While public health discussions around sexually transmitted infections traditionally focus on chlamydia, gonorrhea, syphilis and HIV, an unexpected gastrointestinal pathogen is commanding urgent attention: Shigella.
Shigellosis is an acute, highly contagious infection of the intestinal lining. While historically recognized as a classic foodborne and waterborne illness, the bacteria are also readily spread through direct or indirect oral-anal sexual contact. Because an infectious dose requires as few as 10 to 100 bacterial cells, a single exposure during intimate contact can transfer the pathogen.
According to a study in The Lancet, sexually transmitted Shigella infections increased by an average of 15% annually between 2015 and 2020. That trajectory has not slowed: through September 2026, the CDC recorded 13,921 cases, putting the nation on pace to eclipse 2025’s total of 14,200. Even more concerning for infectious disease clinicians is the emergence of extensively drug-resistant strains, turning what was once a routine, easily treated infection into a serious therapeutic challenge.
Curbing this spread will require greater awareness of early symptoms, clear public health guidance on transmission routes and consistent use of barriers and hygiene precautions.
What is shigellosis?
Shigellosis is a serious bacterial enteric disease caused by four species of Shigella: Shigella sonnei, Shigella flexneri, Shigella boydii and Shigella dysenteriae. Shigella sonnei and Shigella flexneri are the most common causes of clinical illness in the United States.
Shigella is estimated to infect about 500,000 people a year in the United States and to claim an estimated 600,000 lives worldwide, primarily among young children in low-resource areas, according to the National Institutes of Health (NIH).
Epidemiologists classify the bacterium as one with an “extraordinarily low infectious dose.” A microscopic smear of Shigella containing fewer than 100 organisms can survive gastric acidity and migrate to the large intestine, where acute infection occurs, unlike many foodborne pathogens, which require ingestion of thousands or millions of bacteria to survive gastric acidity. The usual modes of transmission involve eating food or drinking water that has been contaminated by the bacteria (or handling diapers in a daycare setting). Still, the bacteria are now a well-recognized emerging sexually transmitted enteric infection (STEI) with disproportionate transmission rates among men who have sex with men (MSM).
What’s happening in your body
After ingestion, Shigella bacteria pass through the stomach and small intestine to the colonic epithelium of the large intestine, where they begin an aggressive, tissue-destructive invasion. According to the Mayo Clinic, the bacteria attach directly to mucosal epithelial cells and M cells of the follicle-associated epithelium via specific virulence factors. The bacteria enter host cells through macropinocytosis once they adhere.
In the host cell cytoplasm, Shigella survives, grows rapidly and recruits host actin filaments to form “actin rocket tails.” In this manner, the bacteria travel through intercellular spaces into neighboring epithelial cells without being released into the extracellular space, where they are protected from circulating antibodies.
It is a horizontal infection along the colonic lining that triggers an extensive inflammatory reaction. There is infiltration of the mucosal layer with neutrophils and white blood cells, with micro-abscesses, extensive ulceration and sloughing of the mucosa. This severe inflammatory destruction impairs the colon’s ability to retain water and electrolytes and causes the characteristic symptom of bacillary dysentery: bloody, mucopurulent stools with pain.
Causes of shigellosis
As explained by the Cleveland Clinic, exposure to infected feces, either directly or indirectly via the fecal-oral route, is the underlying cause of shigellosis. Transmission routes depend on the setting and population dynamics, as defined by CDC clinical parameters.
Direct oral-anal contact during sexual activity is an important source of infection among adults. This involves rimming, anal manipulation with hands or oral contact with any fingers or skin that have touched the perineum or oral contact with sex toys that have touched the perineum.
In larger populations, infections are often caused by eating contaminated food or drinking contaminated recreational water. This is commonly caused by raw produce being rinsed in water that has been polluted by agriculture or by swimmers ingesting untreated water in lakes, splash pads and improperly chlorinated pools.
