California’s mushroom poisoning outbreak is the largest in U.S. history, according to public health officials.
The outbreak has left 47 people infected and 4 dead. Four of the patients require liver transplants, according to the state health department. The three most recent cases were reported this week. Poisoning occurs after the peak growth season of wild mushrooms has ended.
All three patients this week were from the same family and were all hospitalized at Stanford Medical Center, according to Napa County Public Health Officer Dr. Christine Wu.
The first people to become ill in this outbreak occurred in November 2025. Patients ranged in age from 19 months to 84 years, according to the California Department of Public Health (CDPH).
The outbreak significantly exceeds the typical reporting of fewer than five cases of mushroom poisoning each year in California, according to the health department. Starting in November 2025, hospitals in 12 counties will provide treatment to patients with symptoms of addiction.
Death Cap and Western Destroying Angel mushrooms have reportedly been collected from a variety of locations, including cities, counties and national park areas in Northern California and the Central Coast region, beyond the initial clusters identified in Monterey and the San Francisco Bay Area.
According to the state Department of Health, “Amatoxin-containing mushrooms are blooming unexpectedly and beyond normal seasonal expectations in parts of Northern California, California’s Central Coast and Southern California following recent spring rains. Western destroying angels typically bloom in the spring, while death caps typically decline until late winter.”
“However, unusual environmental conditions, such as continued rain in recent weeks, have likely contributed to an unusually strong resurgence of these poisonous mushroom chambers in late spring. Because these mushrooms are so similar to several edible mushroom varieties at various stages of growth, even individuals with foraging experience have had difficulty distinguishing them from safe varieties.”
“Both Death Cap and Western Destroying Angel mushrooms contain potentially fatal amatoxin, which is not removed by boiling, cooking, or drying the mushrooms prior to consumption. CDPH is urging individuals to avoid picking or eating wild mushrooms due to the high risk of potentially fatal amatoxin poisoning.”
Amatoxins produced by mushrooms can damage the kidneys, liver and gastrointestinal tract. Symptoms of amatoxin poisoning can take up to 24 hours to appear, including nausea, vomiting, diarrhea, and abdominal pain. More serious reactions, such as fatal liver damage, may occur within 2 to 3 days. Amatoxins are responsible for the majority of all fatal mushroom poisonings. Consuming an amount as small as a sugar cube can be fatal.
