New diagnostic tests for bird flu

On the final day of the recent HPA conference, delegates heard about work that the Agency is carrying out to prepare for an avian flu pandemic. This includes the development of laboratory tests to diagnose cases in humans, as well as studies to look at the likely effectiveness of airport screening and travel restrictions in preventing the spread of pandemic.

Professor Pat Troop, Chief Executive of the Agency said “Following the continued outbreaks amongst poultry in Asia, the threat of an avian flu pandemic is ever more real and the Agency is committed to ensuring it has the capacity to respond should person-to-person transmission occur and human cases are seen in the UK. It is essential that our plans are up-to-date, and that we have the ability to diagnose the disease quickly so as to respond as effectively as possible.”

Speaking about the new diagnostic tests, Dr Maria Zambon, Director of the Influenza laboratory at the Agency said, “Over the past year we have made great strides in the development of tests for avian flu, and are confident that we could quickly identify any cases in the UK. We have a rapid test, called a polymerase chain reaction (PCR) test, which is capable of identifying the virus and therefore showing us if a person is infected with a strain of avian flu in a matter of hours . Being able to rapidly diagnose if people are suffering from avian flu is essential, so that we can take the appropriate public health action to best protect the population.

“We have also developed a second test which identifies if people have been exposed to avian flu by measuring the antibody response that they produce after coming into contact with the virus. Such tests are needed because the ones used for normal human flu strains are not sensitive enough. It can also help in an outbreak situation where it can be used to see if people have come into contact with the virus. This capability is essential in helping us prepare for a pandemic because such tests can also be used to see how effective vaccines are against avian flu strains. This test is currently only used by the Agency and the Centres for Disease Control in America, but could be deployed to any other countries which experience outbreaks of avian flu amongst humans.”

New modelling research was also presented showing that the use of entry screening and travel restrictions in the event of a global outbreak of SARS or influenza would do little in preventing the spread of infection to the UK – most likely only preventing the spread of the epidemic by one or two weeks.

Dr John Edmunds, who led the research for the Agency said, “We looked at the possible benefits of entry screening at UK airports for both SARS and influenza should an epidemic occur at one of the top 100 international travel hubs. Using modelling techniques we estimated the number of cases of both infections who were likely to enter the UK via air travel and the proportion likely to be symptomatic. This was calculated by looking at the number of people likely to board a flight during the incubation period and to either develop symptoms during their flight or after arrival in the UK.

“The reason entry screening would be unlikely to have much effect is because only a small proportion of people infected with SARS would show signs of the disease on arrival due to its long incubation period; and although the incubation period for influenza is shorter it is thought that cases would still go undetected and therefore possible spread would still only be delayed by around a week.”

The research also looked at travel restrictions for preventing the spread of influenza, and concluded that if a 90% reduction in travel was introduced to and from areas affected by an outbreak; the peak in epidemics elsewhere would still only be delayed by around a week.

The researchers suggested that interventions on a local level such as the use of antiviral drugs or vaccines would be more effective in delaying the spread of the outbreak to other areas.