California’s growing mushroom poisoning outbreak is the biggest-ever in U.S.

Science NewsCalifornia’s growing mushroom poisoning outbreak is the biggest-ever in U.S.Five cases have been reported this month, long after the typical season for the mushrooms behind the illnesses, leaving experts surprised. Of the 47 known cases, four people have died.Listen to this article with a free account00:0000:00One square centimeter of a death cap mushroom, also called Amanita phalloides, can contain enough toxin to be fatal. Anne PringleShareAdd NBC News to GoogleMay 15, 2026, 4:46 PM EDTBy Evan BushCalifornia’s monthslong spate of mushroom poisonings, in which four people have died and 43 others hospitalized, has become the largest known outbreak of its kind in U.S. history, experts say. Subscribe to read this story ad-free Get unlimited access to ad-free articles and exclusive content.Three cases were reported earlier this week, long after the typical growing season for the mushrooms behind the illnesses, leaving public health officials and mycologists puzzled about why the poisonings have been so widespread and what is causing the trend. The three newest cases were among a family that had picked mushrooms in Napa County on Saturday, became sick Sunday and was hospitalized at Stanford Medical Center, according to Dr. Christine Wu, Napa County’s public health officer.Since the outbreak began in November, affected patients have ranged in age from as young as 19 months to as old as 84, according to the California Department of Public Health. Cases have come in clusters, with at least six involving families who likely shared the same batch of foraged mushrooms. Four people have received liver transplants, according to the state’s poison control system. Poisoning cases have been reported in more than 10 counties in the San Francisco Bay Area and along California’s central coast. After cases began to spike in late fall, California health officials warned people not to eat any foraged mushrooms. “This is definitely a much larger-than-usual outbreak. It is las...