UPDATE: Since this was posted, a fifth victim — a 6-year old boy who attended animals displays at the San Diego County Fairon June 22– has been added to this outbreak cluster. He began experiencing symptoms on June 26 and is recovering without hospital care.

A 2-year-old is dead and three other children aged 2 to 13 are sick after visiting a San Diego County Fair petting zoo.

According to the San Diego Health and Human Services Agency (HHSA), the children were infected with a Shiga-toxin causing E. coli bacteria, or STEC, from contact with farm animals at the fair. HHSA and the San Diego County Department of Environmental Health are investigating the cluster of illnesses.

All four children who became ill attended the San Diego County Fair between June 8 and 15. Symptoms set in between June 10 and June 16. The two-year-old boy was hospitalized and died on June 24. The other three children did not require hospitalization, according to officials.

“Our sympathies go out to the family of the child that died from the illness,” said Dr. Wilma Wooten, San Diego County, public health officer.

Del Mar Fairgrounds CEO Tim Fennell said fair officials were “heartbroken” and “devastated” by the boy’s death, which they did not learn of until June 28.

Fair managers learned of the E. coli outbreak Friday morning when country health officials arrived on the scene to investigate. All animals sites were closed to accommodate the health investigators.

Fennell said the areas were shut down as soon as fair managers were instructed to do so by health officials. He said neither the San Diego Country Fair nor the Del Mar Fair, as it was previously known, had a history of E. coli illnesses among attendees before this event.

The current run of the San Diego County Fair began on May 31 and continues through July 4. Fennell said the fair is “devastated” by the toddler’s death, but “moving forward” by taking every precaution during the remaining days.

About 5 percent to 10 percent of people diagnosed with STEC infections develop life-threatening kidney infections, according to Dr. Wooten. Others recover without complications.

The fair closed its animal areas, including the petting zoo.

The investigators have yet to name the source of the E. coli bacteria, but all four of the children who became ill visited the petting zoo or other animal areas. The County Department of Environmental Health re-inspected fair food facilities that the children visited and found no links there to the outbreak.

Most people infected by E. coli bacteria start feeling sick three to four days after they’re infected, though illnesses can start anywhere from one day to 10 days after exposure.

Symptoms typically include severe stomach cramps, watery or bloody diarrhea and vomiting. Symptoms can occur with or without a fever, but when a fever is present, it is usually less than 101 degrees.

San Diego County health officials want any residents who have experienced these symptoms after June 8 to contact them or their health provider.

“Especially if you have diarrhea that lasts for more than three days or diarrhea that is accompanied by a fever higher than 102 degrees Fahrenheit, or blood in the stool, or so much vomiting that you cannot keep liquids down, and you pass very little urine,” officials said.

They also advise thorough hand-washing as the best way to prevent the spread of E. coli. “Always wash your hands thoroughly after contact with animals or their environments,” the county health officials warned.

Many animals carry a wide variety of E. coli bacteria in their bodies without ill effect. However, some of the E. coli strains can cause serious and sometimes fatal infections in people.

Even if people do not come into direct contact with animals at fairs, petting zoos and other locations, they can be exposed to dangerous E. coli from bedding material, dust and contact with surfaces. Foods and beverages should not be taken into animal areas and people should thoroughly wash their hands after visiting animal areas.