Shigella: what the gut infection is, how it spreads and what the CDC found about drug-resistant strains

A gut infection called shigella was back in the headlines on October 10, when Fox News ran a report headlined “Stomach-turning sexually transmitted infection is on the rise, and standard medicines are failing.” The story drew on a report the Centers for Disease Control and Prevention (CDC) published in April.

The report is real and its central number is striking. But the headline version blurs what the CDC found. Shigella infections have not been shown to be surging. What has changed is the bacteria: a growing share of the strains now circulating in the United States resist every antibiotic normally used against them. This explainer sets out what shigella is, how it spreads, who is affected by the resistant strains and what the data can and cannot show.

What is shigella?

Shigella is the name of a group of bacteria, and shigellosis is the illness they cause. A review in The Lancet defines it precisely. Shigellosis is a clinical syndrome caused by invasion of the epithelium lining the terminal ileum, colon, and rectum by Shigella species. The epithelium is the surface layer of cells, and the terminal ileum is the last stretch of the small intestine. The bacteria, in other words, burrow into the lining of the lower gut.

The result is usually a few unpleasant days. Common symptoms of the infection include diarrhea, fever, stomach pain and experiencing a feeling to pass stool when bowels are empty. In severe cases the diarrhea is bloody, which doctors call dysentery. The Lancet review notes that a broad array of uncommon, but often severe, intestinal and extraintestinal complications can occur. Extraintestinal means outside the gut.

It is common. Shigella causes an estimated 450,000 infections each year nationwide, making it a leading cause of diarrheal illness, according to the CDC. The species seen most in the United States is Shigella sonnei, followed by Shigella flexneri.

Worldwide, the burden falls elsewhere. Endemic infections among children aged 1-4 years living in low-income and middle-income settings constitute most of the disease burden. Endemic means constantly present in a place. Despite marked reductions in mortality during the past three decades, the review, published in 2018, put deaths at roughly 164,000 a year.

In a healthy adult in a wealthy country, the illness usually ends by itself. Most infections resolve without requiring treatment with antimicrobial agents; however, antibiotics are indicated for severe illness or to reduce transmission in high-risk settings. Antimicrobial agents are drugs that kill microbes, a category that includes antibiotics.

How shigella spreads

The bacteria leave the body in stool and infect the next person through the mouth. The CDC report says Shigella species cause acute diarrheal illness and spread easily from person to person through fecal-oral transmission or sexual contact, or through contaminated food, water, or fomites. Fomites are objects that carry germs, such as a tap, a toy or a changing table.

What makes shigella so contagious is how little of it is needed. Infection can occur with as few as 10 organisms. Many other gut infections take far larger doses.

That is why it has long been a disease of small children. Children younger than 5 are especially likely to get shigella, according to the CDC, and many outbreaks in the U.S. have been linked to childcare and schools.

Sex is another route, and not a new one. A Texas physician who specializes in sexual health, Andi Toufexis, explained it to Fox News. “Shigella is not considered to be a typical sexually transmitted infection,” Toufexis said. It can pass between partners during sex when one comes into contact with traces of the other’s stool. Shigella is not new, and sexual transmission has been documented since the 1970s, Toufexis said.

A UK research team has described how prominent that route has become in one group. Shigellosis, they wrote, is now a leading cause of sexually transmitted gastroenteritis among gay, bisexual, and other men who have sex with men (MSM). Gastroenteritis is inflammation of the stomach and gut.

Why drug-resistant shigella is in the news

The CDC’s April report looked at samples of the bacteria grown from patients, known as isolates, that state laboratories had submitted to a national surveillance network from January 2011 to October 2023. The agency was looking for one category in particular: extensively drug-resistant (XDR) strains. The report defines XDR as being resistant to ampicillin, azithromycin, ceftriaxone, ciprofloxacin, and trimethoprim-sulfamethoxazole, the five antibiotics doctors normally reach for.

Among 16,788 isolates with resistance data during this period, 510 (3.0%) were XDR. That overall share hides a steep recent climb. The percentage of XDR isolates increased from 0% during 2011-2015 to 8.5% in 2023. The first such strain appeared in 2016, and among the 492 cases with patient details, 415, or 84.3%, were recorded in 2022 and 2023 alone.

The distinction between more infection and more resistance was put sharply by Tyler Evans, a California infectious disease physician who commented on the report for Fox News. “The infection is not surging. The bacteria are changing,” Evans said. “Case counts can hold steady while the treatment options quietly disappear.”

The United States is not the only country to see it. In the UK, laboratories picked up an unusual cluster of one XDR strain, first detected in September, 2021, that spread across all four nations within months.

Resistance has a second cost, which the CDC flags. Shigella can pass its resistance on. The report warns that resistance genes can spread to other enteric bacteria, meaning other bacteria that live in the gut.

Who is getting drug-resistant shigella

Here the new pattern departs from the old one. The CDC summarizes the shift in a sentence. Whereas earlier U.S. outbreaks involved drug-susceptible strains and primarily affected children, national surveillance data indicate that most XDR cases occurred among adult men.