A similar spread of the virus from person to person is also possible in high-contact congregate facilities. It is common in child care settings where young children under five spread bacteria to each other by touching each other’s toys and not washing their hands before putting them in their mouths, and in emergency shelters and encampments among people who are homeless.
Lastly, indirect fomite transmission may occur when contaminated bathroom surfaces, door handles, and diaper-changing surfaces are touched, especially if thorough hand hygiene is not performed.
Health risks and complications
Many healthy adults have a mild gastrointestinal illness that lasts for one week or less; however, shigellosis can lead to serious, life-threatening, systemic and autoimmune complications. The immediate threats are dehydration and electrolyte imbalance; persistent diarrhea and vomiting cause rapid fluid loss, hypovolemic shock and acute renal failure.
The increasing complexity of treatment is complicated by extensively drug-resistant strains. These superbug strains are not susceptible to typical oral antibiotics and often require hospitalization for intravenous treatment.
There are also potential long-term autoimmune risks for patients. People with the HLA-B27 gene type may develop reactive arthritis, which causes joint pain, inflammation of the eyes and painful urination that can last for months or years, notes the CDC.
Hemolytic uremic syndrome is a rare but life-threatening complication associated with the Shiga toxin-producing strains. This toxin is destructive to red blood cells, decreases platelet count and causes acute renal failure.
Can you get shigellosis twice?
Yes, a person can get shigellosis more than once in their lifetime.
Following recovery from Shigella infection, a person’s immune system produces serotype-specific antibodies against the outer lipopolysaccharide (LPS) O-antigen of the infecting strain. But there is little cross-protection of this natural humoral immunity to other Shigella species or to different serotypes of the same species.
Since there are dozens of serotypes of Shigella sonnei, Shigella flexneri, and Shigella boydii, a person who has recovered from an infection with S. sonnei remains vulnerable to S. flexneri. Additionally, natural immunity is only short-lived, even against the same serotype, waning over months and individuals can be reinfected after exposure.
What to do about shigellosis symptoms
Treatment of a suspected Shigella infection should involve immediate fluid replacement, appropriate evaluation by a medical professional and careful avoidance of drugs that can exacerbate the toxicity of the bacteria.
Aggressive oral rehydration is the key to outpatient care. Balanced electrolyte replacement fluids like ORS (oral rehydration salts), broths and electrolyte replacement fluids should be given to patients to replace water, potassium and sodium losses through diarrhea.
Patients need to make sure they do not take an over-the-counter anti-motility drug, such as diphenoxylate-atropine or loperamide (Imodium), to treat diarrhea. Anti-diarrheal drugs inhibit normal bowel muscle contractions, keeping invasive Shigella bacteria and inflammatory toxins within the colon’s lining. This standstill has a markedly detrimental effect on tissue invasion, systemic toxin absorption and the risk of toxic megacolon.
In high-risk patients or in severe illness, the use of specific antibiotics based on stool culture and antimicrobial susceptibility testing is indicated. Due to the high prevalence of resistance, empiric prescribing is not recommended until susceptibility profiles are available to determine which drugs are still effective.
When you have shigellosis, it is important to remember that Shigella bacteria can remain in your stool for several weeks after all signs and symptoms of diarrhea and fever have stopped. To avoid transmitting the virus to a partner, public health experts recommend refraining from any sexual activity that may involve any form of oral-anal contact, rimming or touching of the anal area for at least 14 days after all symptoms have resolved.
When to see a doctor
If you have acute diarrhea with a high fever or severe abdominal cramping, especially if you have recently had oral-anal sex or have traveled recently, it is important to see a health care provider right away.
Dr. Arthur L. Burnett II, MD, advises Blavity Health, “Sexual health is an important part of overall health, yet conversations about it often overlook infections that can spread through intimate contact beyond what we traditionally think of as sexually transmitted infections. Shigellosis is a good example. It can cause significant gastrointestinal illness, and the emergence of drug-resistant strains makes prevention, early recognition and appropriate treatment especially important.”
