Wild mushroom poisoning led to the deaths of four people, researchers with California institutions and the Centers for Disease Control and Prevention said in a new paper.

Amatoxin mushroom poisoning sickened 39 people from November 2025 through March 2026, according to the publication, which was released by the CDC’s quasi-journal on May 28.

The eaten mushrooms included Amanita phalloides, colloquially known as death cap mushrooms.

Of the ill individuals, three needed liver transplants, and four died.

The deceased were a 45-year-old man who foraged mushrooms in a national park, ate them, and died four days later; a 49-year-old man who died after seven days in the hospital; a 29-year-old man who ate 30 mushrooms he foraged in a local forest and died after being diagnosed with gastroenteritis; and a 67-year-old man who ate a single large mushroom and died on his 12th day in the hospital.

“Eating foraged mushrooms remains an activity with high risk for poisoning, especially during rainy seasons, when amatoxin-containing mushrooms can fruit widely,” Dr. Kevin Brandecker, a medical toxicology fellow with the University of California–San Francisco, and co-authors stated. “Educational materials in multiple languages might reduce harmful exposures.”

The situation was the largest outbreak of liver poisoning ever reported in California, and the largest in the United States in decades, researchers said.

The outbreak started on Nov. 16, 2025, when an adult male and his sister arrived at an emergency department for symptoms including nausea and vomiting. Laboratory tests revealed elevated levels of enzymes in the liver. The patients recovered after receiving intravenous fluid and treatment.

Doctors began seeing other patients after large blooms of wild mushrooms in the San Francisco Bay Area following a spate of rainy days in late 2025.

California officials developed a case definition for wild mushroom poisoning and issued an alert that was distributed in multiple languages, because investigators learned that some people primarily spoke other languages.

“Death cap mushrooms contain potentially deadly toxins that can lead to liver failure,” Dr. Erica Pan, California’s state public health officer, said in a statement in December 2025. “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.”

Researchers said on Thursday that officials should warn the public about dangers associated with eating wild mushrooms and educate medical providers on recognizing and treating mushroom poisoning. They said the California Department of Public Health is planning to designate amatoxin poisoning as a reportable condition in the state.