A Hong Kong virologist is also warning that wet markets could be breeding sites for the re-emergence of Sars Hong Kong's ongoing flu outbreak, which has left two people in critical condition, is being monitored by the WHO. And a Hong Kong virologist has warned that wet markets could be breeding sites for the re-emergence of Sars and a more virulent type of flu. The World Health Organisation put out the flu alert on its website after the Department of Health detected four institutional outbreaks of flu, involving at least 31 patients in two elderly homes and two homes for the mentally disabled. The outbreak, involving the H3N2 Panama flu strain, began last week at the Salvation Army Lai King Home for the mentally disabled, where 20 residents, one parent and a member of staff member, were admitted to Princess Margaret Hospital. Eighteen patients are in hospital, with two of them in critical condition in an intensive care unit. The news of the WHO's monitoring of the situation came as the head of the University of Hong Kong's department of microbiology, Yuen Kwok-yung, said wet markets had to clean up their acts to prevent another disaster. 'We are quite confident that Sars comes from wild animals. We are not confident exactly what that wild animal is because even if we find it came from civet cats it might be coming from other animals first to the civet cats or to another wild animal to humans,' he said. 'We have learned a lot of lessons from 1997 outbreaks of H5N1 flu and we have learned lessons this time that in those cases, the epidemic was centred on those people living around wet markets and directly working with wild animals. 'What we need now is to do something about our wet markets, to change our culture, our habit of eating wild animals. 'The hygienic conditions must be drastically improved if we are to stop another disaster from happening in the future.' Professor Yuen also said that the university's research had found that flu viruses could move from ducks and geese to chickens and back, forming potential flu pandemic strains in markets. 'We showed, actually, that virus genes do not flow in one direction. It can flow back into the ducks from chickens,' he said. 'We are predicting actually in the next pandemic of influenza, the virus will jump from ducks to humans.' However, Professor Yuen said that Hong Kong was not experiencing 'a major flu outbreak'. 'It has been shown clearly that these cases are not very severe. Patients are not suffering major illness, such as influenza A H3N2. The outbreak is still quite limited within the elderly people's home and chronic care facilities.' Professor Yuen said he would advise people at risk - those aged over 65, the chronically ill, and workers at nursing homes and other care facilities - to have a flu jab. 'Vaccines protect you from dying, especially elderly patients.' He said the university had now developed a diagnostic test for Sars with an accuracy rate of more than 90 per cent, detecting genetic material of the coronavirus in nose secretions. Professor Yuen was speaking after the University of Hong Kong received $5.5 million from the Swiss bank UBS to help fund its research into the development of a Sars vaccine.