Travel: Planes, Trains, and Germs (cont.)

It's not just SARS - and it's not just China. In 1979 a commercial airliner sat on the tarmac for three hours with its ventilation system shut down. Someone on board had the flu -- and, within three days, so did nearly three-fourths of the plane's passengers.

SARS and influenza, of course, are only two of the multitude of bugs lurking out there. But the case of Flight 112 suggests that the current understanding of the spread of airborne disease aboard aircraft, which is based on tuberculosis investigations, may be outdated. Emergency medicine specialist Mark A. Gendreau, MD, senior staff physician at Lahey Clinic Medical Center, Burlington, Mass., recently reviewed what is and isn't known about infectious disease spread during air travel.

"The CDC and World Health Organization say you risk getting an infection only if you are sitting within two rows of someone who has something - and only if you are sitting there for more than eight hours," Gendreau tells WebMD. "But Flight 112 was only three hours long, and people sitting as far as seven rows back were affected. So that says, 'Wait a minute folks.' That old advice may have worked for tuberculosis, but what about SARS and other infectious diseases? More study into that is needed."

There's a lot we don't know, agrees Roy L. DeHart, MD, MPH, senior consultant in occupational and aviation medicine at Vanderbilt University, Nashville, Tenn. And if anyone understands the various health risks of flying, it's DeHart. He capped his 23-year Air Force career as commander of the USAF School of Aerospace Medicine. Former director of occupational and environmental Medicine at the University of Oklahoma, he's an FAA-certified senior aviation medical examiner.

"We don't know what that passenger next to you is contributing to the air stream as he is inhaling and exhaling," DeHart tells WebMD. "With flights coming out of developing countries where prevention programs are not as strong as they might be, it is not unusual that a person may have a problem like tuberculosis. It spreads. Usually just to two or three people, but if a patient is found on board, health authorities have a tough job trying to track those people down. It can be a horrendous problem. There can be hundreds of patients spreading whatever, wherever. Major spread is possible. So, yes, there can be problems."

Which Is Healthier: High-Flying Planes or High-Rise Offices?

Air passengers often complain about aircraft ventilation. But Gendreau notes that a normal airplane cabin changes its air 15 to 20 times an hour. A typical office building changes its air 12 times an hour.

High efficiency particulate air (HEPA) filters scrub the air on some planes. The filters may be able to trap airborne viruses because they catch the droplets that carry the viruses. But 15% of U.S. commercial airliners carrying more than 100 passengers lack HEPA filters.