Hemolytic uremic syndrome (HUS) is defined by a triad of microangiopathic hemolytic anemia (charac- terized by schistocytes and helmet cells, as shown in Fig. 1), thrombocytopenia, and renal dysfunction. It is a leading cause of acquired renal failure in children in the US. In almost all diagnosed HUS cases there is a preceding diarrheal illness, which defines typical HUS. The most common pathogens causing HUS are Escherichia coli (specifically toxin-producing O157:H7, along with other E. coli strains), followed by Shigella, and finally, a variety of other less com- mon bacterial causes. If the disease is not preceded by a diarrheal prodrome, then it is considered atyp- ical HUS.