• Age ≥ 9 months and \< 18 years at the time of randomization.

• In addition, only for subjects \< 1 year and ≥ 15 years, confirmation of STEC infection determined by:

‣ Detection of generic Stx, Stx1, Stx2, or Stx1/Stx2 in stools by enzyme immunoassay (EIA); or

⁃ Detection of stx, stx1, stx2, or stx1/stx2 genes in stools by Polymerase Chain Reaction (PCR); or

⁃ Detection of specific anti-polysaccharide (IgM) antibodies in serum; or

⁃ Fecal culture positive for E. coli O157 confirmed by serogroup-specific seroagglutination.

• Hospitalization at the participating institution.

• History of onset of diarrhea within 10 days prior to STEC-HUS diagnosis at the participating institution.

• Diagnosis of STEC-HUS defined as a subject with signs of renal damage, hemolysis, and platelet consumption:

‣ Signs of renal damage defined as:

• Serum creatinine value above the ULN for age and sex, and GFR below the LLN for age, sex, and height.

⁃ Presence of hemolysis documented by:

• LDH levels above the ULN for age, and/or

∙ Presence of schistocytes in peripheral blood smear.

⁃ Platelet consumption according to any of the following laboratory criteria:

• Peripheral blood platelet count \< 150 × 103/μL, and/or

∙ A ≥50% decrease in peripheral blood platelet count compared to a sample collected within the previous 24 hours.

• Informed consent form signed and dated by the subject or, the legal guardian(s), with the subject's assent as appropriate based on age and regulatory guidelines in the region.

• Subjects who have already had menarche must have a negative pregnancy test.