Sexually Transmitted Shigella: A Growing Drug‑Resistant Threat

A gut pathogen best known for causing food‑borne diarrhea is increasingly spreading through sexual contact, raising alarms about a new, hard‑to‑treat sexually transmitted infection (STI). Recent surveillance shows that drug‑resistant Shigella strains are no longer rare anomalies but are becoming endemic in certain communities, particularly gay, bisexual and other men who have sex with men (GBMSM).

Rise of Extensively Drug‑Resistant Shigella in the United States

In the United States, roughly 450,000 people acquire shigellosis each year, a number that can lead to dysentery and severe dehydration. Historically, the bacterium spread mainly via contaminated food or water during travel and among young children in day‑care settings. Since the turn of the century, however, Shigella has emerged as a sexually transmitted pathogen.

Data from the U.S. Centers for Disease Control and Prevention (CDC) reveal a steep climb in extensively drug‑resistant (XDR) isolates. In 2011, none of the tested Shigella samples showed resistance to five commonly used antibiotics. By 2023, that proportion had risen to 8.5 percent. The upward trend continued into 2024, with the CDC’s latest antimicrobial‑resistance report noting that XDR Shigella still accounts for a notable share of isolates nationwide.

Clinical observations mirror the surveillance numbers. At the University of California, Los Angeles (UCLA) medical center, microbiologist Shangxin Yang reported seeing roughly one case of XDR Shigella per month in 2023‑2024, compared with just a single case for the entire year of 2022. “It’s almost like an explosion of this pathogen in the community,” Yang told CIDRAP News.

The burden of severe illness is significant. CDC analysis indicates that more than a third of patients with XDR shigellosis required hospitalization, and among those with documented HIV status, nearly half were HIV‑positive. These patterns highlight the intersection of antimicrobial resistance, sexual health, and existing health disparities.

Sexual Transmission Becomes a Major Route Among MSM Communities

While sexually transmissible shigellosis was first described in 1974, it represented a small fraction of cases at that time. Recent evidence shows that sexual contact now drives a substantial proportion of infections, especially within GBMSM networks. The pathogen’s ability to cause outbreaks in these communities is facilitated by asymptomatic shedding and overlapping sexual networks.

Several challenges impede accurate tracking. Patients and clinicians may not recognize Shigella as an STI, and sexual histories are often omitted from medical records. Consequently, true incidence may be under‑reported. Nevertheless, molecular studies have identified distinct Shigella lineages circulating primarily among MSM in major U.S. cities.

Researchers note that many of the strains carried by sexual transmission have acquired resistance to multiple antibiotic classes, rendering standard first‑line therapies ineffective. Some isolates are now classified as extensively drug‑resistant, leaving clinicians with few reliable treatment options.

Global Perspective: UK and European Trends

The situation is not confined to the United States. In the United Kingdom, the UK Health Security Agency (UKHSA) reported that in 2025, 86 percent of Shigella sonnei isolates and 94 percent of Shigella flexneri isolates tested showed resistance to antibiotics—figures that underscore the extent of the problem among sexually active populations.

Geneticist Kate Baker of the University of Cambridge, senior author of a recent The Lancet Infectious Diseases study, described a parallel surge in the UK. She warned that many men who have sex with men remain unaware of the rising risk posed by sexually transmitted Shigella. “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 in a July 2024 press release.

Across Europe, the European Centre for Disease Prevention and Control (ECDC) has documented increasing reports of Shigella outbreaks linked to sexual transmission in countries such as Germany, France, and the Netherlands. The agency notes that the convergence of antimicrobial resistance and sexual network dynamics creates a challenging public‑health scenario.

Public Health Recommendations and Prevention Strategies

Given the limited treatment options, prevention remains the cornerstone of control. Health agencies advise the following measures:

• Avoid sexual contact with anyone who has experienced diarrhea in the preceding two weeks.
• Use condoms or dental dams during oral and anal sex.
• Wash hands, genitals, and any sex toys before and after sexual activity.
• If symptoms such as abdominal cramping, fever, or bloody diarrhea develop, seek medical evaluation and testing for Shigella.
• Inform sexual partners of any diagnosis so they can also be tested and treated.

Clinicians are urged to routinely ask patients presenting with dysentery about recent sexual activity and to consider Shigella in the differential diagnosis, especially when the patient belongs to a high‑risk network. Because XDR Shigella often requires specialized susceptibility testing, early identification can guide appropriate therapy and limit further spread.

Looking Ahead: Research Needs and Policy Implications

The emergence of sexually transmitted, drug‑resistant Shigella raises several research questions. Scientists are investigating whether “bystander resistance”—where exposure to antibiotics for unrelated infections selects for resistance in co‑colonizing bacteria—plays a role in the observed patterns. Preliminary data suggest that changes in STI treatment guidelines, such as reduced use of azithromycin for gonorrhea, may influence the trajectory of azithromycin resistance in Shigella, though causation remains unproven.

Surveillance systems need to integrate sexual‑history variables to capture the true burden of sexually transmitted Shigella. Enhanced rapid diagnostics, point‑of‑care susceptibility testing, and genomic monitoring can help detect outbreaks sooner and track resistance evolution.

From a policy perspective, aligning STI prevention programs with enteric disease control efforts may yield synergistic benefits. Education campaigns targeting GBMSM communities, combined with improved access to testing and treatment, are essential to curb the spread of this evolving threat.

Health, Science, Society, News