shock, altered mental status, or ileus 2

Why no antibiotics for STEC? Antibiotics may increase the risk of HUS by promoting bacterial lysis and subsequent release of Shiga toxin. 2

If STEC is Ruled Out and Other Pathogenic E. coli is Suspected

Empiric antibiotics may be considered in specific circumstances: 1, 2

Indications for empiric treatment while awaiting culture results:

• Infants <3 months of age with suspected bacterial etiology 1, 2
• Patients with documented fever (in medical setting), abdominal pain, bloody diarrhea, and bacillary dysentery syndrome (frequent scant bloody stools, fever, cramps, tenesmus) 1, 2
• Recent international travelers with temperature ≥38.5°C and/or signs of sepsis 1, 2
• Immunocompromised patients with severe illness and bloody diarrhea 1, 2

Antibiotic selection: 1, 2

• Adults: Fluoroquinolone (ciprofloxacin 500 mg twice daily for 3 days or 750 mg single dose) OR azithromycin (500 mg daily for 3 days or 1 gram single dose), depending on local resistance patterns and travel history
• Children: Third-generation cephalosporin for infants <3 months or those with neurologic involvement; azithromycin for other children based on local susceptibility patterns
• Geographic considerations: Azithromycin is preferred for travelers from Southeast Asia and India due to high fluoroquinolone resistance 2

Modify or discontinue antibiotics once pathogen is identified and STEC is confirmed. 2, 4

Monitoring and Supportive Care

All patients require close monitoring for HUS development: 1

• Approximately 10% of STEC patients who develop HUS do not have bloody diarrhea initially
• Monitor for hemolytic anemia, thrombocytopenia, and acute renal failure
• Serial abdominal examinations in severe cases

Reassess patients who fail to improve: 1, 4

• Fluid and electrolyte balance
• Nutritional status
• Consider non-infectious causes (lactose intolerance, inflammatory bowel disease, irritable bowel syndrome) if symptoms persist ≥14 days

Critical Pitfalls to Avoid

• Never give antibiotics empirically for bloody diarrhea without first considering STEC - this is the most dangerous error as it increases HUS risk 1, 2
• Do not use antimotility agents (loperamide) in children <18 years or in any patient with bloody diarrhea until STEC is excluded 4
• Do not neglect aggressive rehydration while focusing on antimicrobial decisions - volume depletion is a major risk factor for diarrhea-related deaths and HUS complications 1, 2
• Asymptomatic contacts should NOT receive empiric antibiotics 1, 4