DVT: anatomy of a panic

As airlines face lawsuits in the UK and Australia from survivors of deep-vein thrombosis (DVT) – and as recent reports claim the UK government will order airlines to issue DVT health warnings with tickets for long-haul flights – the preoccupation with DVT seems to be reaching new heights.

There is an ongoing scientific debate about the relationship between long-haul flights, which mean passengers sitting still for long periods, and DVT, blood clots that form in the legs. In recent months new research findings have been published, some of which suggest a link between long-haul flying and DVT. But this debate sheds little light on the growth of popular concern about DVT. The scientific discussion seems to go on in a parallel universe, only tangentially related to the world of media and public debate, which is governed by quite different laws.

— The development of the science

According to a commentary in the medical journal The Lancet, despite the reporting of cases of DVT after flying back in 1954, and numerous following case-reports and retrospective studies, before 1999 research was unable to calculate ‘the relative or absolute risk of thrombosis’ due to flying, as a result of ‘inherent deficiencies in the design of these studies’ (1).

Since 1999, there have been a number of notable studies that have been published:

In 1999, Emile Ferrari found that long-distance travel was associated with an 3.98 times increased risk of developing DVT (2). That is, the average risk of developing DVT in a month after going on a long journey would be around four times that of a normal month. The following year, a study by MM Samama found a slightly lower associated risk of 2.35 (3) – but another study in 2000 by RA Kraaijenhagen found no significant relationship (4).

A study by John Scurr in May 2001 caused controversy, after finding an incidence of thrombosis approximately 40 times that of previous studies. Scurr discovered minute blood clots forming in the calves of approximately one in 10 air passengers (5). But this study was criticised by Jack Hirsh and Martin O’Donnell in the same issue of The Lancet, who suggested that the ‘startling’ result was best explained by a major flaw in the study method (6).

The jury, then, is still out. Some scientists have found evidence for a link between flying and DVT – others have found evidence indicating that there is no link. And both sets of evidence are disputed. But the scientists do agree on one thing: if there is an increased risk of DVT caused by flying, it is small and mainly affects individuals who are already predisposed to DVT – such as people who have had recent surgery, have blood clotting disorders, or are pregnant (7).

This uncertainty is not surprising. After all, if causality was direct and strong – if people were getting off planes and collapsing on a regular basis – the DVT panic in the UK would surely have kicked off before October 2000.

— The development of a panic

The concern with DVT began seriously, not after a new report, but after 28-year-old UK resident Emma Christoffersen tragically collapsed and died after a 20-hour flight from Australia in October 2000 (8). Her story captured the public imagination: she was young, healthy and just about to get married. As her fiance Tim Stuart put it, ‘[DVT] seems to strike at random, and in a way it’s just like Russian roulette. It could happen to anyone.’ (9)

Following Emma Christoffersen’s death, the issue took off quickly. Her story made the headlines; her Member of Parliament Paul Flynn, Labour MP for Newport West, asked the UK government to give guidance to air travellers about the risks from long-haul flights; and a UK House of Lords select committee was formed to look at the dangers.

By January 2001, John Smith, Labour MP for Vale of Glamorgan, said he planned to introduce a law to highlight the risks of developing DVT on long-haul flights after the death of one of his constituents (10); two DVT-suffering passengers said they would sue airlines (11); and British Airways announced that it would provide passengers with leaflets giving advice on health matters – including dealing with the risk of fatal blood clots (12). And from October 2000 to today, DVT has repeatedly resurfaced in the news, often with shock-horror headlines.

Scientific evidence played little role in the development of events. Instead, the science was spun to suit the stories, rather than impacting upon the debate in its own terms.

Any scientific evidence was reported selectively. Scientific research that seemed to confirm the danger of DVT received headline coverage, while research that found no link was barely mentioned. John Scurr’s study, which found the strongest link between DVT and flying, was reported in the main UK papers, with headlines like ‘Flight blood clots “hit one in 10″‘ and ‘Blood clots may affect one in 10 air travellers’ (13). The criticism of his study by Jack Hirsh and Martin O’Donnell received at best a brief mention. RA Kraaijenhagen’s study, which found no link between flying and DVT, has received little coverage.

Evidence was distorted – and conjecture cemented as fact. The best example of this is the way Scurr’s ‘one in 10’ statistic has become accepted across the board – with articles on DVT claiming something like, ‘One in 10 long-haul passengers is at risk of the blood-clotting condition, according to the medical journal The Lancet‘, and then going on to detail DVT deaths (14). But this is misleading – in a number of ways.

Firstly, ‘the condition’ that Scurr found in one in 10 of his subjects was not illness or death, but tiny symptomless blood clots, which had no effect on their health. Secondly, Scurr’s findings were criticised by peers who claimed an error in the study method – and even the authors themselves emphasised that it was a pilot study and that the unexpected findings should be viewed with caution. Thirdly, the medical journal The Lancet is a forum for scientific publication and debate, not a party organ with a fixed line – articles in The Lancet have found evidence both for and against a link between DVT and flying (15).

In other media reports, scientific evidence about statistical risks was replaced with the subjective experiences of people who had suffered DVT after flying. This approach seems to have impacted upon some scientists themselves: when presenting his research into DVT and flying, Dr John Belstead made the comment that ‘one in a million doesn’t sound a lot, but it’s a lot for the people concerned’ (16). Some newspapers published lists of people who died from DVT after flying (17).

