Incidence

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.

Conclusions:

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

Experts such as Colucciello, Pinneo, and Schreiber* agree that PE deaths each year number about 200,000. Several studies, such as a 4-year study at Tripler Army Medical Center in Hawaii, have concluded that 50% of DVT/PE cases are attributable to air travel. Of 200,000 PE deaths the 50% due to air travel would be 100,000. This is conservative because it doesn't include stroke and heart attack deaths caused by air travel thrombosis.

CDC's National Center for Health Statistics provides tables showing leading causes of death in age groups 20-24, 25-34, 35-44, and so on. But these tables don't list PE deaths separately; they are included in cardiovascular disease deaths.

To compare air travel thrombosis deaths with other leading causes of death in the 20-44 age groups, we counted the cases in Airhealth.org's registry, finding that 47% are in the 20-44 range. If 100,000 deaths are caused by air travel and 47% are in the 20-44 age group, then there are 47,000 air travel thrombosis deaths in the 20-44 age range.

The following tables are NCHS Leading Causes of Death with lines inserted showing the ranking of estimated air travel thrombosis deaths.

Ages 20-44

Air travel thrombosis............ 47,000
Accidents.............................34,540
Cancer................................21,4041
Heart disease.......................16,767
Suicide ................................13,727


All ages
.
Heart disease....................710,760
Cancer................................553,091
Stroke.................................167,660
Respiratory disease...........122,009
Air travel thrombosis.........100,000


In addition to the death toll, there are about 330,000 disabilities due to chronic DVT and 70,000 disabilities due to stroke. (This is based on our study finding that there are one million air travel thrombosis cases. One third of these become chronic DVT ("post-phlebitic syndrome") and 7% are disabling strokes.) Again, this is conservative because it doesn't include heart failures caused by flight-induced arterial clots.



Marathon Runners

An unexpected finding is that the majority of victims are athletic, usually endurance-tupe athletes like marathon runners. We know of at least six Olympic athletes who were victims. When the public realizes that some of their finest young athletes are becoming disabled for no good reason, there will be no sympathy for the airlines that tried to conceal this.

Airhealth.org Executive Director Michael Reynolds presented a paper on young athletic DVT cases at an International Angiology Union conference in Paris in January 2003. His work has also been published in The Lancet and Airline Pilot. Reuters calls Airhealth.org "The most comprehensive source of information on air travel thrombosis."

*See Research bibliography at www.airhealth.org.