Germs in the middle seat

At this moment I'm sitting in a Chicago O'Hare airport waiting room reading a news article on MSNBC's website telling me I am in more danger from breathing the air here in the terminal than I would be breathing the air on the airplane when it reaches cruising altitude. This was the conclusion from a just published study done by the National Institute for Occupational Study and Health (NIOSH), the federal research agency on workplace health problems, and two collaborating universities, Harvard and University of Massachusetts. NIOSH has been looking into the environment of the cabin crews, but of course the flying public shares the same air so the findings are also of interest to those of us who stand and wait. Or sit and wait, in this instance. We've discussed it here before, so consider this an update.

The problem of dissemination of a nasty pathogen via the air travel network has been on the minds of pandemic flu planners from the outset. It seems obvious this would be a natural mode of long distance spread. There are plenty of instances of infected people getting sick in one place and traveling to another to infect others who then travel, etc. The question has been whether the closed environment of an airplane cabin, with its high population density breathing refiltered air would be an especially efficient way to infect whole plane fulls of people. Many people are convinced they are more likely to come down with respiratory infections after air travel. But we really know very little about the risks. The NIOSH study was designed to provide some more information on possible exposure to bacteria in the air of planes:

The researchers, who boarded 12 Boeing 767 flights operated by two unnamed U.S. carriers, measured bacteria on randomly chosen flights lasting 4 ½ to 6 ½ hours. All told, they took 513 airborne bacterial samples. The results were reassuring in one sense, said McKernan: The cabin air in the middle of flights, when the aircraft reached peak cruising altitude and top speed, was healthful.

For members of the traveling public -- worried about the transmission of infectious diseases by breathing "recycled" air on aircraft and remembering colds they picked up from a flight -- the findings are somewhat counter-intuitive: Cabin air three or four hours into a long-haul flight may not smell especially fresh but it's evidently safe. The flights studied used a mix of 50 percent recirculated air and 50 percent fresh air.

[NIOSH scientist Dr. Dr. Lauralynn McKernan] and her team did find higher concentrations of bacteria at two other times: when passengers were boarding the aircraft, and when they were deplaning. The concentrations didn't pose immediate threats to health, she said.

However, said McKernan, the results do suggest that when passengers pick up a bug on their flights, they do it when they're literally rubbing elbows with other travelers at their seats, or shedding microbes from clothing and skin when they wake up, bustle about and grab bags from the overhead compartment as the aircraft taxis to the airport gate. (David Armstrong, MSNBC)

Planes these days are packed to the gills. I have several hours in a middle seat to luxuriate in until well past midnight tonight. I can't wait. manwhile I will be strapped in next to two people on either side and three people front and back. And that's just on my side of the plane. On the other side are another nine people. Since the air flow in a plane's cabin isn't longitudinal but transverse, if any of them are shedding virus these are the folks -- including me -- more likely to inhale a virus. The good news is that it isn't a whole plane full. The bad news is . . . well you what what the bad news is.

The article points out that this isn't different than other crowded situations, like school dances, the bus or subway or the political rally. But the issue with planes is that the three or six or nine people that may be exposed are traveling. When they reach their destinations they will disperse and potentially could seed widely separated communities.

Or maybe not. The risk of becoming infected during air travel is still largely unknown. This was a study of bacteria in the air, not viruses and not illness. It is quite possible that viruses travel farther and are more prevalent than bacteria or on the contrary are less common and more localized. Maybe the filters are good for bacteria but not viruses. Or vice versa. We still don't know, but this study does direct our attention to local contacts less than the general cabin environment.

Meanwhile I'm sitting here in this airport lounge and it is filling up. People everywhere. I feel a tickle in the back of my throat. I wonder if I'm coming down with something.

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My husband flies for a living, both up front and in the passenger cabin. Since he started to use hand gels and wash his hands religiously, he hasn't been ill. He logs thousands of hours a year in airports, pilot lounges, hotels, and the planes themselves. He makes sure he doesn't touch his eyes, nose, mouth or eat without washing or using gel.
Before he started that regime, he would be ill with a virus or bacterial infection several times a year and spread it around. I know that's just our experience, but if people used hand gels and washed up before they are or touched mucus membranes maybe they'd get sick less often.