The relatives of DVT victims were promoted as spokespeople to highlight the importance of the issue – particularly the parents of Emma Christoffersen, who have since set up a lobby group, Victims of Air Related DVT Association (VARDA) (18). It looks like one heartless journalist even rang up Ada Thomas two weeks after her son collapsed and died after a 10,000-mile flight home from his honeymoon in Hawaii to get her to react to RA Kraaijenhagen’s finding that there was no significant link between flying and DVT. Not surprisingly she said: ‘It is ridiculous to talk about a myth. My son’s death was caused by him sitting in that plane for so long.’ (19)

The concern about DVT has also been fuelled by the idea that ‘whatever the evidence says, you can’t be too careful’. So the UK House of Lords select committee on DVT noted the ‘current paucity’ of data showing any link between DVT and flying – but went on to say that passenger health had been ‘woefully neglected’ by airlines, and recommended health and safety briefings before flights, and display cards at ticket sale points asking passengers ‘are you fit to fly?’ (20).

Then there are the scare profiteers. There may well be some truth in the claim that airlines were reluctant to admit the link between flying and DVT – but just as airlines have a potential financial interest in damping down concerns, there are other groups that have a contrary interest in inflaming them.

Most immediately, there are the lawyers currently bringing multimillion-pound claims in the UK and Australia. There are also producers of the new anti-DVT products, a rapidly expanding market. An aeroplane has been built with a running track (costing a cool £270,000 to hire), perfect for nervous suits after the near-death of a chief executive suggested there was nothing ‘economy class’ about DVT. Mediven travel stockings (around £20 per pair) use John Scurr’s research as publicity: their website reports his study outline, then says that ‘the second group of 115 volunteers had been fitted with Mediven travel stockings….In this group of 115 volunteers no one person showed any thrombosis in the deep veins of the legs’ (21).

The Airogym foot exerciser, invented by a retired pilot concerned with passenger health, has seen an unexpected leap in sales recently. One salesperson for Airogym said the impact of recent media reports on anti-DVT products (22) had been ‘absolutely huge…sales have gone up by four to five times…every time we are mentioned sales just leap’, (and Emirates airline recently brought half a million Airogyms for their passengers). Club Direct made the headlines by becoming the only travel insurance company that offers legal costs if an insured passenger contracts DVT, something that others were perhaps justified in labelling a ‘marketing exercise’ (23).

And MP John Smith seems to be making a name for himself out of the issue – not only bringing a bill before the UK House of Commons, but also making publicity-grabbing statements in the media, such as: ‘[DVT] could be a greater problem than that of asbestos. It could even be a greater public health problem than that of BSE.’ (24)

The end result of the development of a panic is public anxiety. Independent research in January 2001 found that, out of people who make long-haul flights, 89 percent said that they were aware of the issue of DVT and flying, 38 percent said they were ‘concerned and have already taken precautions’, and 27 percent said they were ‘concerned and have thought about taking precautions’.

The DVT scare has yet to reach its first birthday – but already more than half of those who travel now spend some of their flight worrying about what terrible fate might befall them, instead of thinking about something more interesting instead.

Read on:

spiked-issue: Blood clots

(1) Venous thromboembolism after long flights: are airlines to blame?, by Jack Hirsh and Martin J O’Donnell, The Lancet, 12 May 2001. To access this article, first register at http://www.thelancet.com

(2) Ferrari E, Chevallier T, Chapelier A, Baudouy M, ‘Travel as a risk factor for venous thromboembolic disease: a case-control study’, Chest 1999; 115: 440-44

(3) Samama MM, ‘An epidemiologic study of risk factors for deep vein thrombosis in medical outpatients: the Sirius study’, Arch Intern Med 2000; 160: 3415-20

(4) Kraaijenhagen RA, Haverkamp D, Koopman MMW, et al, ‘Travel and risk of venous thrombosis’, The Lancet 2000; 356: 1492-93. Click here here to download a copy of this article in .pdf format

(5) Frequency and prevention of symptomless deep-vein thrombosis in long-haul flights: a randomised trial, by John H Scurr et al, The Lancet, 12 May 2001. To access this article, first register at http://www.thelancet.com

(6) Venous thromboembolism after long flights: are airlines to blame?, by Jack Hirsh and Martin J O’Donnell, The Lancet, 12 May 2001. To access this article, first register at http://www.thelancet.com

(7) See Box 2, Predisposing factors for DVT, Report by the house of lords select committee on DVT and flying

(8) See Blood clot kills woman after flight, Guardian, 23 October, 2000

(9) Quoted in Guardian, 23 November 2001

(10) MP’s action over long-haul deaths, BBC News Online, 9 January, 2001

(11) Air passengers to sue over blood clots, BBC News Online, 8 January, 2001

(12) MP’s action over long-haul deaths, BBC News Online, 9 January, 2001

(13) These two headlines from BBC News Online and the Daily Telegraph

(14) This quote from a BBC News Online article

(15) For example, articles questioning the link between DVT and flying in The Lancet:

‘Travel and risk of venous thrombosis’, Roderik A Kraaijenhagen et al, The Lancet, Volume 356, no 9240, 28 October 2000 (Click here here to download a copy of this article in .pdf format)

Venous thromboembolism after long flights: are airlines to blame?, by Jack Hirsh and Martin J O’Donnell, The Lancet, 12 May 2001. To access this article, first register at http://www.thelancet.com

(16) Reported in Airlines rapped over blood clot deaths, BBC News Online, 28 March, 2001

(17) For example, see the Daily Telegraph, 10 January 2001, and Observer, 21 January, 2001

(18) See Varda on the Aviation Health Institute website

(19) BBC News Online, 27 October, 2000

(20) Airlines neglect passengers’ health, says Lords report, Guardian Unlimited, November 22, 2000

(21) See the Mediven website

(22) For example, Daily Telegraph, 9 August 2001

(23) Guardian Unlimited, April 17, 2001

(24) BBC News Online, 16 January, 2001