Science1 publisherNot yet confirmed elsewhere2 min readPublished
Extensively drug-resistant Shigella rose to 8.5 percent of US isolates by 2023
CDC surveillance of nearly 17,000 Shigella isolates found extensively drug-resistant strains rose from 0 percent in 2011 to 8.5 percent in 2023. The resistance narrows what doctors can prescribe and is pushing clinics to ask how patients caught the infection.
The Scientist · Science desk
What happened
- Once spread mainly through contaminated food, water and day care, Shigella began emerging as a sexually transmitted infection around the turn of the century.
- Among some groups of gay, bisexual and other men who have sex with men, Shigella is now regarded as endemic.
- More than a third of patients with extensively drug-resistant shigellosis were hospitalized, according to the CDC data.
- Nearly half of the drug-resistant patients whose HIV status was known were living with HIV.
- In 2025, UK Health Security Agency testing found 86 percent of Shigella sonnei and 94 percent of Shigella flexneri samples resistant to antibiotics.
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Why it matters
- constraint For the severe cases that need treating, UKHSA says the usable antibiotics are becoming limited. A routine first-line prescription is no longer a safe assumption.
- decision If sex-acquired Shigella needs a different drug than the travel-acquired kind, clinicians have to ask how a patient was infected before choosing treatment.
- cost In earlier UK research, up to a third of sexually transmitted Shigella patients were hospitalized for four to five days, an inpatient cost for an illness often assumed to clear on its own.
- precedent The US and UK are tracking the same rise, and the CDC's Naeemah Logan calls it part of a broader global pattern. Clinics elsewhere can expect these strains.
Surveillance like this captures how resistant the bacteria are, while how they spread is harder to measure. Patients and clinicians often do not know Shigella can pass through sex, and a sexual history is frequently missing from the chart [15]. Sexually transmissible shigellosis was first reported in 1974, when it was a minority of cases [13]. The evidence that sex is now a major route is an inference from who is infected [14]: the resistant isolates came overwhelmingly from adult men, many reporting no recent international travel [9]. Historically the bug arrived in contaminated food and water during travel, or among children in day care [4].
Shigella causes diarrhea, vomiting and sometimes dysentery [2]. The CDC's count ran to nearly 17,000 isolates over 2011 to 2023 [7], an average of about 1,300 a year [29]. The United States records roughly 450,000 shigellosis infections a year [3]. The 8.5 percent resistant to five common antibiotics describes tested bacteria only [8].
At UCLA, the molecular biologist Shangxin Yang said the hospital now sees about one extensively drug-resistant case a month, against a single case in all of 2022 [10][11]. "It's almost like an explosion of this pathogen in the community," Yang said [12]. That is roughly a twelvefold jump [28]. The figure comes from one hospital. It moves with how much testing and referral the lab sees, and it does not measure population incidence.
Kate Baker, a geneticist at Cambridge and senior author of a recent study in The Lancet Infectious Diseases, found the same surge in Britain [19]. There, the two strains most often passed through sex among gay and bisexual men are the ones now showing high resistance [23]. "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 [20].
Why the sexually transmitted strains resist more drugs is unsettled. Baker's 2026 study points to "bystander resistance" [26]: an antibiotic aimed at one infection reaches other bacteria in the body at a drug or dose that does not clear them, selecting for resistance as a side effect [27]. Alicia Calvo-Villamanan, a researcher at the Gulbenkian Institute for Molecular Medicine in Lisbon, noted an association tied to the UK dropping azithromycin from its gonorrhea treatment guidelines [1].
What to watch
- Whether US or UK authorities revise first-line antibiotic recommendations for Shigella as resistance keeps climbing.
- Whether clinics start recording sexual history and typing strains so treatment can match how an infection was caught.
- Whether Baker's bystander-resistance hypothesis holds up, including the suggested link to changes in gonorrhea treatment guidelines.