Summary Background The zoonotic pathogen Shiga toxin-producing Escherichia coli (STEC) O157:H7 emerged during the 1980s as a causative agent of foodborne outbreaks associated with haemorrhagic colitis and haemolytic uraemic syndrome, which can be fatal. We investigated the emerging lineage IIc that was causing outbreaks of STEC O157:H7, identified and quantified the domestic and non-domestic reservoirs, and quantified patient exposures across the population of England.