“In this issue of Eurosurveillance, a collaborative group of investigators, led by the WHO Collaborating Centre for Reference and Research on Escherichia and Klebsiella, report several intriguing and important new findings on the nature and possible origin of the epidemic strain. Firstly, using well- validated genotyping methods, Scheutz et al. provide convincing evidence that the STEC strain causing the outbreak in Germany is in fact not a typical virulent STEC strain, but instead is a much rarer hybrid pathotype that harbours the phage-mediated Shiga toxin determinant with an enteroaggregative E. coli (EAggEC) background, more precisely described as enteroaggregative, Shiga toxin/verotoxin-producing E. coli (EAggEC STEC/VTEC). Secondly, they also identify in this strain the presence of the receptor for iron-chelating aerobactin, known to be a virulence factor associated with the extra-intestinal E. coli pathotype. Thirdly, they provide new data attesting to a close genetic relatedness of the German outbreak strain to previously described similar EAggEC STEC/VTEC strains. These findings are relevant for identifying the ecological reservoir and evolutionary origin of the epidemic agent, gaining a better understanding of the biological determinants of unusual disease severity and clinical complications seen in outbreak cases and the design of specific diagnostic tools for detection and treatment of STEC cases, and identification of the epidemic strain for accurate outbreak monitoring.”