The spread of sexually transmissible drug-resistant shigellosis in England: a genomic epidemiology study

BACKGROUND: Shigellosis, caused by Shigella bacteria, is a leading cause of diarrhoeal disease globally. In the last two decades, Shigella circulation in high-income countries has expanded from being a sporadic travel-associated illness to also being an endemic sexually transmissible illness among men who have sex with men (MSM). We aimed to characterise the nature and drivers of this multimodal Shigella transmission in a high-income setting. METHODS: In this genomic epidemiology study, we used Shigella sonnei isolates referred for national surveillance from 138 laboratories across 15 UK health regions. Cases that had recent (defined as in the past 28 days) travel to Africa, Asia, or Latin America and the Caribbean were defined as high-risk travel-associated cases. Presumptive MSM (pMSM) cases were defined as men aged 16-60 years without recent high-risk travel history. Non-pMSM were defined as cases that were not pMSM or high-risk travel. We implemented phylodynamic and geospatial modelling on national genomic surveillance data of S sonnei isolates collected in the UK between Sept 20, 2004, and Feb 28, 2020, to quantitate and compare geospatial spread and transmission intensity of S sonnei across demographic groups (the primary outcome). We also determined the relative influence of antimicrobial resistance on pathogen dynamics in these demographic groups and evaluate the emergence of an extensively drug-resistant S sonnei clade collected in England between Jan 1, 2016, and Dec 30, 2021, as a secondary analysis. FINDINGS: 3514 isolates were collected during the study period. Of these isolates, 1197 (34·1%) came from pMSM, 1269 (36·1%) from non-pMSM, and 1048 (29·8%) from high-risk travel. We found that sexually transmitted S sonnei spread more rapidly (ie, had a greater mean pairwise spatial distance after 2·5 years or less of evolutionary time: pMSM 117·4 km [95% CI 100·7-132·3], non-pMSM 45·8 km [32·6-62·1], p