Traveler's Thrombosis: A Systematic Review

Mohammed T. Ansari; Bernard M.Y. Cheung; Jia Qing Huang; Bo Eklof; Johan P.E. Karlberg

Disclosures

J Travel Med. 2005;12(3):142-154. 

In This Article

Abstract and Introduction

Background: Anecdotal evidence suggests a possible link between travel and venous thromboembolism (VTE). We systematically evaluated the evidence from observational studies.
Methods: We searched studies evaluating the risk of venous thrombosis in relation to traveling from MEDLINE and EMBASE up to March 2004, together with a hand search of reference lists from retrieved literature, and we contacted some of the experts. Observational studies estimating the risks of VTE and isolated calf vein thrombosis were eligible. Methodologic quality was assessed based on prior criteria, and meta-analysis was considered where applicable.
Results: A total of 194 English-language publications were initially identified. Sixteen studies were included: 9 case-control, 2 prospective controlled, and 5 other observational studies. They differed drastically in study designs, selection of controls where applicable, mode and duration of travel, and subtypes of VTE under consideration. Ten studies concluded that travel, mostly through air and of prolonged duration, is a risk factor for venous thrombosis and/or pulmonary embolism, and the risk increases for passengers with preexisting venous thrombosis risk factors. Outcomes examined ranged from asymptomatic isolated calf muscle vein thrombosis to severe fatal pulmonary embolism.
Conclusions: Current literature is controversial over any association between travel and VTE, and although the quality and power of these studies have been variable, studies of higher quality have shown a strong and significant association between prolonged air travel and VTE. No conclusions could be drawn about other modes of transportation. Since VTE is a disease of multifactorial causation, those with preexisting VTE risk factors are most vulnerable.

Venous thromboembolism (VTE) has been identified following all sorts of prolonged travel associated with immobility,[1,2] for which the term 'traveler's thrombosis' has been suggested.[3] A meeting of experts on VTE organized by the World Health Organization (WHO) in 2001 concluded that an association between air travel and VTE probably exists, but that the risk was not quantifiable because of the lack of adequate data.[4] In this regard, a scientific executive committee project—the WHO Research into Global Hazards of Travel (WRIGHT project)—has been initiated as a set of coordinated studies to rigorously evaluate any relationship between VTE and air travel.[5]

Estimates of the incidence of traveler's thrombosis are variable depending upon the particular aspect of VTE under consideration, the observation period, the mode and duration of travel, and the study design and criteria. Scurr and colleagues reported an incidence of 10% of asymptomatic calf vein thrombosis in air travelers above 50 years of age traveling for more than 8 hours from a randomized controlled trial.[6] Symptomatic VTE estimates by Dimberg and colleagues varied from 0.1 to 0.25 per 1,000 among World Bank employees exposed to recent air travel varying with the case finding method.[7] Lapostolle and colleagues estimated the incidence of immediate/early-onset fatal pulmonary embolism (PE) as between 1.5 to 4.8 per million among passengers flying for more than 6 hours.[8] In a recent prospective study on air travel, Hughes and colleagues suggested that up to 1% of long-haul air travelers may develop VTE.[9]

Given the fact that > 1.6 billion passengers undertake air travel alone in 1 year,[10] and that other modes of transport may also be associated with VTE, travel-associated VTE (TAVTE) is a major concern. We therefore performed a systematic review of published studies on TAVTE to reassess the association. We also considered estimating the magnitude of risk of VTE among travelers if data permitted.

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