Increase in Shigella cases linked to a single strain prompts UK outbreak probe

The UK Health Security Agency has reported a rise in Shigella sonnei infections associated with international travel, with genomic analysis identifying a single strain linked primarily to hotels in Cabo Verde (Cape Verde)

The UK Health Security Agency (UKHSA) has identified an increase in the number of Shigella sonnei – a World Health Organization priority pathogen – cases caused by a particular strain of the gastrointestinal pathogen. In response, the UKHSA, working alongside the devolved public health authorities in Scotland, Wales and Northern Ireland, has initiated a multi-agency outbreak investigation.

Shigella sonnei (S. sonnei), is one species within the Shigella genus, a group of gastrointestinal bacteria known to cause symptoms that include severe diarrhoea, fever and abdominal cramps. In rare cases, particularly among immunocompromised patients, infection can progress to sepsis.

Transmission occurs through contact with contaminated faecal matter, either directly via person-to-person contact or indirectly through contaminated food, water or environmental surfaces. Infection is frequently associated with overseas travel to regions where shigellosis is endemic.

Further laboratory investigation of bacterial isolates referred to the UKHSA’s Gastrointestinal Bacteria Reference Unit in London, and the Scottish Microbiology Reference Laboratory in Glasgow, has shown that the observed increase in cases has been driven by a single strain. This conclusion was reached following analysis of whole genome sequencing data which has enabled detailed comparison of bacterial genomes at high resolution.

Since October 2025, a total of 137 confirmed cases have been identified. Genomic analysis placed these cases within a single nucleotide polymorphism single-linkage cluster based on whole genome sequencing, a pattern consistent with exposure to a common source. Cases have been reported across all regions of England, where 113 individuals have been affected, as well as in Scotland with 12 cases and Wales with a further 12 cases. The age of affected individuals has ranged from birth to 81 years, with a median age of 54 years.

The highest number of cases has occurred among those aged between 50 and 59 years, accounting for 55 cases – 40.1 per cent of the total. Across all age groups, 72.3 per cent of cases – equivalent to 99 individuals – have been female.

Epidemiological evidence gathered to date has suggested a strong association between the outbreak and travel to Cabo Verde. Among the 137 confirmed cases reported since 1 October 2025, 116 individuals reported recent international travel. Of these, 109 people, representing 94.0 per cent of those with travel history, reported travel to Cabo Verde, with most visits involving the Santa Maria and Boa Vista areas. For the remaining cases, travel information has not been available.

Genomic analysis has shown that this strain of S. sonnei does not carry known resistance determinants to commonly used antimicrobial agents prescribed for the treatment of traveller’s diarrhoea. This finding has implications for clinical management and suggests that standard antimicrobial therapies remain appropriate where treatment is required.

International communications and investigations have continued as public health authorities seek to clarify the source and extent of the outbreak. Travellers seeking advice have been directed to the National Travel Health Network and Centre website, TravelHealthPro, which provides up-to-date travel health guidance, including specific information for Cabo Verde.

For further information click here