Telling a first-person story about a health problem is a popular frame in medical writing, and it can be effective as long as the author adheres to the principles of high quality, evidence-based reporting.

An article on the front page of The Washington Post’s Health section in mid-January demonstrated how the personal narrative can go very wrong, however.

In the piece, John Donnelly—a former Boston Globe science reporter turned freelance writer and PR consultant—recounted how he developed potentially dangerous blood clots in his legs after taking a long-haul flight to the Philippines. The condition, called deep vein thrombosis (DVT), can occur after prolonged periods of immobility and can be life threatening if a clot breaks loose, travels in the bloodstream, and blocks an artery in the lungs, causing a pulmonary embolism (PE).

After experiencing shortness of breath and calf pain on runs in Manila and then back home in Washington, DC, Donnelly went to the hospital. What followed was a dramatic episode in which a technician, upon discovering the clots, exclaimed, “Oh, my god. Don’t move,” and fetched a doctor who, in turn, told Donnelly, “You’re lucky,” and prescribed two anticoagulants to prevent the clots from getting bigger and further clots from forming.

“So began my education on deep vein thrombosis,” Donnelly wrote in his testimonial for the Post. But the lessons he learned were incomplete.

Donnelly endured a terrifying ordeal that would have rattled anyone. DVT/PE is a serious condition, affecting 300,000 to 600,000 Americans every year, killing 60,000 to 100,000 of them, according to the Centers for Disease Control and Prevention. But Donnelly’s experience also led him to produce an article that badly mischaracterized the dangers of long-distance airplane travel. Here’s what he “found out”:

DVT is frequently called “economy-class syndrome” because of the number of people who get it after sitting immobilized in cramped seats on long flights.

I started hearing from friends, including many who work in global health, a subject I’ve been writing about for the past two decades. A friend who once worked at the World Health Organization said he once had DVT/PE after a long flight and now injected himself with an anti-clotting medicine 30 minutes before every long-distance trip; he said that enough people at WHO had DVT/PE from flights that it was almost an occupational hazard.

The science on DVT/PE directly contradicts both paragraphs. On Tuesday, the American College of Chest Physicians released the ninth edition of Antithrombotic Therapy and Prevention of Thrombosis, its guidelines for the prevention, diagnosis, and treatment of thrombosis. Researchers stated that there is no evidence to support “economy class syndrome” and advised long-distance travelers against the use of aspirin or anticoagulants to prevent DVT/PE.

For long-distance travelers at increased risk of DVT/PE (which includes people who’ve had it before, like Donnelly and his friend) the College of Chest Physicians suggested getting up and walking around frequently, exercising the calf muscles, sitting in an aisle seat (to facilitate mobility), and in some cases using graduated compression stockings, which help prevent blood from pooling and clotting in the legs during periods of immobility. But the guidelines advise against stockings for those who aren’t at increased risk. And they stress that antithrombotic drugs should be evaluated on an individual basis with the help of a physician, as some of them can cause severe bleeding and other life-threatening conditions.

“There has been a significant push in health care to administer DVT prevention for every patient, regardless of risk. As a result, many patients are receiving unnecessary therapies that provide little benefit and could have adverse effects,” said the chair of the guidelines panel, Gordon Guyatt, in a press release. “The decision to administer DVT prevention therapy should be based on the patients’ risk and the benefits of prevention or treatment.”

Donnelly’s implicit suggestion that even high-risk, long-distance travelers consider taking anti-clotting medicine, without adding a word of precaution, is therefore dangerous and irresponsible; his suggestion that there is such a thing as “economy class syndrome” is simply naïve and misleading.

The College of Chest Physicians stressed repeatedly in its guidelines that the chance of developing DVT/PE following long-distance air travel is very low. There is no definitive evidence suggesting that dehydration, alcohol intake, or sitting in economy class (as opposed to business or first class) increases a person’s risk. Sitting in a window seat does increase one’s risk, but only because it impedes mobility.

In addition to window seats and having already had DVT/PE or pulmonary embolism, risk factors include cancer, recent surgery, advanced age, estrogen use (including oral contraceptives), pregnancy, and obesity. The association between air travel and DVT/PE is strongest for flights longer than eight to 10 hours, and most passengers who develop the condition after long-distance travel have one or more risk factors. Immobility related to car, bus, and train travel can also increase the risk of DVT/PE.

To be fair, the news guidelines appeared three weeks after Donnelly’s article, but a few phone calls surely would have prevented him from carelessly touting “economy class syndrome” and the use of anticoagulants. Instead of quoting any chest, heart, or blood doctors, however, he relied on a couple of infectious disease experts who are highly regarded in their fields, but unqualified to speak about the risk of DVT/PE from long-distance travel. He also cited a website called ClotCare.com, without mentioning that its “premier sponsor” is Sanofi-Aventis, which makes DVT drug Lovenox.

The new guidelines have drawn significant media coverage in the last week, and most articles have conveyed their content fairly accurately, although a few articles didn’t do a good job explaining the difference between absolute and relative risk.

The College of Chest Physicians’ guidelines found that the chance of developing DVT/PE in the month following a flight longer than four hours is one in 4,600 flights. An article on CNN.com mentioned the statistic as well as the finding that “the risk rises by 18% for each two-hour increase in the duration of travel,” all of which is accurate. But the piece should have stressed that an increase in relative risk of 18 percent amounts to a very small increase in absolute risk—so the chance of developing DVT/PE is .02 percent after a four-hour flight, and only .03 percent after a six-hour flight.

Likewise, an article in USA Today reported that, “A report by the World Health Organization in 2007 found that for every four hours of immobilization, the chance of experiencing a blood clot doubles [link added],” which sounds scary, but belies the fact that, even then, the health organization said the absolute risk was only about one in 6,000.

Finally, a CBS News/Associate Press story reported that, “The average risk for a deep vein blood clot in the general population is about 1 per 1,000 each year. Long-haul travel doubles the chance, but the small risk should reassure healthy travelers that they’re unlikely to develop clots….” Again, this is true, but the piece could’ve done more to emphasize how small the risk is by explicitly stating that where the risk of DVT/PE for non-travelers is a tenth of a percent, it’s only two-tenths of a percent for those with more wanderlust.

None of these flaws was as bad Donnelly’s personal-narrative-gone-wrong, however. Frightening experiences with a medical problem can make a very effective frame in health reporting (to see it done right, check out Alice Park’s first-person coverage of the new DVT/PE guidelines in Time). But the writer must buttress his or her tale with a thorough accounting of the scientific evidence and quotes from qualified sources. Unfortunately, Donnelly did neither.

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Curtis Brainard is the editor of The Observatory, CJR's online critique of science and environment reporting. Follow him on Twitter @cbrainard.