San Diego County Health and Human Services Agency announced four confirmed cases linked to animal contact. While three cases didn't result in hospitalization, a 2-year-old boy was hospitalized and died from a complication June 24.
The children between the ages of 2 and 13 visited the fair from June 8 to 15 and had symptoms from June 10 to June 16.
The exact source of the bacteria is still under investigation, but all four reported having contact with animals at the fair.
Fair officials have now closed public access to all animal areas, including the petting zoo, but plan to keep the fair open.