Since the devastating foodborne EHEC outbreak in Norway in 2006, where more than 60 % of the patients developed the severe condition HUS, I have been particularly interested in the bacterium causing this outbreak. Why was this E. coli strain so pathogenic? We believe that increased knowledge on how the gene content of the replication region of Stx phages is associated with virulence of the host EHEC strain will help us to develop better treatment-strategies for EHEC infections in the future.