AIR should be circulated twice as fast in aircraft cabins during outbreaks of diseases such as SARS, according to a review of how diseases spread on passenger planes.
The review challenges the prevailing notion that only passengers sitting within two rows of an infected person are at risk. This rule of thumb is based on the spread of tuberculosis aboard aircraft, but the review highlights a case in March 2003 when a single passenger with SARS infected 18 others (both confirmed and probable) on a flight from Hong Kong to Beijing (see Diagram). 鈥淭his was just a three-hour flight, and some infected passengers were seven rows from the one passenger that had the disease,鈥� says team member Mark Gendreau of the Lahey Clinic Medical Center in Burlington, Massachusetts.
The review says that passengers are usually well protected by the ventilation systems on most commercial aircraft. All the air in the cabin goes through the system every 3 to 5 minutes, and half is replaced with fresh air. The ventilators clear half the airborne particles with each cycle, and even more if they have filters, although these are not mandatory.
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Passengers can also protect themselves by turning their air blowers to deflect stale air away from where they are sitting. Hand-washing is also important as flu often spreads by contact.
However, models also suggest that doubling the circulation rate would halve the risk of infection (The Lancet, vol 365, p 989). Airlines serving regions beset by disease outbreaks should consider increasing ventilation rates, the review concludes. This strategy could be useful if bird flu ever starts spreading from person to person, Gendreau says.
But Ron Behrens at the London School of Hygiene and Tropical Medicine doubts whether airlines will oblige. 鈥淲ith cost pressures already as high as they are, if it adds 拢20 to the cost of a ticket, they鈥檒l say no,鈥� says Behrens.
He thinks that infection rates are probably higher in departure lounges than on planes.
