Scientists have noticed an outbreak and ongoing transmission of a strain of Escherichia coli O157 in England and Scotland in 2019.

Researchers concluded the infection source was likely Scottish cattle and the outbreak strain was found in ground (minced) beef in July 2019. The mysterious part was that only half of 14 patients linked to the outbreak could be explained by exposure to raw beef products sold at one retailer.

In August 2019, public health investigations systems in Scotland and England found seven people infected with the same strain of Shiga toxin-producing E. coli (STEC) O157:H7. Four of them from England and three in Scotland. 

Public Health England, Public Health Scotland, the Food Standards Agency, and Food Standards Scotland were part of the outbreak investigation team. 

In the past three years of routine whole-genome sequencing for STEC isolates in England, the outbreak strain had not been detected. The strain was similar to STEC O157:H7 from UK beef cattle isolated during a study in 2015, according to the research published in the journal Epidemiology and Infection.

Analysis of surveillance questionnaire data identified handling raw beef and shopping at the same national retailer as the common exposure.

Six of the seven cases in July and August reported shopping at the same retailer and five consumed ground meat, burgers, or sliced ham from the delicatessen. Two people reported handling raw ground beef or raw beef burgers.

A survey of ground beef at retail identified the same strain in a product sample sold by the supermarket, providing microbiological evidence of the link. Two samples from the same branch of the retailer in late July 2019 were positive for the outbreak strain, although this was not a location at which any of the patients reported shopping.

A review of surveillance data at Public Health Scotland identified a further sick adult from early April 2019 from the north of Scotland who reported contact with farm animals including cattle.

Between September and November 2019, another four primary and two secondary patients infected with the same strain were identified. Of these, one person reported consuming beef and none shopped at the implicated retailer but they did visit the same petting farm. All four people who visited the farm denied direct contact with cattle and didn’t eat there.

Of the new patients, six were from in England. All but one were female, and ages ranged from 2 to 30, with the median being 4 years old. Three people were admitted to hospital, two reported bloody diarrhea, one had fever, and two children developed hemolytic uremic syndrome. No deaths were recorded. Dates of onset ranged from mid-September to early November 2019.

An inspection by health officers at the petting farm found the facilities and hygiene standards were satisfactory. A total of 26 fecal samples from different species at various locations across the farm were tested in early December but were negative for STEC O157:H7. Boot sock samples from walking through the premises were also negative.

Scientists concluded that these six cases appear to be the result of ongoing transmission of the outbreak strain either via the food chain, contact with animals, or via person-to-person contact.

The food sample that tested positive for STEC O157:H7 during the microbiological survey of ground beef was sourced from a Scottish cow, slaughtered in that country, and minced at a cutting plant in England owned by the retailer.

Movement data on sheep and cattle from the petting farm revealed no similarities with that of cattle from the matching ground beef isolate.

Investigators could not identify other stores that were supplied by the cutting plant behind the outbreak cluster, or whether cattle from the same herd linked to the ground beef sample were slaughtered at a different slaughterhouse and cutting plant supplying other retailers and food outlets.

Source: Food Safety News