Extensively Drug-Resistant Shigella Is Rising in the United States

Shigella bacteria cause shigellosis, a diarrheal illness that must be reported nationally in the United States. They are highly infectious — as few as 10 organisms can cause infection — and spread easily from person to person through fecal-oral contact or sex, or through contaminated food, water or objects. Most infections clear up without antibiotics, which are reserved for severe illness or for curbing spread where the risk is high.

A growing share of infections, though, are extensively drug-resistant (XDR): resistant to ampicillin, azithromycin, ceftriaxone, ciprofloxacin and trimethoprim-sulfamethoxazole. No oral antibiotic approved by the Food and Drug Administration treats them, other oral options are limited, and the resistance genes can pass to other gut bacteria. This CDC report describes how XDR shigellosis has spread and whom it affects.

The data

State and local public health laboratories send Shigella isolates to PulseNet, CDC's molecular surveillance network, according to their own protocols and capacity. From January 1, 2011 — when azithromycin was added to the panel of CDC's National Antimicrobial Resistance Monitoring System — to October 20, 2023, 16,788 isolates had resistance data, from whole-genome sequencing, laboratory susceptibility testing or both. The two methods agree closely, and sequencing became more common over the period.

An isolate counted as XDR if it tested resistant to all five drugs, or if sequencing found resistance genes for each (at least two for ciprofloxacin).

A rising share

Sequenced Shigella isolates submitted to PulseNet, and the percentage that were extensively drug resistant, United States, 2011–2023. CDC, MMWR.

• 510 isolates (3.0%) were XDR. The first were identified in 2016.
• The XDR share rose from 0% in 2011–2015 to 8.5% in 2023, and 84.3% of XDR cases occurred in 2022–2023.
• 167 XDR isolates (32.7%) were also resistant to chloramphenicol. None were resistant to meropenem or fosfomycin.
• Of 505 XDR isolates with species data, 65.9% were S. sonnei and 34.1% S. flexneri — nearly twice S. flexneri's 18.5% share of all sequenced Shigella. That share varied by place and time, peaking at 84.6% in the Northeast in 2021 and reaching 54.8% in the West in 2023; in the Midwest, S. flexneri first appeared in 2023. It was highest in Oregon (15 of 21), California (48 of 111) and Colorado (24 of 60).
• Of 498 isolates with a known source, 97.0% came from stool and 1.8% from blood.

Who got sick

Shigellosis in the United States has historically been a disease of children, mostly caused by drug-susceptible strains. XDR shigellosis is different:

• Adults, mostly men. The median age was 41. Of 492 patients with age and sex recorded, 86.2% were adult men, 10.0% adult women and 3.9% under 18.
• Race and ethnicity. Of 388 with race recorded, 75.3% were White, 11.9% Black or African American and 5.2% Asian; 19.3% of 270 with ethnicity recorded were Hispanic or Latino.
• HIV. Of 116 with HIV status recorded, 54 (46.6%) had HIV.
• Severity. Of 258 with hospitalization data, 97 (37.6%) were hospitalized. No deaths were reported.
• Mostly not travel. 76.2% of 227 reported no recent domestic travel, and 82.4% of 205 no recent international travel.

Data on sexual exposure were too incomplete to analyze, but earlier studies found sex between men to be an important route of Shigella transmission. XDR strains are a particular worry for people with weakened immune systems, including people with HIV, who face higher risk of severe illness and fewer treatment options, and XDR Shigella has been reported alongside other bacterial sexually transmitted infections. S. flexneri has been linked in published studies to more severe outcomes — dysentery, hospitalization and a higher death rate — so the combination deserves further study.

Treatment

Clinicians should base treatment on susceptibility results from a clinical laboratory whenever possible. No best treatment for XDR shigellosis has been established. Chloramphenicol is not routinely recommended in the United States. Pivmecillinam, fosfomycin and oral carbapenems such as sulopenem might work, but as of 2025 none was FDA-approved for shigellosis.

Limitations

• Surveillance probably undercounts XDR Shigella: not every isolate was sequenced or tested, many positive specimens from culture-independent tests were never cultured, cases go undiagnosed and unreported, and submissions varied by place and over time.
• Susceptibility results were not available for every isolate, though sequencing agrees with them more than 95% of the time.
• Sequencing was limited before 2019 and varies by state, which could explain some regional differences and part of the rise.
• Demographic, behavioral and clinical data were often incomplete, and travel history was missing for about half of patients.

With no FDA-approved oral treatment, prevention, early detection, therapy guided by susceptibility testing, and prompt reporting are the main defenses.

Sources

• Logan N, Birhane MG, McDonald SL, et al. "Emergence of Extensively Drug-Resistant Shigellosis — United States, 2011–2023." MMWR 75(13). CDC. The report says XDR cases have made up a growing share "since 2015" but also that the first XDR isolates were identified in 2016; the latter is given here.