Listeria and hepatitis A bacteria have been found in 35 food samples collected by health inspectors over the past six months. The discovery prompted a warning yesterday for pregnant women to be wary of salads, soft cheeses, sashimi and oysters, which can carry the listeria bacteria and could cause miscarriages, premature births and still births. Chilled ready-to-eat foods are particularly vulnerable to contamination by the listeria bacteria. Assistant director of food surveillance and control Dr Gloria Tam said: 'Luckily, listeria intoxication is not widespread in Hong Kong and it is not very common among Chinese communities elsewhere, but it is very dangerous for pregnant women.' Pregnant women with listeriosis may suffer flu-like symptoms, chills, fever, headache, back pain and sore throats, she said. It also poses a threat to elderly and long-term patients. 'Although we have not discovered any cases in Hong Kong, it is important to bring awareness to the public. All chilled food must be kept below four degrees Celsius,' Dr Tam added. She said the hepatitis A virus, which could cause liver damage, was strongly linked to the Asian preference for shellfish and hotpots. The high-risk season was from November to January, when people cooked hotpots. The two bacteria were found in 35 out of 27,600 food samples tested by 9,000 microbiological analyses and 18,600 chemical analyses. Dr Tam would not give a breakdown of how many instances of listeria and hepatitis A finds there had been. But the overall trend for the six-month period had been satisfactory as microbiological and chemical testing failure rates had fallen to less than one per cent from 1.6 per cent and 1.3 per cent, respectively, in 1998 and 1999 she said. Dr Tam said 25 butchers had been found guilty of selling contaminated pork in 208 prosecutions. The butchers were caught using pig offal and sulphur dioxide in meats. She said people who ate contaminated meat would experience an increased heart beat, breathing problems and suffer from the shakes. Dr Tam suggested that shoppers check to see if fresh meat had been adulterated with sulphur dioxide, which becomes shinier and less sticky to the touch. It was extremely difficult for shoppers to identify whether meats had been contaminated with pig offal, she added.