Schwarz et al1 reported that the incidence of venous thrombosis among long-haul flight travelers was 2.8% compared with 1.0% in controls. However, 20 of 27 events in travelers and 10 of 12 events in controls were isolated calf muscle vein thromboses (ICMVT). The authors conclude that ICMVT may be used as a surrogate marker of air travel–associated deep venous thrombosis (DVT) and that while "the natural history of ICMVT is not known . . . ICMVT has been suggested to be the first step toward deep venous thrombosis."
Susan R. Kahn. Venous Thrombosis in Long-Haul Travelers. Arch Intern Med. 2004;164(15):1699–1700. doi:10.1001/archinte.164.15.1699-b