Two siblings, Kade and Kallan Maresh from Maple Lake, Minnesota, were stricken with E. coli O157, possibly after visiting a petting zoo.

The family’s Caring Bridge site broke the sad news on Sunday when it reported that Kallan lost her battle with the deadly strain.

Bill Hudson of CBS Minnesota reports she died one week after shiga toxin-producing E. coli O157 raced through her young body.

“It’s very serious, potentially fatal,” says George Canas, M.D., with Kidney Specialists of Minnesota.’

The state Health Department is investigating where the E. coli exposure was. Possibly, something as simple as a trip to a petting zoo and transferring the bacteria onto the child’s hands and their mouth. It’s also common to acquire an exposure by eating unsanitary meat, produce or dairy.

The severe case eventually claimed Kallan’s life just a week after she was rushed to Masonic Children’s Hospital. Fortunately, her older brother, Kade, continues his fight, although his situation remains extremely serious.