Two residents at an assisted living facility in Northern California are dead and another four hospitalized after being served soup with poisonous wild mushrooms.

According to Placer County sheriff’s officials cited by the Sacramento Bee, Barbara Lopes, 86, and Teresa Olesniewicz, 73, died after eating the soup that had been prepared by a caregiver at the facility.

The caregiver who prepared the soup was among the six people sickened, Sheriff's Lt. Mark Reed told reporters.

While the identities of those hospitalized have not yet been released, the incident, which took place at the Gold Age Villa in Loomis on Friday, is being investigated as an accident. The caregiver "just didn't know" the mushrooms were poisonous, Reed told the Bee.

Michael Weston, an official with the California Department of Social Services, which licenses senior care facilities, spoke with the newspaper but had no further information. He said the facility is licensed to care for up to six elderly residents.

Dr. Pierre Gholam, a liver specialist at University Hospitals in Cleveland, told ABC News that wild mushroom poisonings have become more common of late. More than two dozen patients have arrived in the past three years with telltale mushroom poisoning symptoms, he said, including diarrhea followed by kidney and liver failure.

Gholam, who spoke to with the news outlet by phone, said doctors from across the country report similar increases in mushroom poisoning cases, even in areas not typically known for them, such as the Midwest.

Specialists usually see case clusters in Northern California and in the Northeast.

"Clearly, there is something that has changed in my mind that has led to more mushroom poisoning cases," he said. "It looks like a nationwide phenomenon."

Gholam suggested that more people could be picking their own mushrooms in the bad economy to save money.

The mushrooms were picked on the Loomis, Calif., property.