In early August 2015 a number of cases of Escherichia coli O157 phage type 8 verotoxin type 2a (MLVA profile 17-9-6-13-8-4-5-5 or a single locus variant thereof) were found to be genetically clustered by whole genome sequencing (WGS) and to share the same SNP address.

As of 3 September, the cluster comprises 38 confirmed cases, with one additional probable case and four possible cases for which WGS results are pending. Onset dates for confirmed and probable cases range from 29 July to 12 August 2015. Cases are widely distributed across England, with one case in Wales but none identified in Scotland to date. In England, the majority of confirmed cases (seven each) have been reported from Anglia and Cheshire and Merseyside, with 14 additional Health Protection Teams across the country also affected and reporting between one and three cases each. Most cases are female aged 18 to 73 years.

Analysis of enhanced questionnaires has shown that 33/38 confirmed members of the cluster had exposure to pre-packed salad and that 19 of these had purchased their pre-packed salad at the same supermarket chain. A focused survey carried out with 24 of the confirmed cases indicated that the most common exposures were to two salad products from one supermarket chain which share one ingredient. Trace-back has been initiated and one packer/distributor has been identified which is supplied by three farms. Samples are being collected from the supermarket chain outlets visited by cases, the distributor/packer and from the supply farms.

Investigations to determine the exact source and cause of contamination are on-going.

Burying the outbreak announcement in a monthly report and not going public about the source is a public health fail.