Aircraft Cabin Air Recirculation and Symptoms of the Common Cold

Zitter JN, Mazonson PD, Miller DP, Hulley SB, Balmes JR

In recent years, new commercial aircraft have been designed to recirculate cabin air, leading to concerns of an increase in the transmission of infectious disease among passengers. Previous aircraft designs used only fresh air, whereas the new designs recirculate approximately 50 percent of the cabin air to increase fuel efficiency. In a recent study, the authors concluded that recirculated air did not increase the incidence of colds or upper respiratory tract infection (URI) symptoms in passengers. Materials and Methods The study was conducted between January and early April 1999 with 1,100 passengers traveling from the San Francisco Bay area in California to Denver, Colorado. Participants had to be 18 years or older, English speaking, willing to complete a brief questionnaire in the boarding area, and willing to complete a follow-up telephone questionnaire five to seven days after the initial contact. Participants could not have engaged in air travel during the previous week (including connections that day), had plans for additional air travel before the follow-up interview, or had a cold when the initial questionnaire was distributed. To sample evenly between airplanes that used fresh and recirculated air, as well as to control for differences in aircraft, the study targeted only Boeing 727s and 737s, as well as DC-10s. 727s and 737s are designed similarly, with the exception that 727s use fresh air and 737s use recirculated air. DC-10s use either fresh or recirculated air, depending on when the aircraft was built. In the follow-up questionnaire, symptoms that suggested the presence of a URI were assessed using the questionnaire developed by Jackson, et al. The least restrictive definition was the self-report of a cold. The next most restrictive definition was the self-report of a cold and a runny nose, which highly correlates with the clinical diagnosis of a URI. The most restrictive definition of a URI was a Jackson score higher than 13 (consisting of the sum of eight respiratory symptoms, including headache, sneezing, chilliness, sore throat, malaise, nasal discharge, nasal obstruction, and cough, each measured from 0 to 3). Results Of the original 1,501 participants enrolled in the study, follow-up data was collected on 1,100. A total of 516 (47%) of the 1,100 respondents traveled aboard airplanes with fresh-air ventilation and 584 (53%) traveled on planes with recirculated-air ventilation. There were 196 passengers on DC-10s and 904 on 727 or 737 models. Of the 240 flights studied, 114 (46%) used fresh-air ventilation systems, whereas 136 (54%) used recirculated air systems. Proportions of the three URI-symptom outcomes among passengers flying on the two types of airplanes (fresh, recirculated) were compared without adjustment for group differences. There were no significant differences for any of the outcomes. Self-reported colds occurred in 21 percent of passengers in airplanes with fresh air and 19 percent of passengers in airplanes with recirculated air (P=0.34). Self-reported colds and a runny nose occurred in 11 percent and 10 percent of these passengers, respectively (P=0.7). Jackson scores higher than 13 occurred in 3 percent of both groups (P>0.99). Conclusion No evidence was found to indicate that aircraft cabin air recirculation increases the risk for URI symptoms in passengers traveling aboard commercial jets. AMA July 2002;288(4):483-486. Return to Top