Abstract
We investigated a large outbreak of Escherichia coli O157 in the United Kingdom (UK) with 165 cases between 31 May and 29 July 2016. No linked cases were reported in other countries. Cases were predominately female (n = 128) and adult (n = 150), 66 attended hospital and nine had features of haemorrhagic uraemic syndrome. A series of epidemiological studies (case–control, case–case, ingredients-based and venue-based studies) and supply chain investigations implicated mixed salad leaves from Supplier A as the likely outbreak vehicle. Whole genome sequencing (WGS) indicated a link with strains from the Mediterranean and informed the outbreak control team to request that Supplier A cease distributing salad leaves imported from Italy. Microbiological tests of samples of salad leaves from Supplier A were negative. We were unable to confirm the source of contamination or the contaminated constituent leaf although our evidence pointed to red batavia received from Italy as the most likely vehicle. Variations in Shiga toxin-producing E. coli surveillance and diagnosis may have prevented detection of cases outside the UK and highlights a need for greater standardisation. WGS was useful in targeting investigations, but greater coverage across Europe is needed to maximise its potential.
Highlights
In June and July 2016, a large outbreak of Shiga toxinproducing Escherichia coli (STEC) serotype O157:H7 occurred in the United Kingdom (UK)
Confirmed cases were cases with onset or specimen date from 31 May 2016 onwards and a cultured STEC O157 isolate confirmed at the Public Health England (PHE) Gastrointestinal Bacterial Reference Unit (GBRU) as phage type (PT) 34 eae+ stx2+ stx1−, and a member of the 5-SNP single linkage cluster with the address 5.156.1329.2502.2965.3081.%
There were 124 primary and 10 secondary cases and 31 cases referred to as ‘unsure’ who could not be classified as primary or secondary (Figure 3). They were part of a protracted outbreak/cluster (n = 17), were asymptomatic (n = 2), epidemiologically linked to a confirmed case with a missing date of onset (n = 4), or unsure whether they were a contact of case (n = 8)
Summary
In June and July 2016, a large outbreak of Shiga toxinproducing Escherichia coli (STEC) serotype O157:H7 occurred in the United Kingdom (UK). The increase was first observed in the south-west of England where isolates of STEC O157:H7 phage type (PT) 34 eae+ stx2+ stx1− were recovered from 24 cases reporting gastrointestinal symptoms within 1 week (20 to 26 June 2016). This represented a 10-fold increase over the expected rate at this time of year in England and Wales. A local outbreak investigation was initiated on 22 June 2016 (Figure 1). Cases were subsequently observed across England and Wales, and Public Health England (PHE) convened a national outbreak control team (OCT) on 29 June to coordinate the investigation and response
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