What is the most likely complication in a patient with a 5-week history of mildly bloody diarrhea, suspected to be caused by Enterohemorrhagic Escherichia coli (EHEC) or Shigella, aside from gram-negative sepsis?

Most Likely Complication: Hemolytic Uremic Syndrome (HUS)

In a patient with 5 weeks of mildly bloody diarrhea suspected to be EHEC or Shigella, the most likely complication is hemolytic uremic syndrome (HUS), not gram-negative sepsis. 1

Why HUS is the Primary Concern

Approximately 8% of patients diagnosed with STEC O157 infection develop HUS, a life-threatening condition characterized by thrombocytopenia, hemolytic anemia, and acute renal failure. 1 This risk is particularly elevated with EHEC infections producing Shiga toxin 2 (Stx2), which is more potent and consistently associated with progression to HUS. 1

Key Clinical Features Supporting HUS Risk:

• Duration of symptoms (5 weeks) suggests persistent infection with ongoing toxin exposure, increasing the cumulative risk of HUS development 1
• Bloody diarrhea is present in approximately 90% of STEC patients who develop HUS, though 10% may develop HUS without visible blood 1
• EHEC strains carrying stx2 genes are specifically associated with increased risk of both bloody diarrhea and HUS 1

Why Not Gram-Negative Sepsis?

While sepsis is a recognized complication of Shigella infections, it is not the most common or characteristic complication of EHEC/STEC infections. 2

Sepsis Considerations:

• Shigella sepsis occurs primarily in severely ill, malnourished patients and is more common in hospital-based studies from developing countries 2
• Blood cultures should be obtained if there are signs of septicemia, systemic manifestations, or in high-risk groups (infants <3 months, immunocompromised patients) 1
• However, the hallmark complication of EHEC is HUS, not bacteremia 1, 3

Critical Monitoring Requirements

Daily platelet count monitoring is essential during days 1-14 of diarrheal illness, as patients with a decreasing platelet count trend are at greater risk of developing HUS. 1 Monitoring can stop when the platelet count begins to increase or stabilize with resolved symptoms. 1

Additional Laboratory Surveillance:

• Complete blood count with differential - elevated WBC count (>10,000 cells/µL in ~65% of E. coli O157 cases) and high neutrophil counts often occur in patients who subsequently develop HUS 1
• Peripheral blood smear for red blood cell fragmentation when HUS is suspected 1
• Creatinine and blood pressure monitoring for signs of volume overload and acute renal failure 1

Critical Management Pitfall

Avoid antibiotic therapy in STEC infections, particularly those producing Shiga toxin 2 or when the toxin genotype is unknown, as antimicrobial therapy is associated with increased risk of HUS and more severe disease. 1, 4 This is a strong recommendation with moderate-quality evidence. 1

Exception for Shigella:

• If Shigella is confirmed (not STEC), empiric antimicrobial therapy with fluoroquinolone or azithromycin is appropriate for ill patients with fever, bloody diarrhea, and bacillary dysentery 1

Protective Intervention

Early intravenous fluid administration during the diarrhea phase reduces the risk of oligoanuric renal failure among children who subsequently develop HUS. 1 Dehydration at admission is associated with increased need for dialysis in post-diarrheal HUS. 1