title: Venous thromboembolism associated with air travel: a report of 33 patients.
abstract: BACKGROUND
  The medical literature suggests long distance travel, particularly air travel, may be a risk factor for venous thromboembolism, but the risk is poorly quantified.
  
  
  METHODS
  We reviewed 134 records of patients hospitalized with venous thromboembolism for comments regarding recent travel. Patients who had traveled within 31 d prior to venous thromboembolism were defined as recent travelers.
  
  
  RESULTS
  Of 134 patients records, 66 (49%) had documented inquiries regarding travel and 33 (50%) were recent air travelers. Data regarding demographics, mode of travel, day of onset of symptoms in relation to travel, and other risk factors for venous thromboembolism were abstracted from the records of the recent travelers. There were 12 (36%) travelers who had no other predisposition for venous thromboembolism. All had traveled non-stop by aircraft for 4 or more hours; none was identified as a crew-member. The median day of onset of venous thromboembolism was on travel day 4 (range: day 1-31). There were 8 (24%) patients who had onset during air travel or on the day of arrival, and 27 (82%) had onset by travel day 15. Air travel for 4 or more hours within the preceding 31 d was the most common risk factor for venous thromboembolism in our study patients and was present in 50%. This incidence is much higher than previously described, perhaps due to limiting the study population to those in which the presence or absence of travel was documented.
  
  
  CONCLUSIONS
  Prospective studies are needed to better define the risk factors for venous thromboembolism among long distance air passengers and crew-members, and to determine effective preventive measures.
authors.affiliation: Department of Medicine, Tripler Army Medical Center, Honolulu 96859-5000, USA.
authors.forename: A
authors.initials: A
authors.lastname: Mercer
authors.forename: J D
authors.initials: JD
authors.lastname: Brown
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001359:Aviation; D003710:Demography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012307:Risk Factors; D013923:Thromboembolism / Q000209:etiology*; D013997:Time Factors; D014195:Travel