Public health officials in Arizona have concluded that the Arizona State Fair was the source of a Shiga toxin-producing E. coli outbreak that sickened 18 people, most of them children, during October and November 2025. The findings, detailed in a report released in March 2026, describe an outbreak that hospitalized 11 individuals and caused six cases of hemolytic uremic syndrome (HUS), a severe kidney complication.
The outbreak was first detected on Nov. 3, 2025, when a local children’s hospital notified the Maricopa County Department of Public Health of an unexpected increase in STEC infections among pediatric patients. Nine cases had been identified over a single weekend. Hospital staff noted that five patients reported attending an event with petting zoo exhibits. A subsequent alert from the Arizona Department of Health Services confirmed a statewide increase, with cases reported in both Maricopa and Pinal counties.
The event, identified in the report as Event A, was later confirmed to be the Arizona State Fair, which ran from Sept. 19 to Oct. 26, 2025. More than 1 million people attended the fair during its month-long run. Thirteen of the 18 outbreak cases reported attending the fair on Oct. 26, the final day of operation, and 11 of those individuals visited the animal areas.
A Historical Pattern of Petting Zoo Outbreaks
The Maricopa County outbreak is the latest in a long series of STEC outbreaks linked to animal contact exhibits across the United States. The pattern is well-documented and spans more than two decades.
In 2004, the North Carolina State Fair experienced one of the largest petting zoo outbreaks of E. coli O157 on record. Approximately 108 people fell ill, including 15 cases of hemolytic uremic syndrome. The outbreak was linked to two commercial petting zoos at the fair, and investigations identified environmental contamination with the outbreak strain in areas where animals were exhibited and where waste was deposited.
The following year, in 2005, three separate outbreaks of E. coli O157:H7 infections occurred among agricultural fair, festival, and petting zoo visitors in North Carolina, Florida, and Arizona. The Arizona outbreak involved two children who were hospitalized after visiting a municipal zoo’s temporary animal contact exhibit. The same strain of E. coli O157:H7 was found both in the children and in 12 petting zoo animals.
More recently, a 2019 outbreak at the San Diego County Fair resulted in the death of a 2-year-old boy and sickened nearly a dozen other children. All cases reported visiting the animal areas, including the petting zoo, or having other animal contact at the fair. The source was never definitively identified despite extensive investigation.
In September and October 2023, the Tennessee Department of Health identified an outbreak of STEC O157:H7 infections among elementary school students who attended field trips to a farm animal exhibit at the Appalachian Fairgrounds. The outbreak affected over 64 children. Five children, ranging in age from 15 months to 7 years, developed acute renal failure due to hemolytic uremic syndrome and required renal replacement therapy. All children presented with vomiting, diarrhea, and abdominal pain, and all had laboratory confirmation of E. coli O157:H7 in stool samples.
What Makes STEC Dangerous
Shiga toxin-producing E. coli is a group of bacteria that live in the gastrointestinal tracts of humans and animals. While most strains of E. coli are harmless, STEC strains produce toxins that can cause severe illness. The bacteria are commonly associated with exposures to contaminated food, water, or infected animals, including farm animals and petting zoos.
What distinguishes STEC from other foodborne pathogens is its potential to cause hemolytic uremic syndrome, a life-threatening condition that attacks the kidneys and can lead to multiple organ failure and brain damage. Approximately 5 to 15% of STEC infection cases progress to HUS.
The symptoms of STEC infection typically appear three to four days after exposure, though the range can extend from one to ten days. Most often, patients experience severe diarrhea, stomach cramps, and vomiting. Diarrhea is often bloody, and fever is typically absent or minimal. In some people, particularly children under five years of age, the infection progresses to HUS. Symptoms of HUS include decreased urination, swelling of the limbs, high blood pressure, and paleness. Complications may include seizures, blood-clotting problems, kidney disease, stroke, or coma.
There is no specific treatment for STEC infections. Medical management focuses on hydration and supportive care. Antibiotics are not recommended and may actually increase the risk of developing HUS. Antidiarrheal agents are similarly discouraged for the same reason.
Ruminant Animals as Carriers
The animals most commonly implicated in STEC outbreaks at petting zoos are ruminants: cattle, goats, sheep, and pigs. These animals can carry STEC in their gastrointestinal tracts without becoming ill themselves. They lack the vascular receptors for the Shiga toxins that the bacteria produce, so the toxins cannot destroy red blood cells in these animals as they do in humans.
