. 2007 Jan 17;22(1):107–114. doi: 10.1007/s11606-006-0016-0

Table 2.

Cohort studies

Author (ref) year subjects	Description of subjects		Travel type, duration	Subjects with VTE/total	Incidence (95% CI)	Standards met*
Author (ref) year subjects	Travelers/controls	Cases	Travel type, duration	Subjects with VTE/total	Incidence (95% CI)	Standards met*
Clerel¹⁰ 1999 32,000,000	Travelers: all arriving air passengers	Passengers transported to hospital from airport with confirmed PE diagnoses	Air, mean 12.7 h	PE: 15/32,000,000	0.5 (0.3–0.8) per million	1,2,4,7
Lapostolle¹⁷ 2001 135,290,000	Travelers: all arriving air passengers	Passengers transported to hospital from airport with confirmed PE diagnoses	Air, <3 h	PE: 0/88,490,000	0.00 (0.0–0.04) per million^†	1,4,7,8
			Air, >=3 to <6 h	PE: 1/9,180,000	0.11 (0.01–0.71) per million
			Air, >=6 to <9 h	PE: 9/22,530,000	0.40 (0.19–0.79) per million
			Air, >=9 to <12 h	PE: 33/12,370,000	2.66 (1.83–3.79) per million
			Air, >= 12 h	PE: 13/2,720,000	4.77 (2.66–8.41) per million
Belcaro¹⁸ 2001 778	Travelers: volunteer passengers planning long distance air travel	Travelers with diagnosis of DVT from screening ultrasound exam	Air, 10–15 h	Low-risk^‡ DVT: 0/355	0.0% (0.0–1.0)^†	2,6,7
Belcaro¹⁸ 2001 778			Air, 10–15 h	High-risk^‡ DVT: 11/389	2.8% (1.4–5.0)	2,6,7
Schwarz¹⁹ 2002 320	Travelers: volunteers planning long distance air travel	Subjects with diagnosis of DVT from screening ultrasound exam	Air, >8 h	DVT: 0/160	0.0% (0.0–2.3)	2,3,4,6,7
Schwarz¹⁹ 2002 320	Controls: age, sex matched nontraveling volunteers		–	DVT: 0/160	0.0% (0.0–2.3%)	2,3,4,6,7
Schwarz²⁰ 2003 2,311	Travelers: volunteers planning long-distance air travel	Subjects with diagnosis of DVT from screening ultrasound exam	Air, >8 h	DVT: 7/964	0.7% (0.3–1.5)	2,3,4,6,7
Schwarz²⁰ 2003 2,311	Controls: nontraveling volunteers		–	DVT: 2/1,213	0.2% (0.02–0.6)	2,3,4,6,7
Perez–Rodriguez²¹ 2003 41,035,332	Travelers: all arriving air passengers on international flights	Passengers transported to hospital from airport with confirmed PE diagnoses	Air, <6 h	PE: 0/28,038,726	0.00 per million^†	1,4,7,8
			Air, 6–8 h	PE: 1/3,926,208	0.25 (0.00–0.75) per million
			Air, >8 h	PE: 15/9,070,398	1.65 (0.81–2.49) per million
Hughes²² 2003 878	Travelers: volunteers planning long-distance air travel	Passengers with elevated D-dimer or symptoms suggestive of VTE during 3-mo follow-up period and VTE diagnosis confirmed by objective test	Air, 39.4 h (mean)	VTE: 9/878 PE: 4; DVT: 5	1.03% (0.5–1.9)	2,4,6,7,8
			Air, <24 h	VTE: 0/123	0.0% (0.5–3.0)
			Air, >24 h	VTE: 9/752	1.2% (0.6–2.3)
Kelman²³ 2003 9,257,842	Travelers: all arriving passengers on international flights	All inpatients with the discharge diagnosis of DVT or PE who had arrived on an international flight within 14 d	Air	VTE: 246/9,257,842	26.6 per million (23–30)	1,4
Jacobson²⁴ 2003 899	Travelers: volunteers planning long-distance air travel	Subjects with diagnosis of DVT from screening ultrasound exam	Air, 11 h	DVT: 0/434	0.0% (0.0–0.9)	2,6
Gajic²⁵ 2005 8,860	Travelers: patients having elective surgery after long-distance air travel	Patients having new-onset VTE within 28 d of Surgery	Air, >5,000 km	VTE: 11/223	4.9% (2.5–8.7)^†	4,7
Gajic²⁵ 2005 8,860	Controls: patients having elective surgery but no long-distance air travel	Patients having new-onset VTE within 28 d of Surgery	<5,000 km	VTE: 13/8,637	0.2% (0.08–0.3)	4,7

CI confidence interval, DVT deep venous thrombosis, VTE venous thromboembolism, PE pulmonary embolism, CTPA computed tomographic pulmonary arteriography, V/Q scan ventilation perfusion scan.

*See Appendix for explanation of standards.

^†Differences between groups significant, P < 0.001.

^‡Low risk: no known VTE risk factors; high risk: previous DVT, known coagulation disorder, severe obesity, limited mobility, cancer, large varicose veins.