The government's quick test for the H7N9 flu virus in imported poultry at the border may not be enough to stop infected birds entering the city, a University of Hong Kong microbiologist says.
Ho Pak-leung said the 3 per cent sample size for the test was too small to pick up signs of infection by a disease that had the ability to infect a large number of humans while showing up in a small number of birds.
"Only a very small proportion of birds have been infected, according to test results on the mainland," said the infectious-diseases expert.
He earlier warned that the new virus could be more threatening to humans than sister-virus H5N1 because it had shown a greater ability to transmit rapidly from birds to humans, could spread over wider areas and was more difficult to detect.
"It is a very worrying sign," he said. "It seems only a very small number of sick birds are enough to infect so many humans - meaning the virus can be passing to humans very rapidly."
None of the more than 500 samples taken from the imported birds tested positive in the new, quick H7N9 test introduced by the government last week. The Centre for Food Safety said all the birds had been released for sale.
Four new suspected human cases of the H7N9 flu virus reported in Hong Kong yesterday tested negative for the virus.
The mainland's Ministry of Agriculture last week took 2,099 samples from farms and markets in some affected provinces and only 17 samples - or less than 1 per cent - tested positive.
"Just looking at the statistics, it means Hong Kong may not be able to detect anything from the imported birds if we are only testing 3 per cent of them," Ho said.
Former government veterinary officer Howard Wong Kai-hay agreed the new virus was harder to trace when infected birds appeared healthy - a major difference from H5N1, which usually killed the bird. But he said the quick test should be adequate to pick up signs of infection.
Hong Kong Poultry Wholesalers Association chairman Tsui Ming-tuen urged the government to cover wholesale markets with a bird net to prevent sick wild birds from spreading disease to poultry for sale.
Secretary for Food and Health Dr Ko Wing-man said sales of live chickens would not be suspended for now. He warned poultry farmers and traders in a meeting yesterday that they were a high-risk group and should take protective measures.
The Doctors Union advised its members to stock up on enough personal protective equipment for themselves and their staff to last at least a month.
In a meeting with Director of Health Dr Constance Chan Hon-yee, Shenzhen quarantine bureau officials said they would advise cross-boundary students who showed flu symptoms not to go to school in Hong Kong. They might also be put under medical surveillance. Hong Kong would be told of any diagnosed cases.
Click on each balloon for more information on individual patients infected with the avian flu virus: blue, patients infected with the H7N9 virus under treatment; red, those infected with the H7N9 who have died; and pink, those with H1N1 avian flu virus.