California officials are warning foragers after an outbreak of poisoning linked to wild mushrooms that has killed one adult and caused severe liver damage in several patients, including children.

The state poison control system has identified 21 cases of amatoxin poisoning, likely caused by death cap mushrooms, the health department said Friday. The toxic wild mushrooms are often mistaken for edible ones because of their appearance and taste.

“Death cap mushrooms contain potentially deadly toxins that can lead to liver failure,” Erica Pan, director of the California department of public health, said in a statement. “Because the death cap can easily be mistaken for edible safe mushrooms, we advise the public not to forage for wild mushrooms at all during this high-risk season.”

One adult has died and several patients have required intensive care, including at least one who might need a liver transplant.

Wet weather fuels the growth of death cap mushrooms, and officials warn against any wild mushroom foraging to avoid confusion. Residents in central California’s Monterey county became ill after eating mushrooms found in a local park, according to county health officials. Another cluster of cases were in the San Francisco Bay Area, but state health officials warned that the risk is everywhere.

There were more than 4,500 cases of exposure to unidentified mushrooms logged at the US’s Poison Centers in 2023, according to their National Poison Data System annual report. Roughly half were in young children, whom experts warn may pick and eat a mushroom while playing outside.

California’s poison control system sees hundreds of cases of wild mushroom poisonings each year. The death cap mushroom and the destroying angel mushroom look and taste similar to edible mushrooms, so experts warn that a mushroom’s color is not a reliable way of detecting its toxicity. And whether it is eaten raw or cooked does not matter.

People can have stomach cramping, nausea, diarrhea or vomiting within 24 hours after ingesting a toxic mushroom. Though gastrointestinal symptoms may improve, health officials warn that patients can still develop serious complications, including liver damage, that surface later.

People looking for guidance on diagnosing or treating mushroom poisoning can contact the poison control hotline at (800) 222-1222.