Global warming and increased mobility have extended Hong Kong's peak flu season by three months to June, almost the same as in Guangdong, the retiring head of the Centre for Health Protection said yesterday. Leung Pak-yin, who takes over as the Hospital Authority's director for quality and safety tomorrow, made this revelation while repeating his warning that a flu pandemic would remain a threat and that Hong Kong should stay prepared. The peak flu season is particularly dangerous as bird flu and human flu viruses could mix in an infected person or host animal, sparking a pandemic that could be as severe as the 1918 Spanish flu. At a farewell reception yesterday, Dr Leung said: 'We are still having H5N1 cases in birds in Hong Kong. You can see the threat [of pandemic flu] is getting bigger, especially around the world. The immediate challenge to the Centre for Health Protection is still the possibility of an influenza pandemic.' Thirteen wild birds have been confirmed with H5N1 this year. Dr Leung said Hong Kong's peak flu season could last until June, instead of January to March. 'We are not sure if this trend will persist in the years to come. Last year it started to change a bit because of global warming and the pattern of movement of people. Now the peak may be coinciding with the peak in Guangdong. Before, we had different peaks.' Dr Leung, previously a deputy director of health and deputy director of food and environmental hygiene, said his 'temporary posting' with the authority was for three years, having taken unpaid leave from the department. Dr Leung, who will be paid a similar salary during his new posting, will be succeeded by Thomas Tsang Ho-fai, a 40-year-old consultant in community medicine who will be promoted from D2 to D4 as controller. From his previous salary of HK$110,000 to HK$116,800 a month, Dr Tsang will now receive HK$145,150 to HK$149,150. There was speculation that Dr Leung was being groomed for a more senior position at the Hospital Authority or with the Health, Welfare and Food Bureau. Both he and Dr Tsang are fast-rising stars who caught the attention of director of health Margaret Chan Fung Fu-chun, now director-general of the World Health Organisation, when they worked with her during the Sars outbreak in 2003. Dr Tsang was on her bird flu team in 1997 when H5N1 killed six people. He obtained his medical degree at the University of Hong Kong in 1990 and earned a Masters in public health from Johns Hopkins University School of Medicine in Maryland, US, in 1992. From 1998 to 2000 he studied at the US Centres for Disease Control and Prevention in Georgia.