This genomic epidemiology study characterised the transmission dynamics and antimicrobial resistance (AMR) fitness of *Shigella sonnei* in England using 3,514 isolates from national surveillance (Sept 2004–Feb 2020), comparing spread and transmission intensity across presumptive MSM (pMSM), non-pMSM, and high-risk travel-associated cases, with a secondary analysis of extensively drug-resistant (XDR) emergence (2016–2021).
Sexually transmitted *S. sonnei* spread significantly faster (mean pairwise spatial distance at ≤2.5 years: pMSM 117.4 km vs. non-pMSM 45.8 km, p<0.0001) and generated 100 more transmission chains per given population size (95% CI 41–171, p=0.0020) than domestically acquired non-sexual cases. Azithromycin-resistant isolates showed 1.71× relative fitness growth in pMSM networks, and ceftriaxone resistance was linked to XDR clade emergence.
- pMSM classification is presumptive (proxy based on age/sex/travel history), not confirmed by self-reported sexual behaviour data. - Study period ends Feb 2020, predating COVID-19 disruptions to sexual networks and gonorrhoea treatment guideline changes that may affect current dynamics. - Findings are from England/UK, limiting direct generalisability to other high-income settings with different sexual health infrastructure.
Standard enteric disease prevention (handwashing, food hygiene) will not curb sexually transmitted shigellosis in MSM — clinicians should treat it as a distinct STI requiring tailored interventions and stewardship. The fitness advantage of azithromycin and ceftriaxone resistance in this population signals an urgent need to coordinate AMR strategies across shigellosis and gonorrhoea treatment guidelines.
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