A deadly mold outbreak was reported in Montana after a gastrointestinal illness struck 51 people and killed two.
Scientists from the U.S. Centers for Disease Control and Prevention (CDC) have opened an investigation after diners at Dave’s Sushi in Bozeman reported diarrhea, nausea, vomiting and abdominal pain shortly after their meal.
The culprit: undercooked morels.
Although the fungi are not considered poisonous, it was the toxins in the undercooked edible wild mushroom that led to the diseases.
Undercooked morel mushrooms were linked to an outbreak of serious intestinal complaints among restaurant patrons in Montana last year
CDC researchers initially had difficulty identifying what was wrong with the mushrooms that had made people sick
“Vomiting and diarrhea were reported to be profuse, and hospitalized patients had clinical evidence of dehydration,” CDC officials wrote in their findings, which were published as part of the Morbidity and Mortality Weekly Report.
In the three weeks the restaurant served a special sushi roll with salmon and morels, 51 people became ill after eating there; three were hospitalized and two died.
As people began reporting their illnesses in March and April of last year, the CDC began tracking the source of the apparent outbreak.
They discovered that 51 people had eaten at the Dave’s Sushi restaurant between March 27 and April 17.
Morel mushrooms grown in China and imported fresh (not dried) were part of a special sushi roll at the restaurant.
Based on interviews with people who had eaten at the restaurant during that period, a matched case-control study found that diners who ate morels became ill, while those who did not eat them did not.
‘Consumption of morels, which are generally considered edible, was strongly associated with gastrointestinal diseases,’ the report is reading. ‘A dose-response relationship was identified, and consumption of raw morels was more strongly associated with disease than consumption of those that had been at least partially cooked.’
They also found that the more people ate, the sicker they seemed to get.
Researchers tried to figure out what the problem might be. They collected samples of the restaurant’s mushrooms 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 must be thoroughly cooked
Although it seemed clear that the morels were the cause of the disease, all tests came back negative.
In addition, six other restaurants that received shipments of morels from the same mushroom vendor reported no illnesses among their customers.
What the CDC researchers found, however, was that some people ate the mushrooms more cooked, while others ate them more raw.
Other restaurants in the area served morels from the same supplier, but none of their customers became ill.
For the sushi special, the morels were prepared differently depending on the day.
“On April 8, the morels were served partially cooked: a hot cooked sauce was poured over the raw morels, after which they were marinated for 75 minutes,” the report said. “On April 17, the morels were marinated uncooked and cold before being served.”
Researchers 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 partially cooked mushrooms on April 8.
Clearly cooking had some effect.
Morel mushrooms contain toxins that can make people sick if not cooked properly.
There is some debate among scientists about what these toxins are, but many believe they are called hemolysins.
This class of toxins destroys red blood cells, leading to illness and possibly death.
But the hemolysins can be destroyed by thoroughly cooking mushrooms, experts say.
“Morrels should be thoroughly cooked before consuming because cooking is likely to reduce toxin levels in the mushrooms,” CDC scientists wrote in their report.