Transmission occurs through contact with contaminated haircoats, bedding, farm structures, or water. Visitors, particularly young children, at open farms, petting zoos, and agricultural fairs can become exposed by direct animal contact or by contact with contaminated bedding, farm structures, or soil. The bacteria can also be present on fence railings, in animal saliva, and in areas where animals roam.
Investigations have demonstrated that environmental contamination is a significant factor. In the 2004 North Carolina State Fair outbreak, the outbreak strain was isolated from shavings collected from a baby stroller and from the shoes of petting zoo visitors. High numbers of animals in enclosed areas likely concentrated E. coli O157 in the environment.
The Role of Hand Hygiene
Public health guidance consistently emphasizes handwashing as the primary defense against STEC transmission at animal exhibits. The CDC recommends washing hands with soap and running water immediately after touching animals or anything in the areas where they live, roam, or eat. Hand sanitizer with at least 60% alcohol can be used when soap and water are unavailable, but it is not a substitute for washing, particularly when hands are heavily soiled or greasy.
However, the Maricopa County outbreak investigation revealed significant gaps in hand hygiene infrastructure at the Arizona State Fair. Of the case-patients who visited the animal areas at the fair, only five of 11 reported the availability of handwashing stations. Eight reported the availability of hand sanitizer stations, and eight reported washing their hands after animal contact.
Hand sanitizer alone is insufficient to eliminate STEC. The bacteria are not effectively killed by alcohol-based sanitizers when hands are contaminated with organic matter. The CDC explicitly notes that handwashing with soap and water is preferred because hand sanitizers do not work equally well for all classes of pathogens.
Regulatory Responses and Prevention Measures
The Arizona outbreak has prompted legislative action. A bill introduced in the Arizona Senate would mandate handwashing stations at all animal exhibits, along with signage warning about the dangers of these attractions and a monitor to ensure that visitors wash up when leaving the area. The legislation follows reports that there were no handwashing stations at the state fair attractions.
The Maricopa County Fair announced in April 2026 that it would exclude a petting zoo from its attractions, a direct response to the 2025 outbreak that sickened at least 18 people, including 13 children.
National guidance from the CDC and the National Association of State Public Health Veterinarians recommends several measures to reduce risk at animal contact exhibits. These include designing facilities to separate animal areas from food consumption areas, providing adequate handwashing stations, ensuring that handwashing facilities are accessible and well-maintained, and excluding ill animals, especially those with diarrhea, from public contact.
Venue operators are also advised to consider the layout of animal exhibits to prevent contamination of visitor areas. In one analysis of the North Carolina State Fair outbreak, investigators noted that a food vendor was positioned near the exit of a petting zoo, a management error that may have facilitated fecal-oral contact.
The Broader Context
STEC infections are not limited to petting zoos. The bacteria are also commonly transmitted through contaminated food, particularly raw or undercooked ground beef, leafy greens, unpasteurized milk, and raw milk cheese. In 2025, a Washington state outbreak linked to aged raw milk cheese from Twin Sisters Creamery sickened multiple people. An outbreak in France that same year, detected in January, involved 18 confirmed cases of HUS in adults caused by a Shiga toxin-producing E. coli strain negative for the locus of enterocyte effacement. The outbreak was linked to raw-milk cheese and included cases from Scotland and Belgium.
In August 2025, an outbreak of STEC O26:H11 linked to a family music festival in Ceredigion, West Wales, was investigated. Five genomically identical confirmed cases were identified across Wales and Scotland.
The Maricopa County report notes that during the outbreak period of Sept. 19 through Nov. 30, 2025, 58 STEC cases were reported to the county health department, compared with a five-year average of 32 cases for the same period, a statistically significant increase.
Looking Forward
The recurrence of STEC outbreaks linked to petting zoos has prompted calls for stronger regulation and better education. The nonprofit organization Parker’s Promise, founded after a child developed HUS following exposure at an agricultural summer camp, is campaigning for mandatory operational rules at agritourism businesses and other agricultural organizations. The group advocates for laws requiring such businesses and camps to provide handwashing stations and warning signs.
The Maricopa County report itself notes that while Event A was identified early as a potential exposure source, investigators could not definitively identify a single source of contamination. Whole genome sequencing identified 16 highly related isolates with 0 to 2 single nucleotide polymorphism differences, indicating a common source, but no conclusive animal source was identified.
For public health officials, the outbreak serves as a reminder that animal contact exhibits remain a persistent source of preventable illness. The Arizona State Fair outbreak adds to a body of evidence spanning more than 20 years that STEC transmission at petting zoos is not an isolated phenomenon but a recurring public health challenge requiring consistent oversight, adequate infrastructure, and sustained education for both venue operators and the public.
