Shigella Can Spread Through Sex and Drug-Resistant Strains Are Making Severe Infections Harder to Treat

Shigella, a group of bacteria that causes intestinal infection, can spread through contaminated food and water, close contact and sexual activity. England's surveillance data show an increase in diagnoses potentially acquired through sexual contact, alongside high levels of resistance to antibiotics used to treat severe illness.

UK Health Security Agency figures recorded 2,560 diagnoses in its presumptive sexual-transmission group in 2025, up from 2,318 in 2024 and 2,052 in 2023. The classification is based on a surveillance proxy rather than confirmation of each person's sexual behaviour or how they acquired the infection.

Why Shigella Is a Sexual Health Concern

Shigella causes shigellosis, an intestinal infection that can lead to watery or bloody diarrhoea, stomach cramps, fever and an urgent need to pass stool. Symptoms commonly begin one to two days after infection, and most people recover within five to seven days without antibiotics.

The bacteria spread when faecal matter from an infected person reaches another person's mouth. During sexual activity, that can happen through contact involving contaminated skin, hands or objects, including sex toys.

The CDC estimates that about 450,000 Shigella infections occur in the US each year, including an estimated 242,000 infections involving antimicrobial-resistant bacteria. It says antimicrobial-resistant Shigella infections have been increasing since 2016.

Only a small amount of the bacteria is needed to cause illness. Transmission can also occur through contaminated food, water and surfaces, so shigellosis is not exclusively sexually acquired.

Sexually associated transmission has particularly affected gay, bisexual and other men who have sex with men. However, the risk is not confined to any sexual orientation: sexual activity involving exposure to faecal matter can transmit the bacteria.

England's Data Show High Levels of Drug Resistance

Among bacterial samples included in UKHSA's 2025 resistance analysis, 359 of 416 Shigella sonnei isolates, or 86%, and 461 of 490 Shigella flexneri isolates, or 94%, were classified as multidrug-resistant or extensively drug-resistant.

These figures concern tested samples in the report's presumptive men-who-have-sex-with-men group, rather than all Shigella infections in England.

UKHSA uses adult men who do not report international travel, or whose travel history is unknown, as a proxy for presumptive men who have sex with men who may have acquired Shigella through sexual transmission. Its laboratory datasets do not routinely record sexual orientation or sexual behaviour, and the agency acknowledges that the classification is imprecise.

The findings nevertheless show substantial resistance to antibiotics used to treat serious infections. Among the S. sonnei isolates analysed, 83% had resistance markers for ciprofloxacin, 58% for azithromycin and 73% for ceftriaxone.

In this report, extensively drug-resistant, or XDR, refers to isolates with genetic markers of resistance to all three of those antibiotics. More than half of the S. sonnei isolates were classified as XDR.

US and European Data Highlight Treatment Difficulties

US surveillance found that extensively drug-resistant, or XDR, Shigella accounted for 8.5% of submitted isolates with resistance data in 2023, compared with none during 2011–15. That percentage describes samples included in the analysis, not every Shigella infection in the country.

The US definition of XDR covers resistance to five commonly used antibiotics, so its figures are not directly comparable with UKHSA's three-drug classification.

European outbreak investigations have also highlighted the consequences of resistance. In March 2022, the World Health Organization reported an XDR S. sonnei outbreak affecting the UK and other European countries, with very limited treatment options for severe cases.

Among 37 cases interviewed during that investigation, nine people, or 24%, had been hospitalised. That proportion describes the interviewed outbreak group, rather than the hospitalisation risk for every Shigella infection.

More recently, the European Centre for Disease Prevention and Control warned in May 2026 about increasing transmission of multidrug-resistant and extensively drug-resistant Shigella in Europe. It reported more than 2,300 infections caused by MDR or XDR Shigella linked to seven genetically distinct clusters since 2023.

The concern is greatest when severe illness or a higher risk of complications makes treatment necessary, but resistance limits the antibiotics available.

What People Can Do to Reduce the Risk

Most people with shigellosis recover without antibiotics, with rest and fluids often sufficient for mild illness. A healthcare professional may prescribe treatment for more serious infections, although resistance can make antibiotic selection more difficult.

CDC advises people with shigellosis not to have sex while ill and to wait at least two weeks after diarrhoea ends before resuming sexual activity. The bacteria can remain in stool after symptoms improve.

Washing hands, genitals and the anus before and after sexual activity, cleaning sex toys and using appropriate barriers can reduce exposure. These precautions reduce risk but do not guarantee prevention.

The public-health concern is that a highly contagious intestinal bacterium has an established sexual transmission route, while resistant strains can leave fewer antibiotic options when severe infections require treatment.