Health experts in the United Kingdom have raised concerns over the spread of a bacterial infection that can cause severe diarrhoea and is becoming increasingly resistant to antibiotics.
The infection, known as shigellosis, is caused by Shigella bacteria. Although it is commonly associated with contaminated food, water and surfaces, it can also spread through sexual contact involving exposure to tiny amounts of infected faecal matter.
Researchers have warned that some sexually transmitted strains are becoming increasingly difficult to treat, raising concerns about the effectiveness of commonly used antibiotics.
Cases Rise in England
Data released by the UK Health Security Agency (UKHSA) shows that suspected sexually transmitted Shigella diagnoses in England increased from 2,052 in 2023 to 2,318 in 2024 and 2,560 in 2025.
The figures represent a continued rise in cases, with London accounting for more than half of the reported diagnoses in 2025.
The infection predominantly affects gay, bisexual and other men who have sex with men in England, although Shigella can infect anyone.
According to UKHSA, some tested samples showed resistance to several antibiotics, including resistance to all three commonly recommended first-line treatment options in more than half of the tested Shigella sonnei samples.
These resistance findings apply to the samples tested for antibiotic susceptibility, not necessarily every person diagnosed with the infection.
Why Experts Are Concerned
Shigellosis can cause frequent diarrhoea, sometimes containing blood, alongside abdominal cramps, fever, nausea and vomiting.
Symptoms often begin within a few days of exposure. While many people recover without antibiotics, severe cases can require medical treatment and, in some instances, hospitalisation.
Antibiotic resistance occurs when bacteria develop the ability to survive medicines that previously killed them or stopped their growth. This can leave doctors with fewer effective treatment options.
Research published in The Lancet Infectious Diseases in July 2026 also highlighted how sexually transmitted Shigella strains can spread through connected social and sexual networks, creating additional challenges for public health authorities.
Researchers say conventional advice focused on food safety and handwashing alone may not adequately address transmission during sexual contact.
How the Infection Spreads
Shigella is transmitted through the faecal-oral route. Infection can occur when microscopic amounts of infected faecal matter reach the mouth through contaminated food, water, hands, surfaces or sexual activity.
The bacteria are highly infectious, meaning even a small amount can cause illness.
Health authorities recommend careful handwashing, good hygiene during and after sexual activity, changing condoms between anal and oral sex, and cleaning shared sex toys and equipment.
People experiencing persistent or severe diarrhoea, bloody stools, fever or significant abdominal pain should seek medical advice. Anyone who suspects a sexually transmitted infection should tell their healthcare provider so appropriate testing and treatment can be considered.
Health Officials Urge Awareness
UK health authorities continue to monitor the infection and its growing resistance to antibiotics.
The warning highlights a broader public health concern: the spread of drug-resistant bacteria can make infections harder to manage and increase the risk of complications when effective treatments become limited.
Shigellosis is not exclusively a sexually transmitted infection, and the term “virtually untreatable” does not mean every case is untreatable. Many infections resolve without antibiotics, but some resistant strains leave clinicians with fewer reliable options.
Public health experts stress the importance of recognising symptoms, seeking timely medical attention and taking preventive measures to reduce transmission.
