The outbreak reported in November 2021 affected 17 people with the Shigella strains being similar to those of Shigella sonnei isolated from people returning to the UK from Egypt.
However, the 17 did not have any travel history but instead reported to have eaten at a restaurant or food outlet in the week prior to symptom onset. 11 dined at branches of the same national franchise.
According to a study published in the Journal of Food Protection, all cases were adults and 14 were female.
In the same period, spring onions from the same Egyptian grower were linked to an enteroinvasive E. coli (EIEC) outbreak, as stated by the Statens Serum Institute (SSI) in Denmark. They said there was evidence of floods at harvest time and came to the conclusion that human waste contamination of river water had contaminated the crop.
The disease-causing pathogen, however, was distinct.
“It is plausible that this event contributed to the temporally linked outbreak described in this study, despite the two outbreaks being caused by different pathogens,” said researchers.
Spring onions were shown to be a common element in the patient meals after ingredient-level studies. A single Egyptian producer was identified as the source of the spring onions served at the restaurants that were investigated as part of the food chain studies.
The South West England-based UKHSA Health Protection Team began looking into a cluster of five Shigella sonnei cases in mid-November 2021. As a result, it was discovered that sick persons frequently visited the same chain restaurant.
Later in November, the problem was upgraded to a national response after cases were found in two additional English regions.
Shigella sonnei was found in 17 confirmed cases with sample dates between December 5 and December 24, 2021, and 2 suspected cases with onset dates between November 2 and December 16.
One of the three branches of a national restaurant chain provided the meals for eleven cases. Six patients had no known connections to the restaurant, but four of them had additional restaurant exposures, including two who remembered eating spring onions.
In two cases, no takeaways or dining out were mentioned in the week before the development of symptoms, reports Food Safety News.
65 samples in total, including 51 items and 14 ambient swabs, were evaluated from two branches of the restaurant chains. All the samples tested negative for Shigella species including three samples of spring onions.
In October, spring onions were sourced from the UK; however, in November, they were imported from Egypt. Three of the restaurants that were implicated bought spring onions from two different supply chains that included the same Egyptian producer, according to a food chain probe.
Fluoroquinolones and third-generation cephalosporins, the first- and second-line recommended treatments for shigellosis in the UK, respectively, were less effective against the outbreak strain.