Ten years ago this week, a doctor who had been treating severe respiratory illness in Guangdong checked into a Hong Kong hotel. A day later he checked himself into hospital after realising he had caught the virulent disease. By then he had spread it to other hotel guests. Like him, many were to die. As a result, he was identified as the first super spreader of Sars, or severe acute respiratory syndrome, which killed 299 of the 1,755 people it infected in the city. Hong Kong has well and truly recovered from this low ebb in its history. However, while it may now seem a distant memory, we forget the lessons of it at our peril. We should heed the reminder sounded by the emergence of a new Sars-like virus and confirmation that the deadly H5N1 bird flu virus has infected two young adults and killed one of them in Guiyang, capital of Guizhou province. True, the city is now far better prepared for dealing with an epidemic than when it felt its way in the dark in the fight against Sars. But microbiologists are more concerned about other threats - not least the H5N1 strain of bird flu. The new Sars-like virus, called novel coronavirus after the original coronavirus, is known to have infected 12 people, of whom six have died. Most had travelled recently in the Middle East. The infection of a new patient in Britain with close personal contact with another is seen as evidence that it can spread from person to person. Suspicion that it has come from animals has prompted World Health Organisation director general Dr Margaret Chan Fung Fu-chun, Hong Kong's health chief during Sars, to warn the public to expect an increasing trend of animal diseases jumping to humans, which was true of 70 per cent of infectious diseases over the past three decades. Asian people should take heed that contributing factors to animal sickness were hygiene standards where poultry and pigs were raised, she said. She praised Hong Kong's intense surveillance system for infectious disease. That is reassuring, given that the city is an international hub in the middle of Asia, the origin of previous deadly pandemics. But complacency is only human, especially after the swine flu scare a few years ago proved to be a seasonal flu. If the city is to avoid a repeat of the community tragedy and economic damage of those few grim months in 2003, the authorities can never relax surveillance and vigilance, or their efforts to encourage good hygiene and health habits.