Risk of venous thromboembolism greatest within two weeks of long-haul flight

Abstract

Question

After a long haul flight, when are people at greatest risk of developing deep vein thrombosis?

Study design

Retrospective review and record linkage study.

Main results

Of the 13,184 people admitted to a Western Australia hospital during 1981–1999 with a primary diagnosis of venous thromboembolism, 5408 (41%) had arrived on an international flight sometime during the same 18 year period. Of these, 153 Australian citizens and 438 non-Australian citizens were admitted within 100 days of flight arrival (see Table 1). Venous thromboembolism was significantly more likely within the first 14 days of flight arrival for both Australian and non-Australian citizens, compared with the number of events expected under the assumption of a uniform distribution across 100 days (P<0.001 for both comparisons). However, these results may have limited generalisability (see notes).

Table 1 Observed and expected venous thromboembolism events by time (days) since flight arrival.
Citizenship	Days since most recent flight arrival
	0–14	15–30	31–60	61–100	Total
Australian
Observed	46	23	32	52	153
Expected*	102.6	113.2	212.3	283.0	711.1
Non-Australian
Observed	200	69	78	91	438
Expected†	105.3	116.2	217.9	290.5	729.9
*Estimated from the total number of arrivals of Australian citizens in Western Australia (4.8 million) and the age- and sex-specific baseline rates for venous thromboembolism in the Western Australian population. There were consistently fewer observed venous thromboembolism events than expected events, suggesting a ‘healthy traveller effect’.
†Also estimated from the baseline rates for venous thromboembolism in the Western Australian population.

Authors’ conclusions

There appears to be an increased risk of venous thromboembolism for 2 weeks after arrival from a long-haul flight.