Deep Veinous Thrombosis in a Sample of Frequent International Travelers - April 28, 2000

Lennart Dimberg, MD, PhD, Occupational Physician, Joint Bank-Fund Health Services Department

DR. ERICSSON: What I'd like to do now is introduce Lennart Dimberg, who, as you know, is one of the co-organizers of this conference. He is an M.D., Ph.D., occupational physician from the World Bank here in Washington. He's a Swedish national. I was wondering what that accent was. And he's worked for the Volvo company in Sweden in various positions for 20 years, also as a corporate medical adviser before joining the World Bank. He's a specialist in general medicine and occupational health. He's published some 20 papers on various occupational health-related topics, and he's a task manager, together with Dr. Striker, for this program.

And now he's going to present a study, a very interesting study, I might say, because I've had a chance to see the paper on it, "Deep Venous Thrombosis in a Sample of Frequent International Travelers."

Lennart?

DR. DIMBERG: Thank you, Charlie.

On December the 16th, 1998, I received an e-mail from a 40-year-old World Bank employee informing me that he was on Coumadin and grounded for 2 weeks. He had come back from a mission in Dubai with stiffness in his right calf, and ultrasonography had revealed deep vein thrombosis. This sonogram shows venous mass representing the calf vein thrombosis.

This e-mail was copied to a number of staff in the Bank and suddenly everybody knew someone with the same experience and demanded a full investigation to the problem. This is what sometimes happens when one person with good connections and wide e-mail distribution lists can send this information around. So we decided to do a study, together with Kenneth Mundt and Sandra Sulsky over at Applied Epidemiology, and Bernhard Liese, who was the Medical Director of our company, of the Bank. Then we started this approach.

A literature review seemed to confirm that there was a known connection between DVT and air travel. There was even a term coined for this condition, "economy class syndrome," referring to an increased risk of DVT due to cramped seating. However, most studies were case reports, and we found no published study on the incidence of populations—in the populations of travelers.

We decided to look into this issue in World Bank staff and felt a little bit like the judge in this cartoon. "Since you have already been convicted by the media, I imagine we can wrap this up pretty quickly."

[LAUGHTER]

Our methods follow these three strategies: A case control study analysis of claims between 1995 and 1998 looking into the Worker's Compensation claims and also with direct interviews through publication in our newsletter, demanding people to inform us about whether they had had venous thrombosis during travel or not.

The case control study was performed using our unique available data of travel information from accounting, and we merged or married together that with demographic and diagnostic information from our medical insurance plan. We used two diagnostic groups: one of all phlebitis and thrombophlebitis and another with more specific DVT of the deep vein thrombosis of the leg, and looked at all diagnoses during 1995 and 1998.

The identities of staff were scrambled, but each individual was only counted once for his diagnosis. Ten random controls were selected for each case, and logistic regression was used to calculate odds ratios.

This was what we found: Between 1995 and 1998, we have an annual average of 8,189 insured staff, with an equal gender distribution. Average 4,951 staff with at least one travel mission during the year. Eighty-one cases of all venous thrombosis were found and 30 cases of DVT of the leg, 8 cases of venous thrombosis within 30 days after travel and three cases of DVT in the leg within 30 days of travel.

Males had an increased risk of thrombophlebitis and other venous embolus. The odds ratio of 1.52 for DVT was statistically significant.

Number of missions increased the risk somewhat for the group undertaking two to three missions/year. There we have an odds ratio of 1.17 for all thrombosis and 1.39 for DVT of the leg.

The number of travel days: 30 to 59 were associated with the relative risk of 1.24, for all venous thrombosis and 1.37 for DVT of the legs.

Two Worker's Comp cases were filed between 1995 and 1998. Of the seven persons responding to our desk-to-desk newsletter, five were confirmed with DVT during this period 1995 to 1998. And here are these cases. Three reported to be without risk factors. However, one person called me yesterday grounded with a second DVT. That was actually the one that called me on December 16, 1998, and now, he was grounded with a second DVT, after a long flight, and he explained that a Factor V Leyden mutation had been found and that he would need to be on Coumadin for the rest of his life. We may have comments around that later. Only one of the five flew economy class.

Conclusion One: Between 1995 and 1998, the average annual incidence of DVT among employees was 0.9 per thousand, and a possible flight-related DVT, 0.1 to 0.25 per thousand travelers. That is about one to two cases per year in the Bank population, depending on case-finding method.

Conclusion Two was: After controlling for age and gender, no association with travel was seen.

Thank you.

[APPLAUSE]

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