What is the recommended treatment for a patient with Shiga toxin-producing Escherichia coli (STEC) infection, characterized by bloody diarrhea and fever?

Treatment of STEC Infection

Antibiotics should be avoided entirely in patients with confirmed or suspected STEC infection, particularly STEC O157 and any strain producing Shiga toxin 2, as they significantly increase the risk of hemolytic uremic syndrome (HUS). 1

Primary Management: Aggressive Supportive Care

The cornerstone of STEC treatment is aggressive rehydration therapy, not antimicrobial therapy. 1

• Use reduced osmolarity oral rehydration solution (ORS) for mild to moderate dehydration 2, 3
• Administer intravenous isotonic fluids (lactated Ringer's or normal saline) for severe dehydration, shock, or altered mental status 3
• Optimal hydration provides nephroprotection and may reduce the risk of HUS progression 4

Critical Contraindication: Antibiotic Avoidance

The Infectious Diseases Society of America provides a strong recommendation (moderate quality evidence) to avoid antimicrobial therapy for STEC O157 and other STEC producing Shiga toxin 2, or when the toxin genotype is unknown. 1

Evidence Supporting Antibiotic Avoidance:

• A 2016 meta-analysis of low risk-of-bias studies demonstrated that antibiotic use is associated with a 2.24-fold increased odds of developing HUS (95% CI 1.45-3.46) 5
• Antibiotics induce expression of Shiga toxins, which are associated with lysogenic bacteriophages, thereby increasing toxin release 6
• No randomized controlled trial has demonstrated effectiveness of antibiotics for preventing HUS in STEC infections 7
• The association between antibiotics and HUS is strongest when analyzing only high-quality studies using appropriate HUS definitions 5, 8

Medications to Avoid

Beyond antibiotics, several other medications are contraindicated in suspected STEC infection:

• Antimotility agents (e.g., loperamide) should not be used 4
• Narcotics should be avoided 4
• Non-steroidal anti-inflammatory drugs (NSAIDs) are contraindicated 4

Before Initiating Any Empiric Antibiotics for Bloody Diarrhea

If a patient presents with bloody diarrhea and fever, STEC must be ruled out before starting empiric antibiotics. 3

• Obtain stool culture and Shiga toxin testing immediately 3
• While awaiting results, empiric antibiotics are generally NOT recommended in immunocompetent adults and children 1
• The only exceptions for empiric therapy in bloody diarrhea are: infants <3 months, patients with documented fever and bacillary dysentery syndrome presumptively due to Shigella, recent international travelers with fever ≥38.5°C or sepsis, and immunocompromised patients with severe illness 1, 2

Monitoring for HUS Development

Approximately 5-8% of STEC-infected individuals will develop HUS, with rates up to 15% in young children infected with E. coli O157:H7. 4

• Monitor hemoglobin, platelets, and renal function closely in all confirmed STEC cases 9
• HUS typically develops after an average of 3-8 days following initial bloody diarrhea 4
• Neurological injury is the most frequent non-renal complication and the first cause of death 4
• Early initiation of plasmapheresis may improve prognosis in severe cases 4

Special Considerations for Non-O157 STEC

For STEC strains that do not produce Shiga toxin 2 (generally non-O157 STEC), the role of antimicrobial therapy remains debatable due to insufficient evidence. 1

• The Infectious Diseases Society of America notes there is insufficient evidence of benefit or potential harm for these specific strains 1
• In the absence of clear benefit and given the potential for harm, a conservative approach avoiding antibiotics is prudent 1

Long-Term Follow-Up

• Any patient with a history of HUS requires long-term renal follow-up 4
• One-third of patients suffer from long-term renal morbidity including proteinuria, hypertension, and decreased glomerular filtration rate 4
• The longer the duration of anuria during acute HUS, the greater the risk of permanent sequelae 4

Common Pitfalls to Avoid

• Never give antibiotics empirically for bloody diarrhea without ruling out STEC first through stool culture and Shiga toxin testing 9
• Do not assume that newer antibiotics or specific classes are safe - the meta-analysis showing harm included various antibiotic classes 5, 8
• Do not treat asymptomatic contacts of patients with bloody diarrhea 1, 2
• Do not use antimotility agents even if diarrhea is severe, as this may prolong toxin exposure 4