People have been reminded to take extra precautions when preparing a traditional Chinese dish, after a sample was found to be contaminated with high levels of bacteria. The sample of vegetable poon choi was one of 34 revealed to be unsatisfactory by the Centre for Food Safety in its fourth round of regular testing for the year, which included results for July and August. Poon choi is a traditional dish served in large bowls. A total of 11,500 samples from six food groups were tested, of which 99.7 per cent were found to be satisfactory, said the acting assistant director of the Centre for Food Safety, Henry Ng Chi-cheung. But the sample of poon choi served at a Tsuen Wan vegetarian restaurant was found to have 100,000 counts per gram of Bacillus cereus, exceeding the safety limit. The bacteria may cause vomiting, abdominal pain and diarrhoea. 'The [breach] could be an indication of unsatisfactory hygiene conditions during food processing and production,' he said. 'Poon choi usually comprises a variety of food items involving complicated processing and meticulous attention in preparing. All food should be thoroughly cooked and served as soon as possible.' He said poon choi should not be prepared too early. When cooked it should be kept above 60 degrees Celsius, or at 4 degrees or lower. The testing also found a bowl of instant noodles with chicken served in a North Point tea shop had 4,900 counts of the bacteria Staphylococcus aureus per gram. The organism causes gastrointestinal infections. Two products at supermarkets were also contaminated: a Romaine heart sample at Jusco in Tai Po had 0.14 parts per million of the heavy metal cadmium, and chilled Indian prawn meat at a Citysuper in Sha Tin was found with 0.025 ppm of nitrofurans, a veterinary drug., Three samples of chilled Indian prawn meat at food supplier Lordly Company in Kwai Chung were also contaminated with the drug.