Health and welfare chief Yeoh Eng-kiong yesterday moved to ease public worries over Tuesday's detection of a strain of bird flu rarely seen in humans. 'There is no evidence of a human-to-human spread,' the secretary for health, welfare and food said. On Tuesday, the Health Department announced that a five-year-old boy was admitted to hospital on November 27 with H9N2 - a flu strain that generally only affects birds. He has since recovered. Dr Yeoh said the question of centralised poultry slaughtering to minimise bird-flu outbreaks was a matter for public consultation. He said he supported the idea but gave no timetable for the consultation. 'Central slaughtering does not guarantee, however, 100 per cent disease-free chickens,' Dr Yeoh said. The World Health Organisation, which has been told about the H9N2 flu case, said it was following it carefully. 'We await with interest the results of tests on the young boy's family and of the investigations at his school,' said spokesman Peter Cordingley, from the WHO Western Pacific regional headquarters in Manila. 'We are also checking with the Beijing health authorities to see if there are any unusual reports from Guangdong province.' Agriculture, Fisheries and Conservation Department officials said last night no H9 virus had been isolated from local wild birds in the past few months, although it promised to remain vigilant in its monitoring programme. The main concern for Hong Kong has been the avian flu H5N1, which killed six out of 18 people infected and led to the culling of poultry in 1997. Three outbreaks have since occurred, the last among wild birds at Penfold Park in Sha Tin Racecourse last December. No further H5N1 outbreaks have occurred since January, following a chicken vaccination programme. Two 'rest days' every month were imposed on poultry markets in March to help curb infections.