CALIFORNIA MUSHROOM POISONING OUTBREAK BECOMES LARGEST IN US HISTORY, KILLS 4 AND SICKENS 43, EXPERTS SAY. (PHOTO).

 California mushroom poisoning outbreak becomes largest in US history, kills 4 and sickens 43, experts say

California is experiencing its largest known mushroom poisoning outbreak in U.S. history, with four deaths and 43 hospitalizations reported as cases continue to spread across the state, public health officials say. The months-long surge has stretched well beyond the typical mushroom growing season, leaving experts puzzled about why the toxic exposures have been so widespread and persistent. New cases reported this week include a family in Napa County who became ill after foraging for mushrooms over the weekend and were later hospitalized at Stanford Medical Center.

Since the outbreak began in November, patients have ranged in age from 19 months to 84 years old, according to state health data. Cases have clustered in multiple incidents where families appear to have consumed the same foraged mushrooms, and at least four patients have required liver transplants. Illnesses have been reported in more than 10 counties across the San Francisco Bay Area and California’s central coast, prompting warnings against eating wild mushrooms. Officials say the primary cause is the highly toxic death cap mushroom, along with the western destroying angel, both of which contain amatoxins capable of causing severe organ failure or death even in small amounts.

Experts say the scale and timing of the outbreak are unusual, with cases continuing outside the typical winter season when these mushrooms are most active. Health officials also say tracking has been complicated because amatoxin poisonings are not uniformly required to be reported, leaving public health agencies reliant on poison control data and hospital reports. Efforts are underway to improve reporting systems and expand multilingual outreach after officials noted many of those affected come from diverse language communities, including Spanish, Mandarin, and several Indigenous languages.

Researchers and mycologists say the situation highlights both environmental and scientific uncertainty, including why toxic mushroom growth has been so widespread this year and why the outbreak is persisting. The death cap mushroom, an invasive species introduced to California nearly a century ago, typically grows near oak and pine trees, while the native destroying angel also poses a significant risk. Both species can closely resemble edible wild mushrooms in some countries of origin, contributing to accidental ingestion among foragers. Scientists say more research is needed to understand the environmental conditions driving the surge and to prevent further poisonings.