This syndrome is seen primarily in children and is associated with ingestion of certain strains of the Shiga toxin-producing Escherichia coli (STEC) especially subtype O157:H7. Other associated pathogens include Campylobacter jejuni, Yersinia pseudotuberculosis, and Salmonella typhi. HUS represents the most common cause of acute renal failure (ARF) in children and may become life-threatening although the prognosis is usually good. The disorder typically follows a prodromal period of bloody diarrhea.

Clinical manifestations include abdominal cramping, bloody diarrhea, tenesmus, vomiting, fever, and microscopic hematuria. Bloody diarrhea is present in the majority of cases and precedes HUS by 1 to 2 weeks. Laboratory abnormalities include microangiopathic hemolytic anemia (elevated reticulocyte count, elevated LDH and total bilirubin, low haptoglobin, and the presence of schisotcytosis on peripheral smear), thrombocytopenia, leukocytosis, hyponatremia, transaminasemia, and elevations in BUN and creatinine secondary to acute renal failure (ARF). Fever is often lacking. Physical examination may reveal hepatosplenomegaly and purpura, usually of the lower extremities and buttocks. Complications include pancreatitis, acute renal failure, seizures, altered mental status, hypertension, cardiomyopathy, cardiac aneurysm, and myocarditis. An early indicator of this disorder is sterile pyuria, which usually manifests 24 to 48 hours before other laboratory abnormalities. Leukocytosis and prior antibiotic use are risk factors for progression from bloody diarrhea to HUS.

A history of diarrhea following exposure to petting zoos, dairy farms, recreational water supplies, or ingestion of unpasteurized apple cider or milk, fresh vegetables, fresh sprouts, or salami should raise the possibility of the diagnosis. When the diagnosis is suspected, proving that the diarrhea is secondary to STEC helps establish the diagnosis. Examination of stool samples for Shiga toxin assay and culture for E. coli O157:H7 on sorbitol-MacConkey agar should be performed. Serologic testing for IgG and IgM antibodies to E. coli O157:H7 lipopolysaccharides may also be used to establish the diagnosis of STEC diarrheal disease.

Therapy is mainly supportive. Antibiotics and antimotility diarrhea medications should not be employed to treat E. coli hemorrhagic colitis as they increase the propensity to progress to HUS. Early, aggressive fluid and electrolyte maintenance during the diarrheal phase is imperative. Dialysis therapy may be required in severe cases. Severe anemia may necessitate transfusion therapy, whereas, platelet transfusions should be avoided unless there are hemorrhagic symptoms or the patient requires a surgical procedure. Plasmapheresis may be helpful for adult patients with HUS.