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Undercooked mushrooms killed two and sickened more than 50 diners at Asian restaurant in Montana, CDC investigation finds
A deadly fungi outbreak was reported in Montana after 51 people were stricken with gastrointestinal illness and two were killed.
Scientists from the US Centers for Disease Control and Prevention (CDC) opened an investigation after diners at Dave's Sushi in Bozeman reported diarrhea, nausea, vomiting, and abdominal pain shortly after their meals.
The culprit: undercooked morel mushrooms.
While the fungi isn't considered poisonous, it was the toxins in the undercooked edible wild mushroom that led to the illnesses.
Undercooked morel mushrooms were linked to an outbreak of severe intestinal distress among restaurant patrons in Montana last year
CDC investigators initially struggled to identify what was wrong with the mushrooms that had sickened people
The Calvatia gigantea, commonly known as the giant puffball, is a colossal fungi found in meadows. Young puffballs have soft clean white skin and firm flesh when cut.
'Vomiting and diarrhea were reportedly profuse, and hospitalized patients had clinical evidence of dehydration,' wrote the CDC officials in their findings, which was published as part of the Morbidity and Mortality Weekly Report.
In the three weeks when the restaurant was serving a special sushi roll with salmon and morels in it, 51 people got sick after eating there - three were hospitalized, and two died.
Once people started reporting their illnesses in March and April of last year, the CDC started tracking down the source of the apparent outbreak.
They found that 51 people had eaten at the restaurant, Dave's Sushi, between March 27 and April 17.
Morel mushrooms grown in China and imported fresh - not dried - had been part of a special sushi roll at the restaurant.
In interviews with people who had eaten at the restaurant during that time period, a 'matched case-control' study revealed that diners who ate morels got sick, while those who did not eat them did not get sick
'Consumption of morel mushrooms, which are generally considered edible, was strongly associated with gastrointestinal illness,' the report reads. 'A dose-response relationship was identified, and consumption of raw morel mushrooms was more strongly associated with illness than was consumption of those that were at least partially cooked.'
They also found that the more people ate, the sicker they seemed to get.
Investigators tried to figure out what the problem could have been. They collected samples of the mushrooms from the restaurant and tested them for pesticides, heavy metals, bacterial toxins, and pathogens.
Morel mushrooms are a popular mushroom to forage in the wild, but experts warn they should be cooked thoroughly
Even though it seemed clear that the morels were the source of illness, all the tests came back negative.
Additionally, six other restaurants who received shipments of morels from the same mushroom vendor reported no illnesses among their customers.
What the CDC investigators did find, though, was that some people ate the mushrooms more cooked, while others ate them more raw.
Other restaurants in the area served morel mushrooms from the same supplier, but none of their customers got sick.
Depending on the day, the morels were prepared differently for the sushi special.
'On April 8, morels were served partially cooked: a hot boiled sauce was poured over the raw morels, after which they were marinated for 75 minutes,' reads the report. 'On April 17, the morels were uncooked and cold-marinated before serving.'
Investigators found that people who ate the less cooked mushrooms on April 17 were about nine times more likely to get sick than people who ate the partly cooked ones on April 8.
Clearly, cooking had some effect.
Morel mushrooms contain toxins that can make people sick if not properly cooked.
There is some debate among scientists about what these toxins are, but many believe they are called hemolysins.
This class of toxin destroys red blood cells, leading to illness and possibly death.
But the hemolysins can be destroyed by cooking mushrooms thoroughly, experts say.
'Morels should be cooked thoroughly before consumption because cooking is likely to reduce toxin levels present in the mushrooms,' CDC scientists wrote in their report.