At least 50 people have been diagnosed as suffering from a parasite-caused meningitis after eating raw or half-raw snails at Beijing restaurants.

A patient suffering from meningtis after eating snails recevies treatment at a hospital in Beijing, August 20, 2006. [Beijing Star Daily]

It is the first time the so-called Guangzhou angiostrongylus meningitis has been found in Beijing, according to the Beijing Municipal Health Bureau's website.

It has warned people not to eat raw seafood, which may carry parasites that threaten health.

The first case, involving a 34-year-old man, was found by the Beijing Friendship Hospital in June.

The patient suffered from unbearable headaches and nausea after eating a dish called cold snail meat in the Shuguo Yanyi Restaurant.

The snail meat was from Amazonian snails Fushouluo in Chinese a popular dish in Sichuan-style restaurants in Beijing

Doctors took samples from the restaurant and found the parasite in two of the snails.

By last Thursday, 23 people had been found to suffer from the meningitis in the capital's hospitals, said the bureau.

They had all eaten cold or spicy snail meat, from Amazonian snails, at branches of the same restaurant.

According to the bureau, five of the 23 were in a serious condition, three had left hospital, and two were seemingly self-cured. No deaths have been reported.

As it can take as long as a month after eating for symptoms to appear, some diners may not link their headache with the snails, and doctors may not be able to find the real reason for the illness.

After local media reported the news, the Beijing Friendship Hospital received more than 90 people over the weekend, all worried they might get the disease since they had eaten snail dishes in the past two months.

The hospital claimed 17 of them were suffering from meningitis. The youngest patient was 13 years old, the Beijing Evening News reported yesterday.

Currently the Shuguo Yanyi Restaurant is not selling the dish while diners elsewhere are refusing to eat Amazonian snails. "After I heard that Fushouluo could lead to meningitis, I decided not to order this dish any more," said Wang Yingchao, 34.

According to the bureau, other seafood may also contain parasites but the Amazonian snail can host more than others.