Germs On a Plane: Flying With the Flu

By Jason Socrates Bardi
Inside Science News Service

WASHINGTON—Attempting to ground planes during pandemics may not be worth the trouble, a panel of experts from the government, academia and the airlines industry heard at a recent meeting in Washington.

One of the major conclusions from the two-day meeting was that restricting air travel during a pandemic, such as the current swine flu strain of influenza that is circulating globally, is not likely to have much of an effect.

This falls in line with recommendations that the World Health Organization made earlier this year when it declared the new swine flu strain of influenza—H1N1—to be a bona fide pandemic. The WHO advised in June that it was safe to travel—including on airplanes.

This advice followed weeks of diminished travel to and from Mexico, where the new strain of H1N1 first emerged. During April, some 2,000 flights a day to Mexico were cancelled—partly because certain countries restricted travel and partly because so many people cancelled their travel plans.

Despite the lower-than-normal travel, pandemic influenza continued to spread around the world, and that is not surprising to scientists like Ben Cooper of the Health Protection Agency in the U.K, one of several panelists at the Washington meeting who said travel restrictions are not likely to work.

Even a little bit of air travel goes a long way in spreading diseases like influenza, Cooper said, so any achievable reductions in flying are not likely to make much of a difference.

At the symposium, organized by the National Research Council's Transportation Research Board, Cooper showed data that modeled the effect of travel restrictions on the spread of a pandemic. Even in the best-case scenario, in which major cities managed to reduce air travel by 99.9 percent after the very first case emerged, Cooper's models showed that a pandemic would merely be postponed by several weeks—arriving later to those cities but establishing outbreaks eventually.

"It delays things a bit, but even such an extreme intervention is not effective," Cooper said.

In reality, there would likely be thousands of cases before any stringent travel restrictions could be put in place, and under a more realistic scenario, restricting travel makes very little difference at all.

Part of the problem is that when people are sick, they fly anyway, despite a consensus among the experts on the panel that people with suspected cases of influenza should not fly. When they do, they risk exposing other passengers—especially those people sitting immediately next to them.

As an example of this, panel member Itmar Grotto, the director of public health services for the Israeli Ministry of Health, described a case that occurred in May, shortly after swine flu first emerged.

A 22-year-old woman returning from a trip to Mexico flew to Israel through Madrid, Spain. She was sick on the flight and later diagnosed with H1N1. Two days after landing, another woman, who had been sitting directly in front of her on the plane from Madrid, fell ill with the same virus.

According to Grotto, even though health officials in Israel could not rule out the possibility that the second passenger was infected elsewhere, she probably caught the flu from the first passenger.

The danger of contracting an infection after sitting next to someone who is sick is not absolute. It depends on how sick that person is, how healthy the other passengers are, and many other factors. In fact, the 22-year-old woman's boyfriend, who sat next to her on the Madrid flight and on the longer flight from Mexico, never contracted her virus. Nor did anyone else on the flight, as far as the Israeli authorities are aware.

Perhaps one of things that helps contain infections on airplanes is the design of air circulation systems on the aircraft. Commercial airlines pack a lot of people into highly confined spaces, often for hours at a time, but have ventilation systems that keep the air relatively fresh.  The air is constantly filtering to remove germs and other dangerous particles and mixed with germ-free air from the outside.

"In reality," said Jeanne Yu, director of Environmental Performance for Boeing Commercial Airlines, "you are continually changing the air in the airplane." Overall, the air in a cabin is exchanged 10-15 times per hour, she said, and studies have shown that overall contaminant levels are relatively low on planes.

Contaminated air is not the only issue, however. Viruses like influenza can survive for hours on surfaces, and one of the easiest ways that someone can catch the flu is to touch a contaminated surface and then touch their eyes, nose, or mouth.

Contaminated surfaces, said University of Arizona in Tucson professor Charles Gerba, "are more important in the spread of a disease than a sneeze." And people today, he added, share more common surfaces with other people than at any time in history.

The bottom line, the panel concluded, is to do those things that have proven to work: wash hands; avoid touching eyes; get vaccinated against the flu, and don't fly if you're sick.