Uncooked cockles are feared to be behind the latest outbreak of cholera, the Department of Health said last night. The department believes Thai cockles that can be eaten raw had been mixed with ones from the mainland which need thorough cooking. 'Consumers who believe the cockles they have bought could all be eaten without being thoroughly cooked could easily contract cholera,' a department spokesman said. He said the Thai cockles, which required health certificates, were imported to the SAR on January 23. 'We will step up our surveillance on the shellfish supply. Consumers are advised to cook the seafood thoroughly,' he said. The department started examining the cockles after three cholera cases were detected. It has tracked down 77 shops, 14 in Hong Kong, 61 in Kowloon and two in the New Territories, selling the mixed cockles. All the retail outlets voluntarily surrendered the shellfish to the department. The department has taken samples of the mixed cockles for contamination test. Results are expected in the coming week. 'Cockles are a high-risk food. Elderly and children are advised to eat the shellfish less because their stomachs do not have a strong acidic system to kill bacteria contained in the food. They have a higher chance of having cholera,' the spokesman said.