MINNEAPOLIS - The Minnesota Department of Health has been unable to determine the source of the E. coli infections that killed a 3-year-old Wright County girl and sickened her brother.

Kallan Maresh and her brother, Kade, became very ill July 9 according to their parents, Tyfanni and Joe Maresh, on their CaringBridge site. A week after becoming sick, Kallan passed away on July 16.

Five-year-old Kade Maresh was treated at the University of Minnesota Masonic Children's Hospital where he had blood transfusions, kidney dialysis and a platelet transfusion as doctors worked to get his blood work back to normal.

RELATED: Young girl dies, boy fights for life after MN siblings contract E. coli

Kade returned home at the end of July, according to the CaringBridge, but "still has a long road of recovery."

The MDH said on Monday that they have completed the investigation into the siblings' infections and were not able to identify a specific source. They said the E. coli infections caused kidney failure in the children.

Investigators looked into every known potential source, the MDH said, including foods, swimming, person-to-person transmission, and farm animal contact such as fairs or petting zoos.

RELATED: MN boy with E. coli leaves hospital

“Unfortunately, we were not able to identify the source of the children’s infections,” said MDH State Public Health Veterinarian Joni Scheftel in a press release. “In particular, we did not find a connection with a petting zoo that the children visited, despite extensive testing of the animals.”

He said the MDH will continue to monitor for cases that could help establish a link or source.