Florida health investigators are still trying to determine the common activity at two recent state fairs that connects more than a dozen people, mostly children, who now have a life-threatening kidney infection.

The number of patients across five counties jumped to 15, with more cases expected, said Florida Health Secretary John Agwunobi. Eleven of the ill are children younger than 10; the adults are older than 40, the St. Petersburg Times reported.

The victims live in Orange, Seminole, Collier, Volusia and Pasco counties and all recently attended the Central Florida Fair in Orlando or the Florida Strawberry Festival in Plant City.

All had diarrhea within the past two to three weeks and all tested positive for a specific strain of E. coli, or showed signs of having hemolytic uremic syndrome, or HUS, a fairly infrequent complication arising from an initial infection of the E. coli bacterium, Agwunobi said.

At least three children were reported in critical condition in Orlando hospitals. One adult was also hospitalized in Orlando.

In addition, Pasco officials are awaiting a medical examiner’s report to determine the cause of death for a 12-year-old girl who collapsed in her home Wednesday morning after running a high fever for four days. Her family said she had visited the petting zoo at the Strawberry Festival.

The Florida Department of Agriculture has launched its own investigation. Animals that were at both fairs are being tested for the E. coli strain, said spokeswoman Liz Compton.