In the event of a new SARS or influenza epidemic, air travel would represent the principal route of international spread. Although airport entry screening has been advocated, its benefit is currently unknown.
Using the incubation periods for influenza and SARS, researchers at the Health Protection Agency estimated the proportion of passengers with latent infection who would develop symptoms during any flight to the UK.
For SARS, they found that the incubation period was too long to allow more than a small proportion of infected individuals to develop symptoms during a flight to the UK (0-3% for European flights and a maximum of 21% for the longest flights from East Asia).
Although influenza has a much shorter incubation period than SARS, the average predicted proportion of people infected with influenza and progressing during any flight was still less than 10%.
Because the proportion of individuals detected is highest from cities with the longest flight duration, screening passengers from the Far East and Australasia derives the most benefit. But, even then, the sensitivity for cities in these areas would still be low, explain the authors.
Early screening is unlikely to be effective in preventing the importation of either SARS or influenza, they conclude.
Although adopting a policy of quarantining all exposed passengers on the detection of a single case could substantially increase the benefit of entry screening, this still leaves the problem that the sensitivity of entry screening is low.
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