Wet weather in many parts of Canada has helped to produce a bumper crop of wild mushrooms, but many are dangerous to eat and can't be easily identified, health officials warn.

The Ontario Regional Poison Information Centre received double the number of calls in September compared to the same month last year, and over half of the callers needed to be hospitalized for ingesting poisonous mushrooms.

The differences between safe and poisonous varieties of mushrooms may not be visible to the naked eye.
(Dean Fosdick/Associated Press)

A case of mistaken mushroom identity can be dangerous. Life-threatening symptoms may result from eating a small part of a wild mushroom.

Deaths from eating mushrooms are rare. In September 2004, a man in Quebec died after eating a toxic mushroom, and a woman in Toronto died the year before from the same cause.

Poison symptoms vary depending on the mushroom species. People should be concerned when there is a delay between the time a mushroom is eaten and symptoms begin, such as:

• Nausea.
• Vomiting.
• Severe diarrhea.
• Abdominal pain and cramping.
• Feeling like the heart is racing.

"The problem is, people just pass those symptoms off as, 'I've got the flu,' " said Heather Ferries, a nurse educator with the poison centre at Toronto's Hospital for Sick Children.

"Meanwhile, what's happening is that the toxin or the poison from the mushroom is actually eating away at your liver. You're developing liver damage from the toxin."

The centre advises people to call after eating a wild mushroom and not to wait until feeling sick. More severe symptoms include sweating, convulsions, hallucinations and coma.

People may think they can tell safe varieties from poisonous ones, but the differences may not be visible to the naked eye, Ferries said. Cooking outdoor mushrooms does not make them safe to eat.

In other cases, newcomers to Canada think that the mushrooms that grow here resemble those found in China and other parts of the world and may not realize until it's too late that dangerous varieties grow here.

"It is dangerous to eat any mushroom that you have found outdoors," said Dr. Margaret Thompson, medical director of the poison centre. "Poisonous and non-poisonous mushrooms grow side by side. Only a mushroom expert can tell the difference, so avoid picking or eating mushrooms altogether."

To avoid mushroom poisonings, the centre recommends checking your lawn for mushrooms before children go out to play, especially after a rainfall. Any mushrooms found growing near a home should be removed and thrown out.