Experts warn of ‘distinct public health threat’ over sexually transmitted gut bug
Sexually transmitted cases of a bacterial gut infection are spreading more rapidly than other strains – and becoming increasingly resistant to antibiotics, according to a study.
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Cases of shigella, which are spread through sexual contact, should “be treated as a distinct public health threat”, researchers said.Shigella is the bacteria behind dysentery, and is most commonly found in faeces and contracted through contaminated food.
Sexually transmitted strains such as shigella sonnei and shigella flexneri mostly impact gay and bisexual men – causing diarrhoea, stomach cramps and fever.
There were 2,560 cases of sexually transmitted shigella in England in 2025, UK Health Security Agency (UKHSA) figures show, up from 2,318 in 2024 and 2,052 in 2023.
A study led by the University of Cambridge alongside UKHSA analysed 3,514 samples of shigella from people over the age of 16 in the UK between 2004 and 2020.
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Around a third (34%) were collected from men who have sex with men, while 36% were domestic cases not associated with sexual transmission. The remaining samples were travel cases brought into the UK.
It found that sexually transmitted cases of the infection spread more than twice as fast in terms of distance compared to other strains.
Over two and a half years, sexually transmitted shigella strains spread more than twice as fast, averaging 117km in distance compared to 46km for non-sexually transmitted strains.
Researchers said the findings, published in the Lancet Infectious Diseases journal, show “the distinct and intensifying sexual transmission of shigellosis, highlighting the urgent need to address sexually transmissible shigellosis as a distinct health threat”.
Professor Kate Baker, senior author of the study from Cambridge’s Department of Genetics, said: “Many men who have sex with men are unaware of the serious and increasing risk posed by sexually transmitted shigella.
“Sexual infection is now a sustained part of shigella transmission in the UK.
“It is vital that this message reaches the communities most affected, so we can help to prevent the spread.
“Sexually transmissible shigellosis needs to be treated as a distinct public health threat, requiring different surveillance, prevention, and treatment strategies.”
Elsewhere, the study found that around 70% of sexually transmitted shigella strains were resistant to at least one clinically relevant antibiotic, compared to 40% of non-sexually transmitted cases and 49% of cases contracted while travelling.
Prof Baker said: “Some advice is obvious, but needs hammering home.
“If you start to feel unwell, or are recently recovering from a scary bout of diarrhoea, do not engage in sexual activity until two weeks after you’re fully recovered, mention your sexual history to your doctor if you seek medical care, and ask about having a full sexual health screen.”
Marc Tweed, from the Terrence Higgins Trust, said the “growing problem” of shigellaamong some sexual networks of gay and bisexual men is “a real cause for concern”.
He added: “Studies have linked transmission with dense sexual networks, multiple partners, sexualised drug use, PrEP use and concurrent sexually transmitted infections.
“But these are associations, not proof that any one behaviour alone is driving the increase.
“If you think you may have shigella, you should contact your local sexual health clinic to book an appointment.”