You may have been told that eating unwashed food “boosts your immune system”, but failing to wash your mixed salad could actually do a lot more harm than good. A staple side to our summer dinners, unwashed pre-packed salad, including rocket leaves, has been linked to an outbreak of E. coli that has killed two and infected more than 150 people in the UK. Public Health England is reminding people to wash their pre-packed mixed salad leaves before they eat them and says it is investigating the cause of the outbreak. E. coli is a bacterial infection that can cause severe stomach pain, bloody diarrhoea and kidney failure, according to the NHS. People usually notice symptoms three to four days after they have been infected, but they can take up to 14 days to start. Most of the E. coli cases identified in England have been in the south-west, but cases have been identified elsewhere in England and in Wales, Scotland and the Channel Islands, The Telegraph reported. Public Health England said the strain involved is likely to have been imported, possibly in leaves from the Mediterranean area. Dr Isabel Oliver, director of Public Health England’s field epidemiology service, said: “We have advised a small number of wholesalers to cease adding some imported rocket leaves to their mixed salad products pending further investigations." The Food Standards Agency (FSA) has also warned people to be thorough when washing vegetables, including salads, that are intended to be eaten raw, The Telegraph reported.