July 8, 2026

expert reaction to genomic epidemiology study of spread of sexually transmissible drug-resistant shigellosis in England

An epidemiology study published in the Lancet Infectious Diseases looks at the spread of sexually transmissible drug-resistant shigellosis. 

Dr Mathew Beale, Senior Staff Scientist and molecular and computational microbiologist, Wellcome Sanger Institute, said:

“This is an impressive and comprehensive analysis of transmission of Shigella sonnei in England.  The dataset is large and well sampled, and the analyses represent cutting edge tools for addressing questions around transmission and spread.  The authors show that sexually transmitted Shigella transmits more rapidly and spreads more broadly than non-sexually transmitted Shigella.  This has been suggested by previous work, but here the authors formally and comprehensively quantify this.  While there are some key limitations, the study is very strong, and given the sample size and comprehensiveness of the dataset, it is likely that the broad findings of the study hold true.

“These limitations are acknowledged by the study’s authors.  Due to the lack of more granular data, the authors assume that most men infected with Shigella without recent travel history to a high risk area come from the GBMSM community, and that most women with Shigella without recent travel history to a high-risk area do not.  This is an assumption made with care and best use of the available data, but the study shows that the non-pMSM group is comprised of 75% women – if it were truly representative of non-sexually transmitted infections we would expect this to be 50%, and this suggests many of the cases the authors infer to be pMSM are not.  Therefore, this suggests that there is the possibility that authors have overestimated the number of pMSM in their study.

“Additionally, the authors also use the location of the laboratory where Shigella samples were tested as a proxy for geographical location of the patient, but this is also problematic, since samples taken for testing are often referred to testing laboratories far from a patient’s home.  It is also worth noting that many individuals involved in GBMSM sexual transmission networks do not acquire their infection close to their home (or to the hospital laboratory), but travel across the country (e.g. to clubs in metropolitan areas such as London), and only present as sick to their GP after returning home.  In general, although the study does indeed show that sexually transmitted Shigella spreads faster, it does not conclusively show that it is growing drug resistance much quicker, in particular because the azithromycin resistance noted actually declined after 2018.”

‘The spread of sexually transmissible drug-resistant shigellosis in England: a genomic epidemiology study’ by Julia E Marshall et al. was published in the Lancet Infectious Diseases at 23:30 UK time on Wednesday 8 July 2026. 

DOI: 10.1016/S1473-3099(26)00227-6

Declared interests

Dr Mathew Beale: “No conflicts of interest to declare.”

This Roundup was accompanied by an SMC Briefing.