The figures are lopsided. Among patients with XDR shigellosis, the median patient age was 41 years, and 86.2% were men. The median is the middle value. Only 19 of the cases were in people under 18.

Many were also living with human immunodeficiency virus (HIV). Among 116 persons with available HIV status, 54 (46.6%) reported HIV co-infection. HIV status was known for fewer than a quarter of the patients, so that proportion is uncertain. The CDC considers the overlap important all the same. The emergence of XDR strains raises concerns for persons with immunocompromise, including those with HIV, for whom treatment options are limited and risk for severe illness is higher. Immunocompromise means a weakened immune system.

Most had not been traveling. Among patients with available travel history, 76.2% (173 of 227) reported no recent domestic travel and 82.4% (169 of 205) reported no recent international travel. These infections were, for the most part, acquired at home.

The illness was often serious. Among 258 patients for whom hospitalization data were available, 97 (37.6%) were hospitalized. No deaths were reported.

The report did not establish how individual patients were infected, because that information was not gathered consistently. It points to earlier research. Sexual exposure data were incomplete and not analyzed; however, previous studies identified sexual contact among men who have sex with men as an important Shigella transmission route.

The UK outbreak fits that reading. Of the people investigators were able to interview there, most were men who have sex with men and who reported sexual contacts in the UK and Europe shortly before they fell ill. And a systematic review covering a decade of reports found resistance described again and again. Thirty-nine manuscripts met the inclusion criteria, and 34 of them described reduced sensitivity or resistance to the main antibiotic classes in shigella circulating among men who have sex with men.

A doctor who sees such cases cautioned against treating this as a matter for blame. Jason Zucker, an assistant professor of medicine at Columbia University Medical Center who was not part of the CDC study, sees shigella cases at a sexual health clinic. “The starting point is recognizing that the sexual practices that can transmit Shigella are common and normal,” Zucker told Healio. Of resistance, Zucker offered an observation from the clinic and was careful about its weight: “it does seem that more are resistant to antibiotics, though I don’t have hard data on that from our clinic specifically.”

How shigella is treated when standard antibiotics fail

For most people, treatment is rest and fluids while the infection passes. The systematic review of sexually transmitted cases makes the same point. While most cases can be managed conservatively, a minority require antimicrobial treatment. Conservatively means without drugs aimed at the bacteria.

The difficulty arises for that minority. The CDC states the gap baldly. No Food and Drug Administration-approved oral antimicrobial agents are available to treat these XDR infections. Oral means taken by mouth, and the Food and Drug Administration (FDA) is the US drug regulator.

There are candidates. Pivmecillinam, fosfomycin, and oral carbapenems (e.g., sulopenem) might be effective, the report says, but as of 2025, none was approved by the Food and Drug Administration (FDA) for shigellosis. None of the 510 XDR samples showed resistance to fosfomycin or to meropenem, a carbapenem given by injection. The report’s summary of the situation is short. Treatment of XDR shigellosis remains challenging because no optimal therapy has been established.

In practice that means testing the particular strain to see which drugs still work against it, and treating on that basis. In the UK outbreak, of 33 cases with clinical data, 19 (58%) received antibiotics, and eight were admitted to hospital.

The systematic review drew a wider conclusion about the drug classes that azithromycin, ciprofloxacin and ceftriaxone belong to. There is little role for macrolides, quinolones or third generation cephalosporins in the management of sexually transmitted shigella in men who have sex with men. Its authors called for new approaches, as antimicrobial options are diminishing.

Vaccines are a longer-term hope. The Lancet review reported in 2018 that the threat has accelerated interest in development of shigella vaccines, many of which are being tested in clinical trials.

How people lower the risk of shigella

Because so few bacteria are needed, prevention comes down to keeping traces of stool away from the mouth. For households and childcare, that means handwashing.

For sexual transmission, Healio summarized the federal guidance. CDC guidelines advise preventing contact with feces during sex, using barriers and washing hands after touching objects that have been in contact with the anal area.

Zucker argued that how such advice is delivered matters as much as what it says. “The goal is to deliver guidance that reduces harm in a way that feels practical and empowering rather than shaming,” Zucker said.

What the shigella data cannot show

How many resistant infections there are. The figures describe samples that reached a laboratory and were tested for resistance. Most infections never get that far. The report notes that many specimens that were positive by culture-independent diagnostic tests were not cultured, and so could not be checked. The true number is higher than 510.

How much of the rise is better detection. Genetic sequencing of samples expanded over the study period. The CDC acknowledges that state sequencing capacity varies, which might contribute to regional differences and observed increases in XDR detection.

How people were infected. Sexual exposure was not recorded consistently, so the report infers the likely route from who the patients were and from earlier studies.

Travel and HIV. Both were unknown for many patients. The report says travel history was missing for approximately one half of patients with XDR shigellosis, and HIV status was missing for more than three quarters.

What has happened since. The data end in October 2023. Whether the share of resistant strains has kept climbing in the three years since is not covered.

What works. No best treatment for these strains has been established.

Whether a bout of diarrhea needs a stool test or antibiotics is assessed by their doctor.

Shigella itself is an old and usually passing illness, and the news is that in a small but growing share of tested infections the usual antibiotics no longer work.