One of the disadvantages of travel is the prospect of ill health – of running into tropical bugs or exotic diseases that can give you an unpleasant souvenir of your time away.

However, according to new research, the factor of your holiday that is most likely to make you feel unwell is not a poorly-cooked dish in a cheap restaurant or a biting insect in a jungle – but the planes that carry you on your journey and the airport where you board them.

An investigation conducted by respected US news programme The Today Show has uncovered worrying evidence of ingrained germs and dirt – and even traces of excrement – in the transport hubs and on the aircraft that we use so regularly.

The show went undercover at an unnamed American airport, and tested key parts of the flight experience for traces of harmful matter and unsanitary conditions.

The results do not make for pleasant reading.

One place that proved to be of immediate concern was the security-scan queue.

Researchers used test swab kits to check for invisible extras in the plastic boxes that are a standard part of security procedures – playing temporary host to all manner of potentially soiled items, including passengers’ shoes, as well as their carry-on bags.

Alarmingly, the study found the boxes to be widely filthy – and in one case, home to small traces of fecal matter, perhaps left by the dirtied sole of a shoe.

There were further unappetising results when the researchers boarded the aircraft.

Although the airline in question has not been named, it is reasonable to think that the findings will be replicated across any carrier where there is a high turnover of passengers.

The worst offenders when it came to on-board hygiene were discovered to be the fold-down tray tables that travellers use for eating in-flight meals.

These were found to be rife with high levels of bacteria – perhaps the result of airlines failing to wipe the tables properly between flights.

Even worse were the plane’s seat belts – touched over the years by thousands of hands, but rarely cleaned or replaced. The researchers uncovered the presence of human ‘bacteroides’ – germs which can cause real damage to health.

‘These are bacteria that live in our gut and our intestines,’ Dr Robert Glatter of New York’s Lenox Hill Hospital told Today.

‘These are dangerous bacteria that cause serious infections.’

Bacteroides can be transferred through simple skin contact.

The investigative team took 13 different samples. Nine of them returned traces of harmful germs.

The results were, however, not entirely negative – with other areas of the air travel experience proving remarkably clean where bacteria might be expected.

A relatively new installation in modern airports, the touch-screen facilities where passengers can scan their passports and check themselves in proved to be germ-free – despite being tapped and pressed by hundreds of different hands every day.

And while plane seat-belts were festering with nasties, the arm-rests between the seats – so often the subject of personal-space battles between travellers – were also clean.

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