T HE GROWTH of air travel means a potentially pandemic pathogen could spread around the world in days. Even in the absence of that risk, few countries’ authorities are keen on admitting travellers who might transmit disease to those already there. Yet the precautions typically employed at airports to screen incomers’ health are rudimentary.

It is easy to lie on a questionnaire. A dose of aspirin or other medication can lower body temperatures to the point where they look normal to the infrared cameras which some airports use to monitor passengers’ faces for fever. In any case, many of those infected might not show symptoms, and may even be unaware that they are ill. A cheap, uncheatable and instant diagnostic tool would thus be a boon at airports. And Dirk Kuhlmeier and his colleagues at the Fraunhofer Institute for Cell Therapy and Immunology in Leipzig, Germany, think they have one.

Dr Kuhlmeier’s invention, being developed as part of a wider project called HyFly that is intended to stop airports being gateways for infection, is based on technology already familiar to travellers, albeit that most will not recognise its name. Ion mobility spectrometry ( IMS ) is used to sniff swabs taken from baggage, clothing and personal items in searches for those carrying drugs or explosives. It can identify minute traces of volatile compounds, which drugs and explosives often emit. It works by measuring the ease with which ions (electrically charged molecules) can be drawn through an inert gas by an electric field. An ion’s mobility depends on its size and shape. Individual compounds can thus be identified, and telltales of illegal activity flagged up.

IMS is used medically, as well, to screen patients’ breath for compounds that indicate lung cancer. Dr Kuhlmeier reckoned he could extend this to detecting signs of respiratory bacterial infection—and laboratory tests that he and his team conducted suggested this was indeed possible. They discovered that they could even distinguish strains that have become resistant to antibiotics from those that have not. This shows that, in theory, IMS could quickly determine from a sample of breath if someone had an illness such as tuberculosis or diphtheria.

Turning theory into practice, however, brings complications. Chief among them is that even healthy people exhale lots of organic compounds. They do so especially if they have been eating spicy food, which contains a confusing array of such molecules. To deal with this, the team have developed an initial sorting stage, using a second technique called gas chromatography, to separate compounds so they are more easily analysed.

Bacteria, though, are only one source of illness. Viruses are equally dangerous. But viruses are not exactly living things and so do not have a metabolism which produces the sorts of compounds that bacteria generate. They do, however, change the metabolisms of the cells they infect. So Dr Kuhlmeier and his colleagues are now looking to see whether IMS can pick up these changes as well. If they succeed it would extend the scope of the technology to illnesses such as influenza and SARS .

The team plan to test their machine—essentially a large breathalyser that has one-use disposable mouthpieces—at clinics later this year, with the help of volunteers who have already been diagnosed with either bacterial or viral infections. These volunteers will also provide details of what they have been eating, so that the influence of various foods can be examined. If all goes well, trials at an airport should follow.