California is experiencing an unprecedented outbreak of mushroom poisonings, prompting urgent action from the California Poison Control System (CPCS), which is operated by the UCSF School of Pharmacy.  

Since Nov. 18, CPCS has identified 23 cases of severe poisoning linked to wild-foraged mushrooms, the highly toxic “death cap” (Amanita phalloides) mushroom. Each of the patients was hospitalized, two required a liver transplant, and one adult has died.

“This is the most massive cluster of amatoxin cases I’ve seen in my 40-plus years in poison control,” said Thomas Kearney, PharmD, CPCS’ acting executive director. “We knew immediately that we were facing an unusually dangerous season.”

A banner year for death caps

Early seasonal rains helped create ideal conditions for toxic mushroom growth, especially in Monterey County and the San Francisco Bay Area, regions known nationally as death cap “hotbeds.” The mushrooms thrive in symbiosis with oak, hardwood, and even pine trees, and mycologists are reporting a “banner year” for their emergence.

This year’s cases span all ages, and include a family cluster of seven with a 19-month-old. CPCS medical directors were the first to flag the trend, prompting rapid coordination with the California Department of Public Health (CDPH), the Department of Health Care Services (DHCS), and the Emergency Medical Services Authority (EMSA), which co-funds and partners closely with CPCS. A statewide advisory issued on Dec. 5 urged the public not to forage or consume wild mushrooms at all.

“This is the beauty of the California Poison Control System,” Kearney said. “Because we operate as an integrated statewide network, we can identify trends early and move quickly with our public health partners.”

A rapidly escalating outbreak

In addition to its central role in statewide surveillance to detect outbreaks early, CPCS provides clinician support and community outreach that allows the state to deliver rapid public health messaging.

The 23 confirmed poisonings occurred in quick succession. All of the patients had foraged the mushrooms, developing symptoms within 6-24 hours. Amatoxin poisoning is one of the most challenging toxic exposures for clinicians to diagnose, because no standard rapid test exists to confirm amatoxin ingestion, and initial symptoms, such as watery diarrhea, nausea, vomiting, abdominal pain, and dehydration, are delayed. Brief improvement can be deceptive, however, as patients may still develop serious to fatal liver damage within 48 to 96 hours after eating even a tiny amount of the mushrooms.

Coordinated response

Treatment is equally complex. Through its 24/7 hotline, CPCS provides clinicians with real-time guidance on triage and symptom management.

“There's a lot of different types of therapies out there, including experimental therapies,” said Craig Smollin, MD, professor of emergency medicine at UCSF Medical Center and medical director for the San Francisco division of CPCS. “Silibinin is one that has been available for many years and has often been tried in these poisonings, but there can often be delays to its administration because it's difficult to get.”

Strengthening public health and prevention

Cultural traditions, recent immigration, and food insecurity sometimes increase foraging risks, according to CPCS, highlighting the need for targeted and culturally specific outreach. Many of the outbreak cases involve immigrant families who may have confused California’s deadly death cap mushrooms with edible lookalike species common in their home countries.  

CPCS also cautioned that social media has amplified risky foraging behavior, with online groups and videos offering misleading or incomplete identification guidance.  

In partnership with CDPH, CPCS has launched a bilingual public education campaign — “Think Before You Pick” —  with explainer videos and shareable materials designed to counter common myths about mushroom safety. The campaign has leveraged social media and other channels to reach a broad audience.

“The single most important intervention that we have at our disposal is to prevent the exposure in the first place,” Smollin said. “If you have ingested a mushroom, you may not have symptoms right away. By actually coming to the hospital earlier on, we at least can provide some treatments that may prevent the toxin from being absorbed.”