Swine flu is spreading in Hong Kong at only half the global rate, and doctors put that down to the city's heightened vigilance following the 2003 Sars outbreak.
The city's so-called secondary attack rate for the flu is 14 per cent, a university study shows. The World Health Organisation says the comparable global rate is close to 29 per cent. The rate for seasonal flu ranges from five per cent to 15 per cent.
But optimism over the finding was tempered by a warning from Undersecretary for Food and Health Gabriel Leung that the virus was spreading around the world at 'unprecedented speed' - and by news that doctors are concerned about delays in treating some of the city's eight severely infected patients.
Professor Leung noted that while ordinary flu takes six months to spread around the world, swine flu had taken only six weeks. He also said: 'This virus is stronger than the seasonal flu virus since it can easily attack people's lower respiratory tract and cause pneumonia.'
Scientists measure how contagious a disease is by calculating its primary and secondary attack rates. The primary attack rate is the number of people in close contact with someone who brings a disease into a community that go on to catch the disease themselves. According to simulations by the University of Hong Kong, the primary attack rate of swine flu in Hong Kong is 1.3.
The number of close contacts these people go on to infect is used to calculate the secondary attack rate. The university study found that this rate is 14 for swine flu in Hong Kong - half the global average.
HKU microbiologist Ho Pak-leung said swine flu spread more slowly in Hong Kong because of the government's 'tight policies' and because people in the city have paid more attention to hygiene since the deadly outbreak of severe acute respiratory syndrome six years ago.