The UK Health Protection Agency (HPA) said an outbreak of Cryptosporidium that affected around 300 people in England and Scotland in May last year showed "strong evidence" of being linked to bagged salad products labeled as “ready-to-eat”.
Most of those sickened had a mild to moderate form of illness and no deaths were associated with the outbreak, said the HPA, which will become part of Public Health England from 1 April.
It was estimated that primary infections occurred over a three day period in early May with more than 300 excess cases reported during the period and those affected were mainly women over the age of 20 years.
Potential sources include consumption of contaminated water or food, swimming in contaminated water or through contact with contaminated food or affected animals.
During the same period in the previous seven years (14 May – 3 June), an average of 54 cases were reported across England, said the HPA.
The strongest association with infection was found to be with consumption of ready to eat pre-cut mixed salad leaves. In the analysis, exposure to pre-cut spinach only reached conventional levels of significance for one retailer, said the HPA.
“A link to spinach from a number of other retailers was also suggested but these were not statistically significant. Together these findings suggest that one or more types of salad vegetables could have been contaminated,” added the HPA report.
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.”
He said the 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 UK Food Standards Agency (FSA), who were part of the outbreak control team led by the HPA, gathered information on the production and distribution of salad vegetables to identify the likely outbreak source.
Investigation of the food chain including practice and procedures throughout each stage of growing, processing, packing and distribution of salad vegetables did not identify a source of contamination.
The FSA told FoodQualityNews.com: “Although the outbreak was associated with bagged salads that were likely to have been labelled as ‘ready to eat’, this would appear to have been an isolated, short-lived outbreak and it does not appear that there are any on-going problems.
“The FSA works with producers and manufacturers who apply stringent controls on the leafy salad supply chain in the UK, minimising potential for contamination. Consumers should still have confidence in the label ‘ready to eat’ but wash other vegetables and fruit.”
An earlier statement from Dr Alison Gleadle, director of food safety at the FSA, had 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’.”