The risk of the bird flu virus jumping the species barrier and infecting humans was played down by a government official and scientists yesterday. It was also disclosed that the H5N1 virus had been detected in chickens at market stalls about a week before the latest outbreak. Secretary for the Environment and Food Lily Yam Kwan Pui-ying said yesterday she could only say that the flu strain affecting farm birds was an H5. 'Even if it was H5N1, it's not the one that affects human beings.' She was referring to the 1997 virus that killed six people. On Tuesday, University of Hong Kong professor of microbiology Kennedy Shortridge said the current outbreak was being caused by an H5N1 strain, but added it was not causing a human health concern. Yesterday, Professor Shortridge said his team had isolated an H5N1 virus, similar to the type that emerged in last year's bird flu outbreak, in samples collected immediately before the last market rest day on January 25. Rest days take place on the 25th of each month for markets to be disinfected and for all unsold birds to be killed. Professor Shortridge said there was no evidence at this stage that the H5N1 virus seen recently could infect humans. On an RTHK radio programme, he said the aim of the anti-bird flu measures adopted for the current outbreak was to stop the virus from reassorting further, as was achieved in 2001. 'The important point is the way the virus is behaving now. We have seen it undergoing many, many reassortments, it's swapping genes around with many other viruses, particularly viruses from aquatic birds,' he said. 'The way it is behaving at the moment is it needs only one little chance to do this [re-assortment] with other viruses . . . it could give rise to a serious virus.' Another animal flu expert, Dr Robert Webster of Tennessee, said that because of Hong Kong's surveillance system, the bird flu virus was picked up at a very early stage. 'Maybe if they simply controlled those very early cases that would be enough,' said Dr Webster, chairman of the department of virology and molecular biology at St Jude Children's Research Hospital, which serves as the World Health Organisation's centre for animal flu. He said Hong Kong had the expertise to deal with any bird flu outbreak. Legislator Dr Lo Wing-lok, an infectious disease specialist, said the recurrence of the H5N1 virus meant it might already have become endemic to Hong Kong. He said the Government should consider anti-bird flu measures aimed at containing the virus rather than complete eradication. He also urged consumers to avoid contact with live poultry, the single common factor in the 18 human infections - six of them fatal - in the 1997 outbreak.