Deadly illness outbreak linked to morel mushrooms may have stemmed from preparation, CDC says

Although morels are generally considered safe, the mushrooms were at the heart of a deadly illness outbreak in Montana last year. An investigation from the US Centers for Disease Control and Prevention, detailed in a report published Thursday, tried to solve the mystery about exactly what went wrong.

Morels, which many consider to be a delicacy, have a honeycomb-like appearance and emerge from the ground for just a few weeks early in the year.

“They are the harbinger of spring, the first to appear usually, and that adds to their mystique,” said Dr. Greg Mueller, chief scientist emeritus at the Chicago Botanic Garden.

Mushroom hunters consider morels one of the most prized varieties, and they’re often featured on higher-end restaurant menus.

“They’re very tasty,” said Dr. Matthew Nelsen, a research scientist at the Field Museum in Chicago.

That may be why a restaurant at the center of the CDC investigation – identified by a state report as Dave’s Sushi in Bozeman, Montana – featured morels as a part of a special sushi roll made with salmon and a handful of other menu items between March and April 2023. When two people died after eating them, though, the CDC was brought in to help investigate what went wrong.

The local health department put out a news release to ask the public to report other potential related illnesses, and a number of people called to say they too had become violently ill after eating at the restaurant.

In the end, 51 people reported getting sick after eating there, and 45 of them reported eating the morels during March and April of last year.

Most of the customers who got sick reported vomiting and serious/severe diarrhea. Four were so sick that they went to the emergency room, and three were hospitalized, in addition to the two people who died, both of whom had underlying health conditions.

The CDC investigation determined that the morel mushrooms were cultivated and imported fresh from China. They were also distributed to restaurants in California, but no one reported being sick in that state.

Investigators learned that the difference between the morels eaten by people who got sick and those who didn’t may have been in how they were prepared.

At the Montana restaurant, the morels were served lightly cooked or raw. At the California restaurants, the morels were thoroughly cooked.

“Although the toxins in morel mushrooms that might cause ill­ness are not fully understood, proper preparation procedures, including thorough cooking, might help to limit adverse health effects,” the report said.

The CDC recommends that morels be refrigerated at or below 40 degrees Fahrenheit (4.4 degrees Celsius), in breathable-type packaging such as a paper bag, and should be cooked thoroughly before being served.

“I recommend cooking all mushrooms, including morels,” Mueller said. “A lot of mushrooms have various toxins that get broken down when they’re cooked, and that makes them safer. Personally, I think that makes them taste a lot better too, since raw mushrooms don’t have a lot of flavor.”

Looking at data for the past 15 years, he said, there are only about 150 reports of mushroom sickness from morels.

“It’s definitely not common, but it happens, and in almost every case, they were eaten raw or undercooked,” Mueller said.

Some people get sick even when they are cooked, Nelsen said, so he suggests starting with a small serving if you don’t know how your body will react to them.

“There’s a lot we don’t know about morels. Different mushrooms affect people differently,” he said. “There’s still a lot of work to be done still to figure out exactly what it is that is making people sick.”

Muller and Nelsen added that people foraging for morels should be sure to pick true morels, not mushrooms known as false morels, because those have toxins in them that could cause serious illness even after cooking.

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