Deadly mushroom poisonings in California mark record US outbreak

California is dealing with what experts describe as the largest known outbreak of deadly mushroom poisonings in U.S. history, with 47 confirmed cases since November, four deaths and at least four illnesses that required liver transplants, according to the California Department of Public Health.

The outbreak has stretched across at least 12 counties in Northern California and the Central Coast, far exceeding the typical statewide total of fewer than five cases of mushroom poisonings per year.

Most illnesses are linked to amatoxin-containing mushrooms, including death caps (Amanita phalloides) and western destroying angels (Amanita ocreata), both highly toxic species that can closely resemble edible mushrooms.

Recent Napa County cases add to growing concern

The latest illnesses were reported in Napa County, where three adults from outside the region were hospitalized after eating wild mushrooms collected in the Deer Park area. The group became sick within a day and was treated at Stanford Medical Center.

Napa County Public Health Officer Dr. Christine Wu said the mushrooms were foraged in a rural part of the county, but warned that dangerous species can appear in many environments.

Health officials note multiple family clusters have been identified, including at least six incidents where relatives shared the same contaminated batch of foraged mushrooms.

Outbreak persists beyond normal season

Experts say the scale and timing of the outbreak are highly unusual. Death cap mushrooms typically peak in winter, yet new cases have continued into late spring.

“This is definitely a much larger than usual outbreak. It is lasting longer and going much further into the year than we would have anticipated,” Heather Hallen Adams, toxicology chair of the North American Mycological Association, said in an NBC News report.

In a typical year, California sees only a handful of amatoxin poisoning cases. This year’s total has already exceeded that baseline many times over, with new cases still being reported.

Researchers say recent rainfall may have contributed to unusually widespread mushroom growth, but the extended duration and intensity remain unexplained.

Statewide spread and language barriers

Cases have been reported from counties including Alameda, Santa Clara, San Francisco, Sonoma, and Monterey, among others, according to the California Department of Public Health.

Patients range from infants as young as 19 months to adults in their 80s. Officials also report that many affected individuals speak Spanish, Mandarin, Russian, Ukrainian, Mam and Mixteco, highlighting the role of multilingual outreach in prevention efforts.

Health experts said some poisonings may stem from traditional foraging practices brought from other countries, where similar looking mushrooms may be edible.

Death cap mushrooms, introduced to California in the 1930s, often grow near oak trees and can be difficult to distinguish from safe varieties, especially in early growth stages.

Public health response and warnings

The California Poison Control System and state health officials are coordinating outbreak tracking and response efforts. Surveillance has been complicated because clinicians are not always required to report amatoxin poisonings directly to the state, making case detection less systematic, NBC News reported.

Officials are relying heavily on poison control reports and are working to add amatoxin poisoning to the state’s list of reportable conditions. Public health agencies have launched multilingual warnings, including radio ads, flyers, and PSAs in several languages, urging residents to avoid consuming wild mushrooms.

Health officials warn that cooking, boiling, freezing or drying wild mushrooms does not neutralize toxins. Symptoms, which include nausea, stomach cramping, diarrhea, vomiting and confusion, can take 6 to 24 hours to appear and may rapidly progress to life-threatening liver failure, according to health officials.

California residents are urged to avoid all wild mushroom consumption, keep children and pets away from mushrooms in outdoor areas, and seek immediate medical care if ingestion is suspected, even before symptoms begin.

Reporter Anthony Thompson can be reached at [email protected], or on Twitter @athompsonUSAT