Advanced DNA testing found a close genetic match between bacteria from confirmed human cases and bacteria collected from the baby goat, according to the health department. Samples from several animals at the petting zoo tested positive for Shiga toxin-producing E. coli, or STEC, but further DNA analysis pointed specifically to the baby goat as the probable cause of the human illnesses.

"These test results provide an important link in our investigation," said Sean Conners, director of environmental health at the Will County Health Department. "While E. coli bacteria are commonly found in animals, our testing identified a close genetic match between bacteria from confirmed human cases and a baby goat at the petting zoo. We also thoroughly reviewed food service operations at the farm and did not identify any concerns."

The health department's confidential survey of people who developed symptoms after visiting the Homer Glen farm received 270 responses. That led officials to confirm two additional lab-confirmed STEC cases, bringing the total to seven. Another 159 respondents were classified as probable cases — people who had a connection to a possible source of exposure and symptoms during the investigation period but did not have lab testing to confirm infection.

Bengtson's closed for the season on Nov. 8, but had voluntarily shut down its petting zoo earlier after health officials informed the farm of the possible link to the E. coli cases. The farm also arranged for a veterinarian to collect samples from the animals.

"We appreciate Bengtson's cooperation throughout this investigation," Conners said. "The farm voluntarily closed its petting zoo when we first contacted them and later arranged for a veterinarian to collect samples from the animals. Their willingness to work with us has been important in helping identify a likely source of the outbreak."

STEC infections can cause severe stomach cramps, diarrhea and vomiting, and can lead to serious complications, especially in young children and older adults. Health officials say the investigation remains focused on the petting zoo, and the farm's food service operations were reviewed without concerns identified.

The outbreak is a reminder for families visiting farms and petting zoos to wash hands thoroughly after contact with animals and to avoid eating or drinking in animal areas. Bengtson's, a popular seasonal attraction in Chicago's southwest suburbs, has drawn generations of visitors for its fall activities.