In 2001, the World Health Organization (WHO) began a 2-
phase project called the WHO Research Into Global Hazards of
Travel (WRIGHT) Project. The objectives of the project were to
confirm that the risk of venous thromboembolism (VTE) is
increased by air travel and to determine the magnitude of risk,
the effect of other factors on the risk, and the effect of preventive
measures on risk.
The key findings of the WRIGHT Phase I report include the following:
- The risk of VTE roughly doubles with flights greater than 4 hours and increases
with longer flights or repeated flights within a short period of time.
- Overall, the absolute risk of VTE appears to be about 1 in 6000 healthy individuals,
but the risk is primarily concentrated in patients with hypercoagulable conditions,
those using birth control pills, or those who have other risk factors such as
obesity, extremes of height (less than 5?2? or greater than 6?2?), older age, and cardiovascular
- The VTE risk is greatest immediately following a flight, but some risk persists
for several weeks afterward.