Shigella: Sexually transmitted diarrhoea superbug on the rise in US

A highly contagious gut bacterium that causes severe diarrhoea and dysentery is increasingly spreading through sexual contact in the United States, morphing into an hard-to-treat superbug.

Historically linked to contaminated food or water, the pathogen Shigella is now behaving like a sexually transmitted infection. According to data from the US Centers for Disease Control and Prevention (CDC), extensively drug-resistant (XDR) strains of the bacterium rose from 0 per cent of analysed samples in 2011 to 8.5 per cent in 2023.

How fast is the superbug spreading?

The surge is being felt directly in clinics. Shangxin Yang, a molecular biologist at the University of California, Los Angeles (UCLA), said hospital workers there are now seeing about one case of extensively drug-resistant Shigella every month. In 2022, they recorded just one case during the entire year.

"It's almost like an explosion of this pathogen in the community," Yang told CIDRAP News.

While anyone can catch it, the infection has become endemic among gay, bisexual, and other men who have sex with men (GBMSM). CDC epidemiologist Naeemah Logan told CIDRAP News that the drug-resistant strains present a "very concerning pattern" among vulnerable populations.

CDC data shows that more than a third of patients with extensively drug-resistant shigellosis required hospitalisation. The infection can be severe, causing bloody diarrhoea, fever, stomach cramps, and dangerous dehydration. In severe cases, it can trigger septic shock and internal bleeding.

A global pattern of resistance

The problem is not confined to the US. In the United Kingdom, researchers have tracked a similar rise. Kate Baker, a geneticist at the University of Cambridge, said the disease has gone from "relatively treatable with off-the-shelf drugs to being close to untreatable" over the last decade.

In 2025, the UK Health Security Agency (UKHSA) found that 86 per cent of Shigella sonnei samples and 94 per cent of Shigella flexneri samples—the two main strains spread sexually in England—were resistant to antibiotics.

Researchers point to "bystander resistance" as a key driver. This occurs when an antibiotic prescribed for a different infection—such as gonorrhoea—inadvertently pressures Shigella bacteria present in the body to mutate and build resistance. When UK national guidelines stopped recommending the antibiotic azithromycin for gonorrhoea, the rise of azithromycin-resistant Shigella slowed down, noted Alicia Calvo-Villamañán, a researcher at the Gulbenkian Institute for Molecular Medicine.

Prevention and next steps

Preventing the spread requires clear communication from healthcare providers. Daniel Richardson, a sexual health consultant at University Hospitals Sussex, urged doctors to ask patients with dysentery about their sexual history.

Because the bacteria is highly infectious—requiring as few as 10 organisms to cause illness—public health agencies recommend washing thoroughly before and after sex, using barriers like condoms, and washing sex toys. The California Department of Public Health also advised avoiding sexual contact with anyone who has had diarrhoea in the past fortnight.