Patient description: A 17 year old boy complains of vomiting, non-bloody diarrhea, abdominal pain, fever, chills and loss of appetite for the past 3 days. He ate a salad at a restaurant prior to his diarrhea onset. Physical exam was remarkable for pallor, jaundice, and diffuse abdominal tenderness. Lab results were as follows: Hemoglobin: 9.7 g/dL Platelet: 110,000 /cu.mm Creatinine: 3.6 mg/dL blood urea nitrogen (BUN): 73 mg/dL direct bilirubin: 2.4 mg/dL lactate dehydrogenase (LDH): 881 IU/L (normal: 110-265 IU/L) Peripheral blood smear showed a moderate number of schistocytes and helmet cells. Shiga-like toxin-producing E. coli (STEC) stx1/stx2 were found in stools. He has no other underlying disease and he is not on any medications.

Clinical trial eligibility criteria: eligible ages (years): 1.0-10.0,  Bloody Diarrhea STEC, Unspecified Hemolytic-Uremic Syndrome Pediatric Kidney Disease Age of ≥ 1 to < 10 y. 2. Signed informed consent from the parent(s)/legal guardian with assent from the subject as appropriate by age and regulatory guidance. 3. Bloody diarrhea based upon history or presentation (by visual inspection). 4. Detection of Stx2 in stool based on enzyme immunoassay (EIA) and/or stx2 based on PCR before randomization. NOTE: The basis for accepting a positive test for stx2 by EIA is based on taking as valid the results yielded from an EIA whose sensitivity and specificity are greater than 98.7% and 100%, respectively (according to the description in the insert) as per recommendation given by the NRL. The Sponsor will select the investigational sites that have in their laboratory such EIA test used in the STEC diagnostic routine algorithm. (Appendix 6). 5. For children between 1 to 5 years old: weight for length/height between percentiles 3 (< 2 z score) and 97 (> 2 z score) corresponding to age (according to the reference tables "WHO Child Growth Standards". 6. For children ≥ 5 years: Body mass index (BMI) between percentiles 3 (<2 z score) and 97 (> 2 z score) corresponding to age (according to the reference tables "WHO Child Standards, Appendix 4)  Any laboratory findings compatible with the development of HUS Microangiopathic hemolytic anemia defined as LDH above the ULN for age with the finding of schistocytes on peripheral smear and a negative Coomb's test, and/or Thrombocytopenia: platelet count < 150 × 103/μL, and/or Renal failure: serum creatinine > ULN adjusted for age and gender despite correction of hypovolemia, and/or hematuria, and/or proteinuria (Table 7.1)11 NOTE: Laboratory results must be obtained within 24 h before the 1st study drug administration; there must be no clinical signs and symptoms of HUS at the time laboratory assessments are obtained. If there is any change in clinical presentation in the 24 h before the 1st study drug administration, laboratory assessments are to be repeated and results reviewed before study drug administration. NOTE: Laboratory and physical examination results must indicate normal hydration before the 1st study drug administration. 2. A history of chronic/recurrent hemolytic anemia, thrombocytopenia, or chronic renal failure. 3. A family history of aHUS. 4. Anuria or oliguria after hypovolemia is corrected. 5. Evidence of clinically significant chronic active disease not medically controlled. 6. History of anaphylaxis, prior administration of equine serum (eg, antitetanus serum or anti-ophidic serum, or anti-arachnid toxin serum), or allergic reaction to contact with, or exposure to, horses. 7. Family relation or work relation with a member of the personnel of the research group. -