Genotypic analysis of Shiga toxin-producing clonal complex 17 in England and Wales, 2014-2022.

Shiga toxin-producing (STEC) are zoonotic, gastrointestinal pathogens characterized by the presence of the Shiga toxin () gene. Historically, STEC O157:H7 clonal complex (CC) 11 has been the most clinically significant serotype; however, recently there has been an increase in non-O157 STEC serotypes, including STEC O103:H2 belonging to CC17. STEC O103:H2 is an STEC serotype frequently isolated in England, although little is known about the epidemiology, clinical significance, associated public health burden or evolutionary context of this strain. Surveillance data and whole-genome sequencing data were analysed to determine the microbiological characteristics and public health burden of CC17, including the clinically significant serotype O103:H2, in England and Wales. Isolates of belonging to CC17 (=425) submitted to the Gastrointestinal Bacteria Reference Unit from 2014 to 2022 were whole genome sequenced, integrated with enhanced surveillance questionnaire data and analysed retrospectively. Overall, diagnoses of CC17 infection increased every year since 2014. Most cases were female (58.5%), with the highest proportion of cases belonging to the 0-4 age group (=83/424, 19.6%). Clinical presentation data identified diarrhoea (92.1%), abdominal pain (72.4%) and blood in stool (55.3%) as the most frequent symptoms, while 20.4% cases were admitted to hospital and 1.3% developed haemolytic uraemic syndrome. The five most common established serotypes were O103:H2 (64.5%), O123:H2 (11.1%), O151:H2 (6.6%), O71:H2 (3.3%) and O4:H2 (2.6%). The majority of CC17 isolates (78.6%) had the virulence gene combination. Nine outbreak clusters of STEC infections that were mainly geographically dispersed and temporally related were identified and associated with foodborne transmission. Nationwide implementation of PCR to detect non-O157 STEC and improvements to algorithms for the follow-up of PCR-positive faecal specimens is recommended. Enhanced surveillance is necessary to assess the incidence of CC17 infection and overall burden of this CC within the UK population.