Ready-to-eat salads blamed for illness outbreak

An outbreak of cryptosporidium that affected about 300 people probably originated in ready-to-eat bagged salads, an investigation has found.

The Health Protection Agency (HPA) said there was "strong evidence" of an association between those who fell ill in England and Scotland and the salads, which were likely to have been labelled ready to eat.

A sample of 25% of those who became unwell found 46% recalled eating mixed-leaf bagged salad from the Morrisons supermarket chain – an "extremely high" rate as not everyone could remember all the products they bought – while 11% ate spinach from the Asda chain, the HPA said.

The outbreak was short-lived, with most of those affected suffering a mild to moderate form of the illness. There were no deaths.

The cryptosporidium parasite causes the disease cryptosporidiosis, of which the most common symptom is diarrhoea. Potential sources include contaminated water or food, and swimming in contaminated water.

The Food Standards Agency (FSA) said its investigation into the outbreak was unable to identify the source of contamination. But it said consumers could still have confidence in the ready-to-eat label.

It added that bagged salads sold in supermarkets were often sourced from the same suppliers for most leaf types, with production lines packing products for several retailers at the same time, which was the situation in this case.

The HPA's head of the multi-agency outbreak control team, Dr Stephen Morton, 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's director of food safety, Dr Alison Gleadle, said: "We'd like to remind everyone of our usual advice to wash all fruits and vegetables, including salad, before you eat them, unless they are labelled ready to eat.

"It's also important to wash hands thoroughly as well as clean chopping boards, knives and other utensils between preparing raw and ready-to-eat foods to prevent cross-contamination."