In May 2011, an outbreak of the hemolytic–uremic syndrome associated with Shiga-toxin–producing Escherichia coli O104:H4 occurred in northern Germany. In this report, the investigation identified sprouts as the likely transmission vehicle. Human infection with Shiga-toxin–producing Escherichia coli is a major cause of postdiarrheal hemolytic–uremic syndrome. This life-threatening disorder, which is characterized by acute renal failure, hemolytic anemia, and thrombocytopenia, typically affects children under the age of 5 years. Shiga-toxin–producing E. coli O157 is the serogroup that is most frequently isolated from patients with the hemolytic–uremic syndrome worldwide. 1 In May 2011, a large outbreak of the hemolytic–uremic syndrome associated with the rare E. coli serotype O104:H4 occurred in Germany. 2 – 5 The main epidemiologic features were that the peak of the epidemic was reached on May 21 and May 22 4 , 5 and that . . .