are often well publicized HUS is most commonly seen in the summer months (see Chapter 94 Infectious Disease Emergencies ) Although children of all ages can develop typical HUS, it most commonly affects children younger than years Approximately 5% to 15% of children who develop culture-confirmed STEC gastroenteritis progress to HUS The use of antibiotics and antimotility agents appear to increase the risk of developing HUS with this infection Early hydration with IV fluids, especially during the diarrheal phase of illness appears to decrease the risk for subsequently requiring RRT secondary to HUS In the majority of patients with STEC enterocolitis, the illness begins with watery diarrhea and evolves to hemorrhagic colitis Vomiting and severe abdominal pain may occur Gastrointestinal complications include bowel wall necrosis, toxic megacolon, peritonitis, intussusception, and rectal prolapse The clinical manifestations of HUS generally present to 10 days after the onset of colitis They may become apparent as the diarrhea is resolving, and the evolution of the clinical signs may be rapid Microangiopathic injury of organs other than the kidneys and intestine may occur Pancreatic involvement can be associated with transient or, rarely, permanent diabetes mellitus Liver injury may manifest as hepatomegaly and elevated transaminases Myocardial ischemia or fluid overload may lead to cardiac dysfunction Approximately one-quarter of children demonstrate some degree of encephalopathy manifested as irritability and/or somnolence Some may experience more severe consequences of CNS involvement including seizures, coma, stroke, hemiparesis, and cortical blindness Clinical assessment The patient may present pale and lethargic Jaundice is present in approximately one-third of patients Given symptoms of severe diarrhea and vomiting, the child may present with evidence of hypovolemia including hypotension and signs of decreased perfusion Alternatively, if oral intake has been maintained in the face of oliguric renal failure, signs of volume excess, including edema and hypertension, may be apparent A CBC will show microangiopathic anemia and thrombocytopenia Assessment of the blood smear demonstrates fragmented erythrocytes, schistocytes, and helmet cells Other studies may include increased reticulocyte count, elevated indirect bilirubin, increased lactate dehydrogenase, and decreased haptoglobin Coagulation studies are