STX1A and hemolytic-uremic syndrome: The absence of serogroup O111, which was found in 2.5% of EHEC-excreting patients, among the HUS-associated EHEC-LST isolates (Table 1) is probably because stx1, which is the most prevalent stx in EHEC O111 [33] is encoded within a defective prophage, which has been immobilized in the EHEC genome [34], preventing the stx loss by phage excision.