美國牛感染禽流感引起了牛奶飲用者的擔憂。牛奶可以安全飲用嗎？

An outbreak of avian influenza in American dairy cattle has shown no signs of slowing in recent weeks. The virus does not typically jump from cows to humans, but in April remnants of the bird flu virus were found in pasteurised milk products. The Food and Drug Administration (FDA) tested 297 commercial dairy products from 38 states and detected high-pathogenic avian influenza (HPAI) viral particles in one in five samples. But as pasteurisation destroys viruses leaving broken remnants such as DNA or bits of the protein coat behind, the next step was to find out if these viral particles were active and infectious, or simply inactive fragments. The agency used egg inoculation tests to find out – the 'gold standard for infectivity'. These tests involve introducing the virus to an egg and incubating it there, to see if the virus reproduces. The tests came back negative, indicating that there was no evidence of live H5N1 bird flu virus in the pasteurised milk. 'This demonstrated conclusively that standard pasteurisation inactivates influence when raw milk is processed,' said a spokesperson for the FDA. 'The FDA has been working with deliberate speed on a wide range of studies looking at milk along all stages of production – on the farm, during processing, and on retail shelves – to inform our understanding of HPAI and its presence in milk,' a spokesperson for the FDA tells the BBC. Based on this research, the spokesperson says the FDA is confident in the safety of the commercial pasteurised milk supply.