According to officials, the outbreak strain has been found at a farm that supplied the milk used to make unpasteurized cheese, which was linked to an E. coli outbreak in the UK.

In total, 36 confirmed and one probable Shiga toxin-producing E. coli (STEC) O145 infections have been reported, with 29 in England and eight in Scotland since late July 2023, with most falling ill in November. The last reported primary patient had symptom onset on Dec. 23, 2023.

Twenty patients were female, with ages of all cases ranging from 7 to 81. Of the 31 patients with available information, 20 had bloody diarrhea, 15 were admitted to the hospital, and four also attended the hospital for their symptoms. One person developed hemolytic uremic syndrome (HUS) and later died.

An investigation into the outbreak by the UK Health Security Agency (UKHSA), the local authority, Public Health Scotland, Food Standards Agency (FSA), Food Standards Scotland (FSS) and the Animal Plant Health Agency (APHA) is nearly completed.

Cheese on a train
based on epidemiological, food chain, and microbiological investigations, an unpasteurized cheese produced by Mrs Kirkham’s in North West England was identified as the source of infection. A recall was issued in December and updated in February.

Interviews and analyses by UKHSA and PHS found that 16 out of 17 patients had consumed a menu item that contained unpasteurized cheese while on board trains operated by the same company. In another case, those who had not traveled by train consumed the same brand of unpasteurized cheese bought from a local shop.

UKHSA said STEC transmission could also occur through person-to-person contact and contact with animals and/or their environment, which likely explains why not all interviewed cases reported eating the implicated cheese. Four people acquired the infection through either person-to-person or environmental transmission.

STEC DNA was detected in two of 43 cheese samples, but only one could be cultured and sequenced. The strain was E. coli O109: H16 and did not match human cases. No STEC was detected in the bulk milk tank or filter samples used by the business when producing cheese.

Significance of positive result
During an APHA visit to the farm, 28 environmental samples were collected, including fresh and aged cattle feces from various locations on site, and two water trough sediment samples. Two cattle fecal samples tested positive for STEC O145. These isolates were genetically indistinguishable from the outbreak strain detected in human cases.

“While the outbreak strain was not detected in the milk tank or cheese samples, this is not unexpected considering the limitations of microbiological sampling during outbreak investigations. A negative test does not prove that raw ingredients or a specific food is not contaminated,” said UKHSA.

“The detection of the outbreak strain in the feces samples from the dairy herd (on the premises which supplied the milk used to make the unpasteurized cheese) provided additional evidence in support of the epidemiological and food chain investigation findings on which the food safety and health protection actions taken in December 2023 were based.”

Tina Potter, head of incidents at the FSA, said: “After a thorough response carried out by multiple agencies and the business to identify the possible source of the outbreak, microbiological evidence from samples taken from the dairy herd has proven a microbiological link between Mrs Kirkham’s cheese and the outbreak of E. coli. This is in addition to the epidemiological and food chain links already identified early on that were relied upon and led to the initial precautionary food safety action being taken.”

Mrs Kirkham’s was recently allowed to resume selling batches of five raw milk cheeses made on or after Oct. 1, 2023. The company said it worked with technical experts at the Specialist Cheesemakers’ Association to review milk production and food safety management systems.

FSA urged consumers to follow the advice in the recall notice and told people not to eat the implicated items. Raw or unpasteurized milk products may contain harmful bacteria that can cause food poisoning. Hence, the message is essential for groups of vulnerable people, including pregnant women and individuals with impaired immunity.