Does E. coli (Escherichia coli) O157:H7 infection without Shiga toxin (stx) or Locus of Enterocyte Effacement (LEE) require antibiotic treatment and can it cause severe disease?

Management of E. coli O157:H7 without Shiga toxin or LEE

Antibiotic treatment is not recommended for E. coli O157:H7 infections, even when Shiga toxin (stx) or Locus of Enterocyte Effacement (LEE) are absent, as the risk of developing complications outweighs potential benefits.

Disease Severity and Pathogenicity

E. coli O157:H7 strains without Shiga toxin or LEE generally have reduced pathogenicity compared to typical STEC strains, but can still cause gastrointestinal illness. The 2017 IDSA guidelines for infectious diarrhea provide clear direction on this issue:

• Strains that lack Shiga toxin production capability may have either lost the Stx phage or be progenitors of STEC O157:H7 1
• These strains can still cause diarrheal illness, though typically less severe than those producing Shiga toxin
• The absence of Shiga toxin significantly reduces the risk of hemolytic uremic syndrome (HUS), which is the most severe complication of STEC infection

Antibiotic Treatment Considerations

The IDSA guidelines specifically address treatment of STEC infections:

• "Antimicrobial therapy for people with infections attributed to STEC O157 and other STEC that produce Shiga toxin 2 (or if the toxin genotype is unknown) should be avoided" 2
• For non-Shiga toxin producing strains, the guidelines note that antimicrobial therapy is "debatable due to insufficient evidence of benefit or the potential harm associated with some classes of antimicrobial agents" 2

Even for strains without Shiga toxin, antibiotics should be avoided for several important reasons:

1. Antibiotics that target DNA synthesis (like ciprofloxacin) can increase Shiga toxin production in strains that may have low levels of toxin not detected by testing 3
2. Antibiotics may trigger conversion of lysogenic phages to the lytic cycle in strains with undetected Stx phages
3. There is insufficient evidence showing clinical benefit of antibiotics for E. coli O157:H7 infections regardless of toxin status

Management Approach

The recommended management approach includes:

1. Supportive care:

   • Oral or intravenous rehydration based on dehydration severity 2
   • Monitor for complications, even though risk is lower without Shiga toxin

2. Avoid medications that may worsen outcomes:

   • No antibiotics (as discussed above)
   • Avoid antimotility agents that may prolong toxin exposure to intestinal mucosa 4

3. Infection control measures:

   • Follow jurisdictional recommendations for outbreak reporting 2
   • Implement appropriate infection control to prevent transmission 4

Monitoring and Follow-up

While the risk of HUS is significantly lower in the absence of Shiga toxin, patients should still be monitored for:

• Persistent or worsening symptoms
• Development of bloody diarrhea
• Signs of dehydration
• Laboratory abnormalities suggesting systemic involvement

Public Health Considerations

All O157 isolates should be reported to public health authorities regardless of H7 or Shiga toxin status 4. This enables:

• Outbreak detection and monitoring
• Implementation of appropriate infection control measures
• Molecular characterization through PFGE subtyping

Conclusion

The absence of Shiga toxin and LEE in E. coli O157:H7 likely indicates reduced virulence, but these strains can still cause gastrointestinal illness. The standard approach remains supportive care without antibiotics, as the risks of antimicrobial therapy outweigh potential benefits even in the absence of Shiga toxin.