Leek and potato soil linked to E. coli outbreak
Soil stuck on leeks and potatoes may have been the source of an E. coli outbreak in the UK earlier this year, according to the Health Protection Agency (HPA).
There were 250 cases scattered across England, Wales and Scotland between December 2010 and July 2011.
The Food Standards Agency said it was a "myth" that dirt did no harm.
The HPA stressed that the vegetables were safe to eat, but reminded people to ensure their food was washed.
Most of the cases were mild, but 74 people needed to go to hospital and one patient, who had underlying health problems, died.
Details of the outbreak were reported weekly to health professionals, but have only just been publicised to the general public.
A spokesperson said: "At the outset it was not clear what was causing the outbreak and we had no information that would have enabled the public to take any steps to protect themselves."
The disease was caused by a rare strain of E. coli called O157 PT8 which is different from the strain that caused the widespread outbreak in Germany.
Infected people were 40 times more likely to have been in a household where loose leeks were handled and 12 times more likely to have been in a household which bought sacked potatoes than people who stayed infection-free.
Dr Bob Adak, head of the HPA's outbreak control team, said: "The vegetables could have carried traces of contaminated soil.
"It is possible people caught the infection from cross-contamination in storage, inadequate washing of loose vegetables, insufficient hand washing after handling the vegetables or by failing to thoroughly clean kitchen equipment, utensils or surfaces after preparing the vegetables."
Dr Andrew Wadge, chief scientist at the Food Standards Agency, said: "It's sadly a myth that a little bit of dirt doesn't do you any harm.
"Soil can sometimes carry harmful bacteria and, although food producers have good systems in place to clean vegetables, the risk can never be entirely eliminated.
"This outbreak is a timely reminder that it is essential to wash all fruits and vegetables, including salad, before you eat them."