In fact, phlebitis is quite common, the result of immobility because of an injury or traveling in a confined space, like a coach seat on a crowded flight. So many travelers are turning up with phlebitis that it is becoming known as "economy class syndrome."

Charter airlines say they cannot promise passengers more legroom, despite fears that cramped conditions on long-haul flights may be contributing to potentially lethal blood clots. Last weekend, it was reported that doctors are to monitor 2,000 passengers travelling between Britain and Australia to look for symptoms of "economy-class syndrome". Researchers suspect that passengers forced to sit for many hours in uncomfortable seats are more likely to experience deep-vein thrombosis or blood clots that develop in the legs and can travel to the lungs and block arteries.

The term "economy class syndrome" has been used to describe the venous problems caused by the cramped seating arrangements in modern aircraft.