A study in the Journal of the American Medical Association shows that passengers get far more colds after they fly aboard airplanes than when they don't fly, and they also get more colds than people who do not fly.
Health experts have long suspected that large passenger airplanes cause colds with their ventilation systems that recirculate air that picks up and carries more germs to cause more colds. However, those who travel in planes that re-circulate cabin air are no more likely to catch colds than travelers on aircraft that pump in fresh air.
The study used questionnaires given to 1,100 passengers leaving the San Francisco area and traveling to Denver between January and April 1999. A week after a flight, 21 percent of the fresh-air passengers and 19 percent of the re-circulated-air passengers reported having a cold. The researchers said the incidence of colds in non-travelers is about 3 percent. Since those breathing recirculated air have the same incidence of colds as those who breathe fresh air pumped into their cabins, doctors must look for another cause of the increased susceptibility to colds.
The authors think that the high number of colds among passengers in both groups could result from factors unrelated to cabin air, such as stress, sleep loss and poor eating habits sometimes associated with travel. The study could also be flawed because people who have to travel across time zones are far more likely to be irritable, tired, feel lousy and be more likely to report that they are sick, even if they are not sick. The airlines are delighted with this study because planes that pump in fresh air are being phased out in favor of less costly, more fuel-efficient models with ventilation systems that re-circulate air. Many airlines use ventilation systems with filters designed to remove viruses and bacteria from re-circulated air, but not all do, and there is no minimum standard for how much outside air is brought into airplane cabins.
Journal of the American Medical Association, week of July 25, 2002
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