Mar 21 2008

Mystery Airline Illness

I am always skeptical of “mystery illnesses.” Whenever a new apparent illness pops up the first question any scientifically-minded person should ask is, “Is it real?” Is there any objective evidence that a real new illness even exists, or are we seeing an apparent pattern that is not real but is just part of the background of known symptoms and illnesses?

Of course the press loves mysteries, and what’s better than a mystery illness; that’s a two-for-one deal – you get the appeal of a mystery and you get to scaremonger the public at the same time. A recent MSN headline proclaims:

Mystery illness sickens airline passengers, crews

The report focuses (as they almost always do) on a specific case – the story of one person dealing with the illness. I understand this is to add a personal and storytelling element to the news report but it has the unfortunately effect of distracting from the relevant science with misleading anecdotes. The case in question is that of a 77 year old woman who started to have shaking episodes following a flight on a commercial jet. She and her husband report that her shaking started the day after the flight and she was previously healthy.

I am always reluctant to make diagnoses based upon second hand reports or even videos of patients that I have not personally examined (advice that Bill Frist should have followed). And so I will not base any conclusions on my viewing of the video of this woman. I will only say that her shaking is compatible with a movement disorder of some type.

The report also mentions that dozens of airline crew have unsuccessfully sued their airline over their symptoms, which are reported as headaches, nausea, and in some cases tremor.

As always it is important to first consider all possibilities and then try to sort among them. One possibility is that there is something in the environment onboard jets that is causing some or all of these cases. It is not impossible that an environmental toxin is causing a toxicity syndrome. It would make sense that crew members are more at risk since they fly frequently.

A second possibility is that flying is causing non-specific symptoms, but not a new illness. Cabins in flight are notoriously dry and there is a drop in air-pressure. At high altitudes there is also a drop in oxygen content, leading to relative hypoxia. This drop in pressure is known to trigger migraines in some people. Dehydration is common and can trigger a number of symptoms, including headaches and nausea. Hypoxia may exacerbate asthma or other pulmonary conditions.

A third possibility is that the observation of illness related to airline travel is a false correlation – similar to the “sick building syndrome.” The fact is, people get sick, and even healthy people will get non-specific symptoms from time to time. Most of the time we cannot track down specific causes for these “symptoms of life.” They could be due to poor sleep, sedentary life-style, dehydration, benign viral infections, or the various degenerative changes of aging. It is important to recognize that there is a constant background of these common symptoms. In addition, there is a constant background of people who develop illnesses for other reasons – genetic, degenerative, or simply unknown.

Amid this background noise there will be many false patterns – like paredolia that causes us to see a face in the random shapes of tree bark or an oil stain. Once the notion that a building or location is causing illness becomes known, however, there is a tendency for people to ascribe their everyday symptoms to this new “mystery illness.” People who were destined to become sick anyway may blame their new illness on the building, or jet cabin, or whatever. And suggestible individuals may even develop symptoms based upon the anxiety that is produced by the fear of an unknown illness.

The evidence I have seen so far favors this third possibility, in my opinion. Airlines have spent millions studying cabin air and there does not appear to be any significant environmental toxins. This does not rule out the possibility, but so far there is little evidence to suggest this. I did find a recent study that showed that using an air purifier to improve cabin air (in a simulated environment) did result in perceived improvement in air quality by the study “passengers”. However this study related improved perception of air quality in jet cabins to air humidity, and recommends adding a humidifier to air treatment. This seems to be an area of active research (there is even a journal of Indoor Air), and there does not appear to be any toxins in the cabin air – but it is impossible to prove a negative. All we can say at this time is that such a toxin is unknown, and I would like to see some evidence for it before concluding that it is causing an illness.

I could also find no epidemiological evidence to suggest that this mystery illness actually exists.

I find it highly implausible that the 77 year old woman contracted a movement disorder one day after exposure on a single flight. That history is much more compatible with an exacerbation of an underlying pre-existing disease (even one that was not yet detected) than a new illness. Perhaps the low pressure or low oxygen on board, or a relative sleep deficit resulting from a traveling schedule unmasked this existing illness. Of course, complete coincidence is also possible.

It is more plausible that cabin crews could be contracting a toxic illness form long-term exposure. But again – let’s see the evidence. Flight crews are also known to be under high stress – so it’s possible that we are seeing the effects of chronic stress on flight crews, not an onboard toxin. Or this could be entirely a “sick building syndrome” applied to jet cabins.

The MSN article mentions that Dr. Clement Furlong is studying this airline illness and is months away from perhaps finding the answer. I find many problems with this reporting, and with Dr. Furlong’s research (as reported).

First it is problematic to study the cause of a disease before it has been established that the disease even exists. What are the diagnostic criteria of this disease, how do we know who has it? It is reported that Dr. Furlong is testing the woman’s blood for possible effects of engine oil on her “protein.” But I am highly skeptical that this woman’s symptoms are caused by her recent flight – so how can we interpret the results of Dr. Furlong’s tests – whether positive or negative?

Dr. Furlong believes that it is possible that an engine oil additive is leaking into the cabin through the air intake and that this may be the mystery toxin. But before you can correlate a toxin to a disease – you need to have a disease, you need to have some objective way of telling who has it and who doesn’t, and hopefully you have some theory of pathophysiology. Otherwise you are just hunting for chance correlations, without any idea how to interpret them.

We might defend this research as just preliminary, and perhaps it is. We do have to gather the pieces of the puzzle one piece at a time. Even still, it is putting the cart before the horse to study the cause of a disease before studying to confirm that the disease is real and to characterize it. Also, if this study is preliminary Dr. Furlong should have been much more careful when speaking to the press. The news reports discussed this airline illness without even questioning whether or not it was real. I also think we need to be especially careful in how we present ongoing research – the reports made it sound as if an answer were right around the corner. This leaves the public with a bottom line impression that may be entirely wrong.

My conclusion at this point is that this is probably a non-mystery and a non-illness – just another manifestation of the well-known sick building syndrome. Looking for previously undetected contaminants in cabin air is reasonable, as are continued efforts to study and improve overall cabin air quality. Before we begin investigating and reporting on such an entity as airline sickness we need to go back and do the basic science that should have been done in the first place. Is there a specific clinical syndrome here (as opposed to a collection of common and non-specific symptoms)? Does this syndrome truly correlate with exposure to commercial jets in flight? Then we can ask what the pathophysiology of this syndrome is, what are the possible causes, and then try to correlate specific toxins or other causes with this pathophysiology.

The reporting is problematic because these stories tend to take on a life of their own. All we need now is a catchy name for this mystery syndrome – like Cabin Sickness Syndrome (that has a better acronym that Airline Sickness Syndrome). Then there will be grass roots organizations to help fight and find the cause of CSS. If Dr. Furlong is not careful he may get sucked into become the celebrity scientist of this new controversial illness. We have seen this all before. At this stage we need to remain skeptical and to put the science first.

Right now we appear to have nothing but vague symptoms, random cases, and a wild guess.


I had a long conversation with Dr. Clement Furlong about this issue, and he gave me more detailed information as well as other resources for follow up. When I digest all of this information I will write a follow up entry. The story is, at the very least, much more complex than what was reflected in the news stories.

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