British supermarket Sainsbury’s has recalled its watercress products due to concerns that the vegetable may be the cause of an E. coli O157 outbreak that has affected 19 Britons since August 1. According to a Sainsbury’s spokesperson, once the Food Standards Agency informed the supermarket their watercress was a possible source, they recalled their six lines of pre-packed salad containing watercress as a precaution. The company has also informed the FSA that in carrying out testing on the affected products, no trace of E. coli O157 has been detected to date. The BBC reports that all recalled watercress was grown on English farms and that Vitacress, the supplier of Sainsbury’s and other companies in the U.K., produces about two million bags of the vegetable a week. The outbreak has affected people in England, Wales and Scotland and at least six have been hospitalized. The exact source of the outbreak is still under investigation.