After a series of “death cap” mushroom poisonings – one of them fatal – California health officials are urging residents not to eat any mushrooms obtained as food unless they are trained experts.
Doctors in the San Francisco Bay Area blamed a wild mushroom, also called Amanita phalloides, for 23 poisoning cases reported to the California Poison Control System since Nov. 18, according to Dr. Craig Smallin, medical director of the system's San Francisco office.
“All of these patients were independently foraging for mushrooms in the wild,” Smollin, a professor of emergency medicine at the University of California, San Francisco, said at a news conference Tuesday. “They all developed symptoms within the first 24 hours, including nausea, vomiting, diarrhea and abdominal pain.”
Smallin said some of the patients were part of cohorts that consumed the same batch of harvested mushrooms. The largest group consisted of about seven people, he said.
All patients were hospitalized, at least briefly. One died. Five remain in hospital. One of them received a liver transplant and another is on the list of donors awaiting a transplant, Smallin said. The age of patients ranged from one and a half to 56 years.
Mushroom collectors say death mushrooms are more common in parts of California this season than in past years, which could be contributing to an increase in poisonings.
“Any mushroom has years when it's fertile and years when it's not… It has a very good season,” said Mike McCurdy, president of the San Francisco Mycological Society. He added that the death cap was one of two main species he identified during an organized group mushroom hunt last week called a foray.
In a press release, Dr. Erica Pan, a California public health official, warned that “because death caps can easily be mistaken for edible, harmless mushrooms, we advise the public not to pick wild mushrooms at all during this high-risk season.”
Dr. Cyrus Rangan, a pediatrician and medical toxicologist with the California Poison Control System, said the “general warning” is necessary because most people don't have the expertise to determine which mushrooms are safe to eat.
Still, he said, “it's rare to see a series of cases like this.”
The California Poison Control System said in a news release that some of the sickened patients speak Spanish and may rely on foraging techniques honed outside the United States. Death's cap mushrooms are similar to other Amanita species commonly eaten in Central American countries, according to Heather Hallen-Adams, chair of toxicology for the North American Mycological Association. Because death caps are uncommon in the region, collectors may not realize the potential risk of their counterparts appearing in California, she said.
Ann Pringle, a mycology professor at the University of Wisconsin-Madison, said there are a number of poisoning cases in which people misidentify something because their experience is not relevant to a new region: “This story comes up again and again.”
Amanita phalloides mushroom in Hungary. The species originated in Europe and is invasive in the United States (Ann Pringle).
Over the past 10 years, mushroom picking has flourished in the Bay Area and other parts of the country. At the same time, information resources about mushroom toxicity—both reliable and otherwise—have also proliferated, including on social media, phone apps, and artificial intelligence platforms. Experts said these sources should be viewed with skepticism.
Experienced mushroom hunters say the practice can be done safely. McCurdy, who has been collecting and identifying mushrooms since the 1970s, said he is irritated by widespread dissatisfaction with foraging.
“No, it's funny… After an incident like this, their first instinct is to say don't collect food,” he said. – Experienced mushroom pickers will not pay attention to this.
But McCurdy suggested people seek help from local mycological societies, which are common in California, and think critically about sources of information on which their lives may depend.
Pringle and McCurdy said they have seen phone apps and social media forums misidentify mushrooms.
“I’ve seen dangerous AI-generated guides,” Pringle said.
Death cap is an invasive species that originated in Europe and arrived in California in the 1930s, most likely via imported seedlings. The mushroom is usually several inches tall, with white gills, a pale yellow or green cap, and often a ring around the base of the stalk.
The species is found on the West and East Coasts, as well as Florida and Texas, according to Hallen-Adams, who is also an assistant professor of food science at the University of Nebraska-Lincoln.
In California it usually grows near oak trees, but sometimes also around pine trees. The body of the fungus is usually associated with the roots of trees and grows with them in symbiosis.
The toxin found in mortal mushrooms, called amatoxin, can damage the kidneys, liver and gastrointestinal tract if ingested. It disrupts the transcription of genetic code and the production of proteins, which can lead to cell death.
Hallen-Adams said U.S. poison control centers receive an average of about 52 amatoxin-related calls each year, but “a lot of things don't get called to poison control centers—take that with a grain of salt.”
Amatoxin poisoning is not the most common type of mushroom, but it is the most dangerous, she added: “90% of fatal poisonings worldwide will be amatoxin.”
It doesn't take much to make a person feel sick.
“One cubic centimeter of mushroom ingested can be a lethal dose,” Hallen-Adams said.
Symptoms of amatoxin poisoning often develop over several hours, improve, and then worsen. There is no standard set of medical interventions that doctors rely on.
“This fungus is very difficult to test,” Rangan said, “and also very difficult to treat.”
One drug doctors use to treat some California patients, silibinin, is still experimental and difficult to obtain.
“All of our silibinin comes from Europe,” Hallen-Adams said.
Death's cap mushrooms have continued to reproduce prolifically since their introduction, and Pringle's research has shown that the species can reproduce bisexually and same-sexly—with a partner or on its own—giving it an evolutionary advantage.
“If Eve can do better, she won’t need Adam,” Pringle said. “One of the things that I'm really interested in is how you can stop the invasion, how you can cure the habitat of the death caps. And at the moment I don't have any solutions to offer you.”
This article was originally published on NBCNews.com
