Scientists warn that a popular HK dish could have a painful aftertaste One quarter of popular freshwater fish that Hongkongers consume carry a type of bacteria that can cause severe diarrhoea for three months, a University of Hong Kong study has found. The bacteria, known as Laribacter hongkongensis, which the university team identified in 2001, can be killed if the fish is cooked properly. It is the first time the bacteria has been linked to community-acquired gastroenteritis with symptoms including diarrhoea and abdominal pain. The team also identified freshwater fish as a 'reservoir' for Laribacter hongkongensis. Microbiologist Yuen Kwok-yung said the team, which also tested patients showing symptoms of gastroenteritis, found one person had diarrhoea for 90 days and another had suffered it 30 times a day. The researchers took random fresh-fish samples from different markets in Hong Kong from 2002 to last year. The study also involved tests on 3,788 patients with symptoms of gastroenteritis. Grass carp, one of the most popular freshwater fish in Hong Kong, topped the 'high risk' list. Of 17 grass carp samples, 59 per cent were found to contain Laribacter hongkongensis. Another high-risk category was big-head carp, with 53 per cent of 17 samples found with the bacteria. Other carriers of the bacteria included mud carp, large-mouth bass and minced freshwater fish meat from 102 freshwater fish samples. However, none of the 102 marine fish samples or samples taken from pork, beef and chicken were found with Laribacter hongkongensis. The study's findings were published in the medical journal The Lancet yesterday. According to the Agriculture, Fisheries and Conservation Department, 16.5 per cent of the 220,848 tonnes of fish consumed by Hong Kong people each year were freshwater fish. Marine fish accounted for 49 per cent and shellfish 34.5 per cent. The bacteria was found in 17 of 3,788 patients who showed symptoms of community-acquired gastroenteritis. Sixteen of the 17 patients had eaten freshwater fish within three days before the onset of diarrhoea. Professor Yuen said it was still not known whether the bacteria existed in other seafood and that further research was required. But he believed that 'intensive farming' methods in confined areas might accelerate its spread. Microbiologist Patrick Woo Chiu-yat, a research team member, said the bacteria also had been found in three patients in Switzerland. It was also found in Japan, Tunisia and Cuba. Dr Woo said the bacteria could be killed if the fish was thoroughly cooked. 'In Hong Kong and other parts of southern China, it is a common cuisine style to steam freshwater fish only for a few minutes,' he said. 'It is safe to eat freshwater fish, but people are warned that they should thoroughly cook the meat to avoid infection.' Dr Woo said patients suffering from severe symptoms were treated with antibiotics.