Flu alert as killer strain is sent to labs by mistake

Public health agencies around the world have been put on alert for an outbreak of lethal influenza after samples of the deadly virus were sent out mistakenly in testing kits.

Public health agencies around the world have been put on alert for an outbreak of lethal influenza after samples of the deadly virus were sent out mistakenly in testing kits.

The samples were of the strain of Asian flu which caused one of the three pandemics of the 20th century, killing between one and four million people in 1957.

They were sent to more than 3,700 laboratories in the US and Canada and 16 other countries in Europe, Asia, the Middle East and South America. Klaus Stohr, an influenza expert at the World Health Organisation, warned that if the virus was not handled properly "it can easily cause an epidemic. If [it] were to infect one person it would spread very rapidly." Laboratories have been ordered to destroy all samples and monitor infections in laboratory workers closely.

The lethal strain was issued by the College of American Pathologists in the US, which routinely sends virus samples to laboratories around the world so they can test their ability to identify different strains correctly. The Asian flu samples were sent out last October and the alarm was first raised on 26 March by a laboratory in Canada which had received its consignment a month earlier.

The Canadian laboratory identified the sample as an influenza A virus of strain H2N2, similar to the one which caused the 1957 pandemic, which caused 70,000 deaths in the US alone.

The H2N2 strain continued to cause annual epidemics until 1968, when it disappeared. So anyone now aged under 36 would be unlikely to have immunity. The strain is not in present flu vaccines.

The World Health Organisation, the US government and the Centres for Disease Control (CDC) in Atlanta were alerted on 8 April. At the request of the US government, the College of American Pathologists asked all laboratories that had received samples of the H2N2 virus to destroy them. The request was made before the error was made public because of fears that the virus could be used in bio-terrorism. The H2N2 virus was classified as a level 2 hazard, indicating it was not considered especially dangerous. But the CDC said it had been considering upgrading the hazard level when it found the virus had been widely circulated.

The WHO said there had been no reports of infection among laboratory workers and that with the proper use of biological safety cabinets and protective clothing, the risk was low. "The risk for the general population is also considered low," it said.

But it added that there was no guarantee every sample could be traced and destroyed because some laboratories could have sent derivatives elsewhere. As a precaution, it recommended all samples issued by the College of American Pathologists, and not just those containing the H2N2 strain, be destroyed.

It said in a statement: "WHO further recommends that bio-safety procedures be reviewed for use on influenza viruses that have not circulated recently in humans and against which the majority of the population would have no protective immunity." The UK is not among the countries which subscribes to the service provided by the College of American Pathologists, and the Health Protection Agency said it was "highly unlikely" that UK laboratories had received the dangerous samples.

The full list of countries and areas where the virus was sent is: Bermuda; Belgium; Brazil; Canada; Chile; France; Germany; Hong Kong; Israel; Italy; Japan; Lebanon; Mexico; Saudi Arabia; Singapore; South Korea; Taiwan and the US.