Evidence of on-going transmission of Shiga toxin-producing Escherichia coli O157:H7 following a foodborne outbreak.

Saira Butt,Jane Maund,Eisin Mcdonald,Richard Elson,David R Greig,Alison Smith-Palmer,Allan Shand,Claire Jenkins,Lesley Allison,Anand Fernandes,Bhavita Vishram

doi:10.1017/s0950268821001278

Abstract

In August 2019, public health surveillance systems in Scotland and England identified seven, geographically dispersed cases infected with the same strain (defined as isolates that fell within the same five single nucleotide polymorphism single linage cluster) of Shiga toxin-producing Escherichia coli O157:H7. Epidemiological analysis of enhanced surveillance questionnaire data identified handling raw beef and shopping from the same national retailer (retailer A) as the common exposure. Concurrently, a microbiological survey of minced beef at retail identified the same strain in a sample of minced beef sold by retailer A, providing microbiological evidence of the link. Between September and November 2019, a further four primary and two secondary cases infected with the same strain were identified; two cases developed haemolytic uraemic syndrome. None of the four primary cases reported consumption of beef from retailer A and the transmission route of these subsequent cases was not identified, although all four primary cases visited the same petting farm. Generally, outbreaks of STEC O157:H7 in the UK appear to be distinct, short-lived events; however, on-going transmission linked to contaminated food, animals or environmental exposures and person-to-person contact do occur. Although outbreaks of STEC caused by contaminated fresh produce are increasingly common, undercooked meat products remain a risk of infection.

Highlights

Shiga toxin-producing Escherichia coli (STEC) O157:H7 emerged as a gastrointestinal pathogen of public health concern in the early 1980s [1]
Descriptive epidemiology of the outbreak In August and September 2019, seven cases of STEC O157:H7 with an identical single nucleotide polymorphisms (SNP) profile were identified through routine surveillance (Fig. 1)
The Incident Management Team (IMT) concluded that the source of infection was most likely Scottish cattle based on the fact that the isolates from humans and Scotch beef samples fell within a five-SNP cluster, the onsets of the majority of the cases followed the identification of the outbreak strain in minced beef in July 2019 and that Scotch beef is a protected geographical indication that animals were born and reared in Scotland

Summary

Introduction

Shiga toxin-producing Escherichia coli (STEC) O157:H7 emerged as a gastrointestinal pathogen of public health concern in the early 1980s [1]. Compared to other bacterial pathogens, infection is rare, but symptoms are severe, including bloody diarrhoea, abdominal pain, vomiting and fever [2]. Transmission to humans occurs via the consumption of contaminated food, direct contact with colonised animals or their environment. Foodborne outbreaks of STEC O157:H7 in England have been associated with contaminated raw or undercooked meat, or cooked meats which had been cross-contaminated; raw milk and raw milk products and contaminated raw vegetables and salads [4]. The infectious dose is low and there is evidence of person-to-person transmission in households and institutional settings [2]

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Conclusion