PORTLAND — May is fiddlehead fern season in Maine, and experts say fern fanatics should steam or boil the seasonal delicacy well to avoid food poisoning.

Many people like the delicate, coiled heads of the ostrich fern cooked with a little butter or vinegar. But several outbreaks of food poisoning in the eastern United States and western Canada in May 1994 were blamed on fiddleheads that were eaten raw or lightly cooked.

As a result, the U.S. Centers for Disease Control recommends boiling fiddleheads for at least 10 minutes or steaming them for 20 minutes.

“If they handle them correctly and cook them properly, they will enjoy them without having to worry about any poisoning or a trip to the emergency room,” said Mahmoud El-Begearmi, a specialist in food safety and nutrition with the University of Maine.

Last May, Kathy Fackelman of Rockwood bought some fiddlehead ferns at a local store and put them raw in her salad.

She ate dinner at 8 p.m., “and I woke up at 2 in the morning and I felt kind of nauseated,” Fackelman said. “I thought about it for a minute or two and decided I was really very nauseated. I made about eight trips to the bathroom with violent diarrhea and vomiting. Finally, I just fell asleep on the bathroom floor.”

The illness went away about 6 a.m. But Fackelman says she will never forget it.

“I’ll be very honest,” she said. “I will never look at another fiddlehead.”

Scientists say the food poisoning is caused by an unidentified toxin. When the fern is boiled or steamed, the toxin either is inactivated or leached from the plant.

Gourmet preparations such as sauteeing are popular because they preserve the vitamin A, vitamin C, iron and other nutrients found in the plants.