There's a bacteria called Shigella. It infects roughly 450,000 Americans every year. It causes bloody diarrhea, severe stomach cramps, vomiting, and fever. In serious cases — up to a third of sexually transmitted cases — it leads to hospitalization. In the worst cases, it can cause septic shock, internal bleeding, and neurological complications.
You've probably heard of it as a stomach bug. The kind that makes the rounds at daycares and comes back from international travel. That's still true.
What's new is that Shigella is also spreading through sexual contact — and it's becoming resistant to the antibiotics we've been using to treat it. Both things happening at the same time is the part that worries infectious disease experts.
What Sexual Transmission Has to Do With This
Shigella is extraordinarily contagious. It takes as few as 10 bacteria to cause an infection — compared to millions for some other pathogens. It spreads through contact with infected fecal matter, which can happen in more ways than most people think about: contaminated food and water, surfaces, and certain types of sexual contact.
The CDC released data this year showing that sexually transmitted Shigella cases have risen significantly, and that the drug-resistant strains are concentrated in these cases. The strains spreading this way are developing resistance faster than strains spreading through food and water — partly because of a phenomenon called "bystander resistance," in which treating one infection with an antibiotic accidentally makes nearby bacteria resistant too.
Cambridge geneticist Kate Baker, who led a major 2026 study on the subject, put it directly: "Many people are unaware of the serious and increasing risk posed by sexually transmitted Shigella. This isn't just one form of sexually transmissible diarrhea. Multiple overlapping variants are emerging, all rapidly becoming resistant to antibiotics."
How Drug Resistant It's Actually Becoming
This is where the numbers get alarming.
In 2011 to 2015, zero percent of US Shigella samples were classified as extensively drug-resistant (XDR) — meaning resistant to five or more commonly used antibiotics. By 2023, that figure had risen to 8.5 percent.
In the UK, which tracks this more closely, 86 percent of one Shigella strain and 94 percent of another tested in 2025 showed antibiotic resistance. Those numbers are UK-specific, but the same strains are present in the US, and the resistance patterns tend to follow similar trajectories.
"Extensively drug-resistant" means the standard antibiotics — the ones doctors have been prescribing for this condition for decades — don't reliably work anymore. What's left is a smaller set of alternatives, some of which have more significant side effects and are harder to access.
The concern isn't that Shigella is about to cause a nationwide crisis on the scale of something like COVID. Most people who get shigellosis still recover without antibiotics at all. The concern is that the resistant strains are becoming more common, the drugs to treat them are becoming fewer, and the people most at risk of serious complications are the ones most likely to encounter the resistant versions.
The Part Doctors Are Getting Wrong
One of the specific problems researchers are flagging: most doctors don't ask about sexual transmission when a patient comes in with diarrhea.
This matters because sexually transmitted Shigella is more drug-resistant than food-and-water-transmitted Shigella. A doctor who doesn't know the transmission route may prescribe an antibiotic that no longer works against the specific strain the patient has — which doesn't help the patient and may contribute further to resistance.
According to researchers at Rolling Out, the missing question — "how do you think you were exposed?" — is one of the most important interventions available, both for individual treatment and for slowing the spread of resistance.
How Worried Should You Be
According to infectious disease experts quoted in Yahoo News, Americans should be "concerned but not overwhelmingly alarmed." Most shigellosis cases still resolve on their own. The resistant strains are a growing percentage of a larger pool, not a dominant strain taking over the entire landscape.
What this report is a signal of — and what experts are trying to communicate — is that the era of "if it's bad enough, we'll just give you an antibiotic" is getting shorter. Every time a class of antibiotics stops working reliably against something, the options narrow. Shigella is one more item on a list that keeps getting longer.
The CDC recommends that anyone with severe or prolonged diarrhea — especially bloody diarrhea — see a doctor rather than waiting it out, and that anyone who tests positive for Shigella tell their healthcare provider about all potential routes of exposure so the right treatment can be chosen.
