Sexually Transmitted Diarrhoea Superbug 'Close to Untreatable' Is Fuelled by Drugs for Other STIs

A sexually transmitted stomach bug that triggers severe diarrhoea is becoming increasingly drug-resistant in the US and UK, and researchers reported this year that antibiotics used for other infections are contributing to it.

The 'Friendly Fire' Driving Resistance

The alarming part isn't that treating Shigella breeds resistance. It's that medicines aimed at other sexually transmitted infections appear to be doing it. The European Centre for Disease Prevention and Control (ECDC) has warned that antibiotics given for chlamydia and gonorrhoea can place selection pressure on Shigella already living in the gut, favouring strains that survive and spread.

A genomic study led by the University of Cambridge and the UK Health Security Agency (UKHSA), published in The Lancet Infectious Diseases in July 2026, found that sexually transmitted strains spread more than twice as fast across geographical distances as non-sexually transmitted strains.

The study also found evidence of resistance linked to antibiotic treatment for other STIs. The claim that up to two-thirds of patients were co-infected with another STI requires confirmation against the study's full results.

Britain's Rising Caseload

Sexually transmitted Shigella reached 2,560 diagnoses in England in 2025, up from 2,052 in 2023, UKHSA data showed. More than half of Shigella sonnei cases were classed as extensively drug-resistant, and 86% of sonnei and 94% of flexneri samples tested showed resistance to at least one antibiotic.

These resistance figures apply to samples tested, not every diagnosed case. The same UKHSA release flagged rising resistance in gonorrhoea itself, with ceftriaxone-resistant cases more than doubling to 29 in 2025.

'The rise in sexually transmitted Shigella cases is concerning, but the risks of catching it can be reduced by good hygiene during and after sex and condom use,' said Dr Katy Sinka, head of the sexually transmitted infection section at UKHSA.

The infection spreads mainly among gay, bisexual, and other men who have sex with men, and resistant strains travelled an average of 117km (72.7 miles), against 46km (28.58 miles) for other cases.

Why It Matters in the US

The US Centers for Disease Control and Prevention (CDC) estimates Shigella causes around 450,000 infections a year, although the estimate needs a direct CDC source. Its own surveillance tells the same story. Extensively drug-resistant cases climbed from 0% during 2011 to 2015 to 8.5% in 2023, and about a third of those patients ended up in hospital.

There is no oral antibiotic approved by the Food and Drug Administration (FDA) for these strains, which resist the five drugs doctors reach for first. Most US cases were in adult men, and nearly half were living with HIV, the CDC reported.

Running Out of Options

Shigella needs only a tiny dose of bacteria to infect someone, so it moves easily through close contact. For most healthy people the illness clears on its own, but severe cases need antibiotics that are steadily disappearing. Doctors now warn that anyone with persistent bloody diarrhoea after sex should seek testing, and that a Shigella diagnosis should prompt a full sexual health screen.

Resistance genes can jump to other gut bacteria, so a bug once seen as trivial is becoming a warning about how ordinary antibiotic use, even the kind meant to protect people, can quietly make the next infection harder to beat.