At least 50 people have been diagnosed with meningitis after eating raw or half-cooked snails in Beijing restaurants, Chinese media reports.
Snails are a popular dish in China
The China Daily said five patients were in a serious condition at different hospitals in the capital.
Many fell ill after eating fushouluo - a snail dish - at restaurants that specialize in Sichuan-style cooking.
The Amazonian snails have been found to harbour parasites that can harm the human nervous system.
This can lead to headaches, facial paralysis and meningitis.
The first case, a 34-year-old man who complained about severe headaches and nausea after eating a dish of cold snail meat, was reported in June.
The man was taken ill after a meal at Beijing's Shuguo Yanyi restaurant.
Tests on snails taken from the restaurant found several infected with a meningitis-causing parasite called Angiostrongylus cantonensis.
Experts believe the actual number of affected patients might be higher than 50.
It can take a month for symptoms to appear - and so the link between the illness and eating a raw snail may not be obvious.
The same species of Amazonian snails is also being blamed for destroying large areas of farmland in the south of China.
More than 160,000 hectares (400,000 acres) of crops have been destroyed in the Guangxi Zhuang region.
The snail was introduced into China in the 1980s and has since become widespread, breeding very rapidly to infiltrate lakes, brooks and ponds across the country.
Health officials in Beijing have also warned people against eating raw fish, crab and shrimp, although those foods are not directly linked to the current meningitis outbreak.