The swine flu virus has passed from humans to pigs for the first time in the city, with University of Hong Kong researchers finding it in two live pigs from Sheung Shui slaughterhouse.
Medical professionals and Secretary for Food and Health Dr York Chow Yat-ngok said the discovery would not pose a greater risk to Hongkongers.
A similar discovery was made in Taiwan yesterday. A health official said the 160 infected pigs were from a farm in Taitung and were mostly healthy. Authorities were looking for the source of infection, as the farm's workers were without flu symptoms.
University of Hong Kong microbiology Professor Malik Peiris, who led a regular influenza virus surveillance programme that made the local discovery, said swine flu had originated from pigs in the Americas, so it was 'quite expected' that the virus would eventually be transmitted back to the animal. The virus had been found in pigs in more than 10 countries.
Peiris said the virus would be present only in pigs' respiratory tracts - meaning it was safe to eat pork. Drinking pig's lung soup also posed no threat, he said, provided the organs were thoroughly cooked. 'The virus will be killed quickly at a temperature of more than 70 degrees Celsius.'
He said the World Health Organisation and World Trade Organisation suggested that eating pork was safe, as long as it was handled hygienically. The chance of catching the flu from neighbours and colleagues was much higher than from pigs, he said.
Peiris said no genetic change or re-assortment was involved in the jump from humans to pigs. 'The virus is more likely to experience genetic change between human beings, as 99.9999 per cent of the virus is in humans, not pigs,' he said.
Peiris said it was not known if the infected samples, taken on October 22, were from local or mainland farms.
Simon Cheng Ka-shing of the Hong Kong Pig Development Association, said farms were often disinfected, as the Agriculture, Fisheries and Conservation Department had stepped up promotion efforts with pig farmers.
A government spokesman said the Food and Environmental Hygiene Department would increase the inspection of slaughterhouses, and would ensure all pigs passed tests.
Mainland authorities had been contacted so they could step up monitoring of farms supplying live pigs to Hong Kong.
Meanwhile, a 74-year-old man became the fifth case in Hong Kong to show resistance to Tamiflu. He was admitted to hospital on October 7, and discharged on October 13.