Are antibiotics avoided in Shiga toxin (Stx) producing Escherichia coli (STEC) infections when Stx genes are detected in a stool sample?

Antibiotics Should Be Avoided When Stx Genes Are Detected in Stool Samples

Antibiotics should be avoided in patients with Shiga toxin-producing Escherichia coli (STEC) infections when Stx genes are detected in stool samples due to increased risk of developing hemolytic uremic syndrome (HUS). 1 This recommendation is strongly supported by clinical guidelines and research evidence.

Rationale for Avoiding Antibiotics in STEC Infections

• The Infectious Diseases Society of America and the Centers for Disease Control and Prevention (CDC) explicitly recommend avoiding all antibiotics in patients with STEC infections 1
• Multiple studies show antibiotics may increase the risk of developing HUS, a serious complication that can lead to kidney failure 1, 2
• Antibiotics that induce the bacterial SOS response (particularly quinolones, trimethoprim, and furazolidone) can trigger increased toxin production by STEC 3
• Laboratory studies demonstrate that certain antibiotics like ciprofloxacin cause:
  • Induction of Shiga toxin-encoding bacteriophages
  • Enhanced Shiga toxin production
  • Increased mortality in animal models 4

Proper Management of STEC Infections

Diagnostic Approach

• All stools from patients with acute community-acquired diarrhea should be:
  • Cultured for O157 STEC on selective and differential agar
  • Simultaneously tested for non-O157 STEC with assays that detect Shiga toxins or their encoding genes 5
• Rapid and sensitive detection methods like real-time PCR can identify STEC from stool specimens with high sensitivity and specificity 6
• Detection of STEC or Shiga toxin should be promptly reported to:
  • The treating physician
  • Public health authorities for case investigation 5

Recommended Treatment Approach

1. Discontinue antibiotics immediately if they were started before diagnosis 1
2. Provide supportive care:
   • Early parenteral volume expansion to decrease risk of renal damage 5, 1
   • Oral or intravenous rehydration therapy based on dehydration severity 1
3. Avoid harmful treatments:
   • All antibiotics (β-lactams, fluoroquinolones, TMP-SMX, metronidazole) 1
   • Antimotility agents 1
4. Monitor for signs of HUS:
   • Thrombocytopenia
   • Hemolytic anemia
   • Renal failure 1

Clinical Considerations and Pitfalls

• Common pitfall: Prescribing empiric antibiotics for bloody diarrhea before STEC is ruled out

  • Approximately 8% of persons with O157 STEC infection develop HUS, with highest risk in children under 5 years 1
  • Early diagnosis is critical to prevent inappropriate treatments 5

• Important caveat: Antibiotics should be avoided even in immunocompromised patients with confirmed STEC infection 1

• Emerging concern: Non-O157 STEC infections are often underdiagnosed but carry similar risks 7

  • Common non-O157 STEC serogroups include O26, O45, O103, O111, O121, and O145 1
  • These require specialized testing for detection

• Mechanism of harm: Antibiotics, particularly quinolones, can induce the bacterial SOS response, leading to:

  • Up to 140-fold increase in stx2 gene transcription
  • Enhanced toxin production
  • Increased risk of bacteriophage-mediated transfer of toxin genes 3

The evidence clearly demonstrates that antibiotics should be avoided when Stx genes are detected in stool samples, with treatment focused on supportive care and careful monitoring for complications.