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A bacteria that causes severe diarrhea is becoming harder to treat as more infections spread through sexual contact. Health experts in the United States and the United Kingdom are warning that growing antibiotic resistance could leave doctors with fewer treatment options.
The bacteria, called Shigella, causes shigellosis. The infection can lead to diarrhea, stomach pain, fever and vomiting. In some cases, it also causes dysentery, a serious form of diarrhea that may include blood.
According to the U.S. Centers for Disease Control and Prevention (CDC), about 450,000 people contract shigellosis each year in the United States.
Drug-resistant Shigella cases are rising
Shigella has long spread through contaminated food and water. It also spreads easily among young children. However, sexual contact has become another important way the bacteria moves between people.
The CDC recently examined nearly 17,000 Shigella samples collected over several years. Its findings showed a rise in strains that resist multiple antibiotics.
In 2011, none of the samples showed resistance to five commonly used antibiotics. By 2023, however, 8.5% of the samples showed extensive drug resistance.
These strains are known as extensively drug-resistant, or XDR, Shigella. Because several standard antibiotics may not work against them, doctors face greater challenges when treating serious infections.
Most of the people infected with these resistant strains were adult men. Many had not traveled internationally in the months before their illness.
At the University of California, Los Angeles, molecular biologist Shangxin Yang has also seen a sharp increase. Hospital workers there now encounter about one case of extensively drug-resistant Shigella each month. In 2022, they recorded just one case for the entire year.
Yang described the rise as an explosion of the pathogen in the community in comments to CIDRAP News.
Sexual transmission raises new concerns
Researchers first reported sexually transmitted shigellosis in 1974. However, it accounted for a smaller share of cases at the time.
Today, health experts recognize sexual contact as a major route of transmission in some communities of gay, bisexual and other men who have sex with men.
Tracking these cases remains difficult. Some patients may not know that sex can spread Shigella. In addition, health care workers may not ask about sexual contact or record that information.
The CDC also found that more than one-third of patients with extensively drug-resistant shigellosis required hospital care. Nearly half of those whose HIV status was known had HIV.
Meanwhile, researchers in the United Kingdom have reported a similar pattern. A study led by geneticist Kate Baker of the University of Cambridge found growing concern over drug-resistant Shigella infections.
In 2025, UK health officials found antibiotic resistance in 86% of tested Shigella sonnei samples and 94% of tested Shigella flexneri samples. Both strains commonly spread through sexual contact among men who have sex with men in England.
Some patients also need hospital care for several days. As resistance grows, doctors may struggle to find effective treatments for severe infections.
How people can reduce the risk
Scientists are still investigating why sexually transmitted Shigella strains often show high levels of antibiotic resistance. One possible factor is called bystander resistance. This occurs when antibiotics used to treat one infection also affect other bacteria in the body, helping resistant strains survive.
However, researchers say more evidence is needed to understand the links between treatments for other sexually transmitted infections and Shigella resistance.
Health officials recommend avoiding sexual contact with someone who has had diarrhea within the past two weeks. They also advise using barriers during oral and anal sex and washing before and after sexual activity.
Anyone who develops symptoms should seek medical advice and ask about testing. Doctors may also recommend screening for other sexually transmitted infections.
Although many Shigella infections clear without antibiotics, severe cases may need treatment. Therefore, identifying the infection and choosing the right medicine are increasingly important.
Health experts say better awareness, testing and careful antibiotic use can help limit the spread of these increasingly resistant bacteria.
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