In a tragic turn of events, four individuals in California have lost their lives after consuming death cap mushrooms, prompting officials to intensify their warnings to mushroom foragers across the state.

Since November 18, health authorities have been alerted to over 35 instances of death cap mushroom poisoning. This alarming trend includes four fatalities and three individuals who have undergone liver transplants.

The California Department of Public Health is strongly advising the public to steer clear of mushroom foraging this year. The death cap mushroom closely resembles several non-toxic types, making it dangerously easy to mistake for a safe option.

Known as one of the deadliest mushrooms globally, the death cap contains amatoxins—highly toxic substances responsible for 90% of fatal mushroom poisonings worldwide.

Several victims of the poisoning have experienced severe and rapidly progressing liver damage, with some cases resulting in liver failure.

The affected individuals, who have ranged in age from just 19 months to 67 years, required intensive medical care, with many being treated in intensive care units.

Also known as the Amanita phalloides, death cap mushrooms look and taste similar to edible varieties, such as field mushrooms. 

Even cooking, boiling, drying, or freezing will still not make the mushrooms safe to eat.

More than 35 cases of death cap mushroom (pictured) poisonings have been reported to health officials since November 18, including four deaths and three liver transplants 

The East Bay Regional Park District said: ‘The best way to stay safe is to ensure that no mushrooms are consumed by humans or pets’

In a typical year, there are between two and five death cap poisonings, said Dr Craig Smollin, medical director for the San Francisco Division of the California Poison Control System.

‘The main thing this year is just the magnitude, the number of people ingesting this mushroom,’ Dr Smollin said.

‘Having almost 40 is very unusual.’

Warm autumn temperatures coupled with early rains are leading to a kind of ‘super bloom’ of death caps in California this year, experts say.

Eating even a small amount can be fatal, and experts warn that a mushroom’s colour is not a reliable way of detecting its toxicity.

Laura Marcelino told the San Francisco Chronicle that her family in the northern California town of Salinas gathered mushrooms that looked like the ones she and her husband used to forage in their native Oaxaca, a state in southern Mexico.

‘We thought it was safe,’ Ms Marcelino, 36, said in Spanish.

Her husband was dizzy and tired the next day, but Ms Marcelino felt fine, and they ate the mushrooms again, heating them up in a soup with tortillas.

The next day, the pair, both seasonal farmworkers, became ill with vomiting and stayed home from work.

Ms Marcelino spent five days in hospital, while her husband had to undergo a liver transplant.

People can have stomach cramping, nausea, diarrhoea or vomiting within 24 hours after ingesting a toxic mushroom and the situation can quickly deteriorate after that, experts say.

An early rainy season caused the toxic mushrooms to pop up in greater numbers in forested parts of the Bay Area, such as Del Valle Regional Park (pictured), which is managed by the East Bay Regional Park District

Early symptoms may also go away within a day, but serious to fatal liver damage can still develop within two to three days.

Death cap mushrooms have been collected in local and national parks across northern California and the Central Coast.

Clusters have been identified in the Monterey and San Francisco Bay areas as well.

The warning has been echoed by the East Bay Regional Park District, highlighting that death caps have been cropping up in large numbers in its parks.

‘I wouldn’t trust myself to go out and pick mushrooms of any kind right now because it really takes an expert to be able to make a differentiation between a poisonous mushroom and a non-poisonous mushroom,’ said East Bay Regional Park District to KTVU.

Additionally, Julie Schreiber, a nationally known mushroom expert, foraging leader, and educator, told the outlet that there have been tons of mushrooms in people’s yards this year, leading more people to collect them.

‘I personally took a mushroom identification class about 35 years ago, and I’ve been foraging and teaching people about foraging for a long time, and I also teach people about cooking and eating mushrooms, and I still feel like there’s a lot that I don’t know,’ said Schreiber.   

The California Department of Public Health said those poisoned have included many Spanish, Mixteco, and Mandarin Chinese speakers, and have therefore responded by expanding its warnings in different languages.

Spanish was the primary language for more than 60 per cent of people poisoned, according to the health department.

The death cap resembles many fungi varieties from around the world that are safe to eat, and it changes in appearance in different stages, Dr Smollin said, going from a brownish-white cap to a greenish cap.

‘Unless you’re an expert who studies mushrooms it can be very difficult to know,’ he said.

Officials advise keeping an eye on children and pets outside where mushrooms grow, and buying mushrooms from trusted grocery stores and sellers.

Treatment is more difficult once symptoms start, so doctors advise people to seek medical care once someone becomes aware that they have eaten a poisonous mushroom or suspects they have.

US Poison Centres said it has seen an increase in exposures of all varieties of mushrooms – not just the death cap – from September through to January by 40 per cent from the same period the previous year.

Death caps are not native to California, and they were accidentally introduced to North America as an invasive species by arriving on the roots of European cork oaks.

Now, the mushrooms are slowly spreading across the West Coast. They are mainly associated with oaks but can also grow on other hardwoods.