Only two people reported eating raw milk cheese in the initial stages of an E. coli outbreak investigation that was later traced to such a product. It is unclear whether this was because of poor recall or because people were unaware they had consumed unpasteurized cheese.
In November 2023, a genetically linked outbreak of Shiga toxin-producing E. coli (STEC) O145:H28 was detected by surveillance systems at the UK Health Security Agency (UKHSA).
There were 36 confirmed cases and one probable illness. Onset dates were available for 29 patients and ranged from July 25 to Dec. 23, 2023, however, the majority fell sick beginning from Oct. 23, 2023.
Analysis of the genome sequencing data confirmed that the 36 human STEC O145 isolates and the two bovine STEC O145 isolates fell within the same cluster. These findings indicated that cattle were the likely source of human infections, via the consumption of contaminated unpasteurized cheese.
A study in the journal of Food Protection revealed that patients were aged between 7 and 93. Including the probable case, 20 sick people were female. Eight confirmed cases lived in Scotland and 28 in England.
One person developed hemolytic uremic syndrome (HUS) and died. Fifteen people were admitted to hospital. Duration of hospitalization for five patients ranged between 1 and 5 days.
Weak signal to cheese
In July 2024, UKHSA notified the FSA of four new cases between June and July, taking the number of sick people to 40, including two deaths. One death was part of this update. While there was a microbiological link between these patients and previous cases, investigations did not identify a food chain link between them and Mrs. Kirkham’s products.
A review of 29 enhanced surveillance questionnaires revealed 18 cases reported traveling first class on trains operated by the same company prior to onset of symptoms and 16 consumed the same meal which included an unpasteurized cheese made by Mrs. Kirkham’s.
Another person who had not travelled by train purchased cheese from a farm shop. During the outbreak investigation, only two people reported eating unpasteurized cheese when responding to the initial questionnaire, despite it being listed as a food exposure item. This may have been because of poor recall or because people were unaware they had consumed unpasteurized cheese.
A review of the menu from the train operator revealed it was not clearly stated in the main description of the items on the grazing plate that cheese was unpasteurized, although it was mentioned elsewhere on the menu.
Cattle samples breakthrough
The implicated cheese was produced by Mrs Kirkham’s. The firm had a regular sampling program for different indicator organisms as well as E. coli O157 and Listeria species. Researchers said unsatisfactory milk results and very high E. coli findings in cheese were obtained during the likely production period.
High E. coli counts exceeding guidance levels of the Specialist Cheese Makers Association were detected in nine of 34 cheese samples, however, there is no legal limit for raw milk cheese. E. coli O109:H16 was isolated from one cheese sampled at the dairy.
Scientists said the investigation provided further evidence that isolation of STEC from food, including dairy products, is challenging.
Microbiological testing of cheese products did not detect the outbreak strain, however STEC O145:H28 was found in two bovine fecal samples collected at the dairy farm where the cheese was produced.
Following the epidemiological analysis implicating the cheese, a recall was issued in December 2023. Mrs Kirkham’s resumed sales of five raw milk cheeses in February 2024.
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