The study involved more than 1,000 passengers flying between the San Francisco Bay area and Denver during the winter and early spring of 1999. About 19 percent of passengers on planes with recirculated cabin air reported colds one week after the flight. In comparison, 21 percent who flew in planes using only fresh air reported colds. The study was published in the July 24 issue of JAMA, the Journal of the American Medical Association.
"I think there's a fairly universal feeling that flying increases your risk of getting colds and other infections, but air circulation may not be the key issue," said John Balmes, MD, UCSF professor of medicine and chief of the division of occupational and environmental medicine at the UCSF-affiliated San Francisco General Hospital Medical Center (SFGHMC). Balmes is senior author on the JAMA paper.
"Filters used on planes with recirculated air are designed to filter out infectious particles, and they may be doing a good job. It may be that just being on a plane, packed with a lot of people is the primary factor in transmission of colds, or maybe traveling is the issue: changing time zones and losing sleep have been documented to increase rates of viral infections. My best advice is to wash up after shaking hands, and avoid touching your nose."
In the study, passengers filled out a pre-flight questionnaire and were interviewed by phone five to seven days after the flight. The researchers were unable to study passengers taking flights longer than two hours, since planes that do not recirculate air are used almost exclusively on shorter routes.