Outbreaks of a serious gastro-intestinal illness in the UK have been linked to eating watercress.
Last September, an outbreak of Verotoxigenic Escherichia coli (VTEC) was linked to watercress, although the underlying cause was uncertain.
By looking at a second outbreak this year, researchers have found that VTEC was transferred from a neighbouring cattle field near to the watercress farm, either through wildlife entering the watercress or run-off water.
Between 30 August and 19 September 2013, 19 cases across England, Wales and Scotland were reported.
Despite trace-back investigations, microbiological testing of watercress and environmental sampling at farms, the source of contamination of the watercress remains unclear.
Two additional cases were retrospectively identified in February 2013.
One had consumed watercress and one pre-packaged salad, both from retailers representing a different supply chain, suggesting that the contamination is unlikely to have occurred at the farms.
Following restocking of watercress at the supermarket chain, one additional case was reported with an onset date of 21 October 2013. The case reported consuming bagged mixed salad containing watercress from that supermarket. No further cases of the outbreak profile have been reported.
The watercress supplier is working with the Food Standards Agency to review their policies and procedures in light of the two outbreaks, while the Gastrointestinal, Emerging and Zoonotic Infections department are remaining vigilant for any new cases of the two outbreak strains or clusters of VTEC cases reporting watercress consumption.