He adds, “People should feel comfortable discussing their sexual health with their healthcare providers and seeking medical attention when symptoms arise. Open, informed conversations and practical preventive measures can help reduce transmission and protect both individual and public health.”
In addition to consultation, certain red-flag complication signs will require urgent emergency medical care. Some of the urgent signs are diarrhea that has blood, is dark colored, or has a large amount of thick mucus or lasts more than three days, or vomiting that lasts for more than three days, and the individual cannot keep down fluids. Emergency care is also important if you have abdominal pain that is not relieved by painkillers, has become quite rigid and hard, or is so painful that even touching the stomach is painful; a fever that is not reduced by fever reducers and that does not go down after 24 hours; and a fever higher than 102°F (38.9°C).
Also, if symptoms of severe dehydration are present, immediate attention is needed. Typically, these symptoms manifest through severe dizziness and lightheadedness when standing, dry mouth, sunken eyes, confusion or little to no urine output in eight hours.
Clinicians will take a new stool sample to confirm the diagnosis and treatment. This specimen is used for stool culture, PCR gastrointestinal pathogen panels, and full antimicrobial susceptibility testing to ensure appropriate antibiotic selection.
“Shigella is not considered to be a typical sexually transmitted infection,” Dr. Andi Toufexis, a Texas-based family medicine physician who specializes in sexual health, says. “However, this gastrointestinal bacterium can be spread through sex when one partner comes into contact with the other’s fecal matter.”
Bottom line
Shigellosis is a highly contagious bacterial gastrointestinal disease caused by Shigella, which is rapidly becoming sexually transmitted and showing worrisome antibiotic resistance. Since a very small amount of bacteria can result in serious colonic inflammation, bloody diarrhea and dehydration, strict attention to hygiene, barrier protection during intimate contact, and the avoidance of anti-motility pills such as loperamide are important. Early medical attention and stool culture testing are key to appropriate hydration and in preventing the dissemination of drug-resistant strains.
Frequently Asked Questions
Who is most prone to getting a Shigella infection?
Young children under the age of five in daycare settings, men who have sex with men (MSM), international travelers visiting areas with poor sanitation and individuals experiencing homelessness face the highest risk of contracting a Shigella infection.
How many people have died from Shigella?
Globally, Shigella infections cause approximately 600,000 deaths each year, predominantly among young children in developing nations. At the same time, in the United States, fatal cases remain relatively rare, resulting in fewer than 40 deaths annually.
Citations
Centers for Disease Control and Prevention. Shigellosis (Week 38) Weekly cases* of notifiable diseases, United States, U.S. Territories, and Non-U.S. Residents week ending September 26, 2026. Cdcgov. 2026;2026. https://stacks.cdc.gov/view/cdc/260550
Marshall JE, Lefrancq N, Mason LCE, et al. The spread of sexually transmissible drug-resistant shigellosis in England: a genomic epidemiology study. The Lancet Infectious Diseases. Published online July 2026. doi:10.1016/s1473-3099(26)00227-6
Hendrick J, Raqib R, Noor Z, Faruque ASG, Haque R, Petri WA. Shigellosis. The Lancet. 2025;406(10511):1508-1519. doi:10.1016/s0140-6736(25)01033-5
Bajwa MR, Adegbole CA, Smith RL. Temporal trends of Shigella outbreaks in the United States, 2009-2022. Front Public Health. 2026;14:1740303. doi:10.3389/fpubh.2026.1740303
Mayo Clinic. Shigella infection – symptoms and causes. Mayo Clinic. November 12, 2020. https://www.mayoclinic.org/diseases-conditions/shigella/symptoms-causes/syc-20377529
Cleveland Clinic. Shigellosis: Causes, Symptoms, Treatments & Prevention. Cleveland Clinic. March 23, 2022. https://my.clevelandclinic.org/health/diseases/17826-shigellosis
CDC. Signs and Symptoms of Shigella Infection. Shigella – Shigellosis. June 27, 2024. https://www.cdc.gov/shigella/signs-symptoms/index.html