A Sars-related virus found in Hong Kong needs to be closely monitored or it might cause an outbreak that could kill 10 per cent of elderly patients who contract it, an expert says. Yuen Kwok-yung, chair of the department of microbiology at the University of Hong Kong, said the human coronavirus HKU had already caused people to fall seriously ill in Hong Kong, the US, Italy and Switzerland. It was discovered in a 71-year-old Hong Kong man who visited Shenzhen three days before being admitted to United Christian Hospital in January 2004 for pneumonia. The man survived. In 2003, Professor Yuen's team was among the first to find that severe acute respiratory syndrome was caused by a mutation of the coronavirus, which, until then, was thought to only cause common colds. The human coronavirus HKU was named after the HKU team that discovered it while testing samples of Chinese horseshoe bats and other animal species. Professor Yuen, who was speaking yesterday at the 8th Asia Pacific Congress of Medical Virology in Hong Kong, said about 10 per cent of elderly patients who contracted pneumonia as a result of having coronavirus HKU would likely die. He said doctors needed to test for coronavirus HKU in pneumonia patients. The Chinese horseshoe bat is the reservoir for both Sars and HKU coronaviruses. The bat was still being offered in southern Chinese restaurants and markets, Professor Yuen said. In his department's latest research, Professor Yuen said it was worrying that the human coronaviruses had a tendency for 'natural recombination'. 'In the future, we want to understand more and more because perhaps the recombination event will cause explosive outbreaks,' the professor said. 'The important thing is continuous monitoring.' As well as upper respiratory tract infections, the virus was also associated with seizures in children and gastroenteritis, and occurs in winter, he said. The co-infection between Sars and HKU coronaviruses was also seen in Guangdong and Hong Kong bats, he added. Meanwhile, 1,206 adults, including 360 in Hong Kong, were vaccinated 21 days apart with two doses of an experimental H5N1 prepandemic influenza vaccine in a clinical trial. Daniel Chu of Queen Mary Hospital said the vaccine was safe and effective against the H5N1 strains in Vietnam and Indonesia, which are genetically different.