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WHO launches study of venous thrombosis and air travel

The World Health Organization (WHO) today announced the launch of a comprehensive research programme to investigate the unresolved issues regarding travellers’ thrombosis.

The study will include epidemiological, pathophysiological and clinical studies, the first of which are expected to commence within a few weeks. Preliminary results from some of the studies will be available within a year although the full programme will take up to four years to complete.

Full funding for the first phase of the programme has now been secured, with the confirmation today that the UK government will contribute 1.8 million Euros to the project in the first two years. Additional funding is anticipated from the European Commission and negotiations are continuing with other governments about funding for the second phase.

The research programme aims to determine the frequency and causes of travellers’ thrombosis, to identify who is at greatest risk and what may be done to prevent it. The research will be carried out by experts from several countries. It includes studies in three principal areas.

- Epidemiological studies will assess the frequency of occurrence of thrombosis amongst travellers and identify which groups are most at risk. The impact of pre-existing risk factors, such as a previous history of thrombosis, use of oral contraceptives or HRT, recent illness, operation or injury and genetic susceptibility will be examined. Factors such as class of travel and in-flight behaviour (e.g. alcohol consumption, leg-exercises and use of compression stockings) will also be considered.

- Pathophysiological studies will investigate the causal mechanisms and in particular, whether factors other than immobility, such as low cabin pressure and oxygen levels, might be responsible for venous thrombosis after air travel, which has been the most prominent focus of public attention.

- Clinical studies will focus on the effectiveness of possible preventive strategies. On completion of the programme, it should be possible to give clear guidance to the travelling public regarding both the magnitude of any risk and the most appropriate preventive measures.

The studies will be conducted in two phases. The first phase will include two epidemiological studies, which will look at the incidence of thrombosis in large populations of frequent flyers.

The first phase also includes two pathophysiological studies. One of these will look at the effects on the blood of low air pressure and reduced oxygen levels, such as might be encountered during air travel in an hypobaric (low pressure) chamber. The other will look at changes in the coagulability of the blood during actual air travel . It is anticipated that the second phase will commence during 2003, subject to further funding. This will comprise a large epidemiological study, in which 200,000 air travellers will be followed for a month, to assess the incidence of thrombosis. A large clinical study will also be performed to assess the effectiveness of various preventive strategies, such as exercise, compression stockings and anti-clotting drugs. The final report for the programme will be presented in 2006.

The Scientific Executive Committee for the programme today welcomed the news that full funding of the first phase has been approved. ‘The UK government and the European Commission have taken a clear lead in addressing this important public health issue.’ said Professor Fred Paccaud, Chair of the Scientific Executive Committee and Professor of Social and Preventive Medicine at the University of Lausanne.

The Scientific Executive Committee will be assisted by an Advisory Board, which will provide additional guidance on the scientific and practical aspects of the research and monitor progress. Members of the Advisory Board will include prominent members of the international scientific community, as well as representatives of the airlines, passengers and funding agencies.

The Advisory Board will be chaired by Dr Derek Yach (Executive Director, Non-Communicable Diseases, World Health Organization).

"WHO is committed to promoting research in to the link between air travel and deep vein thrombosis as it is an important public health problem," Dr Yach said.

The research programme will be conducted under the auspices of the WHO and the International Civil Aviation Organisation (ICAO). The International Air Transport Association (IATA) is fully committed to the programme and has undertaken to give its full support.

In recognition of the widespread interest in this area of research, a wider debate will be promoted with other researchers and interested parties through the establishment of the WRIGHT forum. This will take the form of an annual meeting at which the progress of the project will be reported and new data emerging from elsewhere will be discussed. The Scientific Executive Committee will also explore other information strategies to inform the wider public of the progress of the studies before the final report.

Note to Editor

The protocol for the World Health Organization Research Into Global Hazards of Travel (WRIGHT) programme was developed following a consultation in March 2001, at which medical experts, representatives of the airlines and regulatory authorities met to identify the important gaps in the current knowledge of the issue.

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For more information contact:

Reshma Prakash
Telephone: (+41 22) 791 3443
Fax: (+41 22) 791 4832
E-mail: prakashr@who.int