Enterohaemorrhagic E. coli Infection

Enterohaemorrhagic Escherichia coli (EHEC), a subset of Shiga toxin producing E coli, causes haemorrhagic colitis and haemolytic uraemic syndrome through Shiga toxin 1 and 2.

• Serotype O157:H7 is most common; non-O157 serogroups (O26, O111, O103, O145) also occur.
• Reservoir is cattle; spread follows undercooked beef, raw milk, contaminated produce and water, and person to person transmission (infective dose below 100 organisms).
• Haemolytic uraemic syndrome develops in about 5 to 15 percent of infected children and is the leading cause of acute kidney injury in children in some settings.

Incubation 3 to 4 days (range 1 to 8 days).

• Severe abdominal cramps, initially watery diarrhoea that turns grossly bloody within 1 to 2 days; fever is absent or low grade.
• Haemolytic uraemic syndrome 5 to 10 days after onset: pallor, oliguria, oedema, hypertension, petechiae, seizures and confusion.
• Differential diagnosis: Shigella dysentery, Campylobacter, Salmonella, inflammatory bowel disease, ischaemic colitis, intussusception, appendicitis, thrombotic thrombocytopenic purpura, atypical haemolytic uraemic syndrome.
• Complications: haemolytic uraemic syndrome, thrombotic microangiopathy, acute kidney injury, central nervous system involvement (stroke, seizures, coma), bowel necrosis or perforation, rectal prolapse, pancreatitis, cardiomyopathy, diabetes mellitus after pancreatic injury, and chronic kidney disease.

Stool Shiga toxin immunoassay or PCR (stx1, stx2), and culture on sorbitol MacConkey agar for O157 (non-O157 needs toxin testing).

• Full blood count (anaemia, thrombocytopenia below 150 x 10^9/L, leucocytosis), blood film showing schistocytes, reticulocytes, lactate dehydrogenase, haptoglobin, creatinine, urea, electrolytes, coagulation screen (normal), Coombs test (negative).
• Urine for haematuria and proteinuria; monitor creatinine and platelets daily for 2 weeks in children with bloody diarrhoea.
• Neuroimaging for neurological signs.

Supportive

• Early isotonic intravenous volume expansion in the first 4 days (for example 0.9 percent sodium chloride or Ringer lactate 10 to 20 mL/kg boluses, then maintenance) reduces progression to haemolytic uraemic syndrome and dialysis.
• Avoid antimotility drugs, NSAIDs and opioids.
• Haemolytic uraemic syndrome: strict fluid balance, treat hypertension (amlodipine 0.1 to 0.2 mg/kg daily or nifedipine), correct hyperkalaemia, nutrition support, dialysis for refractory fluid overload, hyperkalaemia, acidosis or uraemia.
• Transfuse packed red cells slowly for haemoglobin below 7 g/dL; platelets only for active bleeding or procedures.

Pharmacological

• Antibiotics are avoided in suspected or confirmed EHEC because they may increase Shiga toxin release and haemolytic uraemic syndrome risk.
• Eculizumab (complement inhibitor) is used in severe neurological disease or refractory disease: adults 900 mg IV weekly for 4 doses, then 1200 mg at week 5 and every 2 weeks (children dosed by weight); meningococcal vaccination and penicillin prophylaxis are needed.
• Plasma exchange has unproven benefit and is not an initial treatment.

Special groups: children (the main group at risk of haemolytic uraemic syndrome), older adults (thrombotic thrombocytopenic purpura-like illness), pregnancy (nephrology and obstetric review).

Red flags: bloody diarrhoea with falling platelets, rising creatinine, oliguria, neurological signs, leucocytosis above 20 x 10^9/L.

Follow-up: renal function, blood pressure and urinalysis at 6, 12 months and annually for those with haemolytic uraemic syndrome; exclude infected individuals from childcare or food handling until two negative stool samples at least 24 hours apart.