In a paper published this week in the open-access journal PLoS Medicine Frits Rosendaal and colleagues from Leiden University Medical Center, Academic Medical Center Amsterdam and Nestle Medical Services, provide the first absolute estimate of risk of venous thrombosis after air travel.
The authors surveyed 8,755 employees of international companies collecting data on their travel and whether or not they developed thromboses (deep vein thromboses and pulmonary emboli) afterwards.
The employees were followed up for a total of 38,910 person-years, during 6,872 of which they were exposed to a long-haul flight. In the follow-up period, 53 thromboses occurred, 22 within 8 wk of a long-haul flight.
The researchers then calculated that there was an incidence rate of 3.2/1,000 thromboses per year exposed to long haul travel compared with 1.0/1,000 per year in individuals not exposed to air travel; this rate is equivalent to a risk of one event per 4,656 long-haul flights.
Venous thrombosis has been linked to air travel since 1951 but despite a number of previous studies the absolute risk of symptomatic venous thrombosis after long-haul travel has not previously been calculated.
Knowledge of the absolute risk of symptomatic thrombosis after air travel is important so that travellers can accurately assess their risk of developing thromboses and decide whether prophylactic measures against thromboses are worthwhile.
The authors found that the risk of thromboses increased with exposure to more flights within a short time frame and with increasing duration of flights.