Sexually transmitted diarrhea is spreading rapidly across the US and is now ‘close to untreatable’

A bacterial illness historically linked to poor sanitation is now finding new avenues of transmission.

Shigella bacteria infect roughly half a million people in the United States each year, triggering gastrointestinal symptoms such as stomach pain, cramps, fever, vomiting, and diarrhea containing blood or mucus, which is the hallmark of dysentery.

Beyond causing severe physical discomfort, the infection can become life-threatening by dehydrating the body, causing septic shock, neurological complications, or internal bleeding.

Historically, children under five years old, travelers to areas with lower sanitation standards, and individuals experiencing homelessness faced the highest risk of contracting the bacteria.

Transmission typically occurs when infected fecal matter enters the mouth via unwashed hands or contaminated food and water. Remarkably, as few as 10 organisms are enough to make a person ill.

However, medical researchers have noticed a shift in how the disease moves through the population. Emerging data shows that sexual contact is increasingly driving infections, creating new public health challenges.

Spreading through sex

The population currently seeing one of the fastest increases in shigella infections includes gay, bisexual, and other men who have sex with men.

Experts describe the bacteria as endemic within these communities, meaning it maintains a constant presence. A July study indicated that the spread of the disease through sex grew 15% faster year over year between 2015 and 2020 compared to transmission through travel, food, or nursery outbreaks.

Some researchers suggest that sexual contact may now represent the primary transmission route, though incomplete intake questioning at clinics makes precise tracking difficult.

A widespread lack of awareness regarding these transmission pathways continues to fuel new cases.

"Many men who have sex with men are unaware of the serious and increasing risk posed by sexually transmitted Shigella," said Cambridge geneticist Kate Baker, a lead author on the July study.

Becoming a superbug

Compounding the problem of rapid transmission is the rise of antibiotic resistance. According to the Centers for Disease Control and Prevention (CDC), drug-resistant strains of the infection rose from 0% in 2011 to 8.5% in 2023.

Most of these resistant cases have affected adult men, with patients contracting the strain through sex requiring an average hospital stay of four to five days.

"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 said.

Experts suspect that bystander resistance may be contributing to the problem. This occurs when an inappropriate antibiotic is prescribed for a pathogen, failing to kill the target while granting the bacteria an opportunity to adapt.

"This isn't just one form of sexually transmissible diarrhea," Baker told Science Alert. "This is multiple overlapping variants emerging that are all quickly becoming resistant to the drugs we use to treat them. It's highly likely that if you contracted your Shigella through sex, you require different treatment to someone who contracted it through travel."

Treating and preventing shigella

While mild cases often resolve within a week using rest and fluids, severe cases traditionally rely on antibiotics to shorten the illness and reduce contagiousness.

Because growing drug resistance makes standard treatments less reliable, health officials emphasize preventative hygiene measures.

Recommended precautions include washing hands, genitals, and the anus with soap and water before and after sexual activity, as well as cleaning sex toys thoroughly.

Using barrier methods like condoms and dental dams can also lower risk. Additionally, public health guidance from the California Department of Public Health offers a straightforward rule: "Don't have sex with someone who has had diarrhea in the last two weeks."