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|Updated May 5, 2006|
The Lancet (9/8/01) published an abstract of Airhealth.org's analysis of 21 sources of data concluding that, of two million DVT cases and 200,000 PE deaths each year in the US, half are caused by air travel. (Full text below) Subsequent studies have also found large numbers of cases of air travel thrombosis, such as Gianni Belcaro's LONFLIT series in which more than 2,500 air travelers were given ultrasound scans before and after long flights, finding that about 3% developed clots larger than .5 cm. His latest study, LONFLIT Business 2003, finds 4.9% of frequent business-class travelers developing one or more clots per year.
Economy class syndrome: how many cases?
We found 21 sources for this report.
1. Warfarin is the 11th most-prescribed drug in the US with $500 million sales (per American Family Physician, 2/1/99). This works out to treatment of about 5 million persons. J. Hirsch (Management of Deep Vein Thrombosis and Pulmonary Embolism) says 2 million of those are DVT/PE victims, with 600K hospitalized, 60K fatalities. In '98 the Mayo Clinic Health Letter also reported 600K hospitalized, 60K fatalities.
2. Figures from population-based studies are: Heit, .8 per thousand per year, Oger 2 per thousand, and Adam.com, 4 per thousand. Schreiber reports that 5% of the population develops DVT sometime during the course of a lifetime.
3. DVT is, more often than not, silent or asymptomatic. Caprini says 94% are silent. The actual number of cases is about twenty times greater than the number of symptomatic cases. If they are silent, why worry about them? People with silent DVT are at risk of PE, which can strike without warning and may be fatal. No preventable DVT should be allowed to occur, even if silent.
4. DVT/PE is undiagnosed and misdiagnosed more often than not, according to Schreiber, Zamula, and others. The actual number of symptomatic cases is probably twice the number of diagnosed cases.
Causes of Death:
1. The July 2000 National Center for Health Statistics report of leading causes of death showed 941 thousand heart disease deaths, 541 thousand cancer, 158 thousand stroke. If PE deaths are around 200,000, as many sources report, then PE is the third leading cause of death.
2. Dr Graham Pineo finds 150-200K annual PE deaths. Evelyn Zamula finds 630K PE cases with 220K fatalities. Colucciello found 200K DVT/PE deaths. Schreiber reports 200K deaths and says PE is the leading cause of preventable hospital deaths.
3 . PE is, often as not, undiagnosed and misdiagnosed (Zamula). PE often causes fatal cardiac arrest or arrhythmia. Without an autopsy, no one knows that PE was the cause of the heart failure. Zamula quotes Jan M. Orenstein, MD, professor of pathology, George Washington University School of Medicine and Director of Autopsy, saying "Pulmonary emboli are a relatively common finding at autopsy, usually unsuspected and frequently the cause of death." Angrist reports that PE is the most undiagnosed and misdiagnosed entity in all of medicine.
4. DVT also leads to disability or death from stroke. About 25% of adults have a right/left shunt, a small hole in the heart that allows venous blood to pass into arterial circulation without passing through the lungs. This allows clots to pass on to the brain, causing stroke. Stroke can also result from clots formed in the arterial system, such as in atrial fibrilation, which is more likely during air travel, while coagulability is elevated. In 1950 stroke was the 11th leading cause of death. Today it is third, and it is on track to pass cancer in about ten years. How much of this is due to air travel is not known. Most strokes caused by air travel would occur several days or more after the trip and no one would know it was caused by air travel.
Of air travel thrombosis victims contacting Airhealth.org, about 7% suffered strokes. Of 168,000 stroke deaths, about 80% are ischaemic, caused by clots. Of those, 40% are cryptogenic, probably caused by a clot passing through a right/left shunt. Of those, probably 33%, or about 17,000 are due to air travel. Again, this is conservative because it doesn't include those caused by arterial clotting.
5. PE leads to pulmonary hypertension in perhaps 5% of victims, which often leads to necessity for heart/lung transplant or, failing that, death.
How much of this is caused by air travel?
1. Gianni Belcaro's LONFLIT studies are finding about 3% of air travelers developing clots on long flights. Most are silent or asymptomatic. But they still pose a risk of recurrent DVT and potentially fatal PE. Every preventable DVT should be prevented. US airlines carry about 600 million passengers. If half make journeys over four hours, and 10% of those develop clots, and 6% of those produce symptoms, there would be 1.8 million victims. Allowing for nearly half to be undiagnosed or misdiagnosed, the result is one million victims, consistent with other findings.
2. Several studies tabulated the percentage of DVT/PE victims caused by air travel. Simon found 66% of DVT/PE attributable to air travel. Mercer Brown found 50% and that air travel was the most common risk factor. Benoit found 50%. A Tripler Army Medical Center 4-year study also found 50%. In Honolulu, Eklof et al studied 254 DVT/PE patients and found 20% had developed clots during air travel. Ferrari found 6% in Nice, and Nissen found 5% in Germany.
3. Dr. Russell Rayman of the Aerospace Medical Association, says no one knows the incidence of air travel thrombosis, but it is rare.
A conservative conclusion is that, of the 2 million treated for DVT, 1 million are caused by air travel. Of 200 thousand PE deaths, 100 thousand are caused by air travel. Of 158,000 stroke deaths, 80,000 may be due to air travel. This is conservative. For every diagnosed and treated DVT, there are 20 silent cases, per Caprini. Many more deaths due to heart failure, and pulmonary hypertension are caused by air travel.
Leading Causes of Death