Thousands of flights to Mexico were canceled last year in response to the outbreak of the H1N1 virus there. And the SARS scare in 2003 prompted airports and airlines to adopt emergency measures, among them screening passengers for high fevers as they boarded.
No wonder, then, that an aircraft’s cabin is commonly seen as a particularly effective purveyor of communicable disease. True, jet travel can spread diseases from one continent to another far faster than in the past. But recent studies, including a report in August by the National Research Council’s Transportation Research Board, make a case that, in general, an airplane is no more a health threat to occupants than any other enclosed environment, like a theater or subway.
“There is always an increased risk of infection whenever you enter a confined space, but an aircraft cabin is no worse an environment than the office you sit in every day,” said Dr. Mark Gendreau, an emergency and aviation medicine expert at the Lahey Clinic in Burlington, Mass.
Cabin air, he said, is refreshed about 15 times an hour, compared with less than 12 an hour in an office building. On most full-size jets, the air is also circulated through hospital-grade HEPA filters, which are supposed to remove 99.97 percent of bacteria and the minuscule particles that carry viruses. The cabin air is also divided into separate ventilation systems covering every seven rows or so, limiting the ability of germs to travel from one end of the plane to the other.
Still, that does not rule out the prospect of diseases spreading from passenger to passenger on a long flight. Travelers tend to ignore doctors’ advice to avoid flying if they are sick, exposing unsuspecting seatmates to a threat of infection, the research panel noted.
In the summer of 2007, federal agencies, including the Department of Homeland Security and the Centers for Disease Control and Prevention, developed a “do not board” list to stop people with serious infectious diseases from flying to or from the United States. The impetus came from some well-publicized cases, including the May 2007 incident in which an American man infected with tuberculosis flew to Europe for his wedding, and then promptly dropped out of sight. He was later placed under quarantine by the United States government when he returned via Canada.
Four years before that, after an outbreak of SARS, or severe acute respiratory syndrome, airports and airlines adopted emergency screening measuresas the disease spread quickly around the world. There is no evidence, however, that large numbers of passengers were affected during those episodes, and the few identified cases involved people sitting within a few rows of an infected person.
While prominent pandemics have garnered the most attention, it is garden variety ailments, like colds or stomach viruses, that travelers should be worried about, members of the research panel said. And air travelers are more likely to pick up these bugs by touching a lavatory doorknob or a latch on an overhead bin. Charles P. Gerba, a professor at the University of Arizona and an expert on public hygiene, said research showed that viruses like influenza can survive for hours on such surfaces, which are not necessarily disinfected in routine cleaning between flights.
In fact, Dr. Gendreau of the Lahey Clinic said that the first thing he did upon boarding a plane was to take out an alcohol-based hand sanitizer and wipe down his tray table and other hard surfaces.
Many road warriors have their own rituals for staving off a sickness that could ruin not just their trip but any business they hope to gain. Stephen Wood, chief market strategist for North America at Russell Investments in New York, said that despite flying some 120,000 miles a year, he never became ill while traveling because he relied on some basic common sense practices, like drinking lots of water during a flight and avoiding alcohol.
But many frequent fliers say a long flight can leave them feeling as if they have the flu, even if they are perfectly healthy. Medical experts attribute that achy sensation to the effects of the lower oxygen and the aridity of air inside a plane that is at a cruising altitude of 35,000 feet and above. Even though most cabins are pressurized at around 8,000 feet above sea level, it is a higher altitude than most people are used to, and the swift ascent and descent of the plane only exaggerate the effects. “Fliers may actually be experiencing a mild case of mountain sickness,” Dr. Gendreau said.
Airplane manufacturers do not dispute this. The air inside a plane must be dry as a desert to protect the metal fuselage from the dangers of corrosion, said Ken Price, an interiors expert at Boeing . As a result, humidity levels can dip below 10 percent, contributing to any discomfort a traveler may experience on a flight. The company’s new 787 Dreamliner will have “much more humidity than any current plane,” he said, because it is made from composite materials that are more flexible. The Airbus A350, another midsize plane being developed by a European aerospace consortium, will also be built mainly from composites.
The next generation of planes will be pressurized at closer to 5,000 feet above ground, and Mr. Price said that tests showed that the difference in cabin pressure would help reduce the aches and pains associated with long flights.