The truly nasty bug, which reportedly causes diarrhea containing blood and mucus, is thought to be spreading through sex... and it's getting tougher to treat.
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Shigella bacteria is a problem that medical experts and unlucky victims have been dealing with for decades. It sends nearly 500,000 people a year running for their toilets, according to The New York Post.
However, the bug doesn't just come with explosive, mucus-filled diarrhea. Like regular bouts of diarrhea, it can leave victims dehydrated. However, Shigella's added issues, like blood in the stool, can also lead to a host of complications. These include septic shock and internal bleeding.
To top it off, the bug is on the rise and growing more resistant to drugs.
Traditionally, travellers to less sanitation-minded destinations and children under 5 are the prime sufferers of Shigella bacteria. However, another demographic has seen a sharp increase in recent years.
A July 2026 study found that cases of the bug from sex grew 15% faster than other leading causes.
To make matters worse, few victims, who are predominantly gay and bisexual men, realize they picked up the bug from sex.
"Many men who have sex with men are unaware of the serious and increasing risk posed by sexually transmitted Shigella," Kate Baker, a Cambridge geneticist who led the study, explained.
Why the Diarrhea-Causing Bug May Be Creating Drug-Resistant Strains
With the increase in cases comes the issue of the treatment drugs becoming less effective. The theory is that some folks seeking treatment aren't diagnosed correctly, leading to doctors prescribing the wrong antibiotics. This causes a phenomenon dubbed "bystander resistance," with the bug picking up a sideways immunity to antibiotics because the incorrect one was used, allowing it to survive and thrive.
"This disease has gone from being relatively treatable with off-the-shelf drugs to being close to untreatable over the course of the last decade or so," Baker added.
In some cases, Shigella can cause victims to be hospitalized for days. Experts also speculate that the version picked up through sex may be harder to treat.
"This isn't just one form of sexually transmissible diarrhea," Baker explained to Science Alert.
"This is multiple overlapping variants emerging that are all quickly becoming resistant to the drugs we use to treat them," she added. "It's highly likely that if you contracted your Shigella through sex, you require different treatment to someone who contracted it through travel."
Meanwhile, experts advise the public to keep their sanitation game tight. Proper handwashing and making sure to wash private areas and any toys used during sexual activity are frontline preventive measures.
Of course, safe sex (condoms and dental dams) should also be employed.
That said, The California Department of Public Health added another, more blunt, piece of advice.
"Don't have sex with someone who has had diarrhea in the last two weeks," they advised, per The Post.
