Rare English E. coli O103 outbreak linked to raw milk cheese

Researchers have detailed the first E. coli O103 outbreak in England traced to raw milk cheese.

In June 2022, routine microbiological surveillance at the UK Health Security Agency (UKHSA) identified 12 Shiga toxin-producing E. coli (STEC) O103:H2 cases.

People fell ill between May and June 2022. Seven cases were female, and ages ranged between 8 and 88 years old with a median of 58 years old. Ten patients lived in different parts of England and two were from Wales.

According to a study in the journal Epidemiology and Infection, nine patients reported diarrhea; seven reported abdominal pain; five had bloody stools and nausea, and one reported fever and vomiting. No-one attended emergency healthcare but one person was hospitalized as a result of STEC infection.

Soft cheese link
Patients were initially interviewed with an enhanced surveillance questionnaire that collects information on food history, contact with animals, and environmental exposures for seven days prior to the onset of illness. Following a review of the data, it was noted that a number of cases reported eating the same artisan cheese, and sick people were re-interviewed using a modified trawling questionnaire to get a more detailed history focused on dairy and salad products.

Food history questionnaires identified cheese, particularly an unpasteurized brie-style cheese, and mixed salad leaves as potential vehicles. Nine people reported soft or hard cheese consumption and eight ate salad leaves at home. Of those who had eaten soft cheese, six ate brie and of these, four consumed a specific brand of unpasteurized brie-style cheese. Another case could not recall the brand but did eat brie from an artisan shop that stocked this same soft cheese.

Eleven cases and 24 controls were included in a case-control study. Consumption of the brie-style cheese of interest was associated with illness.

The implicated soft cheese was produced by one company, which made raw drinking milk, three kinds of unpasteurized soft cheese, and pasteurized skyr yoghurt. Products were distributed via wholesalers, retail premises, or directly via the onsite shop, at events, or online.

Based on information given to investigators, it is likely that contaminated batches were produced between mid-March and April 2022. The cheese producer carried out a regular sampling program for indicator organisms, E. coli O157 and Listeria species. Unsatisfactory milk results and high E. coli findings in cheese were obtained during the likely production period.

Findings from testing
Microbiological results for the cheese products and implicated dairy herd taken in July 2022 did not identify the outbreak strain, but did find stx genes and STEC.

A total of 30 food and environmental samples from the producer’s canteen were tested for STEC. Stx DNA was detected in four of 14 cheese samples, but isolates could not be culture confirmed.

A veterinary officer visited the farm supplying milk and collected 30 fecal samples including 28 from the milking parlor yard, and two from a separate area with calves. Of these, stx genes were detected in three samples and two were confirmed as O26:H11 – different from the outbreak strain. Enteropathogenic E. coli positive for the eae gene (EPEC) were found in 11 samples.

When the link was identified, production of unpasteurized dairy products was suspended by the business and a review of practices was performed. Results of further microbiological testing of unpasteurized milk and cheese were satisfactory and no further cases were reported, indicating that it was likely a one-off contamination event. The cause of contamination remains unknown but it coincided with calving season at the farm.

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