Passengers who fly aboard planes that recirculate the air in the cabin are no more likely to catch colds than travelers on aircraft that pump in fresh air, a study suggests.
Still, all of the air travelers in the study got a lot of colds _ significantly more than would be expected in those who don't fly.
Health experts have long suspected that recirculated air carries more germs and causes more colds.
Researchers called the latest findings encouraging because planes that pump in fresh air are being phased out in favor of less costly, more fuel-efficient models with ventilation systems that recirculate air.
"Recirculation of cabin air did not emerge as a risk factor for the development of upper respiratory-tract infection symptoms in our study," wrote Dr. Jessica Nutik Zitter of the University of California at San Francisco and her colleagues.
The study, published in today's Journal of the American Medical Association, involved questionnaires given to 1,100 passengers leaving the San Francisco area and traveling to Denver between January and April 1999.
A week after their flights, 21 percent of the fresh-air passengers and 19 percent of the recirculated-air passengers reported having a cold.
The researchers said the incidence of colds in nontravelers is about 3 percent.
Researchers said the high number of colds among passengers in both groups could result from factors unrelated to cabin air, such as stress, sleep loss or poor eating habits sometimes associated with travel.