San Diego — A 2-year-old boy has died and three others were sickened after contraction the E. coli bacteria at the San Diego County Fair, local health officials said. The exact source of the bacteria is still under investigation, but all four reported having contact with animals at the fair.

A Friday night release from the 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 on June 24.

"Our hearts, our prayers, our thoughts go out to the family and friends of this child," San Diego County Fair CEO Tim Fennell said in a statement.

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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. Fair officials have now closed public access to all animal areas, including its petting zoo. Officials plan to sanitize all buildings that house animals at the fair.

"Safety is and will continue to be our number one priority," said Katie Mueller, the fair's deputy general manager, according to CBS affiliate KFMB.

The fair is scheduled to remain open until July 4.