Abstract
Sexually transmissible enteric infections (STEIs) are commonly associated with transmission among men who have sex with men (MSM). In the past decade, the UK has experienced multiple parallel STEI emergences in MSM caused by a range of bacterial species of the genus Shigella, and an outbreak of an uncommon serotype (O117 : H7) of Shiga-toxin-producing Escherichia coli (STEC). Here, we used microbial genomics on 6 outbreak and 30 sporadic STEC O117 : H7 isolates to explore the origins and pathogenic drivers of the STEC O117 : H7 emergence in MSM. Using genomic epidemiology, we found that the STEC O117 : H7 outbreak lineage was potentially imported from Latin America and likely continues to circulate both in the UK MSM population and in Latin America. We found genomic relationships consistent with existing symptomatic evidence for chronic infection with this STEC serotype. Comparative genomic analysis indicated the existence of a novel Shiga toxin 1-encoding prophage in the outbreak isolates, and evidence of horizontal gene exchange among the STEC O117 : H7 outbreak lineage and other enteric pathogens. There was no evidence of increased virulence in the outbreak strains relative to contextual isolates, but the outbreak lineage was associated with azithromycin resistance. Comparing these findings with similar genomic investigations of emerging MSM-associated Shigella in the UK highlighted many parallels, the most striking of which was the importance of the azithromycin phenotype for STEI emergence in this patient group.
Highlights
Certain enteric pathogens traditionally associated with food-borne or person–person spread can be transmitted sexually
Combining the evolutionary analysis of outbreak and contextual Shiga-toxin-producing Escherichia coli (STEC) O117 : H7 isolates with traditional epidemiological markers yielded insights into the possible origins, and potentially ongoing nature of the outbreak
In addition to the six isolates known to belong to the outbreak, the encompassing outbreak clade included a further four isolates, three of which were recovered from patients recently returned from travel to Latin America in 2010, 2013 and 2016
Summary
Certain enteric pathogens traditionally associated with food-borne or person–person spread can be transmitted sexually. There has been an intensification of MSM-associated diarrhoeal disease caused by diverse bacteria of the genus Shigella since 2009 [3], which genomic studies have revealed is associated with antimicrobial resistance (AMR) [4,5,6]. In addition to these prolonged and overlapping shigellosis epidemics, a domestically transmitting outbreak of a Shiga-toxin-producing Escherichia coli (STEC) O117 : H7 was observed in 2014 in the UK MSM community [7]. STEC are an important cause of gastrointestinal symptoms worldwide, and certain virulence determinants, such as the locus of enterocyte effacement (LEE) pathogenicity island (PAI) and the Shiga toxin (Stx) subtype 2a are associated with epidemic emergence, and the elaboration of more severe disease syndromes such as haemolyticuraemic syndrome [8, 9]
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