More than twice as many people have fallen ill this year with a strain of bacteria that causes food poisoning, experts say.
The bacteria causes severe diarrhoea
The Health Protection Agency says over 350 cases involving a relatively rare strain of bacteria called Salmonella Newport have been reported.
Usually, 150 cases are seen each year.
Lettuce from various catering, fast food and take-away premises have been identified as the likely cause of the outbreaks around the UK.
People in North East Lincolnshire, Birmingham and the West Midlands, Northern Ireland and the Isle of Man have been affected.
Together with colleagues in the NHS and Local Authorities, the HPA carried out an investigation into these separate outbreaks.
Dr Bob Adak from the HPA said: "We usually only see around 150 cases of this particular strain of Salmonella each year, so when these separate outbreaks were reported to us we knew something was happening.
"Our Salmonella Reference Laboratory carried out additional testing and has found that the strains of the bacteria are identical."
Overall, 33 of the people who caught the bug needed hospital treatment. There have been no deaths.
Dr Adak said they were trying to establish any common foods eaten in the days before people became ill.
"In some of the local investigations the results suggest that consumption of lettuce from various catering, fast food and take-away premises are the likely main cause of the outbreaks.
"The HPA have been working closely with the Food Standards Agency to look at the supply chain of these salad products and to see if we can identify where they became contaminated."
He said it was possible that the foods responsible for these outbreaks had now been used up.
Pat Troop from the HPA said: "We are working with the food industry to go back to the growers where we think it's come from and, hopefully, that will stop the outbreak happening."
Judith Hilton, head of microbiological safety at the Food Standards Agency, said: "The risk of food poisoning can be reduced by good food hygiene practices.
"These include thorough washing and preparing of lettuce away from other foods to avoid cross-contamination and storing it in the fridge before it is served, because at warmer temperatures salmonella can grow.
"A clean kitchen and good personal hygiene are also obviously important."
Salmonella infection causes severe diarrhoea, cramping abdominal pain, nausea and sometimes vomiting.
The symptoms can last for several days, but most people, make a full recovery within a week.