California’s Deadly Mushroom Poisoning Outbreak Is Now the Largest in U.S. History

California health officials are issuing urgent warnings after what experts now believe may be the largest and deadliest mushroom poisoning outbreak ever recorded in U.S. history.

The growing California mushroom poisoning outbreak has already affected at least 47 people since November 2025, with four reported deaths and several patients requiring liver transplants. 

Recent cases in Napa County sent three more adults to the hospital after they consumed foraged mushrooms gathered near Deer Park.

Why Deadly Mushrooms in California Are Spreading So Quickly

Health officials say unusually wet weather across parts of California has fueled a major surge in dangerous mushroom growth this year.

Experts believe species like death cap mushrooms and western destroying angels are behind many of the poisonings. These mushrooms closely resemble edible varieties, making them extremely dangerous, even for experienced foragers.

One of the biggest concerns is that cooking, boiling, freezing, or drying the mushrooms does not remove the toxins. And even a small amount can cause severe liver damage or death.

Officials also say some victims may have mistaken the mushrooms for edible species that are common in other countries, particularly among immigrants who are familiar with similar-looking mushrooms from home.

Mushroom Poisoning Symptoms Can Take Hours to Appear

Part of what makes poisonous wild mushrooms so dangerous is that the symptoms don’t always appear right away.

According to California health officials and poison control experts, early mushroom poisoning symptoms can include:

• Nausea

• Vomiting

• Diarrhea

• Stomach pain

• Confusion

• Dehydration

In many cases, people initially start to feel better before severe liver failure begins developing internally. Doctors say anyone who may have eaten a toxic wild mushroom should seek medical help immediately, instead of waiting for symptoms to worsen.

Why Experts Are So Concerned About This Outbreak

Usually, California only sees a handful of severe mushroom poisoning cases in a year. This outbreak is markedly different.

Officials say the combination of heavy rain, warmer conditions, and growing interest in mushroom foraging may all be contributing factors behind the surge of deadly mushrooms in California.

Health departments across the state are strongly advising people not to eat wild mushrooms, unless they are identified by highly trained experts. And, even then, it still might not be wise. 

While mushroom foraging may look peaceful and earthy on social media, it may be a dangerous endeavor. This outbreak is a serious reminder that one small mistake can quickly become life-threatening.

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