By G in INdiana (not verified) on 16 May 2008 #permalink

G: Thanks. You've mentioned this in the past and it always interests me. It is consistent with these data in the sense that it suggests that it is not breathing the air in the plane that is a risk but contact in some form. Since he doesn't sit with the rest of us it still leaves open the question of aerosol transmission from person to person but tends to suggest the importance of transmission through inanimate objects. I hope we sort this out at some point as it is of practical importance.

There is also the contrary stance, that a constant travel, and therefore constant reshuffling and re-addition of a milieu of bacteria can also help keep the prevalence of more virulent things lower.

they could test these things in a study.
Just collect experiences from all these Gs.
The Gel-company should have done it.
NIOSH should have done it.

Is there more flu in areas/countries with
much (air-)travel ? easy to measure

Jared: Not very likely. For transmissible pathogens for which the population has no previous experience the outcome is likely to be negative, IMO.

But the issue with planes is that the three or six or nine people that may be exposed are traveling. When they reach their destinations they will disperse and potentially could seed widely separated communities.

Boy is this true. When I was younger I worked as a critical care transport physician for a major children's hospital. The sickest child I've ever had to stabilize at a small hospital for transport back to a tertiary center was a little girl with meningococcemia who'd recently flown to the US from a European country. Public health and the airline worked unbelievably hard to locate passengers that were at greatest risk and I'm fairly certain they weren't able to notify everyone that deserved prophylaxis.

On a happy note, the little girl who I thought would die in transport survived our helicopter trip and three months later I was invited to her discharge party from the hospital. She made a full recovery other than losing the tips of a few fingers and an itty bitty part of her nose.

There are, however, potential public health issues with air quality aboard airliners which have nothing to do with pathogens.

An increasing body of evidence suggests that aircrew can and will be sickened by repeated exposure to aerosolized toxins coming into the cabin from engine bleed air. A number of such aviation professionals have suffered apparent neurological injury via this route. Some have experienced damage of such severity that they have been unable to continue in their careers. Some members of the public may also have had comparable difficulties.

Modern jet engine oils utilize organophosphate anti-wear compounds such as tricresyl phosphate. These are capable of causing CNS injury when breathed as vapor, even at very low concentrations. Note that this is consistent with well understood health problems from the aerosolized application of organophosphate pesticides on field crops.

Virtually all modern airliners tap warmed, compressed "bleed" air from the engine pods for various purposes (the new Boeing 787 will not do so, but it will be years before those comprise any substantial percentage of the global air fleet). This includes bleed air which is delivered to the cabin and flight deck. If there are deficiencies in the sealing of the engine oil system, this presents the possibility of vapor contamination of the atmosphere inside the hull.

Certain aircraft types, as a function of their design, appear to have much higher rates of vapor exposure for passengers and crew. The BAE 146 is notorious for fumes.


how does the damage from toxins compare to the
damage from small organisms ? I guess it's minor.

Couldn't they just filter the air and provide
each seat+human with a closed plastic balloon
with full filtering of incoming and outgoing air ?

I'm not saying this is reasonable already, but in theory,
in a crisis, it should be possible and not too expensive.

Cough. We returned from a week cruise to Alaska last Monday. Wednesday afternoon we both got sick, and are still suffering from one truly nasty bug. Plane? Ship? Someone on shore? Who knows. (But Alaska was worth it.)

did you report this to some webpage ? to the air-company ?

Or word it here for google-search:
"I was infected on an airplane" , time,location,
(better suggestion ?)

Then, maybe later some researcher can make a study just
with google-hits.

There is another thing that distinguishes travel aboard a plane from other crowded situations, and that is the duration of exposure.

On a subway or most other terrestrial crowded situations, you don't spend hours right next to people, and you have the option of moving away from a person who sounds or appears ill.

In contrast, being stuck for hours in close proximity with people shedding infectious microbes will provide you with a much higher dose of same, vastly increasing your odds of contracting their illness. Or so it seems to me.