Four other people were hospitalized after eating the soup, which included mushrooms harvested by a staff member who apparently was unaware they were toxic.
"We responded out to the facility and interviewed people to make sure there was no foul play," Placer County Sheriff's Lt. Mark Reed told The Sacramento Bee. "There wasn't any ... . It was an accident."
The victims were identified as Teresa Olesniewicz, 73, and Barbara Lopes, 86. They lived at the Gold Age Villa on a rural property in near the town of Loomis, the newspaper said.
Two other people became ill but were not hospitalized, including the caregiver who made the soup.
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