WHO Research into Global Hazards of Travel (WRIGHT) project
Final report of phase 1
The objectives of the WRIGHT (WHO Research Into Global Hazards of Travel) 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 to study the effect of preventive measures on risk.
To address these objectives, several studies were performed during Phase I of the WRIGHT project. Additional proposed studies related to the effect of preventive interventions were deferred to Phase II. The findings of the epidemiological studies indicate that the risk of VTE approximately doubles after a long–haul flight (>4 hours) and also with other forms of travel where travellers are exposed to prolonged seated immobility. The risk increases with the duration of the travel and with multiple flights within a short period. The risk also increases significantly in the presence of other known risk factors of VTE. The risk factors identified as contriubtors to the increased risk of travel-related VTE were obesity, extremes of height, use of oral contraceptives and the presence of prothrombotic blood abnormalities. The absolute risk of VTE per more than four-hour flight, in a cohort of healthy individuals, was 1 in 6000.
The pathophysiological studies supported these findings. The results of the hypobaric chamber studies in healthy volunteers failed to demonstrate any association between hypobaric hypoxia and prothrombotic alterations in the haemostatic system. However, the travel and non–travel immobility study, which included a high proportion of individuals with risk factors, suggested that some flight–specific factors may interact with pre–existing risk factors and result in increased coagulation activation in susceptible individuals over and above that related to immobility. Further study will be required to determine the identity of the culpable factors. Based on these findings, there is a need for travellers to be given appropriate information regarding the risks and for further studies to identify effective preventive measures, which will comprise Phase II of the WRIGHT project.