Routine chemoprophylaxis for travel-associated thrombosis? No.

• Travel and thrombosis are associated. Four case-control studies [1-4] and five cohort and randomized controlled studies [5-9] have clearly established that thrombosis is associated with travel. In the four case-control studies, 11.8% of patients with venous thromboembolism had a history of recent travel, by air or other means of transportation, compared to 6.3% of controls with an odds ratio of 1.98 (1.52–2.57). In the cohort studies (as well as in control arms of randomized studies) about 2.1% of patients suffered a thrombotic event following air travel. Although two casecontrol studies [3,10] failed to detect a direct association between travel and thrombosis and despite the fact that two other studies [7,8] recruited volunteers responding to media ads, all the studies lumped together prove an association.