An outbreak of mushroom poisonings in California is the largest in U.S. history, according to public health officials.
The outbreak has sickened 47 people, killing four. Four of the patients have required liver transplants, according to the state health department. The most recent three cases were reported this week. The poisonings come after the peak growing season for wild mushrooms has ended.
All three patients this week were in the same family and were all hospitalized at Stanford Medical Center, according to Dr. Christine Wu, Napa County’s public health officer.
The first people to fall ill in the outbreak became sick in November 2025. Patients have ranged in age from 19 month to 84 years, according to the California Department of Public Health (CDPH).
The outbreak greatly exceeds the typical report of less than five cases of mushroom poisonings each year in California, according to the health department. Since November 2025, hospitals across 12 counties have provided treatment to patients with poisoning symptoms.
Death Cap and Western Destroying Angel mushrooms have reportedly been collected in a wide variety of locations including city, county, and national park areas across the Northern California and Central Coast regions beyond the initial clusters identified in the Monterey and San Francisco Bay areas.
“Amatoxin-containing mushrooms are unexpectedly blooming beyond normal seasonal expectations across parts of Northern California, Central Coast California, and Southern California following recent spring rains. While Western Destroying Angels typically bloom into spring, the Death Caps typically decline by late winter,” according to the state health department.
“However, abnormal environmental conditions such as the continued rains in recent weeks, are likely contributing to the unusually robust resurgence of these poisonous mush rooms in the late spring. Because they closely resemble several edible mushroom varieties at different stages of growth, even individuals with foraging experience have encountered difficulty distinguishing them from safe-to-eat varieties.
“Both Death Cap and Western Destroying Angel mushrooms contain potentially deadly amatoxins that are not removed by boiling, cooking or drying the mushrooms before consumption. CDPH is urging individuals to avoid picking and eating wild mushrooms while risk of potentially deadly amatoxin poisoning is high.”
The amatoxins the mushrooms produce can damage the kidneys, liver and gastrointestinal tract. Symptoms of amatoxin poisoning can take up to 24 hours to appear and include nausea, vomiting, diarrhea and stomach pain. More severe reactions, like fatal liver damage, can develop within two to three days. Amatoxin is responsible for the majority of all fatal mushroom poisonings. Ingesting as little as the volume of a sugar cube can be fatal.