Aircraft cabin air recirculation and symptoms of the common cold

Context  In recent years, new commercial aircraft have been designed to recirculate approximately 50% of the cabin air to increase fuel efficiency. Some older aircraft use only fresh air. Whether air recirculation increases the transmission of infectious disease is unknown; some studies have demonstrated higher rates of the common cold among persons working in buildings that recirculate air. Objective  To evaluate the role of air recirculation as a predictor of postflight upper respiratory tract infections (URIs). Design, Setting, and Participants  A natural experiment conducted among 1100 passengers departing the San Francisco Bay area in California and traveling to Denver, Colo, during January through early April 1999, and who completed a questionnaire in the boarding area and a follow-up telephone interview 5 to 7 days later. Forty-seven percent traveled aboard airplanes using 100% fresh air for ventilation, and 53% traveled aboard aircraft that recirculated cabin air. Main Outcome Measure  Incidence of reporting new URI symptoms within 1 week of the flight. Results  Passengers on airplanes that did and did not recirculate air had similar rates of postflight respiratory symptoms. The rates of reporting a cold were 19% vs 21% (P = .34); a runny nose and a cold, 10% vs 11%, (P = .70); and an aggregation of 8 URI symptoms, 3% in both groups (P>.99). Results were similar after statistical adjustment for potential confounders. Conclusion  We found no evidence that aircraft cabin air recirculation increases the risk for URI symptoms in passengers traveling aboard commercial jets.