Ready-to-eat salads from Morrisons and Asda caused infection outbreak, HPA say The infection is caused by a parasite in the intestine which causes an acute short term infection, the most common symptom of which is diarrhoea. The pre-packed salads have come under criticism before, with scientists claiming that they would lead to an increase in food poisoning. After the Cryptosporidium outbreak in England and Scotland in May 2012 the HPA launched an investigation. The outbreak was short lived, with most experiencing only moderate symptoms, and the numbers of cases returned to expected seasonal levels within a month of the first cases being reported. When they interviewed the people who became unwell about their food history the HPA discovered the link between the illness and the salads sold at the two supermarkets. This is not the first time pre-packaged vegetable have been linked to illness. A salmonella outbreak in the UK in 2007 was traced back to imported basil while an E.coli outbreak in America in 2006 was linked back to pre-packed baby spinach. A link to spinach from retailers other than Morrisons and Asda was also suggested, but was found to be inconclusive. A spokesperson said: "Together these findings suggest that one or more types of salad vegetables could have been contaminated." The HPA confirmed that they could not identify contaminated products in any particular chain of supermarkets because of the time lapse, but interviewing a sample of those who fell ill was a investigation method accepted by health organisations across the world. The Food Standards Agency also gathered information on the production and distribution of salad vegetables to try to identify the likely source of the outbreak. But despite investigating the food chain, including the practice and procedures throughout each stage of growing, processing, packing and distribution they have not managed to identify a source of contamination. Bagged salad on sale in supermarkets is often sourced from the same suppliers for most leaf types, often with common production lines packing product for several retailers at the same time. This was the situation in this case. Dr Stephen Morton, regional director of the HPA's Yorkshire and the Humber region and head of the multi-agency Outbreak Control Team, said: "This outbreak was fortunately short lived but it was important to see if we could find the source. Our findings suggest that eating mixed leaf bagged salad was the most likely cause of illness. It is however often difficult to identify the source of short lived outbreaks of this type as by the time that the outbreak can be investigated, the affected food and much of the microbiological evidence may no longer be available. As this was an isolated and short lived outbreak there is no specific action for the public to take but we hope the investigations between the FSA and the food industry will help to prevent further outbreaks of this type from happening again. The FSA added: "This would appear to have been an isolated, short-lived outbreak and it does not appear that there are any on-going problems." They said that consumers should continue to have "confidence" in ready to eat products. Dr Alison Gleadle, director of food safety at the FSA, reminded people to keep their kitchens clean and wash non-ready-to-eat vegetables. Morrisons say that there is no conclusive evidence for a link between their salad and the outbreak. There are a number of potential sources for the Cryptosporidium parasite, including consumption of contaminated water or food, swimming in contaminated water or through contact with contaminated food or affected animals