Shigella bacteria resistant to all five antibiotics normally used against them went from undetectable in US surveillance samples to 8.5 percent of tested isolates over a little more than a decade, according to a CDC analysis of nearly 17,000 samples.
There is no FDA-approved oral antibiotic for these strains. That is the operative fact for anyone who develops severe diarrheal illness and needs treatment, and it is why the CDC report emphasizes laboratory testing before an antibiotic is chosen rather than empiric prescribing.
The epidemiology has also shifted in a way that matters for who should pay attention. Earlier US Shigella outbreaks involved drug-susceptible strains and mostly affected children. The extensively drug-resistant cases in this analysis occurred overwhelmingly among adult men, and most had no recent international travel.
Five Antibiotics, None of Them Working
CDC analyzed 16,788 Shigella isolates submitted to PulseNet, its molecular surveillance network for enteric pathogens, from January 2011 through October 2023. Resistance was characterized using whole-genome sequencing and antimicrobial susceptibility testing.
Of those, 510 isolates, or 3 percent, met the definition of extensively drug-resistant: resistant to ampicillin, azithromycin, ceftriaxone, ciprofloxacin, and trimethoprim-sulfamethoxazole. The proportion climbed from 0 percent during 2011 through 2015 to 8.5 percent in 2023.
Species information was available for 505 of the 510 XDR isolates. Of those, 333, or 65.9 percent, were Shigella sonnei, and 172, or 34.1 percent, were Shigella flexneri.
The MMWR report frames the concern in terms broader than one organism, noting that alternative oral treatment options are limited and that resistance genes can spread to other enteric bacteria.
The Case Profile Is Not What Older Guidance Assumes
Among patients with XDR shigellosis, the median age was 41, with an interquartile range of 31 to 54, and 86.2 percent were men. Among 116 patients with HIV status recorded, 46.6 percent reported HIV co-infection.
Among patients with travel history available, 82.4 percent reported no recent international travel and 76.2 percent reported no recent domestic travel, which points to local transmission rather than importation.
Naeemah Logan of CDC's National Center for Emerging and Zoonotic Infectious Diseases was corresponding author on the analysis, which described trends and epidemiologic characteristics of XDR shigellosis nationally. Data from other countries suggest XDR strains spread through sexual networks, though this analysis did not collect the behavioral data needed to draw firm conclusions.
Antibiotic resistance is a global problem driven by overuse and inappropriate use, William Schaffner of Vanderbilt University School of Medicine told Healthline, while noting that US clinicians and public health have worked hard at antibiotic stewardship.
A Dose Small Enough to Change How It Spreads
Shigella is unusually transmissible. As few as 10 organisms can cause infection, a threshold low enough that ordinary hand-to-mouth contact is sufficient.
Transmission occurs by the fecal-oral route through person-to-person contact or sexual contact, and through contaminated food, water, or surfaces. That low infectious dose is why the bacterium historically caused outbreaks in child care centers and households, and why it now moves efficiently through adult networks.
Symptoms usually begin one to two days after exposure and include diarrhea that is often bloody, fever, stomach cramps, and a painful urge to pass stool when the bowel is empty. Most infections resolve within about a week without antibiotics.
Antibiotics are indicated for severe illness or to reduce transmission in settings at high risk for spread, which is precisely where resistance becomes the problem. When treatment is needed, and the strain is XDR, clinicians are left with intravenous or nonstandard options and no approved oral choice.
Testing Before Prescribing, and When to Seek Care
The single most useful action a patient can take is asking whether the laboratory will perform complete antimicrobial susceptibility testing before an antibiotic is selected. CDC recommends testing against azithromycin, ciprofloxacin, ceftriaxone, trimethoprim-sulfamethoxazole, and ampicillin. Shigellosis is nationally notifiable, and timely reporting is what allows health departments to spot clusters.
Medical attention is warranted for bloody diarrhea, fever above 102 degrees, diarrhea lasting more than three days, severe abdominal pain, or signs of dehydration including little urination, dry mouth, or dizziness on standing. Young children, adults over 65, pregnant people, and anyone with a weakened immune system should seek guidance earlier.
Anti-diarrheal medications such as loperamide can prolong illness in Shigella infection and should not be used without clinician advice.
Prevention rests on handwashing with soap and water, which works better than alcohol-based sanitizer against this organism; avoiding preparing food for others while symptomatic and for at least two days after symptoms resolve; and avoiding sexual contact during illness and for two weeks afterward. Sexual health clinics and local health departments offer testing and treatment at low or no cost for people without insurance.
Surveillance Gaps That Blur the Real Picture
Several limits deserve stating. PulseNet receives isolates rather than every case, so the sample is not a census. Of the isolates with resistance data, most were characterized by sequencing alone rather than by susceptibility testing, and many clinical laboratories do not run complete panels, which means XDR strains are likely undercounted. The data also end in October 2023, so the current national picture is unknown.
The report cannot establish how much of the increase reflects true spread versus improved detection through whole-genome sequencing.
What CDC has called for is strengthened surveillance, routine susceptibility testing and timely reporting, as summaries of the report noted. For readers, the relevant next development is whether an oral treatment option emerges and whether more laboratories adopt complete panels. Neither has happened yet.
Frequently Asked Questions
What makes Shigella extensively drug resistant? Resistance to all five recommended antibiotics: ampicillin, azithromycin, ceftriaxone, ciprofloxacin, and trimethoprim-sulfamethoxazole.
How common is it? Three percent of nearly 17,000 isolates CDC analyzed from 2011 through October 2023, rising to 8.5 percent of isolates in 2023.
Who is most affected? Adult men, who made up 86.2 percent of patients, with a median age of 41 and most reporting no recent travel. Among those with HIV status recorded, 46.6 percent had HIV.
Can it still be treated? No FDA-approved oral antibiotic exists for XDR strains. Most infections resolve without antibiotics; severe cases require susceptibility-guided therapy.
What are the symptoms? Diarrhea often containing blood, fever, stomach cramps, and a painful urge to pass stool. Symptoms typically begin one to two days after exposure.
How does it spread? Fecal-oral contact, including person-to-person and sexual contact, and contaminated food or water. As few as 10 organisms can cause infection.
What should I ask my doctor? Whether the laboratory will perform complete antimicrobial susceptibility testing before an antibiotic is selected.
