Instead of calling a high-profile press conference yesterday, officials opted for a low-key announcement of the first human infection of bird flu since 1997. After sending a press release to the media at 5.16pm to confirm that a nine-year-old boy was infected, a 'government source' held a briefing and revealed that the boy's eight-year-old sister and his father, 33, had died. The source denied that the government was trying to avoid 'politically sensitive' issues. Journalists were asked not to quote the name of the source and no photographs were permitted. Hong Kong's top health official, Secretary for Health, Welfare and Food Yeoh Eng-kiong, and top officials of the Hospital Authority did not release any statements. A medical source suggested this was because the government did not want to embarrass mainland officials. 'It is very clear that the boy's infection originated on the mainland,' the source said. The source admitted that many in the medical community were wary of being critical of the mainland, not wanting to damage relations. Mainland authorities have been denying H5 outbreaks in local farms, but 10,000 chickens have been returned to the mainland in the past two years after being found to carry the H5 antibody.