Haemolytic Uraemic Syndrome
A 4-year-old girl is admitted with 2 days of reduced urine output and pallor. Six days ago she developed crampy abdominal pain and diarrhoea that became bloody, three days after eating an undercooked beef burger. Haemoglobin is 7.4 g/dL, platelets are 42 × 10⁹/L, the blood film shows schistocytes, the direct antiglobulin test is negative, and creatinine is 180 micromol/L. Which culture is most likely to identify the causative organism?
- A.Stool cultureCorrect
- B.Blood culture
- C.Urine culture
- D.Throat swab culture
Explanation
This child has typical haemolytic uraemic syndrome, and the causative organism is Shiga toxin-producing Escherichia coli, most often serotype O157:H7, which is identified by stool culture on sorbitol-MacConkey agar together with stool Shiga toxin immunoassay or polymerase chain reaction. The triad of microangiopathic haemolytic anaemia with schistocytes, thrombocytopenia and acute kidney injury following a prodrome of bloody diarrhoea is diagnostic. Shiga toxin absorbed from the colon binds globotriaosylceramide receptors that are densely expressed on glomerular endothelium, causing endothelial swelling, platelet activation and fibrin deposition in the renal microvasculature; red cells are mechanically fragmented as they pass through these narrowed vessels, which is why the direct antiglobulin test is negative and distinguishes this from autoimmune haemolysis. The organism remains confined to the gut lumen and does not invade the bloodstream, so blood cultures are characteristically sterile and urine cultures are unhelpful. A throat swab would be relevant to streptococcal disease, not to this illness. Management is meticulous supportive care with careful fluid and electrolyte balance, transfusion for symptomatic anaemia and dialysis when needed; antibiotics and antimotility agents are avoided because they increase toxin release and the risk of haemolytic uraemic syndrome. Eculizumab is reserved for atypical, complement-mediated disease, which lacks a diarrhoeal prodrome and often recurs.
Why each option
- A.
- Correct. Shiga toxin-producing Escherichia coli is recovered from stool, with sorbitol-MacConkey culture plus toxin testing.
- B.
- The organism does not invade the bloodstream in typical haemolytic uraemic syndrome, so blood cultures are sterile.
- C.
- Urine culture identifies urinary tract pathogens and has no role in diagnosing the trigger of this syndrome.
- D.
- A throat swab would target group A streptococcus, which is unrelated to diarrhoea-associated haemolytic uraemic syndrome.
Reference: Nelson Textbook of Pediatrics, 22nd ed., 2024
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